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Rotational rheometry test of Portland cement-based materials - A systematic literature review
(2024)
This study systematically reviews 62 papers on the use of rotational rheometry to assess the fresh state behavior of Portland cement-based materials. The research highlights the wide variation in test methods and aims to provide a comprehensive overview. Findings reveal that 50.0% of studies employed vane geometry, despite its limitations in providing transformation equations. Regarding dynamic shearing tests, 67.0% followed a consensus using a pre-shearing step and a step-wise routine with stabilization times ≥ 10 s. While the Bingham model is commonly used, the study emphasizes the importance of considering shear-thinning behavior in cementitious materials. Models like Herschel-Bulkley and modified Bingham may be more appropriate. This review offers insights into testing conditions for rotational rheometry of cementitious materials, serving as a foundation for future research in the field.
Early detection of fatigue cracks and accurate measurements of the crack growth play an important role in the maintenance and repair strategies of steel structures exposed to cyclic loads during their service life. Observation of welded connections is especially of high relevance due to their higher susceptibility to fatigue damage. The aim of this contribution was to monitor fatigue crack growth in thick welded specimens during fatigue tests as holistically as possible, by implementing multiple NDT methods simultaneously in order to record the crack initiation and propagation until the final fracture. In addition to well-known methods such as strain gauges, thermography, and ultrasound, the crack luminescence method developed at the Bundesanstalt für Materialforschung und -prüfung (BAM), which makes cracks on the surface particularly visible, was also used. For data acquisition, a first data fusion concept was developed and applied in order to synchronize the data of the different methods and to evaluate them to a large extent automatically. The resulting database can ultimately also be used to access, view, and analyze the experimental data for various NDT methods. During the conducted fatigue tests, the simultaneous measurements of the same cracking process enabled a comprehensive comparison of the methods, highlighting their individual strengths and limitations. More importantly, they showed how a synergetic combination of different NDT methods can be beneficial for implementation in large-scale fatigue testing but also in monitoring and inspection programs of in-service structures - such as the support structures of offshore wind turbines.
This study explores the acceleration of material design in the concrete industry, focusing on improving carbonation resistance, a key factor in the durability of concrete structures. Traditional tests for carbonation resistance are lengthy, but with the construction industry aiming for sustainable production, finding a balance between carbonation resistance and CO2 footprint is crucial. Our research employs two innovative methods: 1. Applying the Sequential Learning App for Materials Discovery (SLAMD), an AI materials design framework, to an extensive dataset of real-world concrete compositions to selectively test materials that meet market demands: maximum durability, optimal eco-durability, and the best cost-durability trade-off. 2. Investigating 1H Nuclear Magnetic Resonance (NMR) relaxometry as a quick alternative for characterizing carbonation behavior, as it saves time compared to traditional tests and assesses the complete material's pore space. Specific NMR features are then integrated into the material design model, with the model's performance compared against traditional approaches. The results of our study are compelling, demonstrating that materials can be precisely tailored to meet specific requirements with minimal data points. This marks a significant stride in the concrete industry, indicating that NMR-based, low-fidelity surrogate characterizations, combined with a focused, data-driven design approach, can substantially accelerate the development of durable, sustainable concrete mixtures.
Ground Granulated Blast-Furnace Slag (GGBFS), a by-product of the iron-making process, has gained significant attention as a supplementary cementitious material and has become increasingly popular in recent years due to its remarkable properties. GGBFS can significantly reduce the environmental impact of cement production when it comes to building concrete structures. GGBFS can either be blended with ordinary Portland cement (OPC) (up to a 90% replacement), or it can be used in the production of alkali-activated materials (AAMs). However, a comprehensive understanding of the pore solution composition is necessary for understanding various aspects of cementitious materials and their durability, including corrosion behavior, passivation of steel, and resistance to deteriorative processes. In the present work, the pore solutions of seven different GGBFS-containing cements (alkali-activated slag, alkali-activated slag/fly ash blends, a hybrid alkaline cement, CEM III/C, and CEM III/B) were extracted and analysed by inductively coupled plasma-optical emission spectroscopy, ion chromatography, pH, redox potential, and conductivity measurements. For comparison, a Portland cement pore solution was analysed similarly. The Concentrations of reduced sulfur were noteworthy in all GGBFS-containing cements, particularly in alkali-activated cements, where concentrations were notably higher compared to standard cements. The redox potentials of the pore solutions were primarily dictated by the concentrations of reduced sulfur, although other factors may contribute. Additionally, sulfur species in the pore solutions had an impact on pH, electrical conductivity, and other properties pertinent to the corrosion of reinforcements.
While alkali-activated binders offer certain advantages over traditional Portland cement binders, particu¬larly in terms of resistance against chemical attacks and potentially environmental footprint, their degra¬dation mechanisms remain incompletely understood at present, specifically carbonation. Thus, this study investigates the impact of natural and accelerated carbonation (1% and 4% CO2) on three different compositions of alkali-activated concretes: 100% calcined clay (C100) binder, 100% ground blast furnace slag (S100) binder, and a 40% calcined clay and 60% blast furnace slag blend (C40S60). C100 concretes exhibit faster carbonation kinetics, with five times greater natural carbonation depths than S100. This difference diminishes under accelerated carbonation, showing a 1.5 times difference for 1% CO2 and complete carbonation for 4% CO2 at 90 days. The results thus confirm that accelerated carbonation testing of low-Ca alkali-activated concretes yields results that are not representative of natural carbonation. The C40S60 sample demonstrates a carbonation profile similar to a CEM I concrete, i.e., a high carbonation resistance. Microstructure analysis indicates the formation of three polymorphs of calcium carbonate for S100 (calcite, vaterite, and aragonite), with a higher CO2 concentration favouring aragonite over vaterite. C100 exhibits no calcium carbonates; instead, sodium carbonates form, including trona for 4% CO2 and natrite for both accelerated tests. C40S60 shows calcium and sodium carbonates, although to a lesser extent, containing predominantly calcite and minor signals of natrite. Suitable compositions, like C40S60, prove as effective during natural or accelerated carbonation tests as conventional Portland cement concrete.
In the field of computational science and engineering, workflows often entail the application of various software, for instance, for simulation or pre- and postprocessing. Typically, these components have to be combined in arbitrarily complex workflows to address a specific research question. In order for peer researchers to understand, reproduce and (re)use the findings of a scientific publication, several challenges have to be addressed. For instance, the employed workflow has to be automated and information on all used software must be available for a reproduction of the results. Moreover, the results must be traceable and the workflow documented and readable to allow for external verification and greater trust. In this paper, existing workflow management systems (WfMSs) are discussed regarding their suitability for describing, reproducing and reusing scientific workflows. To this end, a set of general requirements for WfMSswere deduced from user stories that we deem relevant in the domain of computational science and engineering. On the basis of an exemplary workflow implementation, publicly hosted at GitHub (https:// this http URL), a selection of different WfMSs is compared with respect to these requirements, to support fellow scientists in identifying the WfMSs that best suit their requirements.
Multiscale modeling of linear elastic heterogeneous structures via localized model order reduction
(2024)
In this paper, a methodology for fine scale modeling of large scale linear elastic structures is proposed, which combines the variational multiscale method, domain decomposition and model order reduction. The influence of the fine scale on the coarse scale is modelled by the use of an additive split of the displacement field, addressing applications without a clear scale separation. Local reduced spaces are constructed bysolving an oversampling problem with random boundary conditions. Herein, we inform the boundary conditions by a global reduced problem and compare our approach using physically meaningful correlated samples with existing approaches using uncorrelated samples. The local spaces are designed such that the local contribution of each subdomain can be coupled in a conforming way, which also preserves the sparsity pattern of standard finite element assembly procedures. Several numerical experiments show the accuracy and efficiency of the method, as well as its potential to reduce the size of the local spaces and the number of training samples compared to the uncorrelated sampling
Thermal transient problems, essential for modeling applications like welding and additive metal manufacturing, are characterized by a dynamic evolution of temperature. Accurately simulating these phenomena is often computationally expensive, thus limiting their applications, for example for model parameter estimation or online process control. Model order reduction, a solution to preserve the accuracy while reducing the computation time, is explored. This article addresses challenges in developing reduced order models using the proper generalized decomposition (PGD) for transient thermal problems with a specific treatment of the moving heat source within the reduced model. Factors affecting accuracy, convergence, and computational cost, such as discretization methods (finite element and finite difference), a dimensionless formulation, the size of the heat source, and the inclusion of material parameters as additional PGD variables are examined across progressively complex examples. The results demonstrate the influence of these factors on the PGD model’s performance and emphasize the importance of their consideration when implementing such models. For thermal example, it is demonstrated that a PGD model with a finite difference discretization in time, a dimensionless representation, a mapping for a moving heat source, and a spatial domain non-separation yields the best approximation to the full order model.
Since 2016 ISO Technical Committee (TC) 265 is working on standardization the whole CCS-process chain. Around 30 countries are working together to provide international guidelines. As ISO 27913 was the first standard finished within these activities it is already in the stage of first revision.
The objective of ISO 27913 is “to provide specific requirements and recommendations on certain aspects of safe and reliable design, construction and operation of pipelines intended for the large-scale transportation of CO2 that are not already covered in existing pipeline standards such as ISO 13623, ASME B31.8, EN 1594, AS 2885 or other standards. Existing pipeline standards cover many of the issues related to the design and construction of CO2 pipelines; however, there are some CO2 specific issues that are not adequately covered in these standards. The purpose of this document is to cover these issues consistently. Hence, this document is not a standalone standard, but is written to be a supplement to other existing pipeline standards for natural gas or liquids for both onshore and offshore pipelines.”
This contribution shall provide information on the content, the current stage of the revision process, encourage to contribute to this standard and make listeners aware to consider the influence of ISO standard on documents currently in draft.
Since 2016 ISO Technical Committee (TC) 265 is working on standardization the whole CCS-process chain. Around 30 countries are working together to provide international guidelines. As ISO 27913 was the first standard finished within these activities it is already in the stage of first revision.
The objective of ISO 27913 is “to provide specific requirements and recommendations on certain aspects of safe and reliable design, construction and operation of pipelines intended for the large-scale transportation of CO2 that are not already covered in existing pipeline standards such as ISO 13623, ASME B31.8, EN 1594, AS 2885 or other standards. Existing pipeline standards cover many of the issues related to the design and construction of CO2 pipelines; however, there are some CO2 specific issues that are not adequately covered in these standards. The purpose of this document is to cover these issues consistently. Hence, this document is not a standalone standard, but is written to be a supplement to other existing pipeline standards for natural gas or liquids for both onshore and offshore pipelines.”
This contribution shall provide information on the content, the current stage of the revision process, encourage to contribute to this standard and make listeners aware to consider the influence of ISO standard on documents currently in draft.
Despite the advances in hardware and software techniques, standard numerical methods fail in providing real-time simulations, especially for complex processes such as additive manufacturing applications. A real-time simulation enables process control through the combination of process monitoring and automated feedback, which increases the flexibil- ity and quality of a process. Typically, before producing a whole additive manufacturing structure, a simplified experiment in form of a bead-on- plate experiment is performed to get a first insight into the process and to set parameters suitably. In this work, a reduced order model for the transient thermal problem of the bead-on-plate weld simulation is devel- oped, allowing an efficient model calibration and control of the process. The proposed approach applies the proper generalized decomposition (PGD) method, a popular model order reduction technique, to decrease the computational effort of each model evaluation required multiple times in parameter estimation, control and optimization. The welding torch is modeled by a moving heat source, which leads to difficulties separating space and time, a key ingredient in PGD simulations. A novel approach for separating space and time is applied and extended to 3D problems allowing the derivation of an efficient separated representation of the tem- perature. The results are verified against a standard finite element model showing excellent agreement. The reduced order model is also leveraged in a Bayesian model parameter estimation setup, speeding up calibrations and ultimately leading to an optimized real-time simulation approach for welding experiment using synthetic as well as real measurement data.
Currently, mandatory requirements and recommendations for the detection of irregularities in laser beam welded joints are based on classic micrographs as set out in the standard ISO 13919-1:2019. Compared to classic micrographs, computed tomography enables a non-destructive, three-dimensional and material-independent mode of operation, which delivers much more profound results. Even in building material testing, methods with limited informative value can be checked and supplemented by CT examinations.
FenicsXConcrete
(2023)
Additive manufacturing (AM) has revolutionized the manufacturing industry, offering a new paradigm to produce complex geometries and parts with customized properties. Among the different AM techniques, the wire arc additive manufacturing (WAAM) process has gained significant attention due to its high deposition rate and low equipment cost. However, the process is characterized by a complex thermal history making it challenging to simulate it in real-time for online process control and optimization.
In this context, a reduced order model (ROM) using the proper generalized decomposition (PGD) method [1] is proposed as a powerful tool to overcome the limitations of conventional numerical methods and enable the real-time simulation of the temperature field of WAAM processes. These simulations use a moving heat source leading to a hardly separable parametric problem, which is handled by applying a novel mapping approach [2]. This procedure makes it possible to create a simple separated representation of the model, which allows to simulate multiple layers.
In this contribution, a PGD model is derived for the temperature field simulation of the WAAM process. A good agreement with a standard finite element method is shown. The reduced model is further used in a stochastic model parameter estimation using Bayesian inference, speeding up calibrations and ultimately leading to a calibrated real-time simulation.
It is well known that cement manufacture, including CaCO3 calcination and clinker formation, is associated with substantial energy consumption and significant greenhouse gas emissions. Alkali-activated binders (AAB) and concretes made from them can significantly contribute to reducing CO2 emissions caused by the construction industry. However, to what extent and for how long concretes made from AAB can protect the steel in reinforced concrete components from corrosion is still unclear. Unlike PC-based binders, AABs are made by reacting alkaline solutions with solid precursors such as fly ash and ground granulated blast furnace slag (GGBFS). Therefore, steel reinforcement corrosion mechanisms in AAMs differ from PC-based binders. The present study aims to evaluate the corrosion behavior of steel rebar in alkali-activated materials (AAMs) synthetic pore solution with different chemical concentrations representing different GGBFS and Flay Ash based binders by performing electrochemical tests to measure the corrosion rate and corrosion potential of steel rebar. This information can be used to improve the design of AAMs in order to ensure a longer service life for these materials.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. These polymers are characterized by a high permeability and reasonable permselectivity. The latter point is somehow surprising because for microporous systems a more Knudson-like diffusion is expected then a size dependent temperature activated sieving process. It was argued in the framework of a random gate model that molecular fluctuations on a time scale from ps to ns are responsible for the permselectivity.
Here series of polymers of intrinsic microporosity (PIMs) as well as microporous polynorbornenes with bulky Si side groups and a rigid backbone are considered. The polymers have different microporosity characterized by high BET surface area values.
First inelastic time-of-flight neutron scattering measurements were carried out to investigate the low frequency density of state (VDOS). The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. It was found that the frequency of the maximum position of the Boson peak correlates with the BET surface area value.
Secondly elastic scans as well as quasielastic neutron scattering measurements by a combination of neutron time-of-flight and backscattering have been out. A low temperature relaxation process was found for both polymers. This process was assigned to the methyl group rotation. It was analysed in terms of a jump diffusion in a three-fold potential. The analysis of the dependence of the elastic incoherent structure factor on the scattering vector yields the number of methyl groups which might be immobilized.
The neutron scattering experiments were accompanied by fast scanning calorimetry and broadband dielectric investigations as well as atomistic molecular dynamic simulations.
Steelmaking slag is a by-product of steel production, of which 4.5 Mt were produced in 2020 in Germany alone. It is mainly used in road construction, earthwork and hydraulic engineering. A smaller part is returned to the metallurgical cycle, used as fertiliser or landfilled.
With this use, iron oxides still contained in steelmaking slag are lost. In addition, the possibility of producing higher-grade products from steelmaking slag is foregone. In recent decades, many researchers have investigated the production of Portland cement clinker and crude iron from basic oxygen furnace slags (BOFS) via a reductive treatment. Carbothermal treatment of liquid BOFS causes a reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density. Simultaneously, the chemical composition of the reduced slag is adapted to that of Portland cement clinker.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as a reducing agent. The resulting low-iron mineral product has a similar chemical composition to Portland cement clinker and was rich in the tricalcium silicate solid solution alite (Ca3SiO5). Based on its chemical and mineralogical composition, similar to that of Portland cement clinker, the reduced BOFS has the potential to react comparably. In our study, the reduced BOFS produced less hydration heat than OPC, and its hydraulic reaction was delayed. However, adding gypsum has shown to accelerate the hydration rate of the reduced BOFS compared to that known from the calcium silicates of Portland cement clinker.
Further research to improve the hydraulic properties of the reduced slag is essential. If successful, producing a hydraulic binder and crude iron from BOFS has economic and ecological benefits for both the cement and steel industries.
Algal biofilm façades are an alternative to traditional green façades which can help to improve biodiversity and air quality within cities. They present a low maintenance approach in which subaerial algae are grown directly on concrete substrates. The intrinsic bioreceptivity of the substrate is a critical factor in successful facade colonisation. Existing research has identified several environmental and material properties which influence concrete bioreceptivity, however a consensus has yet to be made on which properties are most influential and how the interaction between properties may promote algal biofilm growth under specific conditions.
Even after autoclaving for 2 weeks in the temperature range of 120 to 200 °C, CEM I paste with a water-to-cement ratio of 0.5 still contains some low-crystalline C-S-H. The conversion of low-crystalline C-S-H to crystalline is faster with increasing temperature. The observed low-crystalline and crystalline C-S-H phases (reinhardbraunsite, jaffeite) indicate that the sampleshave not reached equilibrium yet under these experimental conditions. However, there is a good agreement between experiment and thermodynamic modelling for the other solids indicating that the used datasets are suitable for this application.
Building envelopes & natural rock surfaces represent the frontier between solid material surfaces, biosphere and the atmospheric environment – and are subject to permanent change in structure and chemistry. These surfaces are a natural habitat of subaerial rock biofilms (SAB) that are an important stage of primary succession. As their metabolic processes have a great impact on the composition of the near-surface layers of the earth biofilms on natural and manmade hard substrates are a research focus of geomicrobiology. In technical systems immobilized algae biofilms are already used successfully for wastewater cleaning. Algae can eliminate bacteria from the water and at the same time increase the oxygen concentration and the pH value in the water through photosynthesis, which again allows phosphate elimination to take place. Nitrificants contained in the algae biofilm convert ammonium to nitrite and nitrate.
Mineral claddings for building facades could be engineered to sustain either natural or previously established carefully selected algae-dominated biofilms and this way help to clean the air.
For a targeted engineering of the mineral substrates and the biofilms attached to them basic knowledge is however missing. By systematic research in an interdisciplinary team of microbiologists and building material scientists the following questions shall be clarified
• How can a curated biofilm be stabilized on the surface and designed to be durable without compromising the substrate
• What exactly do the biofilms need in terms of moisture in their respective growth stages? Or how long water must be available in what form and quantity to enable growth.
• What is the influence of the substrate on the availability and quality of the (rain) water (water quality, leaching of substances (alkalis) from the building materials, leaching of aerosol components, surface tension, suction tension, thickness of the water molecule layers adsorbed in the pore spaces....)
There are several research groups working on bioreceptive building materials which emphasizes the general interest in the topic. The idea of speeding-up the process by the targeted establishment of biofilms on building façade panels is a unique approach that has so far only been researched at BAM. Architects are very interested in biofilm facades as a new co-designing method of humans and nature reflecting the changing awareness for the loss of biodiversity in cities. If the biofilms need irrigation the evaporative cooling would reduce the urban heat island effect.
Even after autoclaving for 2 weeks in the temperature range of 120 to 200 °C, CEM I paste with a water-to-cement ratio of 0.5 still contains some low-crystalline C-S-H. The conversion of low-crystalline C-S-H to crystalline is faster with increasing temperature. The observed low-crystalline and crystalline C-S-H phases (reinhardbraunsite, jaffeite) indicate that the samples have not reached equilibrium yet under these experimental conditions. However, there is a good agreement between experiment and thermodynamic modelling for the other solids indicating that the used datasets are suitable for this application.
The dataset provided in this repository comprises data obtained from a series of full-notch creep tests (FNCT) performed on selected high-density polyethylene (PE-HD) materials (for further details, see section 1 Materials in this document) in accordance with the corresponding standard ISO 16770.
The FNCT is one of the mechanical testing procedures used to characterize polymer materials with respect to their environmental stress cracking (ESC) behavior. It is widely applied for PE-HD materials, that are predominantly used for pipe and container applications. It is based on the determination of the time to failure for a test specimen under constant mechanical load in a well-defined and temperature controlled liquid environment. The test device used here also allows for continuous monitoring of applied force, specimen elongation and temperature.
Admixtures are important constituents to enhance the performance of concrete. They allow for more efficient use of binders which can mitigate negative environmental impacts from producing cement-based materials. Commonly used rheology modifying agents like polycarboxylate ethers or cellulose ethers are synthetic or semi-synthetic, respectively. This requires additional energy consumption for their production and global supply chains particularly for many developing regions, which will be large consumers of concrete in the future. However, many locally available bio-based polysaccharides could be effectively used instead. These polymers are often overlooked by engineers and scientists due to their limited distribution and inherent complexity, yet they represent an underleveraged source of precursors for admixtures. This study investigates the action mechanisms of some bio-based rheology modifying agents, i.e., acacia gum and miscanthus gum, and provides a comparison to a conventionally modified starch. The results show that the mechanism of action of these polymers is closely related to the composition of the mixture, mixing regime, and the composition of the aqueous phase. Depending on the agent, either plasticizing or stabilizing effects on rheology can be revealed.
In this paper, we demonstrate the value of 1H NMR
relaxometry for studying the hydration of clinker-reduced, more
climate-friendly cementitious binders. The results were obtained
on typical CEM I cements and samples containing two different
reactive agricultural ashes as well as non-reactive biochars as
supplementary cementitious materials. The findings prove that
time-resolved NMR measurements provide valuable additional
information when combined with classical heat flow calorimetry.
In the late 1980s, a new type of corrosion appeared in drinking water installations where galvanized steel pipes failed forming a deep groove with no corrosion at the other surfaces. The reason was discussed quite fiercely between failure analysts and material suppliers. In the end the discussion lead to the solution: inductive welded pipes of a certain sulphur content were prone to selective corrosion. The history of the arguments is discussed using old communications between Wilhelm Schwenk and Wolfgang Stichel, who later published the results in a paper unfortunately only I german.
Thus the knowledge got lost and new cases based on the same material problems are observed in application of so-called C-Steel piping systems. Failure cases are shown.
Steelmaking slag is a by-product of steel production of which 4.5 Mt were produced in 2020 in Germany alone. It is mainly used in road construction, earthwork and hydraulic engineering. A smaller part is returned to the metallurgical circle, used as fertilizer or landfilled.
With this use, iron oxides still contained in steelmaking slag are lost. In addition, the possibility of producing higher-grade products from steelmaking slag is foregone. In recent decades, many researchers have investigated the production of Portland cement clinker and crude iron from basic oxygen furnace slags (BOFS) via a reductive treatment. Carbothermal treatment of liquid BOFS causes a reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density. Simultaneously, the chemical composition of the reduced slag is adapted to that of the Portland cement clinker.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as a reducing agent. The resulting low-iron mineral product had a similar chemical composition to Portland cement clinker and was rich in the tricalcium silicate solid solution alite (Ca3SiO5). Based on its chemical and mineralogical composition, similar to that of Portland cement clinker, the reduced BOFS has the potential to react comparably. In our study, the reduced BOFS produced less heat of hydration compared to OPC and its hydraulic reaction was delayed. However, adding gypsum has been shown to accelerate the hydration rate of the reduced BOFS compared to that known from the calcium silicates of Portland cement clinker.
Further research to improve the hydraulic properties of the reduced slag is essential. If successful, producing a hydraulic binder and crude iron from BOFS could have economic and ecological benefits for both the cement and steel industry.
In the late 1980s, a new type of corrosion appeared in drinking water installations where galvanized steel pipes failed forming a deep groove with no corrosion at the other surfaces. The reason was discussed quite fiercely between failure analysts and material suppliers. In the end the discussion lead to the solution: inductive welded pipes of a certain sulphur content were prone to selective corrosion. The history of the arguments is discussed using old communications between Wilhelm Schwenk and Wolfgang Stichel, who later published the results in a paper unfortunately only I german.
Thus the knowledge got lost and new cases based on the same material problems are observed in application of so-called C-Steel piping systems. Failure cases are shown.
Viscosity modifying agents: Key components of advanced cement-based materials with adapted rheology
(2022)
Viscosity modifying agents (VMAs) are essential ingredients for the production of flowable cement-based materials. This paper presents an overview of commonly used VMAs and attempts to shed some light on the underlying physics at the origin of their mechanisms of action. The main molecular parameters of VMA controlling the rheological properties of the cement pore solution are highlighted. As the mechanisms of action of VMAs in cement-based materials are closely related to their affinity with the surface of cement particles, the adsorption of the main VMA types is discussed. The effect of VMAs on flow properties and stability of cement-based materials is presented for VMAs added without any superplasticizer, and then in systems incorporating both VMAs and superplasticizers. Finally, the effect of VMAs in enhancing concrete properties to secure adequate performance of different construction applications, and perspectives for future developments of novel cement-based materials made with VMAs are showcased.
Synopsis: The paper presents the results of a study on the influence of agitation on the structural build-up of fresh cement pastes using a penetration test. It first presents results about the influence of the penetrating shape’s geometry on the influence on the cement paste specimen. Then, results are shown for the load-deflection curves depending upon time and agitation before testing. Based on the observation of the force required to penetrate the sample, conclusions on the structural build-up can be made. The observations were made over the course of time with samples that were left at rest and partly agitated before testing at different time steps. The setup allows to identify the contribution of the chemical reaction to the structural build-up process. The presence of superplasticizer obviously reduces the load that cement paste can withstand, while the loss of thixotropy is found notably lower than that of neat cement pates
Synopsis: Lately, there has been rising attention to superplasticizers (SP) based on polyphosphate esters. However, the influence of the molecular structure of the polyphosphate polymers on time-dependent properties such as structural build-up has not been examined yet intensively. To investigate this effect, three comb polyphosphate superplasticizers with different charge densities were synthesised by free radical polymerisation. Our findings indicate that SP with the lowest and medium charge densities extend the induction period more strongly than the SP with the highest charge density. The reduction of the structural build-up rate is linearly dependent on the dosage and concentration of the functional group of polyphosphate SP in the cementitious system. This study proposes a mathematical equation expressing the relationship between the structural build-up rate during the induction period and the molecular structure of the polyphosphate SP.
The accelerating climate crisis results in a rising demand for ecologically driven concepts. Regarding construction, this does not only include environmentally friendly materials but also the establishment of greenery in urban regions.
This contribution presents the progress of two projects in which textured concrete slabs were designed to grow a stable biofilm of photosynthetic eukaryotic organisms. The greened panels represent an alternative to classic fa9ade greening with plants. Current literature suggests that the development of bioreceptive surface materials in the construction sector is difficult because there are no standardized methodological approaches for measuring said bioreceptivity. Therefore, the long-term. ahn is proposing a suitable measurement concept combining material Science and biology. Among other things, the intrinsic Substrate property pH value is expected to have a significant influence on biological colonization. In the current contribution the focus lies on the theoretical approach and design of experiment regarding this parameter.
Available experimental data will be presented.
Only the nano-scaled structure of the nanocomposite and the dispersion of nanoparticles within the polymer matrix harbor multifunctional potential including superior fire retardancy. Thus, this chapter focuses on the dispersion of nanoplates, based mainly on studies of layered silicates and graphene/graphene-related nanoplates. The nanostructure and properties of the nanocomposites are dependent mainly on thermodynamic and kinetic factors during preparation. Improving nano-dispersion often directly improves flame retardancy. Therefore, the modification of the nanoplates as well as the preparation of nanocomposites becomes very important to control this dispersion. The dispersion of nanoplates functions as a prerequisite for the formation of an efficient protective layer, changing the melt flow and dripping behavior, or the improvement of the char properties.
Concrete has a long history in the construction industry and is currently one of the most widely used building materials. Unfortunately, the concrete industry has a significant impact on the environment by contributing to about 9% of the total anthropogenic greenhouse gas (GHG) emissions. Concrete is a highly complex composite material. However, the main source of concrete's GHG emissions is the cement. This leads to two main strategies when trying to reduce the environmental impact. The first is to reduce the cement within the concrete mix. This can be done by substituting it using additives or increasing the amount of aggregates. Usually this will lead to decreased material properties, like compressive strength or stiffness. The second option is to reduce the amount of required concrete by optimizing the topology of the structure. However, this might require higher compressive strength. In addition, there are other properties like to workability which need to be considered. All in all, this leads to a highly complex optimization problem, which requires the estimation of effective concrete properties, based on the mixture as input to a predictive simulation.
We present an automated workflow framework which combines experimental data with simulations, calibrates the simulation and performs the desired optimization. This workflow includes classical FE models, design guidelines based on model codes, as well as data driven methods. The chosen example is a beam, for which the concrete mixture is optimized to reduce GHG emissions. The first step is an estimation of material parameters, based on experimental data. This includes measures of stochastic distribution, allowing the quantification of the quality of the estimated parameters. The second step is the optimization. It takes into account constraints like the loading capacity after 28 days, the maximum allowed temperature during cement hydration and the maximum time till demoulding. The applied models include a Mori-Tanaka-based homogenization method to estimate effective concrete parameters, an FE simulation including the evolution of the concrete compressive strength and stiffness, the temperature field, displacements, and stress. This research shows a way towards a more performance-oriented material design.
Additive manufacturing (AM) has revolutionized the manufacturing industry, offering a new paradigm to produce complex geometries and parts with customized properties. Among the different AM techniques, the wire arc additive manufacturing (WAAM) process has gained significant attention due to its high deposition rate and low equipment cost. However, the process is characterized by a complex thermal history, dynamic metallurgy, and mechanical behaviour that make it challenging to simulate it in real-time for online process control and optimization.
In this context, a reduced order model (ROM) using the proper generalized decomposition (PGD) method is proposed as a powerful tool to overcome the limitations of conventional numerical methods and enable the real-time simulation of the temperature field of WAAM processes. Though, the simulation of a moving heat source leads to a hardly separable parametric problem, which is handled by applying a novel mapping approach. Using this procedure, it is possible to create a simple separated representation of the model, also allowing to simulate multiple layers.
In this contribution, a PGD model is derived for the WAAM procedure simulating the temperature field. A good agreement with a standard finite element method is shown. The reduced model is further used in a stochastic model parameter estimation using Bayesian inference, speeding up calibrations and ultimately leading to a calibrated real-time simulation.
Multiscale modeling of heterogeneous structures based on a localized model order reduction approach
(2023)
Many of today’s problems in engineering demand reliable and accurate prediction of failure mechanisms of mechanical structures. Thus, it is necessary to take into account the heterogeneous structure on the smaller scale, to capture the underlying physical phenomena. However, this poses a great challenge to the numerical solution since the computational cost is significantly increased by resolving the smaller scale in the model. Moreover, in applications where scale separation as the basis of classical homogenization schemes does not hold, the influence of the smaller scale on the larger scale has to be modelled directly. This work aims to develop an efficient concurrent methodology to model heterogeneous structures combining the variational multiscale method (VMM) [1] and model order reduction techniques (e. g. [2]). First, the influence of the smaller scale on the larger scale can be taken into account following the additive split of the displacement field as in the VMM. Here, also a decomposition of the global domain into subdomains, each containing a fine grid discretization of the smaller scale, is introduced. Second, local reduced approximation spaces for the smaller scale solution are constructed by exploring possible solutions for each subdomain based on the concept of oversampling [3]. The associated transfer operator is approximated by random sampling [4]. Herein, we propose to incorporate the actual physical behaviour of the structure of interest in the training data by drawing random samples from a multivariate normal distribution with the solution of a reduced global problem as mean. The local reduced spaces are designed such that local contributions of each subdomain can be coupled in a conforming way. Thus, the resulting global system is sparse and reduced in size compared to the direct numerical simulation, leading to a faster solution of the problem.
In recent years, the use of simulation-based digital twins for monitoring and assessment of complex mechanical systems has greatly expanded. Their potential to increase the information obtained from limited data makes them an invaluable tool for a broad range of real-world applications. Nonetheless, there usually exists a discrepancy between the predicted response and the measurements of the system once built. One of the main contributors to this difference in addition to miscalibrated model parameters is the model error. Quantifying this socalled model bias (as well as proper values for the model parameters) is critical for the reliable performance of digital twins. Model bias identification is ultimately an inverse problem where information from measurements is used to update the original model. Bayesian formulations can tackle this task. Including the model bias as a parameter to be inferred enables the use of a Bayesian framework to obtain a probability distribution that represents the uncertainty between the measurements and the model. Simultaneously, this procedure can be combined with a classic parameter updating scheme to account for the trainable parameters in the original model. This study evaluates the effectiveness of different model bias identification approaches based on Bayesian inference methods. This includes more classical approaches such as direct parameter estimation using MCMC in a Bayesian setup, as well as more recent proposals such as stat- FEM or orthogonal Gaussian Processes. Their potential use in digital twins, generalization capabilities, and computational cost is extensively analyzed.
In recent years, the use of simulation-based digital twins for monitoring and assessment of complex mechanical systems has greatly expanded. Their potential to increase the information obtained from limited data makes them an invaluable tool for a broad range of real-world applications. Nonetheless, there usually exists a discrepancy between the predicted response and the measurements of the system once built. One of the main contributors to this difference in addition to miscalibrated model parameters is the model error. Quantifying this socalled model bias (as well as proper values for the model parameters) is critical for the reliable performance of digital twins. Model bias identification is ultimately an inverse problem where information from measurements is used to update the original model. Bayesian formulations can tackle this task. Including the model bias as a parameter to be inferred enables the use of a Bayesian framework to obtain a probability distribution that represents the uncertainty between the measurements and the model. Simultaneously, this procedure can be combined with a classic parameter updating scheme to account for the trainable parameters in the original model.
This study evaluates the effectiveness of different model bias identification approaches based on Bayesian inference methods. This includes more classical approaches such as direct parameter estimation using MCMC in a Bayesian setup, as well as more recent proposals such as stat-FEM or orthogonal Gaussian Processes. Their potential use in digital twins, generalization capabilities, and computational cost is extensively analyzed.
For extrusion-based 3D concrete printing, the early age mechanical behavior is influenced by various time dependent phenomena: structural build-up, plasticity as well as viscosity. The structural build-up is governing the stability and early-age strength development of the fresh printable cementitious materials and with that influencing the printability, buildability, and open time of the printing process. Generally, it is influenced by a number of factors, i.e. composition of the printable material, printing regime, and ambient conditions (temperature, humidity, etc.). There are several approaches to model the structural build-up of cementitious materials. All models are based on a time-dependent internal structural parameter describing the flocculation state, which is assumed to be zero after mixing and increases with time. The approaches differ in the definition of the time dependency (linear, exponential, bi-linear). Usually, the parameters are defined for a specific material composition without considering the influence of ambient conditions.
In this contribution, the bi-linear structural build-up model [Kruger et al., Construction and Building Materials 224, 2019] is extended by the temperature influence. Temperature changes will occur in real life printing processes due to changing ambient conditions (summer, winter, day, night) as well as the printing process (pressure changes etc.) and have a significant impact on the structural build-up process: an increase of the temperature leads to a faster dissolution of cement phases, accelerates hydration and boosts the Brownian motion. For that reason, the model parameters are simulated as temperature dependent using an Arrhenius function. Furthermore, the proposed extended model is calibrated based on measurement data using Bayesian inference. A very good agreement of the predicted model data with the measured control data was reached. Additionally, the structural build-up model is integrated into a viscoelastic and elastoplastic mechanical model, simulating the whole mechanical behavior during layer deposition.
Basic oxygen furnace slag (BOFS) is a by-product of steelmaking of which about 10.4 Mt are produced annually in the EU. BOFS is mostly used in road construction, earthwork and hydraulic engineering. However, in this use, the iron bound in BOFS is lost and the opportunity to produce higher value products from BOFS is forgone.
In recent decades, many researchers have investigated the production of both Portland cement clinker and crude iron from BOFS via a thermochemical reductive treatment. The reductive treatment of liquid BOFS causes a reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density and can be recovered. An advantage of this process is that simultaneously the chemical composition of the reduced BOFS is adapted to that of Portland cement clinker and the hydraulic reactive mineral alite (Ca3SiO5) is formed.
In this study, German BOFS was reduced in a small-scale electric arc furnace and a low-iron mineral product rich in alite was produced. Despite a chemical and mineralogical composition similar to that of Portland cement clinker, the reduced BOFS produced less heat of hydration, and its reaction was delayed compared to Portland cement. However, adding gypsum accelerated the hydration rate of the reduced BOFS.
Further research to improve the hydraulic properties of the reduced BOFS is essential. If successful, the production of a hydraulic material and crude iron from BOFS could have economic and ecological benefits for both the cement and steel industry.
FAIR (findable, accessible, interoperable and reusable) data usage is one of the main principals that many of the research and funding organizations include in their strategic plans, which means that following the main principals of FAIR data is required in many research projects. The definition of data being FAIR is very general. When implementing that for a specific application or project or even setting a standardized procedure within a working group, a company or a research community, many challenges arise. In this contribution, an overview about our experience with different methods and tools is outlined.
We begin with a motivation on potential use cases for the application of FAIR data with increasing complexity starting from a reproducible research paper over collaborative projects with multiple participants such as Round-Robin tests up to data-based models within standardization codes, applications in machine learning or parameter estimation of physics-based simulation models.
In a second part, different options for structuring the data (including metadata schema) are discussed. The first one is the openBIS system, which is an open-source lab notebook and PostgreSQL based data management system. A second option is a semantic representation using RDF based on ontologies for the domain of interest.
In a third section, requirements for workflow tools to automate data processing are discussed and their integration into reproducible data analysis is presented with an outlook on required information to be stored as metadata in the database.
Finally, the presented procedures are exemplarily demonstrated for the calibration of a temperature dependent constitutive model for additively manufactured mortar. A metadata schema for a rheological measurement setup is derived and implemented in an openBIS database. After a short review of a potential numerical model predicting the structural build-up behavior, the automatic workflow to use the stored data for model parameter estimation is demonstrated.
Structural build-up describes the stability and early-age strength development of fresh mortar used in 3D printing. lt is influenced by several factors, i.e. the composition of the print able material, the printing regime, and the ambient conditions. The existing modelling approaches for structural build-up usually define the model parameters for a specific material composition with out considering the influence of the ambient conditions. The goal of this contribution is to explicitly include the temperature dependency in the modelling approach. Temperature changes have signifi cant impact on the structural build-up process: an increase of the temperature leads to a faster dissol ution of cement phases and accelerates hydration. The proposed extended model includes temperature dependency using the Arrhenius theory. The new model parameters are successfully calibrated based on Viskomat measurement data using Bayesian inference. Furthermore, a higher impact of the temperature in the re-flocculation as in the structuration stage is observed.
Dredging sediment refers to materials removed from the bottom of a water body during dredging operations. Mainly the dreading mud contains clay, silt, sand, water, and alkalis. This work incorporated dredging mud into the calcium sulfoaluminate cement at replacement levels of 0%, 10%, 30%, and 50% by weight. Pastes were evaluated after 1d, 28d, and 90d- hydration through mechanical strengths and the reaction rate by isothermal conduction calorimetry. XRD and MIP characterized the reaction products. The findings showed that small replacements (10% and 30%) increased early strength with higher ettringite formation in the system at 1d of curing. However, the evolution of mechanical strength was lower than the reference (0% replacement) over time. The results showed that in low replacement dosages, the dredging mud act as a nucleation site for the hydration of calcium sulfoaluminate phases.
The global demand for concrete is growing, and with it, its carbon footprint. Current literature proposes biochar, a product of pyrolysis, as a possible car-bon sink to reduce the carbon footprint of concrete. This work investigates the microstructure of Portland cement pastes with 0%, 5%, and 25% of the cement replaced with wood biochar, since this should influence its macro-scopic mechanical properties. MIP, gas sorption, NMR, and µ-CT were used to analyze the pore space of the three materials. The combination of these methods, each with different resolution, enables a multi-scale investigation of biochar impact on the microstructure of cement pastes. NMR confirmed that biochar can absorb moisture and, thus, reduces the effective water-to-cement ratio. MIP and gas sorption results show 0% and 5% volume re-placement have similar gel pore structure. The results from µ-CT investiga-tions suggest that biochar may reduce the formation of larger pores. The in-clusion of non-reactive porous particles such as biochar increase the porosity of the material and should act as a weakness in terms of mechanical proper-ties. Overall, this study highlights the need to carefully tailor replacement rates to control the impact of biochar on the microstructure concrete mixtures and sees a strong need for further studies on mechanical properties.
Understanding the fundamentals of bioreceptivity enables the developement of functionalized materials. Concrete as the most used building material worldwide is of special interest as microbially greened panels may represent an alternative to classic façade greening with plants. This project includes extensive outdoor experiments, in which eight differently structured concrete panels are weathered under different conditions, aiming to grow a stable biofilm of photosynthetic eukaryotic organisms. Documentation and data analysis of this experiment will be demonstrated using an example of one of the surfaces.
In the maritime context of offshore operation, corrosion, in combination with the materials used, poses a particular challenge to ensure safe operation over long indefinite periods and to minimise susceptibility to failure. Until today, only a few corrosion protection systems have proven themselves for the interaction of efficiency, installation, and maintenance in the offshore sector. In addition, available corrosion test methods sometimes have major deficits about conclusions of the durability. Therefore, there is more research and development needed.
The flagship project H2Mare of the Federal Ministry of Education and Research aims to enable the production of green hydrogen and PtX products at high seas. Research is being driven forward by the partners in four individual projects, where BAM is involved in two.
In PtX-Wind, major kinds of corrosion attacks at offshore constructions are characterized and investigated, and suitable corrosion protection measures determined. In TransferWind, attention focusses on transferring scientific results into standardization.
This poster at the H2Mare Conference 2023 presents an overview of the investigation methods and contribution of the department “Corrosion and Corrosion Protection”.
Main message: Sustainability, or in other words, exploiting environmental conservation for the economic welfare and prosperity for all, would revolutionise the plastics industry were it to become predominant practice as a linear, fossil-fuel–based economy is switched to a carbon circular economy. Food for though is given by dint of a critical overview of the current trends in sustainable flame-retardant polymeric materials.
Introduction:
Transforming the plastics industry into a carbon circular economy over the next 30 years requires an immediate revolution entailing the development of cutting-edge materials and the planning of future industrial production plants. Hence, the innovative field of flame-retardant polymeric materials should lend its strength to drive this challenge. Visionary solutions are proposed to inspire us, while the implementation of economically feasible concepts can take us forward into the future.
Experimental The synthesis, processing, polymer analysis, thermal analysis, and investigation of fire behaviour from our own research are performed according to the state of the art, mostly in accordance with the pertinent ISO standards. Indeed, some of our equipment is part of the accredited lab; for the other methods we fulfil equivalent quality standards in terms of maintenance, calibration, participation in round robins, etc. Work steps such as the synthesis or preparation of new materials are usually outsourced or done with partners that have the relevant core competence. The talk also presents examples from other groups whose experimental is described in the corresponding scientific papers.
Results and Discussion An overview of current trends towards producing sustainable, flame-retardant polymeric materials is presented, using examples from the literature and by sketching our own projects performed in recent years. The examples are structured along a common theme leading from the use of old and new natural materials with some intrinsic flame retardancy, via flame-retardant biopolymers and biocomposites, to using renewable sources for flame retardants with the objective of exploiting natural sources available as industrial waste streams. Natural flame retardants and adjuvants are highlighted, although the status of most may be assessed as merely motivating our vision. Nevertheless, there are natural material streams finding their way into polymer mass production as fillers, adjuvants, polymers, or renewable educt sources. Natural substances originating from industrial waste streams open the door to sustainable solutions, because they are often available at low cost and avoid competition for land with farming or virgin forests. Aside from this main topic, remarks will address the recycling of flame-retarded polymeric materials; vitrimers are mentioned as a potential material for recyclable thermosets. At the end of the day, only convincing property profiles will prevail both for exploiting renewable sources and circular design, including cost effectiveness, sufficient availability, consistent quality, processibility, mechanical properties, and flame retardancy. However, sustainability must not be merely tolerated as an additional demand, but should instead be recognized as a solution, because sustainability aspires to ensure our economic welfare now and in the future.
Acknowledgement:
The examples shown from own project were supported by funding grants: BMBF WTZ: 01DN16040, DFG Scha 730/19-1, VW-Stiftung: Experiment No: 97437, DFG Scha 730/20-1, BMBF KMU Innovativ 031B1289B.
Slow crack growth (SCG) under the influence of external fluid media, usually termed environmental stress cracking (ESC), is still one of the most frequent origins of severe damage and failure of polymeric materials. For polyethylene (PE) this is relevant for mass products, like bottles for consumer products, but also for high-performance materials for pipes or industrial packaging, including containers for chemicals and other dangerous goods. Especially for high-density polyethylene (PE-HD) the susceptibility to SGC and ESC is depending on the complex interplay between molecular weight and architecture and the resulting semicrystalline morphology, especially the formation of tie-molecules.
A reliable assessment of the resistance against this damage phenomenon is essential for demanding as well as safety-critical applications and has to take into account suitable testing methodologies and conditions in combination with environmental media reflecting the properties representative for typical fillings and relevant components causing ESC. In this context a better understanding of different influencing factors, such as sorption, swelling or surface activity is necessary together with a detailed characterization of different stages of crack propagation and underlying mechanisms. Therefor well-established testing methods, such as the Full Notch Creep Test (FNCT), were complemented by detailed fracture surface analysis using e.g. LSM and SEM in combination with a time-dependent optical monitoring of the progressing crack growth.
For the crack growth also the ratio of fibrillated craze zone to crack opening is important for the deeper understanding of crack propagation and related material parameters which can be additionally addressed by X-ray computed tomography.
A few layer/multilayer graphene (MLG) with a specific surface area of BET ≥ 250 m2/g is proposed as an efficient multifunctional nanofiller for rubbers. The preparation method, i.e., ultrasonically-assisted solution or latex premixing of master batches followed by conventional two-roll milling, strongly influences the dispersion in the elastomeric matrix and is fundamental for the final properties. When homogenously dispersed, single stacks of only approximately 10 graphene sheets, with an aspect ratio of ca. 35, work at low loadings, enabling the replacement of large amounts of carbon black (CB), an increase in efficiency, and a reduction in filler load. The appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing, gas barrier properties, electrical and thermal conductivity, as well as mechanical properties of different rubbers, as shown for chlorine-Isobutylene-Isoprene rubber (CIIR), nitrile-butadiene rubber (NBR), natural rubber (NR), and styrene-butadiene rubber (SBR).[1-5] 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of CB. The stronger interactions between MLG and NR or SBR also resulted in a reduction in the elongation at break by 20% and 50%, respectively, while the same parameter was hardly changed for CIIR/MLG and NBR/MLG. CIIR/MLG and NBR/MLG were stiffer but just as defomable than CIIR and NBR. The strong reinforcing effect of 3 phr MLG was confirmed by the increase of greater than 10 Shore A in hardness. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards flammability. We investigated MLG also as a synergist for reducing the aluminium trihydrate loading in flame retardant hydrogenated acrylonitrile-butadiene (HNBR), polybutadiene chloroprene (BR/CR), and chlorosulfonated polyethylene rubber(CSM).[6-8] The higher the nanofiller concentration is, the greater the improvement in the properties. For instance, the permeability decreased by 30% at 3 phr of MLG, 50% at 5 phr and 60% at 10 phr, respectively. Moreover, the MLG nanocomposites improve stability of mechanical properties against the effects of weathering. In key experiments an increase in UV-absorption and a pronounced radical scavenging were proved as stabilizing mechanisms. In a nutshell, MLG is an efficient multifunctional nanofiller ready to be used for innovative rubber development.
Packaging containers for dangerous goods that include aggressive liquids require that any packaging material that is based on high-density polyethylene has a high degree of stability and durability. This work is focused on testing the environmental stress cracking of the high-density polyethylenes used for such containers in contact with crop protection formulations, in particular, two model liquids established in Germany as standardized test media representatives for crop protection formulations containing the various admixtures typical for such products. One of the liquids is water-based and contains mostly surface-active ingredients, while the other is solvent-based and includes some emulsifiers. Originally established for pin impression tests, these model liquids and their individual components were here used for the first time as environmental media in the Full Notch Creep Test, which addresses the resistance against environmental stress cracking. The Full Notch Creep Test was carried out on five high-density polyethylene types with both model liquids, and also on one selected material with its components. The evaluation was focused on the fracture surface structures, which were visualized by a scanning electron microscope and by optical in situ imaging of the notch opening. While the water-based model liquid and its surface-active individual components induced environmental stress cracking with the characteristic pattern for a craze-crack mechanism and so-called brittle fracture on the surface, the solvent-based model liquid and its soluble ingredients exhibited rather ductile failure behavior, caused by the plasticizing effect on the polymer that reduced the yield stress of the high-density polyethylene.
For both cases, fracture surface analysis, together with side views of the crack opening, showed a clear relation between surface pattern, notch deformation (e.g., by blunting), or crack opening due to crack growth with time to failure and the solubility of the liquids in high-density polyethylene.
Since geothermal wells are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are in many cases extreme in terms of corrosion due to the chemical composition of hydrothermal fluids and temperatures. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities. During operation of a geothermal research facility in Groß Schönebeck copper and lead effects have been found downhole. Occurring mechanisms and measures to prevent precipitation or scaling needed to be investigated as well as potential influences of such precipitates on corrosion resistance of metallic materials used for equipment.
This contribution deals with the evaluation of the corrosion behavior of carbon steel and corrosion resistant alloys in copper and/or lead containing artificial geothermal water, simulating the conditions in the Northern German Basin.
The behavior of these materials in an artificial geothermal water obtained by electrochemical measurements and exposure tests are presented. While carbon steel exhibits precipitation and deposition, higher alloyed material shows different response to such species and a higher resistance in saline geothermal water.
Basing on these results the suitability of the investigated corrosion resistant alloy is given for use in such conditions, whereas carbon steel creates difficulties due to its susceptibility to Cu- and Pb-precipitation.
Significant Cu-deposition and precipitation only occurred in combination with carbon steel. High-alloyed materials prevent the disturbing Cu-agglomeration. Pb-deposition and precipitation only occurred in combination with carbon steel. No negative Pb-effect could be observed in combination with high-alloyed steels. High alloyed corrosion resistant alloys are suitable and shall be chosen for future design of the piping system, either in massive or in cladded form, to prevent unwanted interactions with brine components.
To prevent future alkali-aggregate reaction (AAR) damage, which has occurred frequently in the German highway network in recent years, a new regulation has been drafted. This regulation severely limits the use of alkali-sensitive aggregates by requiring that their suitability be verified by certified inspectors using newly developed AAR concrete tests that involve the external supply of alkali. This has led to a significant limitation in the number of aggregates usable for concrete pavements. A novel AAR avoidance strategy is now being pursued, which aims to enable the use of borderline alkali-sensitive aggregates through the application of an internal water-repellent treatment. The addition of water repellents during concrete production should significantly reduce the ingress of water and external de-icing salts into the concrete pavement, thus reducing the potential for AAR damage.
This paper presents the results of laboratory tests to assess the suitability of this new AAR prevention strategy. Representative, highly AAR-susceptible road paving concrete made with an alkali-sensitive greywacke and various water repellents were used as the basis for these experiments. The tests for concrete suitability included determining the conventional fresh and hardened concrete properties as well as concrete prism tests with external alkaline supply. Building on these results, laser-induced breakdown spectroscopy (LIBS) analyses of de-icing-salt intrusion as well as microscopic examinations for verification of the AAR characteristics were carried out.
The results of the AAR concrete tests with external alkaline supply support the conclusion that, when hydrophobic agents containing a suitable active ingredient are used, the AAR damage process in road paving concrete can be sufficiently prevented.
The adaption of the set-up for gas permeability measurements for ultra-high performance concrete
(2022)
In the framework of this project, a steam pressure vessel was to be developed from ultra-high perfor-mance concrete (UHPC) to withstand process temperatures of 200 °C and the respective steam pressure of 15,5 bar. To guarantee the long-term water vapour tightness of the system, the permeability of two UHPC mixtures were tested after long-term cyclic autoclaving. As UPHC shows a high density and therefore low permeability, measurements after the RILEM-Recommendation (TC 116-PCD) reached their detection limit. Therefore, the measurement set-up was adapted to measure the permeability of highly dense UHPC more reliably and quickly. This adaption includes measurements in a higher pres-sure range, the change of sample size thickness and the usage of Ar as a medium compared with the RILEM Recommendation. Additionally, the system was equipped with two pressure sensors and Ar-flowmeters to guarantee a continuous record of the experimental parameters. The new system was tested and evaluated by comparing measurements with the RILEM recommended system. Preliminary results show that the adapted system is capable to provide efficient and reliable results of concrete with low permeability.
For the construction of hot water storage tanks, ultra high performance concrete proofed to be a suitable building material to ensure water tightness. Common storage tanks build with concrete are designed to endure temperatures up to 90 °C. To increase the energy efficiency however, modern tanks need to withstand temperatures above 100 °C. With increasing temperature and correlating water vapor pressures, the cement must meet new requirements. Thermodynamic modelling is a promising tool for predicting the phase stabilities of minerals in the cement within these temperature and pressure ranges (T/P). Thus, mixture designs can be investigated and optimized with regard to the expected mineral phases in selected T/P-ranges. Additionally, predictions of the long-term material behavior can be derived from thermodynamic data and subsequently the experimental effort can be reduced notably. On the other hand, validation of predictions is needed. The base for the thermodynamic model is a thermodynamic equilibrium and thus, the experimental data for validation should approach the presumed conditions of the equilibrium. This study investigates variable experimental conditions for the hydration of Portland cement at 100 °C to reach a sufficiently progressed development of the phase composition. In case of Portland cement, the highest degree of hydration achievable within a reasonable time span is the most significant parameter. Therefore, Portland cement pastes with w/c ratios from 0.4 to 0.6 and dwell times up to three weeks were examined with powder X-ray diffraction to identify mineral phase changes. At 100 °C and high humidity, Portland cement paste shows the expected mineral phases like portlandite, katoite, and remaining clinker phases. The cement pastes with high water content and long dwell time seem to have the highest degree of hydration, even though the AFm phases stabilize with increasing w/c ratio. A dwell time of two weeks and a w/c ratio of 0.5 was found to provide the mineral composition with the highest degree of hydration including the major phase transitions.
The adaption of the set-up for gas permeability measurements for ultra-high performance concrete
(2022)
In the framework of this project, a steam pressure vessel was to be developed from ultra-high perfor-mance concrete (UHPC) to withstand process temperatures of 200 °C and the respective steam pressure of 15,5 bar. To guarantee the long-term water vapour tightness of the system, the permeability of two UHPC mixtures were tested after long-term cyclic autoclaving. As UPHC shows a high density and therefore low permeability, measurements after the RILEM-Recommendation (TC 116-PCD) reached their detection limit. Therefore, the measurement set-up was adapted to measure the permeability of highly dense UHPC more reliably and quickly. This adaption includes measurements in a higher pres-sure range, the change of sample size thickness and the usage of Ar as a medium compared with the RILEM Recommendation. Additionally, the system was equipped with two pressure sensors and Ar-flowmeters to guarantee a continuous record of the experimental parameters. The new system was tested and evaluated by comparing measurements with the RILEM recommended system. Preliminary results show that the adapted system is capable to provide efficient and reliable results of concrete with low permeability.
The aim of the project LeBeDigital is to present opportunities of digitalization for concrete applications and show a way towards a performance oriented material design.
Due to the high complexity of the manufacturing process of concrete and the range of parameters affecting the effective composite properties, a global optimization is challenging.
Currently, most optimization is only carried out on a narrow scope related to the respective players, e.g. a mix optimization for a target strength, or a design optimization for minimum weight, using a given mix. To enable a path toward a full global optimization
requires a reproducible chain of data, accessible for all contributors.
We propose a framework based on an ontology, which automatically combines experimental data with numerical simulations. This not only simplifies experimental knowledge transfer, but allows the model calibration and the resulting simulation predictions to be
reproducible and interpretable. In addition to an optimized set of parameters, this setup allows to study the quality and uncertainty of the data and models, as well as giving information about optimal experiments to improve the data set.
We will present the proposed optimization workflow, using the example of a precast concrete element. The contribution will focus on the workflow and challenges of an interoperable FEM formulation.
Corrosive geothermal brines are a major challenge to geothermal power-plants. For cost reasons, plant designers favorize low alloyed steels, e.g., carbon steel, which are susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic and saline properties. To solve such problem, coatings or inhibitors would be a protective solution as an alternative to the use of high alloyed materials.
This study investigated a coating system consisting of polyaniline/silicon dioxide basing on locally available resources. Protection against corrosion of carbon steel is shown by long-term exposure and electrochemical tests of coated carbon steels, performed in an artificial acidic and saline geothermal brine, comparable to real conditions at a site in Indonesia.
Therefore, an integrated coating system is presented for corrosion protection, combining the electro-chemical functionality of polyaniline and the physical advantages of silica.
The screening of coatings shows that the modification by adding individual pigment was not sufficient to protect carbon steel even during a short-term exposure, indicated by the discoloration after only seven days of exposure.
Electrochemical tests indicated that the coating cathodically protects carbon steel or slows down the corrosion reaction.
A long-term exposure test confirmed that the PANI/SiO2 modified coating successfully protects the carbon steel in the Sibayak artificial geothermal water at 150 °C for 6 months.
Overview of the state of the art and current trends with the main topics:
- renewable sources in flame retardant polymers (flame retarded bio-polymers and biocomposites; bio-flame retardants, renewable adjuvants from industrial waste)
- flame retardancy meets sustainability
- concepts between analogy and out-of-the-box.
Nuclear magnetic resonance (NMR) with focus on 1H protons is increasingly applied for non-destructive testing applications. Besides mobile NMR, laboratory devices such as the NMR core-analyzing tomograph are used. As their magnetic field is more homogeneous, they enable measurements with higher signal-to-noise ratios (SNR), but with limited sample sizes. The tomograph presented here (8.9 MHz) was constructed for a maximum sample diameter of 70 mm and length of up to 1 m. The resolution, the echo time (min. 50 µs), the SNR and the measurement type can be adjusted by means of exchangable coils. The tomograph enables measurements along the complete sensitive length, slice-selective and even 2- or 3-dimensional measurements. A movable sample lifting system thereby allows a precise positioning of the sample.
Polymeric membranes represent a cost- and energy-efficient solution for gas separation. Recently Polymers of Intrinsic Microporosity (PIMs) have been in a great interest because of their outstanding BET surface area larger than 700m2/g and pore size smaller than 1 nm. PIMs are a promising candidate in gas separation with high permeability and appealing selectivity due to their inefficient packing derived from a combination of ladder-like rigid segments with sites of contortion. However, it is recognized this class of polymers suffer from decrease in performance with time due to physical aging. The initial microporous structures approach a denser state via local chain rearrangements, leading to a dramatic reduction in permeability. As chain packing during film casting and physical aging are the key factors determine the performance in separation applications, characterization of the molecular mobility in these materials has been proved to provide valuable information. In recent research on PIM-1 the archetypal PIM, a molecular relaxation process with high activation energy together with a significant conductivity in the glassy state has been found and explained with the formation of local intermolecular agglomerates due to interaction of π-electrons in aromatic moieties of the polymer backbone. In this work, the dielectric behavior of the polymeric films and their response upon heating (aging) were measured by isothermal frequency scans during different heating/cooling cycles in a broad temperature range down to 133K for the first time. Multiple dielectric processes following Arrhenius behavior were observed. Local fluctuations, Maxwell-Wagner-Sillars (MWS) polarization and structural relaxations were discussed correlating to structural-properties of PIM-1. Up to now, no other work has studied the role of porosity and thermal history of PIM-1 film in dielectric processes. The goal is by eliminating thermal history and considering storing conditions provide better understanding on aging and plasticizing in high free volume glassy polymer PIM-1.
Especially now in times of the energy revolution, the demand for energy-efficient separation processes promotes the advancement of new high-performance materials for use as highly selective separation membranes. Polymers with intrinsic microporosity (PIMs) are of high interest in the field of gas separation membranes. Currently the application of PIMs for membrane technology is still restrained by their strong tendency to physical aging involving a significant loss of their good gas separation properties. Physical aging phenomenon is related to the molecular mobility of PIMs which was investigated by broadband dielectric spectroscopy (BDS) previously [1]. In this work, covalent phosphinine-based framework (Eto-CPSF) was used as a nanofiller (0-10 wt %) in a PIM-1 matrix to potentially enhance the gas transport properties and prevent physical aging. Since molecular mobility is a fundamental parameter determining gas transport as well as physical aging in such a material, our study includes dielectric investigations by BDS of pure PIM-1 and PIM-1/Eto-CPSF mixed matrix membranes to establish a correlation between molecular mobility and gas transport properties. In addition, gas permeability was determined by the time-lag method (0-10 bar pressure) at 35 °C for N2, O2, CH4 and CO2 for all MMMs.
The dielectric behavior of the polymeric films and their response upon heating were measured by isothermal frequency scans during different heating/cooling cycles in a broad temperature range up to 250 °C. Multiple dielectric processes following Arrhenius behavior were observed. Local fluctuations, Maxwell-Wagner-Sillars (MWS) polarization and structural relaxations were discussed correlating to structural-properties of PIM-1. As main result for MMMs, the permeability of PIM-1 for CH4 and CO2 gases were increased significantly with only 5 wt% of nanofiller within the polymer matrix. However, this is not observed for Eto-CPSF concentrations higher than ca. 7 wt% probably due to a microphase separated morphology of the nanocomposite system. Furthermore, the permselectivity of membranes for pair gases O2/N2 and CO2/N2 show enhancement up to a concentration of about 7 wt% Eto-CPSF filler.
Determination of the corrosion product layer resistance on zinc samples by using gel electrolytes
(2022)
Crash barriers, railings, lamp posts, waste glass containers - these are just a few of the many examples of galvanized surfaces. They withstand wind and weather for decades, which is possible thanks to a protective layer made of corrosion products. When designing the atmospheric durability of galvanized components, a linear corrosion loss is assumed. In the past 30 years, however, the surrounding atmosphere has changed a lot. Due to the restriction of sulfur exhaust air, acid rain completely disappeared in Europe and Germany, which has a direct influence on the type and protective effect of the corrosion products. Under the influence of current atmospheric conditions, zinc layers are significantly more resistant and no longer show any linear corrosion loss. The established test methods cannot correctly map this change in neither short-term nor long-term tests and thus provide incorrect results. In order to solve this problem, a new measurement method was developed at BAM that can assess the protective effect of the formed surface layers in a minimally invasive manner without damaging the sample and in short test times. For this new method, gel electrolytes are used and the so-called corrosion product layer resistance RL, which is made up of various surface resistances, is measured electrochemically. As a single measurement, the surface layer resistance can provide information about the existing corrosion protection, while time-dependent measurements assess the stability of the layer. Thus, it is possible again to evaluate the corrosion protection layer. Furthermore, this method can also be used for field measurements on real components.
To reveal the corrosion resistance of casing steel/mortar interface in CO2 injection condition, sandwich samples were prepared and exposed up to 20 weeks in aquifer fluid under 10 MPa and 60 °C. Cross section analysis revealed the crevice corrosion as main mechanism instead of pitting corrosion, which would be expected to happen in the extremely high Chloride concentration. Detailed analysis using EDS line scan shown the slow diffusion of Chloride, suggesting why pitting did not happen after 20 weeks. To mimic the passivated steel surface, the steel coupon was passivated in simulated pore solution having pH 13.5 for 42 days. The passivated coupon was further exposed to NGB solution for 28 days. Electrochemical characterization was performed along the exposure processes to reveal the change in impedance, indicating the corrosion resistance of steel casing/mortar interface.
Significant Cu-deposition and ‑precipitation only occurred in combination with carbon steel. High-alloyed materials prevent the disturbing Cu-agglomeration. Pb-deposition and ‑precipitation only occurred in combination with carbon steel. No negative Pb-effect could be observed in combination with high-alloyed steels. High alloyed corrosion resistant alloys are suitable and shall be chosen for future design of the piping system, either in massive or in cladded form, if formation of crevices with non-metallic materials can be excluded!
A series of field exposure tests according to ISO 9223 up to 9226 was carried out at different locations to determine the corrosivity and the corrosion progress of different test sites throughout northern and eastern Germany. Standard test specimens of steel, zinc, copper and aluminium were exposed to rural, city and marine atmosphere at test sites of the Bundesanstalt für Materialforschung und -prüfung (BAM). Test sites at city atmosphere comprised exposure on a rooftop, next to a highly frequented road and directly at a motorway. Exposure under marine conditions was carried out at Heligoland in the North Sea. The specimens were stored under sheltered and unsheltered conditions on each test site, respectively. Corrosion rates after the first year of field exposure were determined and used for the classification of the atmospheres and the test sites regarding the corrosivity category.
Results after the first year of exposure were presented at the EUROCORR 2018 in Cracow. The current presentation will present an update of results of the systematic study after five years of exposure. The corrosion progress and the mass loss of the standard metals steel, zinc, copper and aluminium will be presented and discussed with respect to the atmospheric conditions and the time of wetness at the test sites. In addition, the difference between sheltered and unsheltered conditions will be discussed.
With increasing focus on industrialized processing, investigating, understanding, and modelling the structural build-up of cementitious materials becomes more important. The structural build-up governs the key property of fresh printable materials -- buildability -- and it influences the mechanical properties after the deposition. The structural build-up rate can be adjusted by optimization of the mixture composition and the use of concrete admixtures. Additionally, it is known, that the environmental conditions, i.e. humidity and temperature have a significant impact on the kinetic of cement hydration and the resulting hardened properties, such as shrinkage, cracking resistance etc. In this study, small amplitude oscillatory shear (SAOS) tests are applied to examine the structural build-up rate of cement paste subject to different temperatures under controlled humidity. The results indicate significant influences of the ambient temperature on the intensity of the re-flocculation (Rthix) rate, while the structuration rate (Athix) is almost not affected. A bi-linear thixotropy model extended by temperature dependent parameters coupled with a linear viscoelastic material model is proposed to simulate the mechanical behaviour considering the structural build-up during the SAOS test
With increasing focus on industrialized processing, investigating, understanding, and modelling the structural build-up of cementitious materials becomes more important. The structural build-up governs the key property of fresh printable materials -- buildability -- and it influences the mechanical properties after the deposition. The structural build-up rate can be adjusted by optimization of the mixture composition and the use of concrete admixtures. Additionally, it is known, that the environmental conditions, i.e. humidity and temperature have a significant impact on the kinetic of cement hydration and the resulting hardened properties, such as shrinkage, cracking resistance etc. In this study, small amplitude oscillatory shear (SAOS) tests are applied to examine the structural build-up rate of cement paste subject to different temperatures under controlled humidity. The results indicate significant influences of the ambient temperature on the intensity of the re-flocculation (Rthix) rate, while the structuration rate (Athix) is almost not affected. A bi-linear thixotropy model extended by temperature dependent parameters coupled with a linear viscoelastic material model is proposed to simulate the mechanical behaviour considering the structural build-up during the SAOS test.
Numerical simulations are essential in predicting the behavior of systems in many engineering fields and industrial sectors. The development of accurate virtual representations of actual physical products or processes (also known as digital twins) allows huge savings in cost and resources. In fact, digital twins would allow reducing the number of real, physical prototypes, tests, and experiments, thus also increasing the sustainability of production processes and products’ lifetime. Standard numerical methods fail in providing real time simulations, especially for complex processes such as additive manufacturing applications.
This work aims to use a reduced order model for efficient wire arc additive manufacturing simulations, calibrations and real-time process control. Model reduction, e.g. the proper generalized decomposition [1,2] method, is a popular concept to decrease the computational effort. A new mapping approach [3] was applied to simulate a moving heat source with the proper generalized decomposition. Using this procedure even complex models can be simulated in real-time. The physical model is later on calibrated with the use of a stochastic model updating process and the reduced order model, leading to an optimized real-time simulation.
In this contribution, a proper generalized decomposition model for a bead-on-plate wire arc additive manufacturing is presented. It is also coupled with a stochastic model updating process identifying the heat source characteristics as well as the boundary conditions of the transient thermal problem, whereas the heat source shape is simulated using a Goldak heat source
Concrete has a long history in the construction industry and is currently one of the most widely used building materials. Especially precast concrete elements are frequently utilized in construction projects for standardized applications, increasing the quality of the composite material, as well as reducing the required building time. Despite the accumulated knowledge, continuous research and development in this field is essential due to the complexity of the composite combined with the ever-growing number of applications and requirements. Especially in view of global climate change, design aspects as CO2 emissions and resource efficiency require new mix designs and optimization strategies. A result of the material’s high complexity and heterogeneity on multiple scales is that utilizing the full potential with changing demands is highly challenging, even for the established industry. We propose a framework based on an ontology, which automatically combines experimental data with numerical simulations. This not only simplifies experimental knowledge transfer, but allows the model calibration and the resulting simulation predictions to be reproducible and interpretable. This research shows a way towards a more performance oriented material design. Within this talk we present our workflow for an automated simulation of a precast element, demonstrating the interaction of the ontology and the finite element simulation. We show the automatic calibration of our early-age concrete model [1, 2], to improve the prediction of the optimal time for the removal of the form work.
The incorporation of nanoscale particles into elastomers enable a boost in performance and/or a distinct reduction of conventional filler loadings due to their high surface to volume ratio. 2D layered nanoparticles like graphene and graphene-related materials provide a great potential as effective fillers in rubber, especially by enhancing mechanical and barrier properties. The type and properties of the nanoparticles, their interface and the elastomeric matrix materials influence the technical behavior, and therefore the potential application fields of such rubber nanocomposites. Especially crucial for the efficiency of the nanofiller, however, is its best possible incorporation into the elastomer. The dispersing of nanoparticles without agglomerates usually constitutes a challenge when using conventional two-roll milling or internal mixing. Academic approaches for highly dispersed nanocomposites solve this problem but are often energy and time consuming with no feasible scale up possibility. Therefore, an ultrasonic assisted NR latex premixing process was established to produce highly filled masterbatches, enabling the main processing with conventional rubber processing techniques.
Two carbon-based nanoparticles with similar specific surface areas were investigated and incorporated in natural rubber as nanocomposites: A commercially available multilayer graphene (MLG) and a nanoscale carbon black (nCB). The mentioned premixed masterbatches were further processed to nanocomposites by the addition of matrix NR, two-roll milling, and hot pressing (vulcanization). By this procedure an increase in Young’s modulus of 157% (MLG) and 71% (nCB) could be obtained at a concentration level of 3 phr. As anisotropic material behavior was observable for the nanocomposites containing MLG, different measurement methods were investigated to quantify the orientation of the nanoparticles in the nanocomposites: Sorption measurements (swelling in 2 dimensions), hardness and dynamical mechanical analysis (in-plane vs. cross-plane), X-Ray diffraction and transmission and scanning electron microscopy.
A few layer/multilayer graphene (MLG) with a specific surface area of BET=250 m2/g is proposed as an efficient multifunctional nanofiller for rubbers. The preparation method, i.e., ultrasonically-assisted solution mixing of master batches followed by two-roll milling, strongly influences the dispersion in the elastomeric matrix and is fundamental for the final properties. When homogenously dispersed, single stacks of only approximately 10 graphene sheets, with an aspect ratio of 34, work at low loadings, enabling the replacement of large amounts of carbon black (CB), an increase in efficiency, and a reduction in filler load. The appropriate preparation yielded nanocomposites in which just 3 phr are sufficient to significantly improve the rheological, curing, gas barrier properties, electrical and thermal conductivity, as well as mechanical properties of different rubbers, as shown for chlorine-Isobutylene-Isoprene rubber (CIIR), nitrile-butadiene rubber (NBR), natural rubber (NR), and styrene-butadiene rubber (SBR). 3 phr of MLG tripled the Young’s modulus of CIIR, an effect equivalent to 20 phr of CB. The stronger interactions between MLG and NR or SBR also resulted in a reduction in the elongation at break by 20% and 50%, respectively, while the same parameter was hardly changed for CIIR/MLG and NBR/MLG. CIIR/MLG and NBR/MLG were stiffer but just as defomable than CIIR and NBR. The strong reinforcing effect of 3 phr MLG was confirmed by the increase of greater than 10 Shore A in hardness. MLG reduces gas permeability, increases thermal and electrical conductivities, and retards flammability, the latter shown by the reduction in heat release rate in the cone calorimeter. We investigated MLG also as a synergist for reducing the aluminium trihydrate loading in flame retardant hydrogenated acrylonitrile-butadiene (HNBR), polybutadiene chloroprene (BR/CR), and chlorosulfonated polyethylene rubber(CSM). The higher the nanofiller concentration is, the greater the improvement in the properties. For instance, the permeability decreased by 30% at 3 phr of MLG, 50% at 5 phr and 60% at 10 phr, respectively. Moreover, the MLG nanocomposites improve stability of mechanical properties against the effects of weathering. In key experiments an increase in UV-absorption and a pronounced radical scavenging were proved as stabilizing mechanisms. In a nutshell, MLG is an efficient multifunctional nanofiller ready to be used for innovative rubber development.
The presentation shows systematic investigations to describe the corrosion and corrosion product formation processes of pure zinc under the climatic conditions currently prevailing in the Federal Republic of Germany. The investigations in their entirety aim at questioning current and establishing new ways of looking at the formation of corrosion products of pure zinc under atmospheric corrosion conditions. Thus, they make a significant contribution in understanding corrosion protection by zinc and zinc coatings. In particular, the focus is placed on the initial stage of the corrosion product formation. A systematic investigation of this time range, which is characterized by very reactive corrosion products, is only made possible by using gel-type electrolytes. The short periods of time at the beginning of weathering is now measurable and their influence on the formation of corrosion products and the kinetics of layer formation describable. By combining the new electrochemical approach with gravimetric, microscopic and analytical methods, new insights could be gained both on a methodic and scientific level.
Emanating from developing flame retarded biocomposites, we have proposed renewable natural fibers (including keratin) taken from industrial waste as an authentic sustainable approach. More recently, we have investigated non-vegan flame retardant approaches. This paper loves to give you an insight into our ongoing projects on biogenic industrial wastes like leather, bone meal, and insects. Materials were characterized multi-methodically, flame retardant modes of action quantified, decomposition mechanism proposed, and synergisms explained. Considering the large quantities of leather waste (LW) in industrial-scale production, we underline LW as multifunctional bio-adjuvants. LW enhances the flame retardancy of poly(ethylene-vinyl acetate) (EVA) containing phosphorus flame retardants (P-FR). Products/by-products of the invertebrate and vertebrate farming, respectively, are promising bio-based adjuvants in flame retarded bio-epoxy thermosets. While the addition of bone meal yields the formation of an inorganic shield, protein-based powders from insects provide an intumescent behavior. In combination with a P-FR superior charring and self-extinguishing are obtained.
Acknowledgement: In part of this work was supported by the Volkswagen Foundation grant “Experiment!” No. 97437.
Commercially available carbon steels are suitable for compression and pipelines as long as moisture content and impurities are limited. (water 50 to 100 ppmv, SO2 and NO2 ca. 100 ppmv) Corrosion rates increase with increasing water content. (0.2 – 20 mm/a) Condensation of acids and therefore droplet formation is always possible, even at low water contents. A low SO2 content within the CO2-stream might be more important than a low water content. Cr13-steels showed a general susceptibility to shallow pitting and pitting. So, they seem to be not suitable for CCUS applications. Low alloyed steels showed better corrosion behavior (predictable uniform corrosion). For direct contact with saline aquifer fluids only high alloyed steels shall be used.
Elektrochemische Messungen zur hygienischen Bewertung additiv gefertigter Bauteile werden diskutiert. Die Bewertung und Details des Werkstoffs werden beschrieben, Anwendungsbeispiele gezeigt.
2D layered nanoparticles enable a distinct reduction of filler loadings in rubber compounds combined with a boost in performance due to their high surface to volume ratio. They often enable unique property profiles providing a great potential as effective fillers in rubber, especially by enhancing mechanical and barrier properties.
As the best possible incorporation into the elastomer matrix is crucial for the efficiency of the nanofiller, dispersing and exfoliation of the nanoparticles without formation of agglomerates usually constitutes an outstanding challenge - especially when using conventional processing methods. Laboratory-scale approaches for highly dispersed nanocomposites sometimes solve this problem, but these are often too energy and time consuming and provide no scale up possibility for real applications. Therefore, a latex premixing process was established to produce highly filled masterbatches, enabling the processing with conventional techniques.
The presence of nanoparticles greatly impacts the behavior of elastomeric compounds, besides affecting the properties of the final product also the processing is influenced (rheology, crosslinking).
In this study, nanocomposites of natural rubber and multilayer graphene (MLG) were prepared via a latex masterbatch route. Different strategies for masterbatch premixing are compared (stirring vs. ultrasonication, coagulation vs. drying). Dispersion and exfoliation of MLG were determined by transmission electron microscopy. The reinforcing effect of MLG affects the viscosity while the dispersed graphene layers may also act as diffusion barrier/absorbent for the crosslinking agents. In contrast to that, MLG forms physical crosslinks in the final product. Swelling measurements and differential scanning calorimetry allow a differentiation between chemical and physical network links. Different technical properties of the nanocomposites were measured with respect to mechanical and application relevant behavior.
ln most of the ASR-test procedures, the expansion of concrete or mortar specimens is used as an indicator to assess the ASR-potential of an aggregate or a specific concrete mix. For these tests, the specimens are stored in an ASR-provoking environment, where the reaction is accelerated by elevated temperature and humidity. To measure the length change, the storage must be interrupted for at least a few minutes. Düring the 60 °C Concrete Prism Test (60 °C-CPT), the specimens are cooled down to 20 °C for 24 hours, to ensure the same hygrothermal conditions for every measurement. This limits the number of measurements during the test period and may lead to additional effects, that probably influence the expansion development.
With a recently developed device, it is possible to continuously monitor the expansion ofprisms without interrupting the ASR-provoking storage. Due to the dense database of this automated test, the results can contribute to a better understanding of the ASR-process. This study compares results of the automated and conventional 60 °C-CPT. Tests of different aggregates showed, that the results of the automated and conventional test are consistent, but the expansions during the conventional test are generally higher. Preliminary results led to the conclusion, that the cooling for the measurements leads to additional expansions. Therefore, a modified threshold should be discussed for the automated 60 °C-CPT.
The durability of concrete structures due to alkali-silica-reaction (ASR) is usually been assessed by ASR concrete prism tests (CPT). Therefore, the expansion of concrete specimens indicates an alkalisensitivity.
In Germany these tests are performed at 40°C or accelerated 60°C. Nevertheless, ASR prism tests are expensive, power and time-consuming. For these reasons, an alternative chemical test (“mod. BTU-test”) was developed in the past. The “mod. BTU-test” was correlated with German standard CPT.
In this test, the solubility of silica and alumina in the liquid phase is measured by ICP-OES.
For special requirements in concrete road construction, stricter test procedures are necessary. The specimens are repeatedly subjected to cyclic alternating storage in NaCl. On the one hand, the presence of NaCl increases the ASR expansion, on the other hand NaCl also changes the dissolution behaviour of silica and alumina.
For now is not possible to correlate the solubilities of “mod. BTU-test” and ASR expansions influenced by NaCl. Therefore, four aggregates with different ASR sensitivities were chosen and ASR concrete prism tests (in addition with NaCl) have been performed. According to the “mod. BTU-test” the solubilities of silica and alumina in presence of different NaCl concentrations were measured.
This paper is about the regression analysis of silica and alumina dissolution and ASR expansion tests in presence of NaCl. The regression analysis shows the influence of a quasi-continuous and an interrupted cyclic alternating storage. Additionally the effects of temperature and NaCl concentration are investigated. In the end, a suitable NaCl concentration of the “mod. BTU-test” for dissolution experiments is recommended. The “mod. BTU-Test” with NaCl might be a serious and reliable test method for ASR classification for concrete road construction.
To prevent future alkali-aggregate reaction (AAR) damage, which has occurred frequently in the Germanhighway network in recent years, a new regulation has been drafted. This regulation severely limits the use of alkali-sensitive aggregates by requiring that their suitability be verified by certified inspectors using newly developed AAR concrete tests that involve the external supply of alkali. This has led to a significant limitation in the number of aggregates usable for concrete pavements. A novel AAR avoidance strategy is now being pursued, which aims to enable the use of borderline alkali-sensitive aggregates through the application of an internal water-repellent treatment. The addition of water repellents during concrete production should significantly reduce the ingress of water and external de-icing salts into the concrete pavement, thus reducing the potential for AAR damage.
This paper presents the results of laboratory tests to assess the suitability of this new AAR prevention strategy. Representative, highly AAR-susceptible road paving concrete made with an alkali- sensitive greywacke and various water repellents were used as the basis for these experiments. The tests for concrete suitability included determining the conventional fresh and hardened concrete properties as well as concrete prism tests with external alkaline supply. Building on these results, laser-induced breakdown spectroscopy (LIBS) analyses of de-icing-salt intrusion as well as microscopic examinations for verification of the AAR characteristics were carried out.
The results of the AAR concrete tests with external alkaline supply support the conclusion that, when hydrophobic agents containing a suitable active ingredient are used, the AAR damage process in road paving concrete can be sufficiently prevented.
The chapter gives a brief introduction to (nano)compositecomposite materials having the focus on polymer-based nanocomposites. The different dimensionalities of nanoparticles are introduced, along with their distribution in the matrix.
Different application fields of polymer-based nanocomposites, like flame retardancy, filled rubbers, nanofilled thermosets and thermoplastics, separation membranes and nanodielectrics, are considered in greater detail.
Utilisation of alkali-sensitive aggregates for concrete pavements by internal hydrophobisation
(2021)
In order to avoid the increased ASR damage to concrete pavements in the German motorway network in the future, the ARS 04/2013 introduced mandatory suitability tests to exclude alkali-sensitive aggregates in new construction measures. This resulted in a significant reduction of suitable aggregates. Against this background, borderline alkali-sensitive aggregates are to be made usable by adding an internal water repellent agent during concrete casting. The ASR avoidance strategy is based on the significant reduction of the penetration of water and de-icing salt solution into the concrete pavement. Laboratory tests show that, with a suitable active ingredient, the ASR damage process can be significantly reduced with internal hydrophobisation. The disadvantage is that this is associated with a deterioration of the mechanical properties and the resistance to freeze-thaw with de-icing salt. The aim of the ongoing research is to reduce these disadvantages through targeted modification of the hydrophobising agent and air-entraining agent.
Evaluation of corrosion resistance of metallic materials is essential to assure safe and reliable operation of geothermal sites. One need to be aware that corrosion is not a material's but a system property, determined by medium, material and construction aspects. Various corrosion types have to be evaluated. Conditions in laboratory shall reflect on-site reality. Depending on brine composition and temperature suitability of metallic materials can be ranked. Most important outcome of the research is that highly saline geothermal brines require high alloyed materials, for safe long-term operation.
In recent years, the demand for new and sustainable products has been constantly rising. Especially cementitious materials are known for their high carbon footprint and novel approaches will be needed to counterbalance that. The BAM departments 7.1 (building materials) and 4.0 (Material and the environment) try to improve the sustainability of concrete panels by establishing a biofilm on the weather protection layer. Using an ultra-high-performance-concrete allows the production of very thin facade tiles with a small carbon footprint. Furthermore, the durability of these tiles is expected to surpass the one of “normal” concrete facades and offer the possibility of modular renewing of defective tiles instead of a wall, or even remodeling a whole building. The controlled application of biofilms on facades aims to improve biodiversity, microclimate, and air quality in cities. Furthermore, the greening of typically gray surfaces could improve the mental health of the residents. The project focuses on testing a multiplicity of concrete samples, varying e.g., in roughness or pH. The bioreceptivity is analyzed via laboratory tests, as well as in perennial outdoor experiments.
Integrated Coating System for Corrosion Protection of Carbon Steel in Artificial Geothermal Brine
(2022)
Corrosive geothermal brines are a major challenge to geothermal power-plants. For cost reasons, plant designers prefer to use carbon and low alloyed steels, which are susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic and saline properties. To solve such problem, coatings or inhibitors would be a protective solution as an alternative to the use of high alloyed materials.
This study investigated a coating system consisting of polyaniline/silicon dioxide based on resources locally available in Indonesia. Protection against corrosion of carbon steel was shown by long-term (28 day) exposure and electrochemical tests of coated carbon steels, performed in an artificial acidic and saline geothermal brine, comparable to the conditions encountered at a site in Indonesia.
Therefore, an integrated coating system is proposed for corrosion protection, combining the electrochemical functionality of polyaniline and the physical advantages of silica.
We report dielectric and calorimetric studies on metathesis and addition-type polytricyclononenes, both based on the same monomer bearing three pendant OSiMe3 groups. For the addition-type polymer, dielectric spectroscopy reveals a β*-process related to the microporosity, whereas for its metathesis counterpart, the segmental dynamics manifests as an α-process related to a glass transition. Besides active dielectric processes, a significant conductivity contribution is detected for both samples which for the microporous additiontype polymer is three orders of magnitude greater than for the metathesis polymer. The broadband dielectric spectroscopy is complemented by detailed calorimetric investigations, comprising DSC, FSC, and TMDSC. The calorimetric methods detected the glass transition for the metathesis polymer in agreement with the observed dielectric α-process. Furthermore, the already reported gas transport properties for both polymers are compared, setting them in correlation with the observed molecular mobility and conductivity behavior. The discussed results reflect significant differences in molecular mobility of the two polymers affecting the appearance of microporosity which strongly determines the gas transport properties.
The characterization of the mechanical properties and behaviour of adobe masonry is fundamental for the understanding of the structural behaviour of adobe constructions. Thus, in the last decades, experimental studies focused on this topic have been carried out by different authors. Many of the existing experimental works, however, were carried out aiming to support broader studies focused on the seismic behaviour of adobe constructions and are not very detailed. Moreover, authors tend to adopt different procedures in their experimental work, since there are few indications in existing standards for testing adobe masonry. The wide variety in materials used, both for the adobes and mortars, further complicates this work, making it difficult to compare results obtained in different studies. This chapter provides an overview of the indications given by standards and other technical recommendations for the mechanical testing of adobe masonry. It presents a review of existing research on the mechanical behaviour of adobe masonry, addressing studies that focus on: (i) compression behaviour, (ii) shear behaviour, (iii) joint shear behaviour. It provides a global analysis of the existing knowledge, suggesting improvements for normative documents and identifying future Research needs.
The mechanical characterization of adobe bricks is an important first step in the study of the behaviour of adobe masonry. For this reason, in the last decades, different authors have conducted research on the mechanical behaviour of adobes from various regions of the world. Despite the importance of mechanical characterization, there are still only a few standards and normative documents with clear indications for the mechanical testing of earthen materials and, in general, These indications are not thorough and vary among different countries. Consequently, authors tend to adopt different types of test specimens and procedures in their experimental work, thus obtaining results that are not directly comparable. The fact that the materials and procedures traditionally used are also not standardized,varying greatly from region to region, also contributes to the difficulty of comparing results from different studies. This chapter presents a review of the indications provided by codes, standards and other technical recommendations for the mechanical testing of adobe bricks, as well as a detailed review of procedures adopted, and results obtained by different authors regarding the mechanical characterization of traditional adobe bricks. This chapter focuses, in particular, on the behaviour of adobe bricks when subjected to simple compression. It provides an overview of the existing knowledge and identifies needs for future research and development.
If the amount of sulfate within the mix design for concrete is not balanced, ettringite formation which first controls solidification continues while the concrete is hardening. Ettringite forms by reaction of sulfate contained in the cement or in some admixture with calcium aluminate (C3A) as cement component. The “late primary ettringite formation” promotes an increase in volume within the hardened concrete leading to cracks. To analyze the effect of substituting part of ordinary Portland cement (OPC) by a treated brown coal fly ash mortar bars were tested according to ASTM C452. This test method was originally developed to extrapolate from the internal to external sulfate attack and is based on the idea that by testing a concrete mixture containing sulfate the process of deterioration is accelerated because it does not have to diffuse into the concrete before reaction first. In addition to the samples prescribed in ASTM C452 further samples in the size of the German SVA procedure were tested also designed for accessing the external sulfate resistance. The results show that while the replacement of 25 % of cement by brown coal fly ash leads to length changes around the limit defined by ASTM, the substitution of 50 % cement exceeded the limit by a multiple. The progress of expansion is the very similar for the two geometries tested. In-situ XRD measurements confirmed that while for pastes made of OPC the formation of ettringite is completed after 20 hours, this is not true for the mixtures containing the brown coal fly ash.
In a different study the effect of hydrothermal treatment on the phase composition of ultra-high-performance concrete was analyzed. The results show that the sulfate and aluminate resulting from the decomposition of ettringite are bound into new phases.
If this binding is permanent this might allow the larger use of sulfate bearing raw materials.
If the amount of sulfate within the mix design for concrete is not balanced, ettringite formation which first controls solidification continues while the concrete is hardening. Ettringite forms by reaction of sulfate contained in the cement or in some admixture with calcium aluminate (C3A) as cement component. The “late primary
ettringite formation” promotes an increase in volume within the hardened concrete leading to cracks. To analyze the effect of substituting part of ordinary Portland cement (OPC) by a treated brown coal fly ash mortar bars were tested according to ASTM C452. This test method was originally developed to extrapolate from the internal to external sulfate attack and is based on the idea that by testing a concrete mixture containing sulfate the process of deterioration is accelerated because it does not have to diffuse into the concrete before reaction first. In addition to the samples prescribed in ASTM C452 further samples in the size of the German SVA procedure were tested also designed for accessing the external sulfate resistance. The results show that while the replacement of 25 % of cement by brown coal fly ash leads to length changes around the limit defined by ASTM, the substitution of 50 % cement exceeded the limit by a multiple. The progress of expansion is the very similar for the two geometries tested. In-situ XRD measurements confirmed that while for pastes made of OPC the formation of ettringite is completed after 20 hours, this is not true for the mixtures containing the brown coal fly ash.
In a different study the effect of hydrothermal treatment on the phase composition of ultra-high-performance concrete was analyzed. The results show that the sulfate and aluminate resulting from the decomposition of ettringite are bound into new phases. If this binding is permanent this might allow the larger use of sulfate bearing raw
materials.
Analyzing the performance of discrete galvanic anode systems using electrochemical investigations
(2021)
Corrosion of reinforcement is one of the major reasons in questioning the service life of building structures. The application of cathodic protection techniques plays a big role in controlling the corrosion process to ensure a longer service life of building structures. This systematic study compares the efficiency and durability of various discrete galvanic zinc anode systems available in the current market using different criteria for measuring efficiency such as potential measurements, electrolyte resistance measurements and several polarization methods to determine the polarizability of the anodes. The results to validate the performance of long-time exposure of discrete zinc anodes in concrete medium are discussed.
In Germany, the reuse of asphalt has a long tradition. Since the 1980s, the reclaimed
asphalt has been recycled achieving a reuse rate of around 90% and thus a very high
value in the last years. In the future, instead of the amount, the quality of the
reclaimed asphalt will be more important because the recycled asphalt will be reused
again and again. Thus, these asphalt mixes are in the second or even third cycle of
reuse. Concerning this situation, the question arises if asphalt can be reused several
times without any loss in quality. An important factor affecting the asphalt quality is the
binder bitumen. During the production, construction and service life, the ageing of this
binder occurs causing a hardening of the bitumen. To compensate this hardening,
additives for the reclaimed asphalt in terms of rejuvenation agents (rejuvenators) gain
in importance. With these rejuvenators, the physical properties of bitumen can be
modified e.g. the hardness and the stiffness reduced. However, the mechanism of the
rejuvenation agents and the effects of the bitumen chemistry are largely unknown
because the composition of the products varies very strongly. But with growing
knowledge about these mechanisms and effects of the rejuvenation agents, the
chemical composition and thus the physical and ageing behavior of bitumen can be
targeted modified by the use of suitable rejuvenators. In this work, the actual results of
the project Postcarbone road should be presented including investigations about the
chemical and physical mechanisms as well as the efficiency of different rejuvenators.
Further, a model for the cyclic reuse of bitumen should be developed. Based on this
model, the choice of a suitable rejuvenation agent for the considered bitumen or rather
asphalt should be possible. The project Postcarbone road (392670763) is funded by the
German Research Foundation (DFG).
In Germany, the reuse of asphalt has a long tradition. Since the 1980s, the reclaimed asphalt has been recycled achieving a reuse rate of around 90% and thus a very high value in the last years. In the future, instead of the amount, the quality of the reclaimed asphalt will be more important because the recycled asphalt will be reused again and again. Thus, these asphalt mixes are in the second or even third cycle of reuse. Concerning this situation, the question arises if asphalt can be reused several times without any loss in quality. An important factor affecting the asphalt quality is the binder bitumen. During the production, construction and service life, the ageing of this binder occurs causing a hardening of the bitumen. To compensate this hardening, additives for the reclaimed asphalt in terms of rejuvenation agents (rejuvenators) gain in importance. With these rejuvenators, the physical properties of bitumen can be modified e.g. the hardness and the stiffness reduced. However, the mechanism of the rejuvenation agents and the effects of the bitumen chemistry are largely unknown because the composition of the products varies very strongly. But with growing knowledge about these mechanisms and effects of the rejuvenation agents, the chemical composition and thus the physical and ageing behavior of bitumen can be targeted modified by the use of suitable rejuvenators. In this work, the actual results of the project Postcarbone road should be presented including investigations about the chemical and physical mechanisms as well as the efficiency of different rejuvenators.
Further, a model for the cyclic reuse of bitumen should be developed. Based on this model, the choice of a suitable rejuvenation agent for the considered bitumen or rather asphalt should be possible. The project Postcarbone road (392670763) is funded by the German Research Foundation (DFG).
While there is a permanent improvement of concrete pavement mixtures and pavement construction types over the last decades, the state-of-the-art joint sealing materials and joint constructions seem to stagnate on an antiquated empirical level. This status has been reaffirmed in the latest European standard. The consequences in the motorway network due to unsatisfying capability and durabilty of joint sealing systems are unacceptable. In addition, inadequate traffic performance (noise emissions, roll-over comfort) and traffic safety losses in the joint area of concrete pavements are existing challenges. These deficits and weaknesses reflect a demand for joint sealing materials and constructions whose approval requirements take functional aspects into account. Furthermore a sufficient analysis of decisive loads and a practice-oriented method to evaluate the requirements towards performance and durability is still missed. In this contribution decisive loads to German highways are analyzed. The design of test specimen for representative functional testing of joint sealing systems is discussed. The focus is on the geometry of the test specimens and the used concrete mixture. Finally, a new approach for a function-orientated test concept that considers representative load functions is presented. The potential of this approach to validate the durability and capability of various joint sealing systems is also presented using an example.
Basic oxygen furnace slag (BOFS) is a by-product of the steelmaking process, of which about 10.4 Mt are produced annually in the European Union. Besides its predominant use in road construction, earthwork, and hydraulic engineering, it is also possible to use BOFS as a source material for Portland cement clinker.
The main difference in the chemical composition of BOFS from the chemical composition of Portland cement clinker is its high content of iron oxides (7-50 wt.%). In recent decades, many researchers have investigated the production of both Portland cement clinker and crude iron from BOFS via thermochemical reductive treatment. Carbothermal treatment of liquid BOFS causes reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as reducing agent. The produced low-iron mineral product was chemically similar to Portland cement clinker and contained the most important Portland cement mineral alite (Ca3SiO5) as main component. Besides alite, the mineral product contained other Portland cement clinker constituents such as belite (β-Ca2SiO4) and tricalcium aluminate (Ca3Al2O6).
The production of Portland cement clinker and crude iron from BOFS has economic and ecological benefits for both the cement and steel industry. Cement clinker from reduced BOFS may be used as a substitute for cement clinker from conventional cement production, thereby CO2 emissions will be reduced. The steel industry benefits from a high-value application for its by-products that avoids cost expensive landfilling and may even bring economic advantages. However, reductive treatment requires high temperatures and, for economic reasons, has to be carried out immediately after casting of the liquid BOFS, which is a logistical challenge for most steel plants. A cost-benefit analysis is therefore essential.
Basic oxygen furnace slags (BOFS) are a by-product of steel production. In 2016, 10.4 Mt of BOFS were produced in the European Union (EU). The main part of BOFS is used in road construction, earthwork and hydraulic engineering. A smaller part is returned to the metallurgical circle, used as fertilizer or landfilled. However, it is also possible to produce higher value products from BOFS. For example, many researchers have investigated the possibility of producing Portland cement clinker and crude iron from BOFS by a carbothermal post-treatment.
In this study, German BOFS was reduced in a small-scale electric arc furnace using petrol coke as reducing agent. The carbothermal treatment reduces the iron oxides in the BOFS to metallic iron, which accumulates at the bottom of the furnace by density separation. In addition to metallic iron, the process generates a mineral product rich in the tricalcium silicate solid solution alite. As the main constituent of Portland cement clinker, the hydraulic reactive mineral alite is of high economic importance.
In previous studies, the hydraulic reactivity of the mineral product was investigated by testing the compressive strength of blends with 70 wt.% ordinary Portland cement (OPC). Recent investigations focused on the hydraulic properties of the pure mineral product from the reduced BOFS. The heat of hydration of the mineral product was measured by isothermal calorimetry and compared with the heat of hydration of a synthetic low-iron slag and OPC. In addition, the formation of hydration products was investigated with differential scanning calorimetry (DSC) and x-ray diffraction analysis (XRD) on freeze-dried samples after defined curing times. The results of the calorimetric measurements indicate that the mineral product produced less heat of hydration and its reaction was delayed compared to the synthetic low-iron slag and OPC. Hydration products such as portlandite and calcium silicate hydrates (C-S-H) formed later and in lower amounts.
The production of a hydraulic material from BOFS by reductive treatment is of great interest to both the cement and steel industries. The substitution of cement clinker in OPC with a hydraulic material such as reduced BOFS leads to a reduction in greenhouse gas emissions from cement production. The steel industry benefits from an application for its by-products that avoids cost expensive landfilling and may even bring economic advantages. Furthermore, it may be possible to return the recovered crude iron to production.
Currently, the Full Notch Creep Test (FNCT) [1] method is used by material suppliers and end users in industry for the approval of container and pipe materials based on high-density polyethylene (PE-HD). The resistance to environmental stress cracking (ESC) of the material is evaluated using the time to failure of the specimen in an aqueous solution of a detergent [2, 3]. Usually specimens made of sheets with isotropic material properties, manufactured by hot pressing, are employed in order to obtain intrinsic properties of the material in terms of ESC failure. In contrast, the processes used in manufacturing to form containers and pipes, such as extrusion blow molding or extrusion, impose anisotropic properties to the material. These are mostly due to a microstructural orientation (polymer chains or crystallites) [4]. Furthermore, the different cooling conditions significantly affect the size distribution of crystallites as well as the overall morphology. It is therefore essential to understand the influence of process-induced material characteristics on failure due to ESC.
A large number of studies on material properties as a function of microstructural preferential orientation have already been conducted [5-7]. However, effects on ESC as the major failure mechanism of containers and pipes are still rather unexplored [8, 9]. The most important factor is whether primarily intramolecular high-strength covalent bonds or the substantially weaker intermolecular van der Waals forces are predominantly loaded.
In addition to the widely established classification by time to failure, the strain or crack opening displacement (COD) provides valuable information about the evolution and progression of damage as a function of time [10, 11]. Optical strain measurement using digital image correlation allows the differences in COD for isotropic and different angles of orientation of anisotropic specimens to be discussed. Also, a post-fracture surface analysis provides clarification on the craze-crack mechanism of the ESC. These different ESC-related properties of extruded and hot-pressed specimens have been investigated at different environmental medium temperatures and different initial stresses to provide a broad characterization of the fracture behavior of PE-HD.