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Reclassification of bridges, i.e., a change in load rating, using reliability-based methods and a direct update with proof load information has been presented by many authors. However, bridge reclassification has hardly been studied from a decision analytic perspective, i.e., with quantification of the risks and benefits of different classification choices, and the expected benefit gain from proof loading. We derive, explain and exemplify a decision analytic approach for bridge reclassification along with models for (1) elastic and ultimate capacity and their adaptation with proof load information, (2) proof load information with classification outcomes accounting for target reliabilities and, (3) utilities including socio-economic benefits from reclassification. The approach and models are exemplified with a case study based on reclassification of bridges with a low existing classification. Decision rules, for practical use by a highway authority to find the optimal classification, are identified and documented based on: (1) the measurement of the capacity at elastic limit by proof loading, (2) the bridge reclassification benefits, and, (3) the required annual reliability level. From a Value of Information analysis, it is concluded that the proof load information is highly valuable for reclassification in cases of high socio-economic benefits and high reliability requirements.
Two-dimensional covalent organic frameworks (COFs) based on phosphinine and thiophene building blocks have been synthesized with two different side groups. The materials are denoted as CPSF-MeO and CPSF-EtO where CxxF correspond to the covalent framework, whereas P and S are related to heteroatoms phosphorous and sulfur. MeO and EtO indicate the substituents, i.e. methoxy and ethoxy.
Their morphologies were studied by scanning electron microcopy and X-ray scattering. The absence of crystalline reflexes in the X-ray pattern reveal that both materials are amorphous and can be considered as glasses. Furthermore, N2 adsorption measurements indicate substantial Brunauer–Emmett–Teller (BET) surface area values pointing to the formation of three-dimensional pores by stacking of the aromatic 2D layer. An analysis of the porosity of both COFs showed a mean radius of the pores to be of ca. 4 nm, consistent with their chemical structure. The COFs form nanoparticles with a radius of around 100 nm. The thermal behavior of the COFs was further investigated by fast scanning calorimetry. These investigations showed that both COFs undergo a glass transition. The glass transition temperature of CPSF-EtO is found to be ca. 100 K higher than that for CPSF-MeO. This large difference in the glass transition is discussed to be due to a change in the interaction of the COF sheets induced by the longer ethoxy group. It might be assumed that for CPSF-EtO more individual COF sheets assemble to larger stacks than for CPSF-MeO. This agrees with the much larger surface area value found for CPSF-EtO compared to CPSF-MeO. To corroborate the results obtained be fast scanning calorimetry dielectric measurements were conducted which confirm the occurrence of a dynamic glass transition. The estimated temperature dependence of the relaxation rates of the dielectric relaxation and their absolute values agrees well with the data obtained by fast scanning calorimetry. Considering the fragility approach to the glass transition, it was further found that CPSF-MeO is a fragile glass former whereas CPSF-EtO behaves as a strong glass forming material. This difference in the fragility points also to distinct differences in the interaction between the 2D COF molecules in both materials.
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 flexibility and quality of a process. Typically, before producing a whole additive manufacturing structure, a simplified experiment in the form of a beadon-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 developed, 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 temperature.
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.
Combining buffing leather fibers from industrial waste streams with ammonium polyphosphate and bentonite clay is proposed as a flame-retardant additive for polypropylene. The paper addresses how they can be processed into attractive composites with the desired mechanical properties. Buffing leather fibers function as a multifunctional bio-filler and as a synergist for the flame retardant, resulting in fire retardancy successful enough to increase the oxygen index (LOI) by up to 7 vol.-% and to achieve a V0 UL 94 classification. Impressively reduced heat release rates are obtained in the cone calorimeter at 50 kW/m2 irradiation; for instance, the maximum average rate heat evolved (MARHE) drops from 765 to below 200 kW m 2. The synergistic effects are quantified and shown to be very strong for LOI and MARHE. This work opens the door to use waste buffing leather fibers as a promising multifunctional and synergistic bio-filler.
To ensure fire safety, polymers are filled with flame retardants and smoke suppressants. To meet the highest requirements, it is essential to understand the decomposition of those polymeric materials. This study reveals interactions between polymer, smoke suppressants, and flame retardants, and discusses their impact on the materials’ flame retardancy, smoke emission, smoke toxicity, and particle emission in conventional loadings to provide deeper general understanding. Low melting oxide glass, melem, spherical silica, sepiolite, melamine polyphosphate, and boehmite in an aluminum diethylphosphinate flame-retarded polyamide 6.6 were investigated. All smoke suppressants improve the protective layer and act as an adjuvant. Silica and melem performed best under forced flaming conditions. Spherical silica reduces the peak of heat release rate by 39% and the total heat evolved by 14%, whereas 10 wt% melem lowers the total smoke production by 41%. Melem alters the mode of action of aluminum diethylphosphinate from gas to more condensed phase activity. This change reduces flame inhibition and hence smoke toxicity, but further improves the protective layer due to charring reactions in the decomposition mechanism. In addition, the sizes of the smoke particles decrease because of the prolonged time in the pyrolytic zone. This study highlights that interactions between polymer, flame retardants, and smoke suppressants can significantly determine the smoking and burning behavior.
Polymers with intrinsic microporosity (PIMs) are gaining attention as gas separation membranes. Nevertheless, they face limitations due to pronounced physical aging. In this study a covalent organic framework containing λ5-phosphinine moieties, CPSF-EtO were incorporated as a nanofiller (concentration range 0-10 wt%) into a PIM-1 matrix forming dense films with a thickness of ca. 100 μm. The aim of the investigation was to investigate possible enhancements of gas transport properties and mitigating effects on physical aging. The incorporation of the nanofiller occurred on aggregate level with domains up to 100 nm as observed by T-SEM and confirmed by X-ray scattering. Moreover, the X-ray data show that the structure of the microporous network of the PIM-1 matrix is changed by the nanofiller.
As the molecular mobility is fundamental for gas transport as well as for physical aging, the study includes dielectric investigations of pure PIM-1 and PIM-1/CPSF-EtO mixed matrix membranes to establish a correlation between the molecular mobility and the gas transport properties. Using the time-lag method the gas permeability and the permselectivity were determined for N2, O2, CH4 and CO2 for samples with variation in filler content. A significant increase in the permeability of CH4 and CO2 (50 % increase compared to pure PIM-1) was observed for a concentration of 5 wt% of the nanofiller. Furthermore, the most pronounced change in the permselectivity was found for the gas pair CO2/N2 at a filler concentration of 7 wt%.
AbstractThe increasing threat of forest fires on a global scale is not only a matter of concern due to the potential harm they may cause to both human and animal life but also due to their significant role in exacerbating climate change. In light of these circumstances, one might inquire as to whether forest soil can self‐ignite and, if so, under what conditions and at what temperatures this phenomenon may occur. This question is being addressed in the German pilot “Fire science of wildfires and safety measures” of the EU project TREEADS, and the first results are presented below. The importance of basic research into the self‐ignition of forest soil cannot be underestimated, as it provides crucial knowledge to prevent forest fires and protect human and animal health. Furthermore, mitigating the occurrence of forest fires can also play a role in reducing greenhouse gas emissions, contributing to global efforts to combat climate change. The procedure of the hot storage test is an effective means of determining whether a material can self‐ignite. During the investigation of six soil samples, it was found that five of them were indeed capable of self‐ignition. In addition to determining whether the material ignites, the modified hot storage test also analyzed the resulting smoke gases and measured their concentration. The research question of whether regional forest soil is capable of self‐ignition can be answered with yes based on these initial tests. Further experiments are needed to determine if self‐ignition causes forest fires.
Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn.
Understanding the susceptibility to spalling of concrete members in case of fire is important to evaluate the residual load-bearing capacity. The investigations of the spalling phenomenon of a concrete mixture using real scale members are necessary but expensive to carry out. Reducing the specimen size leads to an increase of boundary effects that can result in a reduced spalling or absence of spalling. In this study, fire tests were carried out on unrestrained, single-sided exposed, cuboid shaped specimens (0.6 m x 0.6 m x 0.29 m) as well as unrestrained and steel ring restrained cylindrical specimens (Ø = 0.47 m, h = 0.29 m), which induce different boundary conditions. These fire tests were carried out on two ordinary concrete mixtures. The two mixtures differ only in the type of aggregates (quartz gravel and basalt grit) and were used to investigate the influence of the thermal expansion of the aggregate on the spalling behaviour of the concrete. The results show a significant increase of
the spalling depth due to the restrained thermal expansion achieved by the applied steel rings. Additionally, the type of aggregate has a direct influence on the spalling behaviour of a concrete mixture. The reduction of the boundary effects by the steel rings recreate the test conditions in the centre of a large concrete member. Thus, this type of specimen is suitable to determine the susceptibility to spalling of a material (screening-tests) as preliminary investigations to full scale fire tests.
Pressure-sensitive adhesive tapes are used in several industrial applications such as con-struction, railway vehicles and the automotive sector,where the burning behavior is ofcrucial importance. Flame retarded adhesivetapes are developed and provided, however,often without considering the interaction of adhesive tapes and the bonded materialsduring burning nor the contribution of the tapes to fire protection goal of the bondedcomponents in distinct fire tests. This publication delivers an empirical comprehensiveknowledge how adhesive tapes and their flame retardancy effect the burning behaviorof bonded materials. With a special focus on the interaction between the single compo-nents, one flame retarded tape and one tapewithout flame retardant are examined inscenarios of emerging and developing fires, along with their bonds with the commonmaterials wood, zinc-plated steel, mineral wool, polycarbonate, and polymethylmethacry-late. The flame retardant significantly improved the flame retardancy of the tape as afree-standing object and yielded a V-2 rating in UL 94 vertical test and raised the OxygenIndex by 5 vol.%. In bonds, or rather laminates, the investigations prove that the choiceof carrier and substrates are the factors with the greatest impact on the fire propertiesand can change the peak of heat release rate and the maximum average rate of heatemission up to 25%. This research yielded a good empirical overall understanding of thefire behavior of adhesive tapes and bonded materials. Thus, it serves as a guide for tapemanufacturers and applicants to develop tapes and bonds more substrate specific.
The recommendation is based on the co-authors’ work organized by the RILEM TC 256-SPF “Spalling of concrete due to fire: testing and modelling”. It aims to provide useful information, guidance and best practices in fire spalling assessment to laboratories that perform large-scale tests based on fire resistance test standards. It provides guidance on the spalling observation techniques during testing, as well as post-test spalling quantification/assessment methods. This document is intended to be used in conjunction with the fire resistance test standards, e.g. EN 1363-1 and ISO 834-1.
Future lunar exploration will be based on in-situ resource utilization (ISRU) techniques. The most abundant raw material on the Moon is lunar regolith, which, however, is very scarce on Earth, making the study of simulants a necessity. The objective of this study is to characterize and investigate the sintering behavior of EAC-1A lunar regolith simulant. The characterization of the simulant included the determination of the phase assemblage, characteristic temperatures determination and water content analysis. The results are discussed in the context of sintering experiments of EAC-1A simulant, which showed that the material can be sintered to a relative density close to 90%, but only within a very narrow range of temperatures (20–30 °C). Sintering experiments were performed for sieved and unsieved, as well as for dried and non-dried specimens of EAC-1A. In addition, an analysis of the densification and mechanical properties of the sintered specimens was done. The sintering experiments at different temperatures showed that the finest fraction of sieved simulant can reach a higher maximum sintering temperature, and consequently a higher densification and biaxial strength. The non-dried powder exhibited higher densification and biaxial strength after sintering compared to the dried specimen. This difference was explained with a higher green density of the non-dried powder during pressing, rather than due to an actual influence on the sintering mechanism. Nevertheless, drying the powder prior to sintering is important to avoid the overestimation of the strength of specimens to be fabricated on the Moon.
This paper scopes the specialties of a hazard identification study for large and extra-large unmanned undersea vehicles (UUVs). A generic node/function structure is derived from different large and extra-large UUV designs, partially own vehicle designs from research projects, and partially from commercial vehicles. For each node, a short overview of its components and the proper function or operations is defined. A set of guide words is used to prompt a hazard discussion for each node, which identifies unwanted functions, resulting in potential hazards and unmitigated consequences. Related to the SafeMASS-Report from DNV, this work concentrates on selected topics of the bridge-related function on voyage, control & monitoring, and abnormal situations. For unmanned vehicles without any person on board, these three topics become more important for underwater vehicles with very limited connectivity or temporary disruptions of communication whereby an operator in a remote-control center could only be provided with rough vehicle or mission states. Therefore, vehicle control, whether in hard- or software, must handle most tasks belonging to the considered functions automatically or autonomously. Hence, the most appropriate reactions of the system to unwanted system
behavior must be implemented. This HAZID study could, on the one hand, be used as background for such an implementation, and on the other hand, it is used to verify the implemented actions on the risks and hazards.
Agar gel pads have been used for electrochemical measurements for some time. For zinc in particular, a standard method for measuring the stability of the corrosion product layer is being established. The main interpretation factor is the corrosion product layer resistance RL, as it is easy to determine and interpret. A high corrosion product layer resistance indicates a high level of protection. However, it is not yet known how low the corrosion product layer resistance is for freshly produced zinc samples. As zinc is highly active, it reacts immediately with the environment to form a corrosion product layer, which affects the corrosion product layer resistance. The addition of zinc acetate to the agar gel pads prevents the formation of a surface layer and destroys existing ones.
This makes it possible to measure an almost corrosion product-free zinc surface. This is important in defining the range of corrosion product layer resistance for a protective surface.
We report the selective ring opening copolymerisation (ROCOP) of
oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K
catalyst precisely yielding semi-crystalline alternating poly(esteralt-
thioesters) which show improved degradability due to the
thioester links in the polymer backbone.
We evaluate masked block-structured grids for ocean domains which allow to represent small-scale geometric features without resorting to very small blocks or excessive mesh resolution. The considered approach aims to combine the geometric flexibility of unstructured meshes with the computational efficiency of stencil-based discretizations and is implemented and tested in a quadrature-free discontinuous Galerkin shallow water solver. We investigate the accuracy and the computational performance of the scheme on a range of realistic ocean domains meshed with blocks of different size and provide some comparisons to results obtained on unmasked block-structured grids and unstructured meshes.
Impact resistance of reinforced concrete (RC) structures can be significantly improved by strengthening RC members with thin composite layers featuring high damage tolerance. Indeed, to limit the well-known vulnerability of cement-based materials against impact loading, the synergistic effects of short fibres and continuous textile meshes as hybrid reinforcement has been proved to be highly beneficial. This paper addresses the characterisation of novel cement-based hybrid composites through accelerated drop-weight impact tests conducted on rectangular plates at different impact energies. Two distinct matrices are assessed, with particular interest in a newly developed limestone calcined clay cement (LC3)-based formulation. Important parameters quantifying energy dissipation capability, load bearing capacity and damage are cross-checked to compute the ballistic limit and estimate the safety-relevant characteristics of the different composites at hand. Although textiles alone can improve the damage tolerance of fine concrete to some extent, the crack-bridging attitude of short, well-dispersed fibres in hybrid composites imparts a certain ductility to the cement-based matrices, allowing a greater portion of the textile to be activated and significantly reducing the amount of matrix spalling under impact.
Information on the condition and reliability of an offshore jacket structure provided by a vibration-based structural health monitoring system can guide decisions on inspection and maintenance. When selecting the sensor setup, the designer of the monitoring system must assess its overall benefit compared to its costs before installation. The potential benefit of continuously monitoring the dynamic response of a jacket structure can be formally quantified through a value of information analysis from Bayesian decision theory. In this contribution, we present a framework for optimizing the placement of vibration sensors on offshore jacket structures by maximizing the value of information of the monitoring system. To solve the resulting discrete optimization problem, we adapt a genetic algorithm. The framework is demonstrated in a numerical example considering a redundant jacket-type steel frame. The numerical study shows that monitoring the vibration response of the frame is beneficial. Good sensor setups consist of relatively few sensors located towards the upper part of the
frame. The adapted genetic algorithm performs similarly well as established sequential sensor placement algorithms and holds substantial promise for application to real jacket structures.
The effect of resting time on the rheological properties of cement suspensions is generally explained by early formed structure and overconsumption of polycarboxylate superplasticizers (PCEs). In this paper, we propose that the influence of resting time on the rheological properties is closely related to size variation of non-absorbed PCE. To identify this, glass bead suspensions were prepared with various amounts of PCE and ionic solution, and their rheological properties were evaluated at various times. We found that the yield stress increases with time at higher PCE concentrations and higher ionic strength solutions. Adsorbed PCE during resting tends to bridge the particles rather than disperse them. In addition, it was found that hydrodynamic radius of PCE increased with resting time, and depletion forces resulting from non-absorbed PCE size changes correlate well with the increased yield stress.
In this article, a partial selection of experiments on enhancing the impact resistance of structural components with non-metallic, textile-reinforced concrete is discussed. The focus is on the experimental investigations in which the impact resistance of thin, textile-reinforced concrete plates is characterized. The article discusses the materials, fabrics and test setup used. For the experimental work, a drop tower from the Otto Mohr Laboratory, which belongs to the Technische Universtät Dresden, was used. Furthermore, the experimental results are presented and evaluated using different methods. Based on the collected data, a suitable approach to determining the perforation velocity of an impactor through the investigated thin, textile-reinforced concrete plates is shown.
Polyamide 4.6 (PA46) is a high-heat-resistant polymer, but it has no dripping resistance under fire. Three commercial grades of PA46 are investigated under UL 94 vertical fire test conditions. Their performances are discussed based on the materials’ structural, thermal, and rheological properties. PA46 presents flaming drops, whereas dripping is prevented in the flame-retarded PA46.
Friction-modified PA46 has increased flaming dripping. Temperature profiles of the specimens under fire and the temperature of the drops are measured by thermocouples. A UL 94 vertical test configuration consisting of two flame applications is designed to assess the quantitative dripping behavior of the set of materials by the particle finite element method (PFEM). Polymer properties (activation energy and Arrhenius coefficient of decomposition, char yield, density, effective heat of combustion, heat of decomposition, specific heat capacity, and thermal conductivity) in addition to rheological responses in high temperatures are estimated and measured as input parameters for the simulations. The dripping behavior obtained by simulated materials corresponds with the experimental results in terms of time and drop size. A consistent picture of the interplay of the different phenomena controlling dripping under fire appears to deliver a better understanding of the role of different materials’ properties
The vehicle–track interaction generates forces and consequently vibrations in the environment. The interaction has been analysed by the simultaneous measurements of vehicle, track and ground vibrations during test runs with varied train speeds. The special effects of the passage over a bridge and through a tunnel are studied and compared with the measurements on a conventional ballasted surface line. The maximum amplitudes, narrow band and one-third octave band spectra are presented for the axle-box accelerations and for the track, bridge and ground vibrations. The different frequencies and frequency bands are related to wheel out-of-roundness, track alignment errors, the sleeper passage and the wheelset–track resonance. An axle impulse component has been observed at the track, at the near-field soil and as a scattered version in the far field. Specific results can be found for the bridge track, where clearly speed-dependent bridge resonances occur due to the axle sequence of the train, and for the tunnel track where soft rail pads are responsible for a strong amplification around the wheelset–track resonance. On the other hand, the axle impulses are strongly reduced by the tunnel track, and the scattered axle impulse component is not as relevant as for the surface track. As a consequence, a strong mid-frequency amplitude reduction of the tunnel compared to the surface line has been measured for low and high train speeds by the Federal Institute of Material Research and Testing (BAM) and by other institutes.
The propagation of ground vibrations is theoretically analysed with frequency-wavenumber and simplified methods. Experimental methods are presented which can characterise the site-specific ground vibrations by wave velocities, stiffness and damping. Measurements with hammer and train excitation have been performed at several sites. The one-third octave spectra show the stiffness-dependent amplitudes and the low- and high-frequency filter effects due to the layering and the damping of the soil. Specific train effects, an additional high-frequency filter, the sleeper passage frequency, and an amplified mid-frequency component can be clearly found. The attenuation with distance is analysed in detail where the theoretical exponential and the empirical frequency-dependent power law are considered. Hammer and train excitation show the same site-specific effects which are mainly due to the stronger or weaker damping of the soil. The train attenuation is generally weaker than the hammer attenuation. The attenuation exponent of the power law, which is strongly dependent on the site and the frequency, is reduced for the train vibration by 0.3 to 0.5 in agreement with the theory. Reasons are discussed for the overall power law and for the dominating mid-frequency component.
Polymers that help tailoring rheological properties during the casting process have become inevitable constituents for all kinds of high-performance concrete technologies. Due to lacking industries, these typically crude-oil based admixtures are not readily available in many parts of the world, which limits the implementation of more sustainable high-performance construction technologies in these regions. Alternative polymers, which often demand for less processing, can be derived from local plant-based resources. The paper provides experimental data of flow tests of cement pastes with polysaccharides from Triumfetta pendrata A. Rich, acacia gum and cassava without and in the presence of polycarboxylate ether superplasticizer. The flow tests are amended by observations of the zeta potentials and the hydrodynamic diameters in the presence of and without calcium ions in the dispersion medium. The results show that in the presence of and without calcium ions all polysaccharides provide negative zeta potentials, yet, they affect flowability and thixotropy in different ways. Cassava starch, acacia gum, and the gum of Triumfetta pendrata A. Rich qualified well for robustness improvement, strong stiffening, and additive manufacturing, respectively. The reason for the different effects can be found in their average sizes and size distribution. Due to the promising results, a flow chart for local value chains is derived on the example of yet unused cassava wastes, which can be converted in parallel.
An analytical expression for the frequency response function of a coupled pedestrian-bridge system is presented and evaluated using an experimental measurement campaign performed on the Folke Bernadotte Bridge in Stockholm, Sweden. A finite element model and the modal models that consider the human–structure interaction effect are calibrated with respect to the measurements. The properties of the spring–mass–damper model representing the pedestrians were identified, considering the different structural modes of the system. Good agreement was obtained between the experimental and theoretical frequency response functions. A sensitivity analysis of the obtained solution was performed, validating the determined analytical expression for the frequency response function of the coupled pedestrian-bridge system that takes into account the human–structure interaction effect.
The built environment significantly impacts the health of individuals and populations in various ways. The health and durability of the built environment are intertwined with availability ofnaturally occurring and man-made resources and their supply chains. Therefore, resource con servation is a key to ensure sustainability of built environments. Many industrial wastes can be turned into valuable resources for reuse in construction of the built environment. For instance, biowaste (woody/ leafy biomass and animal waste) have been used to make construction adhesives (Fini et al., 2011), some urban wastes have been used in road construction (Poulikakos et al., 2017; Schmidt et al., 2021), end of life plastics and polymers have made their way to roadway construction, bio-oils and algae harvested from wastewater treatment plants has been used to make antiaging for outdoor building elements to mitigate UV aging (Kabir et al., 2021); sulfur has been used as an extender in asphalt and recycled mineral powders such as silica and alumina have been used to increase strength and durability against acidic compounds (Fini et al., 2019). These are just a few examples of recycling venues with beneficial uses in the built environment.
The construction and operation of the built environment and the traffic that it attracts or facilitates significantly contribute to the emis sion of greenhouse gasses (GHG) and cause air pollution. The direct and indirect impacts of GHG and air pollutants on the environment and so cieties have been weil established. The built environment can be used as a powerful platform not only for recycling and resource conservation but also to remove near-ground gaseous contaminants. This can be done via tailored design and engineering of adsorptive construction materials via recycling of waste materials. For instance, advanced sorbent systems can be made for removing C02, H2S, and formaldehyde from air. This re quires tailored sorbent design, topology optimization, and catalytic conversion of collected gaseous compounds to name a few.
This special issue covers innovative materials, methods, and man agement practices which aim to simultaneously address durability ofthe built environment, air quality, resource conservation, and supply chain resilience. Such innovative materials, methods, and management prac tices will transform the built environment into not only an active contributor to no waste, no pollution for healthy environment, but also a medium that converts the waste and pollution into beneficial products for use in the built environment, thereby promoting resource conser vation. Followings are examples of topics that the special issue is interested in:
• Venuses to advance resource conservation specifically via novel ap proaches in the built environment.
• Innovative construction materials for passive or active adsorption of harmful gaseous emissions to conserve air, energy, and water.
• Advanced materials, methods, and management practices to pro mote well-being of the built environment.
• Smart buildings to promote resource conservation.
• Research convergence in the built environment for zero waste, zero pollution economy.
Non-conventional densely packed concrete mixtures are proposed and evaluated in this paper using engineered recycled mineral admixtures and recycled aggregates obtained from steel slag, quartz mining tailings, and quartzite mining tailings. High fines content sand-concretes containing coarser- and finer-than-cement recycled powders were designed to obtain blends with broader particle-size ranges and improved packing density. As a result, compressive strength up to 99 MPa, cement intensity up to 2.33 kg/m³/MPa, and consumption of recycled material up to 95 vol% were obtained. Compressive strengths up to 66 MPa and cement intensity up to 2.34 kg/m³/MPa were also obtained with the addition of coarse aggregates to such sand-concrete mixtures, with consumption of recycled material up to 96.5%. The results launch new insights on the role of recycled admixtures and aggregates on the mixture design of cement-based composites regarding efficiency improvement and technological performance.
Design : and use of engineered recycled mineral admixtures obtained from industrial and mineral waste are promising strategies to increase the range of materials suitable for use in cement-based composites. In this work, Portland cement-blended pastes containing mineral admixtures designed for improving particle packing were evaluated in the presence of low- and high-charge polycarboxylate-based superplasticizers. The powders were obtained from basic oxygen furnace slag, iron ore tailings, quartz mining tailings, and quartzite mining tailings. The zeta-potentials of the particles were obtained via electrophoretic mobility. The flow properties were evaluated by rheological tests performed in a Couette type rheometer. The hydration kinetics was evaluated by isothermal calorimetry and an adapted method based on the Vicat needle test. The high-charge PCE and the finer mineral admixtures produced more stable blends. Coarser mineral admixtures led to increased flowability and delayed hydration compared to finer ones. Steel slag powders presented the most significant plasticizer effects, but also the largest setting delays and segregation tendency. Quartz-rich superfines reduced the setting delays caused by the superplasticizers. In summary, both superplasticizers were effective in improving flow properties, but the high-charge PCE was effective in preventing segregation in pastes containing mineral admixtures coarser and heavier than cement.
The bond between polymer fibers and the surrounding cementitious matrix is essential for the development of concrete reinforcement. The single fiber pull-out test (SFPT) is the standard characterization technique for testing the bond strength. However, the different phases of debonding cannot be distinguished by the SFPT. This study investigates the debonding of different polymer fibers from the surrounding cementitious matrix with a modified SFPT and proposes methods to change the SFPT setup to generate more valuable information on the debonding mechanism. The SFPT was equipped with linear variable differential transformers (LVDT), digital image correlation (DIC) and acoustic emission (AE) analysis. The results demonstrate that the modified SFPT allows a better understanding of the different phases of debonding during fiber pull-out. Furthermore, bond strength values calculated by different methods reveal that the chemical bond of the investigated polymers is not different as reported by previous studies. Deformation measurements performed using LVDTs and DIC are suitable measuring techniques to characterize the debonding mechanism in SFPT. A correlation between recorded AE and debonding phases was not found.
Abstract: Increasing demand for sustainable, resilient, and low-carbon construction materials has highlighted the potential of Compacted Mineral Mixtures (CMMs), which are formulated from various soil types (sand, silt, clay) and recycled mineral waste. This paper presents a comprehensive inter- and transdisciplinary research concept that aims to industrialise and scale up the adoption of CMM-based construction materials and methods, thereby accelerating the construction industry’s systemic transition towards carbon neutrality. By drawing upon the latest advances in soil mechanics, rheology, and automation, we propose the development of a robust material properties database to inform the design and application of CMM-based materials, taking into account their complex, time-dependent behaviour. Advanced soil mechanical tests would be utilised to ensure optimal performance under various loading and ageing conditions. This research has also recognised the importance of context-specific strategies for CMM adoption. We have explored the implications and limitations of implementing the proposed framework in developing countries, particularly where resources may be constrained. We aim to shed light on socio-economic and regulatory aspects that could influence the adoption of these sustainable construction methods. The proposed concept explores how the automated production of CMM-based wall elements can become a fast, competitive, emission-free, and recyclable alternative to traditional masonry and concrete construction techniques.
We advocate for the integration of open-source digital platform technologies to enhance data accessibility, processing, and knowledge acquisition; to boost confidence in CMM-based technologies; and to catalyse their widespread adoption. We believe that the transformative potential of this research necessitates a blend of basic and applied investigation using a comprehensive, holistic, and transfer-oriented methodology. Thus, this paper serves to highlight the viability and multiple benefits of CMMs in construction, emphasising their pivotal role in advancing sustainable development and resilience in the built environment.
The existing cement and concrete standards are not capable of making full use of the current technology capacity due to strong focus on conventional concrete and thus they are not fit for the current and future challenges of construction industry. The paper highlights shortcomings with regard to the implementation of the existing standards. It can be seen that future-oriented standards are generally required to contribute to a lower-carbon footprint of the industry. These changes are significantly more relevant in sub-Saharan Africa, due to the rapidly increasing urbanisation challenge and the enormous potentials to develop lower-carbon technologies than elsewhere in the world.
The current paper develops a novel accelerated corrosion test method based on Faraday’s law to investigate the performance of different inhibitors in reinforced concrete elements under electrical voltage. Using the proposed method two commercially available and three lab-made inhibitors were tested. Lab-made inhibitors based on potassium fluorosilicate and amine carboxylate showed the best performance over others. Furthermore, it is found that under an electrical potential environment beyond 3.6 V, the higher the concrete strength, the more efficient is the corrosion inhibition. Based on experimental results, a novel model describing the corrosion evolution in reinforced concrete was proposed.
In this work, engineered recycled mineral admixtures were obtained from four different industrial residues: basic oxygen furnace slag, iron ore tailings, quartz mining tailings and quartzite mining tailings.
The grinding performance was evaluated in two different programs and the characterization included chemical and mineralogical composition, particle morphology, and physical properties. Performance evaluations were carried out in blended pastes and mortars, including flow properties, hydration kinetics, soundness, pozzolanic activity, and compressive strength. Coarser-than-cement admixtures allowed better flow performance, greater dimensional stability and more economical production, while finer-thancementn admixtures improved mechanical performance by both filler effect and cementing activity.
The structural build-up of fresh cement paste is often considered as a purely thixotropic phenomenon in literature even though cementitious materials undergo a non-reversible hydration process that can have an influence on the structuration process. In the current paper a method is proposed to validate the impact of the non-reversible structural build-up. It is shown that fresh cement paste samples lose their structural gain almost completely due to thixotropy while the structural build-up due to hydration can be observed but occurs in a significantly lower order of magnitude over the course of the first hours of hydration. In addition, it is shown, that the chemical component of the structural build-up accelerates with the onset of the acceleration period of hydration, while its contribution in the entire structural build-up remains constant.
The retardation mechanism of cement hydration as imparted by the addition of polyphosphate comb superplasticizer to model cement containing C3S, C3A and calcium sulfate hemihydrate is studied using XRD, ss NMR and calorimetry. Our findings show the retardation effect caused by the direct addition of polyphosphate comb superplasticizer differs significantly to that of conventional polycarboxylate superplasticizers. Conversely to polycarboxylates, polyphosphates, at a low dosage, inhibits the silicate reaction without affecting the aluminate reaction and formation of ettringite. Yet, at high doses, both reactions are hampered, and the induction period extended, followed by accelerated aluminate and silicate reactions.
Effect of Polycarboxylate Superplasticizer in Ordinary Portland Cement and Sulfate Resistant Cement
(2023)
Polycarboxylate superplasticizers (PCE) are the most widely used admixtures in today’s cementitious construction materials. The molecular structure has a decisive influence on the effectiveness of PCE, which also can be tailored to serve in a different cementitious system.
The current study investigates the influence of the backbone charge density of PCE on the rheology, hydration kinetics, and adsorption behavior of ordinary Portland cement (OPC) and sulfate-resistant cement (SRC). The results indicate that regardless of the PCE type, OPC requires a higher amount of PCE to be adsorbed to induce changing of rheological parameters and hydration kinetics. Regardless of the cement type, the PCE with a higher charge density exhibits higher adsorption behavior, corresponding to lower viscosity measurement.
Compared to OPC, SRC is more sensitive to the introduction of both PCEs and has a lower saturation dosage, indicating that SRC generally provides better workability properties regardless of the PCE.
There is no consensus on which hydration stoppage method is optimal to preserve the microstructure and mineral composition of samples, especially considering the specific aspects of different testing methods, such as TGA, MIP, or XRD. This paper presents a quantitative comparison between the most popular hydration stoppage strategies and parameters such as the sample piece size, the soaking time in a solvent, and the type, as examined on cement paste hydrated for 7 days. It was found that the carbonation appears either for samples smaller than 2.36 mm and bigger than 4.75 mm or samples soaked in a solvent for longer than 1 h. Fast solvent replacement leads to ettringite diminution and total pore volume increase. Among others, solvent replacement with subsequent gentle heating under a vacuum was found to be the most efficient, whereas it was experimentally demonstrated that isopropyl alcohol stops hydration faster than ethanol and acetone.
Materials that support natural biodiversity on their surfaces can compensate for human activities that have a negative impact on nature and thus contribute to a carbon-neutral and nature-positive world. Specifically designing bioreceptive materials which favor the growth of biofilms on their surface is an approach complementing conventional, macroscopic green façades. But what exactly characterizes a bioreceptive substrate and how do biofilm and substrate interact? How and why does a spontaneous colonization and the formation of biofilms take place? What are biofilms and how can they be established in a laboratory setting? How can this existing knowledge be transferred to the artificial stone concrete so that this material can be tuned to increase (or decrease) its bioreceptivity?
This review paper aims at summarizing the existing state of knowledge on bioreceptive concrete and pointing out inconsistencies and contradictions which can only be removed by more interdisciplinary research in the field.
Quenching and partitioning (Q&P) steels are characterized by an excellent combination of strength and ductility, opening up great potentials for advanced lightweight components. The Q&P treatment results in microstructures with a martensitic matrix being responsible for increased strength whereas interstitially enriched metastable retained austenite (RA) contributes to excellent ductility. Herein, a comprehensive experimental characterization of microstructure evolution and austenite stability is carried out on a 42CrSi steel being subjected to different Q&P treatments. The microstructure of both conditions is characterized by scanning electron microscopy as well as X‐ray diffraction (XRD) phase analysis. Besides macroscopic standard tensile tests, RA evolution under tensile loading is investigated by in situ XRD using synchrotron and laboratory methods. As a result of different quenching temperatures, the two conditions considered are characterized by different RA contents and morphologies, resulting in different strain hardening behaviors as well as strength and ductility values under tensile loading. In situ synchrotron measurements show differences in the transformation kinetics being rationalized by the different morphologies of the RA. Eventually, the evolution of the phase specific stresses can be explained by the well‐known Masing model.
Volumetric changes follow Portland cement hydration reactions: aluminates' hydration is generally expansive, whereas silicates' reaction leads to shrinkage. Determining the volumetric variation at very early ages (i.e., first minutes/hours) presents operational challenges; most standards prescribe the measurement on specimens that are already hardened, while measurements from the fresh state are not standardized. This article reports the first attempt to use in-situ X-ray diffraction (XRD) to measure the early-age volumetric variation of a cementitious paste. For this purpose, a C3A + gypsum paste was assessed for 36 h, measuring its vertical displacement over time through XRD. The results showed that the expansion increased in the first ∼13 h, in line with the ettringite formed up to ∼11 h. In addition, the volumetric expansion agreed well with the heat release in calorimetry. It is concluded that the volumetric variation measurement of cementitious pastes through in-situ XRD is a promising technique, but further studies are needed to make this technique consolidated.
Corrosion monitoring of reinforced concrete structures:The DGZfP specification B12 Collaboration
(2023)
Corrosion monitoring of reinforced or prestressed concrete structures has becomeincreasingly important in recent years. Areas of application include componentsthat are no longer accessible after completion or where potential fieldmeasurements cannot be carried out due to existing coatings. Corrosion monitoringcan also be used to monitor the progress of corrosion in corroding systems, e.g. toprove the success of repair measures according to repair principle 8 in accordancewith EN 1504‐9 or repair method 8.3 in accordance with the DIBt repair guideline.It also could be used to prove the functionality of cathodic corrosion protectionsystems in accordance with ISO 12696. Despite the increasing importance ofcorrosion monitoring, no guidelines orrecommendations existed until 2018. Thisgap was closed by the English version of specification B12,“Corrosion Monitoringof Reinforced and Prestressed Concrete Structures,”of the German Society for Non‐Destructive Testing, which was published in 2021. This article introducesspecification B12 by explaining the basicmeasurement principles and illustratingthe potential of corrosion monitoring in new and existing buildings.
Multiscale modeling of linear elastic heterogeneous structures via localized model order reduction
(2023)
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 by solving 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.
In this work, a methodology based on Fourier transform infrared (FTIR)spectroscopy and multivariate evaluation is presented to estimate the aging sensitivity of bitumen based on the unaged samples and thus without the need for time- and material-consuming aging simulations. For this purpose, factor analysis and linear discriminant analysis are used to develop a statistical model based on the FTIR spectra of unaged bitumen samples, which can be used fast and simple in everyday laboratory work and allows to assign the bitumen to a low, moderate, or strong aging sensitivity. The evaluation of the aging sensitivity is based on the complex shear modulus|G* | and the phase angle δ from the measurement with a dynamic shear rheometer(DSR), whose aging-related changes were captured as the slope in the Black diagram. A relevant influence on the classification concerning the aging sensitivity has the oxygen-containing compounds(sulfoxide, hydroxyl and partly carbonyl compounds), whereby lower contents and thus less preaged bitumen tend to have a stronger aging sensitivity. However, in addition to the oxygen-containing compounds, the structure of the aliphatic and aromatic compounds and, in particular, the interaction of the different structures are decisive for the aging sensitivity
The site of Schöningen (Germany), dated to ca. 300,000 years ago, yielded the earliest large-scale record of humanly-made wooden tools. These include wooden spears and shorter double-pointed sticks, discovered in association with herbivores that were hunted and butchered along a lakeshore. Wooden tools have not been systematically analysed to the same standard as other Palaeolithic technologies, such as lithic or bone tools. Our multianalytical study includes micro-CT scanning, 3-dimensional microscopy, and Fourier transform infrared spectroscopy, supporting a systematic technological and taphonomic analysis, thus setting a new standard for wooden tool analysis. In illustrating the biography of one of Schöningen’s double-pointed sticks, we demonstrate new human behaviours for this time period, including sophisticated woodworking techniques. The hominins selected a spruce branch which they then debarked and shaped into an aerodynamic and ergonomic tool. They likely seasoned the wood to avoid cracking and warping. After a long period of use, it was probably lost while hunting, and was then rapidly buried in mud. Taphonomic alterations include damage from trampling, fungal attack, root damage and compression. Through our detailed analysis we show that Middle Pleistocene humans had a rich awareness of raw material properties, and possessed sophisticated woodworking skills. Alongside new detailed morphometrics of the object, an ethnographic review supports a primary function as a throwing stick for hunting, indicating potential hunting strategies and social contexts including for communal hunts involving children. The Schöningen throwing sticks may have been used to strategically disadvantage larger ungulates, potentially from distances of up to 30 metres. They also demonstrate that the hominins were technologically capable of capturing smaller fast prey and avian fauna, a behaviour evidenced at contemporaneous Middle Pleistocene archaeological sites.
Inelastic incoherent neutron time-of-flight scattering was employed to investigate the low-frequency vibrational density of states (VDOSs) for a series of glassy Janus-poly(tricyclononenes), which consist of a rigid main chain and flexible alkyl side chains. Here, the length of the flexible side chains was systematically varied from propyl to octyl. Such materials have potential applications as active separation layers in gas separation membranes as a green future technology, especially for the separation of higher hydrocarbons. From the morphological point of view, the Janus polynorbornenes undergo a nanophase separation into alkyl side chain-rich nanodomains surrounded by a rigid polynorbornene matrix. Here, the influence of the nanophase-separated structure on the low-frequency VDOS is investigated from a fundamental point of view. The low-frequency VDOSs of these Janus polynorbornene show excess contributions to the Debye type VDOS known as the Boson peak (BP) for all side chain lengths. Due to the high incoherent scattering cross-section of hydrogen, most of the scattering comes from the alkyl side chain-rich domains.
Compared to conventional glass-forming materials, in the considered Janus polynorbornenes, the BP has a much lower intensity and its frequency position is shifted to higher values. These experimental results are discussed in terms of the nanophase-separated structure where the alkyl chain-rich domains were constrained by the surrounding matrix dominated by the rigid backbone. With increasing alkyl chain length, the size of the alkyl chain-rich domains increases. The frequency position of the BP shifts linearly to lower frequencies with the size of these nanodomains estimated from X-ray measurements. The obtained results support the sound wave interpretation to the BP
The reduction in train-induced ground vibrations by different railway lines and by mitigation measures in the propagation path was analysed in a unified approach by two-dimensional finite element calculations. In general, there was no reduction at low frequencies, and the reduction be-came stronger with increasing frequencies. A maximum reduction of 0.1 at high frequencies was established with an open trench. Reductions between 0.7 and 0.2 have been found for the other sit-uations, filled trenches, walls, plates, and blocks, as well as for railway lines on dams, in cuts and in a tunnel. Bridges can produce amplifications due to their resonance frequencies, but also strong reductions due to massive bridge piers. The influence of some parameters has been analysed, such as the bridge span, the inclination of the dam and the cut, the stiffness of the soil, and the tunnel structure. The dynamic track stiffnesses of a surface, bridge, and tunnel track have been calculated using the 3D finite-element boundary-element method for comparison with corresponding meas-urements.
Die Anwendung von Zuggliedern aus Carbon ist durch die außergewöhnlich gute Ermüdungs- sowie hohe Zugfestigkeit des Werkstoffs motiviert. Ferner ergibt sich gegenüber Stahl eine deutliche Reduzierung des Querschnitts. Perspektivisch sollen damit u. a. Stahlzugglieder im Netzwerkbogenbrückenbau ersetzt werden. Das Tragverhalten von Carbonzuggliedern im Brandfall ist jedoch bislang unbekannt. Daher wurden mittels Bauteilbrandversuchen die Versagensmechanismen untersucht sowie anhand gewonnener Versuchsdaten eine exemplarische Einschätzung zur Gleichwertigkeit gegenüber konventionellen Stahlzuggliedern vorgenommen. Der Beitrag beschreibt realmaßstäbliche Brandversuche an mechanisch belasteten Carbonzuggliedern, die im Rahmen des Verbundforschungsvorhabens NeZuCa durchgeführt wurden. Das Versuchsprogramm umfasste vier Carbonzugglieder mit kreisrunden Querschnitten in zwei verschiedenen Durchmessern, 36 mm und 51 mm. In Ermangelung eines präskriptiven Brandszenarios für den im Projekt vorgesehenen Anwendungsfall und aus Gründen der Vergleichbarkeit erfolgte die Brandbeanspruchung nach Einheitstemperaturzeitkurve (ETK). Neben den Längsverformungen der Zugglieder wurden auch die Bauteil und Brandraumtemperaturen aufgezeichnet.
For a comprehensive safety assessment of stationary lithium-ion-battery applications, it is necessary to better understand the consequences of thermal runaway (TR). In this study, experimental tests comprising twelve TR experiments including four single-cell tests, two cell stack tests and six second-life module tests (2.65 kW h and 6.85 kW h) with an NMC-cathode under similar initial conditions were conducted. The temperature (direct at cells/modules and in near field), mass loss, cell/module voltage, and qualitative vent gas composition (Fourier transform infrared (FTIR) and diode laser spectroscopy (DLS) for HF) were measured. The results of the tests showed that the battery TR is accompanied by severe and in some cases violent chemical reactions. In most cases, TR was not accompanied by pregassing of the modules. Jet flames up to a length of 5 m and fragment throwing to distances to more than 30 m were detected. The TR of the tested modules was accompanied by significant mass loss of up to 82%. The maximum HF concentration measured was 76 ppm, whereby the measured HF concentrations in the module tests were not necessarily higher than that in the cell stack tests.
Subsequently, an explosion of the released vent gas occurred in one of the tests, resulting in the intensification of the negative consequences. According to the evaluation of the gas measurements with regard to toxicity base on the “Acute Exposure Guideline Levels” (AEGL), there is some concern with regards to CO, which may be equally as important to consider as the release of HF.
Proof load testing may be performed to confirm the reliability of the bridge for an existing classification or to prove the reliability for a higher classification. In this paper, a probabilistic decision analysis approach is applied to the scenario for the evaluation of target proof load in the situation where information on the bridge resistance model is lacking. In this case, the resistance model is established by proof loading and taking very basic prior knowledge into account. The decision scenario is modelled in the context of the proof load test planner who shall choose the required load level for assessment of a bridge. The choice of the load level depends on the risks due to the testing and the expected benefit gain from the test. Information acquired about the loading response from monitoring during the proof load testing is modelled by taking basis in the model uncertainty formulation. The optimal proof load level for classification of a single lane, simply supported bridge of 8m span subjected to live load from very heavy (gross weight > 80 tons) transport vehicles was calculated. The optimal proof load level was identified as leading to a positive expected benefit gain to the decision maker while also satisfying target reliability criteria for remaining service life. The analysis was performed for the evaluation of bridge performance with respect to five classifications of very heavy transport vehicles with different vehicle weights and configurations.
Composition and Explosibility of Gas Emissions from Lithium-Ion Batteries Undergoing Thermal Runaway
(2023)
Lithium-based batteries have the potential to undergo thermal runaway (TR), during which mixtures of gases are released. The purpose of this study was to assess the explosibility of the gaseous emission from LIBs of an NMC-based cathode during thermal runaway. In the current project, a series of pouch lithium-based battery cells was exposed to abuse conditions (thermal) to study the total amount of gases released and the composition of the gas mixture. First, the battery cells were placed in a closed vessel, and the pressure and temperature rise inside the vessel were measured. In a second step, the composition of gases was analysed using a Fourier transform Infrared (FTIR) spectrometer.
We found that the amount of released gases was up to 102 ± 4 L, with a clear dependence on the battery capacity. This study showed that the concentration of gaseous emissions such as carbon monoxide (CO), methane (CH4), ethylene (C2H4), ethane (C2H6), and hydrogen cyanide (HCN) increased with higher cell capacity. Of the five studied flammable gases, the maximum concentrations of carbon monoxide (16.85 vol%), methane (7.6 vol%), and ethylene (7.86 vol%) were identified to be within their explosible range. Applying Le Chatelier’s law, a calculated lower explosion limit (LEL) of 7% in volume fraction was obtained for the gas mixture. The upper explosion limit (UEL) of the gas mixture was also found to be 31% in volume. A filter comprising pyrobubbles was used for the removal of the studied gas components released during the thermal abuse. The investigation revealed that the pyrobubbles filter was highly effect in the removal of HCN (up to 94% removal) and CO2 (up to 100% removal). Herein, we report the dependency of the method of thermal runaway trigger on the measured maximum temperature.
Two hybrid alkaline cements (HAC) based on Portland clinker, ground granulated blast furnace slag (GGBFS), fly ash and sodium sulfate, as well as an alkali-activated GGBFS/fly ash blend and a Portland cement paste were exposed to a saturated saline solution for 70 days. The combined chemical attack of chloride, magnesium and sulfate ions and the associated changes of the phase assemblage of the materials were studied by X-ray diffraction, thermal analysis and spatially resolved X-ray fluorescence spectroscopy. The experimental results revealed dissolution of ettringite, C-N-A-S-H and calcite, and the formation of gypsum, Kuzel's salt and Friedel's salt; thermodynamic modeling indicated the formation of M-S-H. The resistance of the HAC against attack by the saline solution increased with Portland clinker fraction. The capacity of portlandite to maintain pH at values above 10 is found to be a major factor controlling the resistance of HAC against corrosion in the saline solution.
Although fire safety regulations for buses have been adapted in recent years regarding, for example, fire detection and engine fire suppression systems, the changes in regulations for bus interior materials are minimal. A comparison of fire safety regulations for interior materials in other transport sectors for trains, ships or aircraft reveals a much lower level of requirements for bus materials. Although repeated bus accidents as well as fire statistics show the danger a bus fire can pose to passengers.
In particular, the combination of a fire incident and passengers with reduced mobility led to severe disasters in Germany and other European countries. To enhance the fire safety for passengers, the interior bus materials are crucial as the fire development in the bus cabin determines whether escape and rescue is possible. Against this background, bus interior materials were tested in different fire test scenarios. Measurement of a wide variety of parameters, for example, the mass loss, ignition time, smoke gas composition, heat release rate among others were carried out. Tested materials complied to the newest set of requirements. For this purpose, interior materials and their components had to be identified according to their chemical structure. Parts of the tests were funded by BASt (Federal Highway Research Institute) in the project 82.0723/2018. Experimental results show reaction-to-fire behaviour which lead to very limited times for escape and rescue in case of fire in a bus cabin. Based on the studies on fire behaviour and toxicity assessment, recommendations for improved fire safety regulations for interior materials could be made.
This study provides an analysis on the fire safety of passengers and the fire protection of coaches and buses. A brief review of major bus fire incidents, an overview of current regulations in Europe, and their limitations are presented. The study finds that the current small-scale fire test methods described in UN ECE Reg No. 118 need to be replaced by test methods that can assess the reaction to fire of materials when exposed to ignition sources of varying sizes. To address these shortcomings, the study proposed an expert recommendation to update the material fire safety requirements and testing for buses. Additional measures are proposed, derived from objectives and strategies applied in other transport sectors, and can be tested through existing European and international standards, which are widely used by several industries. These measures aim to extend the time with tenable conditions for a safe evacuation in case of fire, reduce the degree of damage to buses, reduce the risk for fast and excessive thermal exposure on modern energy carriers needed for a more sustainable transport sector.
The addition of nanoparticles as reinforcing fillers in elastomers yields nanocomposites with unique property profiles, which opens the door for various new application fields. Major factors influencing the performance of nanocomposites are studied by varying the type and shape of nanoparticles and their dispersion in the natural rubber matrix. The industrial applicability of these nanocomposites is put into focus using two types of graphene and a nanoscale carbon black, all commercially available, and scalable processing techniques in the form of a highly filled masterbatch production via latex premixing by simple stirring or ultrasonically assisted dispersing with surfactant followed by conventional two-roll milling and hot pressing. Different processing and measurement methods reveal the potential for possible improvements: rheology, curing behavior, static and dynamic mechanical properties, swelling, and fire behavior. The aspect ratio of the nanoparticles and their interaction with the surrounding matrix prove to be crucial for the development of superior nanocomposites. An enhanced dispersing method enables the utilization of the improvement potential at low filler loadings (3 parts per hundred of rubber [phr]) and yields multifunctional rubber nanocomposites: two-dimensional layered particles (graphene) result in anisotropic material behavior with strong reinforcement in the in-plane direction (157% increase in the Young's modulus). The peak heat release rate in the cone calorimeter is reduced by 55% by incorporating 3 phr of few-layer graphene via an optimized dispersing process.
The analysis of the current state of fire statistics and data collection in Europe and other countries is needed to increase awareness of how fire incidents affect buildings and to support pan-European fire prevention and fire mitigation measures.
The terminology and data collected regarding fire incidents in buildings in the EU Member States were mapped to obtain meaningful datasets to determine common terminology, collection methodology, and data interpretation system. An extensive literature review showed that fire data collection systems have been instrumental in informing firefighting strategies, evidence-based planning, prevention, and educational programmes. Differences and similarities between fire data collection systems were also investigated. The amount and quality of the information in fire statistical recording systems appear to be influenced by the complexity and structure with which the data are collected. The analysis also examined the existing fire statistics in the EU Member States and a few other countries. Finally, a detailed investigation of the number of fires, fire deaths, and injuries from 2009 to 2018 in several countries was examined based on data from a report by CTIF. The trends showed differences attributable to the existing fire statistical practices in terms of terminology and data
collection, and interpretation. Part II proposes a common terminology for selected fire statistical variables. The results provide relevant information regarding fire safety at the European level and should be used to guide the development of more uniform fire statistics across Europe.
A series of flexible polyurethane foams (FPUFs) were prepared with single and different combinations of flame retardants and additives. Expandable graphite (EG), phosphorous polyol (OP), copper (II) oxide (CuO), and/or castor oil (CAS) were added to FPUF during the foam preparation in a one-step process. The purpose of the study is to evaluate the synergistic effects of the flame retardants, additives, and the presence of bio-based content on the mechanical properties, flame retardancy, and smoke behavior of FPUFs. The combination of 10 wt % EG and 5 wt % OP in FPUF significantly improves the char yield. In the cone calorimeter experiment, the char yield is nearly three times higher than that with 10 wt % EG alone. The smoke behavior is additionally evaluated in a smoke density chamber (SDC). Comparing the samples with a single flame retardant, 10 wt % EG in FPUF considerably reduces the amount of smoke released and the emission of toxic gases. Replacing the amount of 10 wt % polyether polyol in FPUF with CAS maintains the physical and mechanical properties and fire behavior and enhances the bio-based content. The presence of 0.1 wt % CuO in FPUF effectively reduces the emission of hydrogen cyanide. As a result, this study proposes a multicomponent flame retardant strategy for FPUF to enhance the biomass content and address the weaknesses in flame retardancy, smoke, and toxic gas emissions. A starting point is disclosed for future product development.
Using digital twins for decision making is a very promising concept which combines simulation models with corresponding experimental sensor data in order to support maintenance decisions or to investigate the reliability. The quality of the prognosis strongly depends on both the data quality and the quality of the digital twin. The latter comprises both the modeling assumptions as well as the correct parameters of these models. This article discusses the challenges when applying this concept to realmeasurement data for a demonstrator bridge in the lab, including the data management, the iterative development of the simulation model as well as the identification/updating procedure using Bayesian inference with a potentially large number of parameters. The investigated scenarios include both the iterative identification of the structural model parameters as well as scenarios related to a damage identification. In addition, the article aims at providing all models and data in a reproducibleway such that other researcher can use this setup to validate their methodologies.
This study investigated the effect of incorporating three types of nanosilica (NS), two powders, and one colloidal suspension on the hydration, strength, and microstructure of calcium sulfoaluminate (CSA) cement pastes prepared with and without a superplasticizer (SP). X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and compressive strength tests were performed after 2, 5, and 28 days of hydration. The results showed that both NS powders delayed cement hydration at an early age, which was attributed to particle agglomeration (confirmed by dynamic light scattering). Whereas well-dispersed colloidal NS did not significantly affect the hydration of CSA at the investigated ages. SP incorporation improved the dispersion of CSA cement particles, resulting in a 10% increase in the degree of hydration of ye’elimite at 28 days for the system without NS. Conversely, when the SP was incorporated in NS-containing mixtures, it hindered cement hydration of the systems with powdered NS, but did not significantly affect the cement hydration of the system containing colloidal NS. The SEM images suggested that the SP changed the ettringite morphology, thereby negatively affecting the mechanical strength of the CSA pastes.
problem. One reason is the sensitivity to stress corrosion cracking of the prestressing steel. Failure of prestressing wires can result in collapse of the entire structure without premature indication by transverse bending cracks or considerable deformation. The response of a structure to significant number of prestressing wire breaks was studied on a bridge in Brandenburg, Germany. Two thirds of the prestressing wires in concentrated tendons of two girders were cut before the bridge was demolished. Acoustic Emission Analysis was used to detect the wire breaks. Thus, the number of wire breaks was correlated with results of other measurement techniques, in particular strain measurements on the girders. In preparation of the measurements, the acoustic properties of the bridge were determined and the suitability of Schmidt hammer impacts as an acoustic reference source was validated.
Lithium-ion batteries are a key technology to achieve the goals of limiting climate change due to the important role as traction technology for Electric Vehicles and in stationary energy storage systems. Over(dis) charge, mechanical damage due to accidents or thermal abuse such as fires can initiate an accelerated self-heating process of the batteries, called thermal runaway. A thermal runaway can propagate from cell to cell within a larger assembly of cells such as modules or battery packs and can cause rapid heat and toxic gas emissions. The resulting battery fire can spread to adjacent facilities, e.g. other cars in underground car parks or to a whole building in case of a large stationary energy storage.
For proof of fire protection requirements or to design suitable fire protection systems, Computational Fluid Dynamic (CFD) simulations are getting more and more important. The aim of CFD fire simulations is to predict the global hazards of a fire to its surroundings, that is mainly characterized by the release of heat and smoke and its spread in the fire environment. There are many numerical investigations of lithium-ion batteries in the literature. One class of models is used to simulate the charge and discharge process of lithium-ion batteries and to predict the temperature or voltage evolution inside the battery. On the other hand, there are models describing batteries under abuse conditions to predict the consequences of a thermal runaway event to the local environment, like the temperatures inside a battery or at the battery surface. Henriksen et al. use a generic battery gas mixture to simulate an explosion of vented gases from a Lithium Iron Phosphate battery and compare experimental results for the explosion pressure and the position of the flame front to the outcomes of a simulation with Xifoam. Larsson et al. used a combination of CFD simulations with FDS and thermal model with COMSOL to predict the temperature development of neighboring cells in a thermal runaway propagation. Truchot et al. use a design Heat Release Rate (HRR) curve for a battery based on experimental measurements to build up an overall HRR curve for a truck loaded with 100 lithium-ion batteries. This summed up HRR and corresponding smoke production curve is then used as an input for a simulation of a truck fire in a tunnel with Fire Dynamics Simulator (FDS). The pre-definition of the HRR curve is a frequently used method in fire engineering. It has the disadvantage, that the heat release cannot be influenced by physical processes, such as changed ventilation conditions or extinguishing measures. In this paper, a model is presented that determines the release of heat and gases based on the thermal runaway mechanisms of the battery, which can be used in CFD fire simulations with focus on prediction of fire hazards to nearby environment.
This paper aimed to perform an exploratory literature review, focusing on the aspects of hydration and rheological properties of cementitious composites with açaí fibers. The use of natural fibers as a reinforcement in cementitious matrices has been widely studied, and açaí fiber is a promising option due to its unique characteristics. However, there is still a lack of knowledge regarding the correlation between fiber parameters and the technological properties of composites, which limits the development of new applications, such as 3D printing. The review provided an overview of the main characteristics of açaí fibers and the parameters for their application in cementitious matrices. Alkali treatment with 5% NaOH solution for 1 h shows increased mechanical and physical properties in açaí fibers. Despite the potential advantages of these composites, they pose challenges due to the different fiber surface treatment and interfacial transitions and the processing conditions of the fibers. Although small addition of açaí fibers slightly decreases the cement hydration process, keeping the cross-compatibility index high (>95). To overcome these challenges, it is necessary to evaluate the rheological behavior of cementitious materials with açaí fibers, which has not been reported in the literature. By doing so, it will be possible to optimize the processing conditions and develop new applications, such as additive manufacturing, which has never been explored with açaí fibers.
Messtechnische Systeme zur Dauerüberwachung von Bauwerken ermöglichen Einblicke in deren reale Trag- und Verformungsverhalten. Die Planung und technische Umsetzung solcher Maßnahmen erfordern für die erfolgreiche Erfüllung der Aufgabenstellungen eine hohe Fachkompetenz, sowohl auf der planerischen Seite, als auch für die fachliche Bewertung von angebotenen Monitoringlösungen. Als Hilfestellung dafür wurde von der Deutschen Gesellschaft für Zerstörungsfreie Prüfung (DGZfP) das Merkblatt „Dauerüberwachung von Ingenieurbauwerken“ erarbeitet, welches nun verfügbar ist. In diesem Beitrag werden die Inhalte des neuen Merkblatts vorgestellt und dieses in die vorhandene Literatur eingeordnet.
In the present paper, an approach for updating the continuous stress range distribution of a welded connection of a wind turbine support structure with predicted information from strain measurements is presented. Environmental conditions, such as wind or, in offshore fields, waves and currents, in combination with rotor excitations generate cyclic stresses affecting the reliability of welded joints of the support structure over the service life. Using strain measurements, these conditions can be monitored, and the resulting stress ranges, under consideration of measurement, mechanical and material uncertainties, can be reconstructed. These stress ranges can be used as an input for updating the prior probability density function (PDF) of the stress ranges predicted by the overall dynamics and a detailed design analysis. Applying Bayesian probability theory and decision theoretical implications, the predicted posterior probability density of the stress ranges is calculated based on the design information and uncertainties. This approach is exemplified, and it is shown how the predicted stress ranges and the design stress ranges are distributed. The prior and the predicted posterior stress ranges are used for a reliability calculation for potentially entering a pre-posterior decision analysis
The new crack luminescence method offers the possibility of making fatigue surface cracks in metallic materials more visible during inspections through a special coating system. This coating system consists of two layers, whereby the first layer has fluorescent properties and emits visible light as soon as it is irradiated by UV light. The top layer is black and is designed to prevent the fluorescent layer from emitting if no crack develops in the underlying material. The technique proved particularly useful in a wide variety of fatigue tests of steel components under laboratory conditions. Moreover, it has the potential to be used in various industrial applications. To enable industrial deployment and integration into maintenance strategies, a concept study is developed in this contribution, resulting in a qualification framework that can serve as a foundation for determining the reliability of the crack luminescence system in terms of a probability of detection curve. Within this study, factors causing measurement variability and uncertainty are being determined and their influences assessed. Due to the extension of the system by a moving computer vision system for automated crack detection using artificial intelligence, additional long-term effects associated with structural health monitoring systems need to be incorporated into an extended probability of detection study as part of the technical justification. Finally, important aspects and findings related to design of experiments are discussed, and a framework for reliability assessment of a new optical crack monitoring method is presented, emphasizing the influence of various uncertainty parameters, including long-term effects such as system ageing.
Application of electrochemical methods for studying steel corrosion in alkali-activated materials
(2023)
Alkali-activated materials (AAMs) are binders that can complement and partially substitute the current use of conventional cement. However, the present knowledge about how AAMs protect steel reinforcement in concrete elements is incomplete, and uncertainties exist regarding the application of electrochemical methods to investigate this issue. The present review by EFC WP11-Task Force ‘Corrosion of steel in alkali-activated materials’ demonstrates that important differences exist between AAMs and Portland cement, and between different classes of AAMs, which are mainly caused by differing pore solution compositions, and which affect the outcomes of electrochemical measurements. The high sulfide concentrations in blast furnace slag-based AAMs lead to distinct anodic polarisation curves, unusually low open circuit potentials, and low polarisation resistances, which might be incorrectly interpreted as indicating active corrosion of steel reinforcement. No systematic study of the influence of the steel–concrete interface on the susceptibility of steel to corrosion in AAMs is available. Less common electrochemical methods present an opportunity for future progress in the field.
The current understanding of the carbonation of alkali-activated concretes is ham-pered inter alia by the wide range of binder chemistries used. To overcome some of the limitations of individual studies and to identify general correlations between their mix design parameters and carbonation resistance, the RILEM TC 281-CCC working group 6 compiled carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥ 66 % of the binder) were also included in the database. A preliminary analysis of the database indicates that w/CaO ratio and w/b ratio exert an influence on the carbonation resistance of alkali-activated concretes but, contrary to what has been reported for concretes based on (blended) Portland cements, these are not good indicators of their carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approxi-mating natural carbonation appears to be their w/(CaO + Na2O + K2O) ratio. Furthermore, the analysis points to significant shortcomings of tests at elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at a concentration of 1 % CO2, the outcomes may lead to inaccurate predictions of the carbonation coefficient under natural exposure conditions.
In the processing of nanocomposites, high shear stresses at elevated tempera-tures orient two-dimensional nanoparticles like graphene. This orientationleads to anisotropic mechanical, thermal or barrier properties of the nanocom-posite. This anisotropy is addressed in this study by comparing graphene (few-layer graphene, FLG) with a nanoscaled carbon black (nCB) at a filler contentof 3 phr, by varying the vulcanization, and by comparing different FLG con-tents. Transmission electron microscopy gives insight into the qualitative ori-entation in the nanocomposite with FLG or nCB. The storage moduli paralleland normal to the orientation reveal the direction dependency of reinforce-ment through dynamic mechanical analysis (DMA). Dimensional swellingmeasurements show a restriction of the expansion parallel to the FLG orienta-tion, and an increased expansion normal to the orientation. The vulcanizationsystem and crosslinking determine the respective level of property values, andhigher crosslinking densities increase the anisotropy in DMA resulting invalues of up to 2.9 for the quantified anisotropy factor. With increasing FLGcontent, the anisotropy increases. A comparison of the results reveals swellingmeasurements as the most suitable method for the determination of anisot-ropy. Compared to recent literature, the presented processing induces higheranisotropy, leading to higher reinforcing effects in the direction of orientation
Binary systems composed of Portland cement (PC) and calcium sulfoaluminate (CSA) cement have stood out for applications requiring high early strengths. Nevertheless, the application of these systems may be limited due to their properties in the fresh state, which requires a better understanding of the rheological behavior of these materials. Thus, this study evaluated the incorporation of different polycarboxylate-based superplasticizer (SP) contents (0.15, 0.20, and 0.25 wt%) on PC and PC-CSA binary cement pastes. Rotational rheometry, isothermal calorimetry, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption and desorption tests to assess the pore size distribution of cement pastes were conducted. While the SP incorporation reduced the dynamic yield stress of PC pastes, it progressively increased the yield stress of PC-CSA systems. The increase in SP content increased the main heat flow peak of PC-CSA pastes, although it did not significantly affect the cumulative heat after 160 h of hydration. FTIR and XRD confirm higher ettringite contents in the binary systems and indicate the presence of carboaluminates phases after 7 d of hydration in both PC and PC-CSA and hemicarboaluminate in PC-CSA pastes. The CSA incorporation reduced the cumulative pore volume by up to 32% compared to PC pastes, while the SP content evaluated did not significantly affect the porosity of PC-CSA pastes.
An assessment of the elastic-plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design.
This paper reports on an international ‘round-robin’ exercise conducted in 2022 aiming to take stock of the computational shell buckling expertise around the world which attracted 29 submissions. Participants were asked to perform analyses of increasing complexity on a standardised benchmark of an 8-MW multi-strake steel wind turbine support tower segment, from a linear elastic stress analysis to a linear bifurcation analysis to a geometrically and materially nonlinear buckling analysis with imperfections. The results are a showcase of the significant shell buckling expertise now available in both industry and academia.
This paper is the first of a pair. The second paper presents a detailed reference solution to the benchmark, including an illustration of the Eurocode-compliant calibration of two important imperfection forms.
A thorough characterization of base materials is the prereq- uisite for further research. In this paper, the characterization data of the reference materials (CEM I 42.5 R, limestone pow- der, calcined clay and a mixture of these three components) used in the second funding phase of the priority program 2005 of the German Research Foundation (DFG SPP 2005) are presented under the aspects of chemical and min- eralogical composition as well as physical and chemical properties. The data were collected based on tests performed by up to eleven research groups involved in this cooperative program.
As most of polymeric materials are inherently flammable, flame retardants (FR) are commonly used to reduce their fire risks. Nevertheless, these flame retardant materials are often detrimental to smoke parameters like specific optical density or smoke toxicity. The influence of several smoke suppressants (SP)-zinc stannate, zinc phosphate, titanium oxide and hydrotalcite-were investigated with respect to flame retardancy, smoke emission, particle emission and smoke toxicity in a diethyl aluminum phosphinate (AlPi) flame retardant polyamide 6.6 (PA6.6). It was shown that the interaction between SP, FR and polymer is crucial for smoke and fire properties and can change the mode of action of the FR as well the decomposition mechanism of the polymer. Small amounts of SP show less effect on forced flaming behavior and the optical density, but they can influence flammability and the particle size distribution of the soot particles. The flame retardancy was significantly enhanced by 5 wt.-% zinc stannate in PA6.6 under forced flaming conditions. The charring mechanism was improved, and the mode of action of AlPi switched from the gas to the condensed phase. This resulted of in a reduced PHRR and TSP and an increase in residue yield. The smoke toxicity and optical density were reduced in the smoke density chamber as well. The smoke particles shifted to smaller sizes as the time in the pyrolytic zone increased. The formation of a dense char is assumed to be the key factor to enhance smoke suppression and flame retardancy properties.
Single reuse of asphalt is an approved practice, but its success highly depends on restoring the properties of the aged binder. Rejuvenators have become increasingly important for softening the binder because they make it possible to increase the amount of reclaimed asphalt pavement (RAP) while reducing the dependence on virgin bitumen. The vital questions to be investigated are how the rejuvenators affect the ageing properties of bitumen and if rejuvenators offer the possibility of cyclic bitumen reuse. The main objective of this publication is to present the current state of the art regarding the effects of rejuvenators on bitumen ageing. The results of laboratory life cycle simulations indicate that repetitive ageing and rejuvenation processes are possible, but reuse mainly depends on the rejuvenator type and its interaction with the respective bitumen sample. There are rejuvenators that have good rejuvenating properties but accelerate subsequent ageing, which is essential to consider when evaluating a rejuvenator. Bitumen rejuvenated with petroleum-based products, such as aromatic extracts, performs slightly better after subsequent ageing than when rejuvenated with bio-based products. As there are a limited number of studies simulating cyclic bitumen reuse, more studies are necessary to evaluate the general limits of bitumen reuse.
Reclaimed asphalt pavements (RAP) with increased contents of polycyclic aromatic hydrocarbons (PAH) are restricted for reuse due to their harmful effects on humans and the environment. This work investigated whether Fourier transform infrared (FTIR) spectroscopy is suitable for a fast and simple identification and quantification of PAH in binders recovered from reclaimed asphalts. For this, the binders from 34 RAP samples were recovered using a rapid procedure developed at the Universität Kassel and were examined with infrared spectroscopy. The obtained spectra were pre-processed (Standard Normal Variate transformation, 1st derivative) and evaluated using a combination of factor analysis and linear discriminant analysis. The results showed that various PAH groups with differently pronounced aromatic structures are present in the binders.
However, with FTIR spectroscopy combined with the multivariate methods, a statistical model was developed allowing for the differentiation between the PAH groups and also for the distinction between PAH contents below or above the threshold of 25 mg/kg valid in Germany.
Two types of cements were selected as the reference cement in the priority program 2005 of the German Research Foundation (DFG SPP 2005). A thorough characterization of CEM I 42.5 R has been made in a recent publication. In this paper, the characterization data of the other reference cement CEM III/A 42.5 N are presented from the aspects of chemical and mineralogical compositions as well as physical and chemical properties. The characterization data of the slag, which is the second main constituent of this specific cement besides the clinker, are presented independently. For all data received, the mean values and the corresponding errors were calculated. The data shall be used for the ongoing research within the priority program. Also, researchers from outside this priority program can benefit from these data if the same materials are used.
Supplementary cementitious materials (SCM) can reduce the total amount of Portland cement clinker in concrete production. Rice husk ashes (RHA) can be converted from an agricultural by-product to a high-performance concrete constituent due to a high amount of reactive silica with pozzolanic properties if they are burnt under controlled conditions. The way and duration of combustion, the cooling process as well as the temperature have an effect on the silica form and thus, the chemical and physical performance of the RHA. Various studies on the best combustion technique have been published to investigate the ideal combustion techniques. Yet, the process mostly took place under laboratory conditions. Investigating the difference between the performance of RHA produced in a rural environment and laboratory conditions is useful for the assessment and future enhancement of RHA production, and its application both as building material, for example in rural areas where it is sourced in large quantities, and as additive for high performance concrete. Thus, the paper presents a comparison between RHA produced under rudimentary conditions in a self-made furnace in the rural Bagamoyo, Tanzania and under controlled laboratory conditions at the Technical University of Munich, Germany, with different combustion methods and temperatures. In a second step, RHA was ground to reach particle size distributions comparable to cement. In a third step, cement pastes were prepared with 10%, 20% and 40% of cement replacement, and compared to the performance of plain and fly ash blended cement pastes. The results show that controlled burning conditions around 650 °C lead to high reactivity of silica and, therefore, to good performance as SCM. However, also the RHA burnt under less controlled conditions in the field provided reasonably good properties, if the process took place with proper burning parameters and adequate grinding. The knowledge can be implemented in the field to improve the final RHA performance as SCM in concrete.
Compared with most common construction materials, fiber reinforced cementitious materials are well known to exhibit better physical, working and mechanical properties. In this study, three fibers were selected: polypropylene fiber (PPF) and polyvinyl alcohol fiber (PVAF), which represented synthetic fibers, and sisal fiber (SF), which represented natural fibers. Effects of these fibers on the flowability, rheological properties, and adsorption behavior of the cement paste with polycarboxylate superplasticizer (PCE) were investigated. Furthermore, the above experimental results were verified by measuring the contact angle of the fiber with water and PCE solution and the apparent morphology of the fiber. Results revealed that the addition of fibers significantly reduces the fluidity of the cement paste, while the yield stress and plastic viscosity of the cement paste increase with the addition of fibers. From the contact angle and scanning electron microscope, the surface of SF was relatively rough, and the contact angle of SF with water or PCE solution was the smallest. It can be concluded that the plant fiber has a significant influence on the fluidity and rheology of cement paste.
Meta-analysis of heat release and smoke gas emission during thermal runaway of lithium-ion batteries
(2023)
Herein a meta-analysis of 76 experimental research papers from 2000 to 2021 is given about possible effects on the thermal runaway of lithium-ion battery cells. Data on the hazards of gas emissions and released heat are related to each other and differentiated by cell properties such as, cell geometry, cathode type or state of charge. Quantitative information on the total heat release in the range of 2.0–112.0 kJ Wh−1, the peak heat release rate in the range of 0.006–2.8 kW Wh−1and the smoke gas emission were extracted, normalized in terms of cell energy (Wh), combined in a data library and compared graphically. The total amount of gas emitted (3–48 mmol Wh−1) as well as the released amount of carbon monoxide (1–161 mg Wh−1) and hydrogen fluoride (2–197 mg Wh−1) were investigated as a function of the state of charge and cell geometry. The analysis reveals that the measured values are significantly influenced by the types of calorimeters and smoke gas analyzers used as well as by the type of thermal runaway trigger. This meta-analysis can serve as an important basis for any risk assessment of lithium-ion batteries.
Impact-based classification of extreme rainfall events using a simplified overland flow model
(2023)
In this study, we present a new rainfall classification method based on the potential of individual rainstorm events to generate and sustain overland flow on a simplified urban model surface. Conventional rainfall classification approaches using peak intensities or rainfall sums can lead to mis-judgements of the impact of rainfall events, as they do not explicitly consider the potential of rain to generate and sustain substantial amounts of overland flow on typical sealed urban surfaces. The new method of impact-based rainfall classification proposed here comprises three steps: Identification of rainfall events from high-resolution time series, computation of overland flow depths for each event, and impact-based classification of rainfall events as a function of the magnitude of overland flow. The accuracy of this approach was evaluated by its ability to describe seasonal and annual occurrences of and variations in rainstorm impacts for high-resolution series at three different urban stations in Germany.
The impact of phosphorus-containing flame retardants (FR) on rigid polyisocyanurate (PIR) foams is studied by systematic variation of the chemical structure of the FR, including non-NCO-reactive and NCO-reactive dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO)- and 9,10 dihydro-9-oxa-10 phosphaphenanthrene-10-oxide (DOPO)-containing compounds, among them a number of compounds not reported so far. These PIR foams are compared with PIR foams without FR and with standard FRs with respect to foam properties, thermal decomposition, and fire behavior. Although BPPO and DOPO differ by just one oxygen atom, the impact on the FR properties is very significant: when the FR is a filler or a dangling (dead) end in the PIR polymer network, DOPO is more effective than BPPO. When the FR is a subunit of a diol and it is fully incorporated in the PIR network, BPPO delivers superior results.
The mechanical properties of unstabilised earthen building materials are distinctively influenced by changes in material moisture content. However, this moisture-dependency often remains unconsidered in the calculation of the load-bearing capacity of earth constructions. This paper aims to derive a convenient way to sufficiently consider the impact of different material moisture contents on the mechanical properties of unstabilised earth masonry. Therefore, the influence of relative humidity and temperature on the strength and deformation characteristics of unstabilised earth blocks, earth mortar and earth masonry is evaluated by conducting compression tests under various climate conditions. The results show that the compressive strength and the modulus of elasticity are linearly correlated with the relative humidity, whereas changes in temperature at constant relative humidity have no significant influence. To account the distinct moisture-dependency, a general applicable modification factor for unstabilised earthen materials is provided, which enables the adjustment of the compressive strength and the modulus of elasticity in dependency of arbitrary hygroscopic material moisture contents.
This paper presents an erosion interpretation of cohesive granular materials stressed by an impinging jet based on the results of a micromechanical simulation model. The numerical techniques are briefly described, relying on a two-dimensional Lattice Boltzmann Method coupled with a Discrete Element Methods including a simple model of solid intergranular cohesion.
These are then used to perform a parametric study of a planar jet in the laminar regime impinging the surface of granular samples with different degrees of cohesive strength. The results show the pertinence of using a generalized form of the Shields criterion for the quantification of the erosion threshold, which is valid for cohesionless samples, through empirical calibration, and also for cohesive ones. Furthermore, the scouring kinetics are analysed here from the perspective of a selfsimilar expansion of the eroded crater leading to the identification of a characteristic erosion time and the quantification of the classical erosion coefficient. However, the presented results also challenge the postulate of a local erosion law including erodibility parameters as intrinsic material properties. The paper then reviews the main limitations of the simulation and current interpretation models, and discusses the potential causes for the observed discrepancies, questioning the pertinence of using time-averaged macroscopic relations to correctly describe soil erosion. The paper concludes addressing this question with a complementary study of the presented simulations re-assessed at the particle-scale. The resulting local critical shear stress of single grains reveals a very wide dispersion of the data but nevertheless appears to confirm the general macroscopic trend derived for the cohesionless samples, while the introduction of cohesion implies a significant but systematic quantitative deviation between the microscopic and macroscopic estimates. Nevertheless, the micro data still shows consistently that the critical shear stress does actually vary approximately in linear proportion of the adhesive force.
The corrosivity of atmospheres in Europe has changed significantly in recent decades. For the Federal Republic of Germany, no current values for the corrosion rate based on 1‐year atmospheric exposure of standard specimens can be found in the scientific literature after 2000. This paper presents results from a field exposure study in the Berlin metropolitan area and Helgoland in 2016. Based on standard specimens, values for the corrosion rate and the corresponding atmospheric corrosivity category are determined for open exposure and indirect weathering in a ventilated enclosure as sheltering after 1 year of exposure. The results prove that determined corrosivity categories are material‐specific. Sheltered exposure is a typical atmospheric situation for many building components. It allows statements on the effect of the concentration of airborne substances on the corrosivity beyond the normative requirements.
Polyurethane foams (PUF) are generally flammable, so they are limited in some applications due to strict fire safety requirements. In this study, three distinct industrial benchmark polyurethane foams containing synergistic combinations of expandable graphite (EG) and phosphorous flame retardants (P-FR) were investigated one by one for their fire performance and smoke behavior. This paper aims to substantiate the hypothesis that the combination of EG and P-FR used in polyurethane foams yields a top-notch composite in terms of flame retardancy and smoke behavior by meeting the demanding requirement of low maximum average heat emission (MARHE) and smoke emission in a variety of applications, like advanced materials in construction, lightweight materials for railways, and more.
Leather is considered a luxury good when used in seating and upholstery. To improve safety, flame retardancy in leather is usually achieved through various finishing processes such as spray or roller coating. These treatments require processing steps that cost time and are laborintensive. One avenue to achieving flame retardancy in leather is to add flame retardants during the tanning process. However, the influence on flame retardancy exerted by specific intumescent additives specifically added during leather tanning has yet to be investigated. This work explores the roles played by intumescent additive compounds in flame retarding leather when they are added during tanning instead of applied as a coating. Via a systematic investigation of various compound mixtures, the flame retardant effects in the condensed and the gas phases are elucidated. The results show a strong impact of melamine in the gas phase and of polyphosphates in the condensed phase. Their impact was quantified in fire and smoke analysis, showing a 14% reduction in the peak of heat release rate, strongly reduced burning lengths, and a 20% reduction in total smoke release compared to nontreated leather. These results illuminate the key role played by specific compounds in the flame retardancy of leather, particularly when they are added specifically during the tanning process instead of being applied as a coating.
This method has great potential to reduce processing steps, lower costs, and improve material safety.
Reaktive Brandschutzsysteme finden im baulichen Brandschutz Anwendung zur Erhöhung des Feuerwiderstands von Stahlkonstruktionen. Neben den Anforderungen an die Feuerwiderstandsdauer können damit auch Ansprüche an die Ästhetik erfüllt werden. Die profilfolgende Applikation und die geringen Trockenschichtdicken der Produkte ermöglichen es, das filigrane Erscheinungsbild von Stahlkonstruktionen aufrechtzuerhalten. Neben der thermischen Schutzwirkung muss auch die Dauerhaftigkeit der Brandschutzbeschichtung sichergestellt werden. Die Bewertungsmethoden, die auf europäischer Ebene durch das EAD 350402-00-1106 zur Verfügung stehen, zielen auf eine Nutzungsdauer von zehn Jahren ab. Prüfverfahren für einen darüber hinausgehenden Zeitraum sind nicht beschrieben. In diesem Beitrag werden experimentelle Untersuchungen zum Einfluss der Bewitterung auf das Expansionsverhalten, zur thermischen Schutzwirkung und zu den während des Aufschäumens im Brandfall stattfindenden Reaktionen vorgestellt. Die Versuche wurden an einem wasserbasierten und einem epoxidharzbasierten reaktiven Brandschutzsystem durchgeführt. Die Ergebnisse wurden im Rahmen des IGF-Forschungsvorhabens 20470 N erzielt.
Investigation of the Thermal Stability of Proteinase K for the Melt Processing of Poly(L‑lactide)
(2022)
The enzymatic degradation of aliphatic polyesters offers unique opportunities for various use cases in materials science. Although evidently desirable, the implementation of enzymes in technical applications of polyesters is generally challenging due to the thermal lability of enzymes. To prospectively overcome this intrinsic limitation, we here explored the thermal stability of proteinase K at conditions applicable for polymer melt processing, given that this hydrolytic enzyme is well established for its ability to degrade poly(L-lactide) (PLLA). Using assorted spectroscopic methods and enzymatic assays, we investigated the effects of high temperatures on the structure and specific activity of proteinase K. Whereas in solution, irreversible unfolding occurred at temperatures above 75−80 °C, in the dry, bulk state, proteinase K withstood prolonged incubation at elevated temperatures. Unexpectedly little activity loss occurred during incubation at up to 130 °C, and intermediate levels of catalytic activity were preserved at up to 150 °C. The resistance of bulk proteinase K to thermal treatment was slightly enhanced by absorption into polyacrylamide (PAM) particles. Under these conditions, after 5 min at a temperature of 200 °C, which is required for the melt processing of PLLA, proteinase K was not completely denatured but retained around 2% enzymatic activity. Our findings reveal that the thermal processing of proteinase K in the dry state is principally feasible, but equally, they also identify needs and prospects for improvement. The experimental pipeline we establish for proteinase K analysis stands to benefit efforts directed to this end. More broadly, our work sheds light on enzymatically degradable polymers and the thermal processing of enzymes, which are of increasing economical and societal relevance.
block and mortar types is analysed with particular regard to the influence of varying relative humidity. The uniaxial compressive strength and deformation characteristics of unstabilised earth blocks and mortars as well as of unstabilised earth block masonry are studied in detail and compared to conventional masonry to evaluate whether the structural design can be made accordingly. An increase of 30 % points in relative humidity leads to a reduction of the masonry´s compressive strength between 33 % and 35 % whereas the Young´s modulus is reduced by 24–29 %. However, the ratio between the Young´s modulus and the characteristic compressive strength of earth block masonry ranges between E33/fk = 283–583 but is largely independent of the relative humidity. The results show that the mechanical properties of the investigated unstabilised earth block masonry are sufficient for load-bearing structures, yielding a masonry compressive strength between 2.3 MPa and 3.7 MPa throughout the range of moisture contents
investigated. In general, the design concept of conventional masonry can be adapted for unstabilised earth masonry provided that the rather low Young´s modulus as well as the moisture dependence of both, compressive strength and Young´s modulus, are sufficiently taken into
account.
Intumescent coatings are commonly used in civil engineering to improve the fire resistance of steel constructions. Especially in the case of tension bars, where mostly circular or rectangular solid sections are used, intumescent coatings offer an efficient measure to improve the fire resistance taking advantage of profile-following application and low coating thickness requirements. Thus, the architectural appearance of slender profiles can be preserved. The paper describes real-scale mechanically loaded and unloaded fire tests of circular and rectangular solid steel tension bars with intumescent coating. The aim of these tests is to investigate the influence of the different profile types as well as different bar orientations on the performance of intumescent coatings. The results are used to specify a normative test and assessment procedure to be implemented in a new European standard for determining the contribution of intumescent coatings to the fire resistance of circular or rectangular bars used as tension members.
Tailored crosslinking in elastomers is crucial for their technical applications. The incorporation of nanoparticles with high surface-to-volume ratios not only leads to the formation of physical networks and influences the ultimate performance of nanocomposites, but it also affects the chemical crosslinking reactions. The influence of few-layer graphene (FLG) on the crosslinking behavior of natural rubber is investigated. Four different curing systems, two sulfur-based with different accelerator-to-sulfur ratios, and two peroxide-based with different peroxide concentrations, are combined with different FLG contents. Using differential scanning calorimetry (DSC), vulcametry (MDR) and swelling measurements, the results show an accelerating effect of FLG on the kinetics of the sulfur-based curing systems, with an exothermic reaction peak in DSC shifted to lower temperatures and lower scorch and curing times in the MDR. While a higher accelerator-to-sulfur ratio in combination with FLG leads to reduced crosslinking densities, the peroxide crosslinkers are hardly affected by the presence of FLG. The good agreement of crosslink densities obtained from the swelling behavior confirms the suitability of vulcameter measurements for monitoring the complex vulcanization process of such nanocomposite systems in a simple and efficient way. The reinforcing effect of FLG shows the highest relative improvements in weakly crosslinked nanocomposites.
The current understanding of the carbonation and the prediction of the carbonation rate of alkali-activated concretes is complicated inter alia by the wide range of binder chemistries used and testing conditions adopted. To overcome some of the limitations of individual studies and to identify general correlations between mix design parameters and carbonation resistance, the RILEM TC 281-CCC ‘Carbonation of Concrete with Supplementary Cementitious Materials’ Working Group 6 compiled and analysed carbonation data for alkali-activated concretes and mortars from the literature. For comparison purposes, data for blended Portland cement-based concretes with a high percentage of SCMs (≥ 66% of the binder) were also included in the database. The analysis indicates that water/CaO ratio and water/binder ratio exert an influence on the carbonation resistance of alkali-activated concretes; however, these parameters are not good indicators of the carbonation resistance when considered individually. A better indicator of the carbonation resistance of alkali-activated concretes under conditions approximating natural carbonation appears to be their water/(CaO + MgOeq + Na2Oeq + K2Oeq) ratio, where the subscript ‘eq’ indicates an equivalent amount based on molar masses. Nevertheless, this ratio can serve as approximate indicator at best, as other parameters also affect the carbonation resistance of alkali-activated concretes. In addition, the analysis of the database points to peculiarities of accelerated tests using elevated CO2 concentrations for low-Ca alkali-activated concretes, indicating that even at the relatively modest concentration of 1% CO2, accelerated testing may lead to inaccurate predictions of the carbonation resistance under natural exposure conditions.
The size effect has its origin in fracture mechanics and describes the formation as well as propagation of cracks in brittle and solid materials in dependence of the specimen size. However, the size effect in concrete spalling describes the damage behaviour on a macroscopic scale for different sized specimens in case of fire. Concrete spalling is a very complex and yet not fully understood phenomenon. To reduce the effort of fire tests to analyse the spalling behaviour of concrete mixtures, this study investigates the susceptibility to spalling for six different concrete mixtures and three specimen sizes. The sizes were divided in full scale slabs (1.8 m x 1.2 m x 0.3 m), intermediate scale cuboids (0.6 m x 0.6 m x 0.3 m) and small scale cylinders (Ø0.15 m x 0.3 m). For this purpose, a novel test set-up was built to test six intermediate scale or twelve small scale specimens simultaneously to ensure a similar heating regime for every specimen. All specimens were fire exposed on one side and remained unrestrained. A size effect occurred for four of the six concrete mixtures. Compared to the full scale specimens the spalling was reduced significantly for all smaller specimen sizes. Additionally, spalling did not occur for the small scale specimens. The results show that the specimen size is an essential parameter to investigate the susceptibility to spalling of a concrete mixture. For future investigations the testing conditions must be adjusted for the intermediate scale specimens to recreate the conditions of the slabs.
Hydrous lithium aluminosilicate (L–A–S–H) and lithium aluminate (L–A–H) gels are candidate precursors for glass-ceramics and ceramics with potential advantages over conventional processing routes. However, their structure before calcination remained largely unknown, despite the importance of precursor structure on the properties of the resulting materials. In the present study, it is demonstrated that L–A–S–H and L–A–H gels with Li/Al ≤ 1 can be produced via an organic steric entrapment route, while higher Li/Al ratios lead to crystallization of gibbsite or nordstrandite. The composition and the structure of the gels was studied by thermogravimetric analysis, X-ray diffraction, 27Al and 29Si magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. Aluminium was found to be almost exclusively in six-fold coordination in both the L–A–H and the L–A–S–H gels. Silicon in the L–A–S–H gels was mainly in Q4 sites and to a lesser extent in Q3 sites (four-fold coordination with no Si–O–Al bonds). The results thus indicate that silica-rich and aluminium-rich domains formed in these gels.
The fracture surface of slow and continuous crack propagation during environmental stress cracking of a semicrystalline polyethylene exhibits isotropic roughness exponents at the local scale but resolved across the macroscopic fracture surface a clear position dependence is found. The spatially resolved roughness exponent admits values in the range between 0.1 and 0.4, demonstrating nontrivial exponents in the small length-scale regime. Instead, they vary across the fracture surface according to the stress-state distribution, which suggests that the exponents are intimately linked to the locally dominating dissipation processes during craze cracking.
Hybrid cements are composites made of Portland cement or Portland clinker and one or more supplementary cementitious materials like slag, fly ash or metakaolin, activated with an alkali salt. To date, their hydration mechanism and the phase formation at various temperatures is insufficiently understood, partly due to the large variability of the raw materials used. In the present study, three hybrid cements based on ground granulated blast furnace slag, fly ash, Portland clinker and sodium sulfate, and an alkali-activated slag/fly ash blend were cured at 10 and 21.5°C, and subsequently analyzed by XRD, 27Al MAS NMR, and TGA. The compressive strength of the hybrid cements was higher by up to 27% after 91-day curing at 10°C, compared to curing at 21.5°C. The experimental results as well as thermodynamic modeling indicate that the differences in compressive strength were related to a different phase assemblage, mainly differing amounts of strätlingite and C-N-A-S-H, and the associated differences of the volume of hydration products. While the strätlingite was amorphous to X-rays, it could be identified by 27Al MAS NMR spectroscopy, TGA and thermodynamic modeling. The microstructural properties of the hybrid cements and the alkali-activated slag/fly ash blend as well as the compatibility between thermodynamic modeling results and experimental data as a function of curing temperature and time are discussed.
Numerical models built as virtual-twins of a real structure (digital-twins) are considered the future ofmonitoring systems. Their setup requires the estimation of unknown parameters, which are not directly measurable. Stochastic model identification is then essential, which can be computationally costly and even unfeasible when it comes to real applications. Efficient surrogate models, such as reduced-order method, can be used to overcome this limitation and provide real time model identification. Since their numerical accuracy influences the identification process, the optimal surrogate not only has to be computationally efficient, but also accurate with respect to the identified parameters. This work aims at automatically controlling the Proper Generalized Decomposition (PGD) surrogate’s numerical accuracy for parameter identification. For this purpose, a sequence of Bayesian model identification problems, in which the surrogate’s accuracy is iteratively increased, is solved with a variational Bayesian inference procedure. The effect of the numerical accuracy on the resulting posteriors probability density functions is analyzed through two metrics, the Bayes Factor (BF) and a criterion based on the Kullback-Leibler (KL) divergence. The approach is demonstrated by a simple test example and by two structural problems. The latter aims to identify spatially distributed damage, modeled with a PGD surrogate extended for log-normal random fields, in two different structures: a truss with synthetic data and a small, reinforced bridge with real measurement data. For all examples, the evolution of the KL-based and BF criteria for increased accuracy is shown and their convergence indicates when model refinement no longer affects the identification results.
Im Dezember 2019 wurden bei einer turnusmäßigen Inspektion der B 1-Brücke am Altstädter Bahnhof in Brandenburg an der Havel massive und schnell voranschreitende Schäden festgestellt. Als Ursache für die Risse entlang der Längsträger wurde das Versagen eines signifikanten Anteils der Spanndrähte der konzentrierten Spannglieder vermutet. Die Brücke wurde umgehend für den Verkehr gesperrt und im Mai 2021 gesprengt. Im Vorfeld der Sprengung wurden durch das Bundesministerium für Digitales und Verkehr (BMDV) weiterführende Untersuchungen zum Schadensbild veranlasst, welche vom Landesbetrieb Straßenwesen Brandenburg koordiniert und in den Bauablauf integriert wurden. Das von der Hochschule für Technik und Wirtschaft (HTW) Dresden erstellte Versuchskonzept ist Bestandteil des vorangestellten ersten Teils des Beitrags [1]. Hier im zweiten Teil werden ausgewählte Ergebnisse der umfangreichen versuchsbegleitenden Mess- und Monitoringmaßnahmen beschrieben, welche in Kooperation der HTW Dresden, der Bilfinger Noell GmbH sowie der Bundesanstalt für Materialforschung und -prüfung (BAM) durchgeführt wurden.
Die Infrastruktursysteme der Industriestaaten erfordern heute und in Zukunft ein effizientes Management bei alternder Bausubstanz, steigenden Lasten und gleichbleibend hohem Sicherheitsniveau. Digitale Technologien bieten ein großes Potenzial zur Bewältigung der aktuellen und künftigen Herausforderungen im Infrastrukturmanagement. Im BMBF-geförderten Projekt Bewertung alternder Infrastrukturbauwerke mit digitalen Technologien (AISTEC) wird untersucht, wie unterschiedliche Technologien und deren Verknüpfung gewinnbringend eingesetzt werden können. Am Beispiel der Maintalbrücke Gemünden werden ein sensorbasiertes Bauwerksmonitoring, bildbasierte Inspektion mit durch Kameras ausgestatteten Drohnen (UAS) und die Verknüpfung digitaler Bauwerksmodelle umgesetzt. Die aufgenommenen Bilder dienen u. a. als Grundlage für spätere visuelle Anomaliedetektionen und eine 3D-Rekonstruktion, welche wiederum für die Kalibrierung und Aktualisierung digitaler Tragwerksmodelle genutzt werden. Kontinuierlich erfasste Sensordaten werden ebenfalls zur Kalibrierung und Aktualisierung der Tragwerksmodelle herangezogen. Diese Modelle werden als Grundlage für Anomaliedetektionen und perspektivisch zur Umsetzung von Konzepten der prädiktiven Instandhaltung verwendet. Belastungsfahrten und historische Daten dienen in diesem Beitrag der Validierung von kalibrierten Tragwerksmodellen.
Polymers of intrinsic microporosity (PIMs) are promising candidates for the active layer in gas separation membranes due to their high permeability and reasonable permselectivity. These appealing properties originate from a microporous structure as a result of inefficient segment packing in the condensed state due to a combination of a ladder-like rigid backbone and sites of contortion. However, this class of polymers suffers from a significant decrease in the permeability with time due to physical aging, whereby typically, the permselectivity increases. The initial microporous structures approach a denser state via local rearrangements, leading to the reduction of the permeability. Hence, a detailed characterization of the molecular mobility in such materials can provide valuable information on physical aging. In this work, the dielectric behavior of PIM-1 films and their behavior upon heating (aging) were revisited by isothermal frequency scans during different heating/cooling cycles over a broad temperature range between 133 and 523 K (−140 to 250 °C). In addition, the obtained results were compared with data of samples that were annealed at ambient temperatures over different time scales. Multiple dielectric processes were observed: several relaxation processes due to local fluctuations and a Maxwell−Wagner−Sillars polarization effect related to the microporosity. The temperature dependence of the rates of all processes follows the Arrhenius law where the estimated activation energy depends on the nature of the process. The influence of the thermal history (aging) on the processes is discussed in detail.
A global transition towards more sustainable, affordable and reliable energy systems is being stimulated by the Paris Agreement and the United Nation's 2030 Agenda for Sustainable Development. This poses a challenge for the corrosion industry, as building climate‐resilient energy systems and infrastructures brings with it a long‐term direction, so as a result the long‐term behaviour of structural materials (mainly metals and alloys) becomes a major prospect. With this in mind “Corrosion Challenges Towards a Sustainable Society” presents a series of cases showing the importance of corrosion protection of metals and alloys in the development of energy production to further understand the science of corrosion, and bring the need for research and the consequences of corrosion into public and political focus. This includes emphasis on the limitation of greenhouse gas emissions, on the lifetime of infrastructures, implants, cultural heritage artefacts, and a variety of other topics.
The phenomenon of environmental stress cracking is still a major issue in materials engineering as well as from a scientific perspective. Especially in the case of packaging materials made of high-density polyethylene, assessing the potential of premature damage due to environmental stress cracking is complex because of the large number of components in possible liquid filling goods. As a first guideline, the well-known effect of detergents and dispersants is usually considered, but the interplay with other components, such as organic solvents is often unknown. Particularly challenging in this respect are crop protection products, consisting of several different admixtures in addition to the biologically active ingredients. This study is based on two model liquids representing these admixtures that were established for testing in this context. The model liquids as well as their constituting components were used as liquid media in the Full Notch Creep Test to characterize the environmental stress cracking behavior of a typical high-density polyethylene. Complementary to the time-to failure of a notched specimen obtained from these tests, the crack opening was monitored optically, and the fracture surface was analyzed post-failure by laser scanning microscopy as well as scanning electron microscopy. Based on the results, the effect of various surfactants as well as the influence of organic solvents on environmental stress cracking are discussed.