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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.
This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries.
The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.
A thorough characterization of starting materials is the precondition for further research, especially for cement, which contains various phases and presents quite a complex material for fundamental scientific investigation. In the paper at hand, the characterization data of the reference cement CEM I 42.5 R used within the priority program 2005 of the German Research Foundation (DFG SPP 2005) are presented from the aspects of chemical and mineralogical compositions as well as physical and chemical properties. The data were collected based on tests conducted by nine research groups involved in this cooperative program. For all data received, the mean values and the corresponding errors were calculated. The results shall be used for the ongoing research within the priority program.
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.
Environmental Risk Assessment of Treated Timber in Service - the Environment Focus Group Approach
(2000)
In the context of the Biocidal Products Directive (98/8/EC), and of the OECD work on wood preservatives, the Environment Focus Group (EFG), comprising 8 institutes and the European Wood Preservative Manufacturers Group, has been working on the environmental risk assessment of treated timber in service. A literature review of emissions from treated timber has revealed that very little existing data is usable for environmental risk assessment; the most relevant data are kinetic curves of emissions over time, which show clearly the non-linear emissions behaviour of treated wood over time. The EFG has suggested real exposure conditions for treated timber in the environment, and listed typical exposure scenarios. Five representative scenarios are characterised in detail, for use in the calculation of Predicted Environmental Concentrations (PECs). The existing methods to determine emissions from treated wood have been reviewed. Most existing experimental models cannot be used to predict environmental emissions. Monitoring of commodities in service has its specific constraints. Chemical analysis and ecotoxicity testing have also been reviewed and their relationship has been discussed. Principles for the design of experimental models, for the determination of emission fluxes from treated wood to the environment, have been established.
The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 µm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.
Development of a test system for identifying the bitumen type and the modifier used in a reclaimed asphalt Da Polymer-, Gummi-, wachs- und mehrfachmodifizierte Bitumen seit Jahren im Asphaltstraßenbau eigesetzt werden, kommen diese vermehrt im Ausbauasphalt vor. Zur Bewertung des Ausbauasphalts ist es daher notwendig, die Modifizierungen an der Mischanlage zu identifizieren. Die Ausbildung des Bindemittelsacks beim Erweichungspunkt Ring und Kugel ist charakteristisch für die Modifizierung. Hierdurch können wachsmodifizierte Bitumen (WmB) recht präzise und Polymermodifizierten Bitumen (PmB) teilweise identifiziert werden. Mittels Differential Scanning Calorimetry (DSC) werden die Schmelztemperaturen der Wachse erfasst. Hierdurch können WmB identifiziert und die Wachsarten unterschieden werden. Die Analytik mittels Dynamischem Scherrheometer (DSR) startet mit der Bestimmung der Äquisteifigkeitstemperatur EG*T. Bei EG*T werden Frequenz-, Amplituden- und MSCR-Tests durchgeführt. Die Grenze des LVE-Bereichs dient der Identifizierung von WmB. Anhand der Kennwerte bei 0,1 Hz können PmB erkannt werden. Die Rückformung (MSCRT) dient der Identifizierung von Mehrfachmodifizierungen. Da Gummimodifizierte Bitumen (GmB) bei der Extraktion erkannt werden, können alle Modifizierungsarten identifiziert werden. In den FTIR-Spektren (Fourier-Transformations-Infrarotspektroskopie) der modifizierten Bitumen verursachen einige Polymere und Wachse charakteristische Banden, wodurch diese erkannt werden. Die Identifizierung der übrigen Additive erfolgt mithilfe einer multivariaten Auswertung, wodurch mit Ausnahme der GmB (nicht erforderlich) alle Additive erkannt werden. An Stichproben konnte zudem eine Abgrenzung von Mehrfachmodifizierungen sowie eine Abschätzung der Zugabemenge erreicht werden. DSR und FTIR ermöglichen beide eine schnelle, einfache und zielsichere Identifizierung der Bitumenmodifizierungen. Durch die FTIR-Analytik können die Modifizierungen mit der größtmöglichen Präzision bestimmt werden. Die DSR-Analytik erlaubt dafür zusätzlich eine baupraktische Bewertung der Bindemittel.
As polymer, rubber, wax and multi-modified bitumen are used for asphalt road construction since many years, they increasingly occur in reclaimed asphalt. To assess the reclaimed asphalt, it is therefore necessary to identify the modifications in the mixing plants. The formation of the binder bag at softening point ring and ball is characteristic for modification. In this way, wax modified bitumen (WmB) can be identified rather precisely and to a less extent polymer modified bitumen (PmB) can also be identified. Differential scanning calorimetry (DSC) is used to record the melting temperatures of the waxes. In this way, WmB can be identified and a differentiation can be made between the wax types. The analysis by means of the dynamic shear rheometer (DSR) starts with the determination of the equi-stiffness temperature EG*T. Frequency-, amplitude- and MSCR-tests are performed at EG*T. The limit of the LVE range is used to identify WmB. PmB can be identified based on the characteristic values at 0.1 Hz. Creep recovery (MSCRT) is used to identify multi-modifications. As rubber modified bitumen (GmB) is identified on extraction, all types of modification can therefore be identified. Several polymers and waxes cause characteristic bands in the FTIR spectra (Fourier Transform Infrared spectroscopy) of modified bitumen, which enables the identification of these additives. The other additives except the GmB (not necessary) can be identified by means of multivariate model. Further, due to random evaluations, the differentiation between single- and multi-modification as well as the estimation of the content of some additives is possible. DSR and FTIR both enable fast, simple and accurate identification of the bitumen modification. The modification can be determined with the greatest possible precision by using FTIR analysis. On the other hand, DSR analysis allows additional practical assessment of the binder on site.
The 87Sr/86Sr isotope ratio can, in principle, be used for provenancing of cement. However, while commercial cements consist of multiple components, no detailed investigation into their individual 87Sr/86Sr isotope ratios or their influence on the integral 87Sr/86Sr isotope ratio of the resulting cement was conducted previously. Therefore, the present study aimed at determining and comparing the conventional 87Sr/86Sr isotope ratios of a diverse set of Portland cements and their corresponding Portland clinkers, the major component of these cements. Two approaches to remove the additives from the cements, i.e. to measure the conventional 87Sr/86Sr isotopic fingerprint of the clinker only, were tested, namely, treatment with a potassium hydroxide/sucrose solution and sieving on a 11-µm sieve. Dissolution in concentrated hydrochloric acid/nitric acid and in diluted nitric acid was employed to determine the 87Sr/86Sr isotope ratios of the cements and the individual clinkers. The aim was to find the most appropriate sample preparation procedure for cement provenancing, and the selection was realised by comparing the 87Sr/86Sr isotope ratios of differently treated cements with those of the corresponding clinkers. None of the methods to separate the clinkers from the cements proved to be satisfactory. However, it was found that the 87Sr/86Sr isotope ratios of clinker and cement generally corresponded, meaning that the latter can be used as a proxy for the clinker 87Sr/86Sr isotope ratio. Finally, the concentrated hydrochloric acid/nitric acid dissolution method was found to be the most suitable sample preparation method for the cements; it is thus recommended for 87Sr/86Sr isotope analyses for cement provenancing.
Bitumen is a crucial building material in road construction, which is exposed to continuously higher stresses due to higher traffic loads and changing climatic conditions. Therefore, various additives are increasingly being added to the bitumen complicating the characterisation of the bituminous binder, especially concerning the reuse of reclaimed asphalt.
Therefore, this work aimed to demonstrate that the combination of Fourier transform infrared (FTIR) spectroscopy with attenuated total reflexion (ATR) technique and multivariate evaluation is a very wellsuited method to reliable identify and quantify additives in bituminous binders. For this purpose, various unmodified and modified binders, directly and extracted from laboratory and reclaimed asphalts, were investigated with FTIR-ATR spectroscopy. The determined spectra, pre-processed by standard normal variate (SNV) transformation and the determination of the 1st derivation, were evaluated using factor Analysis (FA), linear discriminant analysis (LDA) and partial least square regression (PLSR). With this multivariate evaluation, first, a significant model with a very high hit rate of over 90% was developed allowing for the identification of styrene-butadiene copolymers (SBC), ethylene-copolymer bitumen (ECB) and different waxes (e.g. amide and Fischer-Tropsch wax) even if the additives do not show any additional peaks or the samples are multi-modified. Second, a quantification of the content is possible for SBC, ECB, and Amide wax with a mean error of RMSE B 0.4 wt% and a
coefficient of determination of R2[90%. Based on these results, FTIR identification and quantification of additives in bituminous binders is a very promising method with a great potential.
In Germany, the reuse of asphalt has a long tradition. Since the 1980s, the reclaimed asphalt has been recycled achieving a reuse rate of around 90% and thus a very high value in the last years. In the future, instead of the amount, the quality of the reclaimed asphalt will be more important because the recycled asphalt will be reused again and again. Thus, these asphalt mixes are in the second or even third cycle of reuse. Concerning this situation, the question arises if asphalt can be reused several times without any loss in quality. An important factor affecting the asphalt quality is the binder bitumen. During the production, construction and service life, the ageing of this binder occurs causing a hardening of the bitumen. To compensate this hardening, additives for the reclaimed asphalt in terms of rejuvenation agents (rejuvenators) gain in importance. With these rejuvenators, the physical properties of bitumen can be modified e.g. the hardness and the stiffness reduced. However, the mechanism of the rejuvenation agents and the effects of the bitumen chemistry are largely unknown because the composition of the products varies very strongly. But with growing knowledge about these mechanisms and effects of the rejuvenation agents, the chemical composition and thus the physical and ageing behavior of bitumen can be targeted modified by the use of suitable rejuvenators. In this work, the actual results of the project Postcarbone road should be presented including investigations about the chemical and physical mechanisms as well as the efficiency of different rejuvenators.
Further, a model for the cyclic reuse of bitumen should be developed. Based on this model, the choice of a suitable rejuvenation agent for the considered bitumen or rather asphalt should be possible. The project Postcarbone road (392670763) is funded by the German Research Foundation (DFG).
With the aim of identifying the origin and the manufacturer of a cement, a reliable procedure that provides unambiguous results is needed. Such procedure could resolve practical issues in damage research, liability issues and forensic investigations. A substantial number of attempts for fingerprinting of building materials, including cement, has already been carried out during the last decades. Most of them were based on concentration analysis of the main elements/components. This review provides an overview of provenance studies of cement and the main approaches commonly used. Provenance studies of cement via isotope techniques are also presented and discussed as representatives of the state-of-the-art in the field. Due to the characteristic properties and the occurrence of carefully selected isotope ratios, unique fingerprints of different kinds of materials can be provided by these methods. This property has largely been explored in various scientific fields such as geo- and cosmochemistry, food forensics, archaeology, geochronology, biomedical studies, and climate change processes. However, the potential of isotope techniques in cement and concrete research for provenance studies has barely been investigated.
Therefore, the review outlines a suitable approach using isotope ratios, which could lead to reliable provenancing of cementitious materials in the future.
Basic oxygen furnace slags (BOFS) are by-products of the steelmaking process. Several researchers have studied the production of Portland cement clinker and metallic iron from BOFS via a reductive treatment.
In this study, we applied a carbothermal reduction of BOFS in a technical-scale electric arc furnace and characterised the clinker-like products. Those clinker-like non-metallic products (NMPs) had a chemical and mineralogical composition comparable to clinker for ordinary Portland cement (OPC) and contained large elongated alite crystals as major component. The pure NMPs reacted more slowly and achieved a lower degree of hydration compared with commercial OPC.
If the reactivity of the products can be further increased by employing specific adaptations, it can be used as a full clinker substitute for OPC. Nevertheless, it is also an option to use the material without further modifications as a cement component or concrete addition, which contributes to the strength development in both cases.
Alkali-activated binders (AAB) can provide a clean alternative to conventional cement in terms of CO2 emissions. However, as yet there are no sufficiently accurate material models to effectively predict the AAB properties, thus making optimal mix design highly costly and reducing the attractiveness of such binders. This work adopts sequential learning (SL) in high-dimensional material spaces (consisting of composition and processing data) to find AABs that exhibit desired properties. The SL approach combines machine learning models and feedback from real experiments. For this purpose, 131 data points were collected from different publications. The data sources are described in detail, and the differences between the binders are discussed. The sought-after target property is the compressive strength of the binders after 28 days. The success is benchmarked in terms of the number of experiments required to find materials with the desired strength. The influence of some constraints was systematically analyzed, e.g., the possibility to parallelize the experiments, the influence of the chosen algorithm and the size of the training data set. The results show the advantage of SL, i.e., the amount of data required can potentially be reduced by at least one order of magnitude compared to traditional machine learning models, while at the same time exploiting highly complex information. This brings applications in laboratory practice within reach.
Materials that confer antimicrobial activity, be that by innate property, leaching of biocides or design features (e.g., non-adhesive materials) continue to gain popularity to combat the increasing and varied threats from microorganisms, e.g., replacing inert surfaces in hospitals with copper. To understand how efficacious these materials are at controlling microorganisms, data is usually collected via a standardised test method. However, standardised test methods vary, and often the characteristics and methodological choices can make it difficult to infer that any perceived antimicrobial activity demonstrated in the laboratory can be confidently assumed to an end-use setting. This review provides a critical analysis of standardised methodology used in academia and industry, and demonstrates how many key methodological choices (e.g., temperature, humidity/moisture, airflow, surface topography) may impact efficacy assessment, highlighting the need to carefully consider intended antimicrobial end-use of any product.
With 8% of man-made CO2 emissions, cement production is an important driver of the climate crisis. By using alkali-activated binders, part of the energy-intensive clinker production process can be dispensed. However, as numerous raw materials are involved in the manufacturing process here, the complexity of the materials increases by orders of magnitude. Finding a properly balanced binder formulation is like looking for a needle in a haystack. We have shown for the first time that artificial intelligence (AI)-based optimization of alkali-activated binder formulations can significantly accelerate research.
The "Sequential Learning App for Materials Discovery" (SLAMD) aims to accelerate practice transfer. With SLAMD, materials scientists have low-threshold access to AI through interactive and intuitive user interfaces. The value added by AI can be determined directly. For example, the CO2 emissions saved per ton of cement can be determined for each development cycle: the more efficient the AI optimization, the greater the savings.
Our material database already includes more than 120,000 data points of alternative binders and is constantly being expanded with new parameters. We are currently driving the enrichment of the data with a life cycle analysis of the building materials.
Based on a case study we show how intuitive access to AI can drive the adoption of techniques that make a real contribution to the development of resource-efficient and sustainable building materials of the future and make it easy to identify when classical experiments are more efficient.
The device performance of polycrystalline chalcogenide thin film solar cells is strongly influenced by different kinds of defects within the material. The presence of sodium or other alkali metals like potassium during the deposition process is well known to influence the electronic properties of the solar cell and thus to improve the efficiency of the final device. Structural analysis of neutron powder diffraction data collected at low temperatures and subsequent profile analysis by the LeBail and Rietveld method demonstrates the impact of sodium on the point defect characteristics in off stoichiometric CuInSe2. The analyzed materials are powder and thin film solar absorber material with addition of NaF and free of sodium. It is illustrated, the so called “sodium effect” cannot be reduced to one single origin. A range of effects, the reduction of InCu donors with a followed increase of VCu acceptors is possible. The main effect is an increased ordered character of the chalcopyrite crystal structure at off stoichiometric composition, when containing sodium.
Chemischer Angriff auf Betonbauwerke - Bewertung des Angriffsgrads und geeignete Schutzprinzipien
(2014)
In verschiedenen Bereichen des Betonbaus ist Beton einem chemischen Angriff von außen ausgesetzt, der die Dauerhaftigkeit des betreffenden Bauteils bzw. des gesamten Bauwerks beeinträchtigen kann. Für einen chemischen Angriff in natürlichen Böden und Grundwässern bestehen normative Vorgaben in DIN 4030-1 [R10] bzw. DIN 1045-2 [R19], um den Angriffsgrad anhand der Art und Konzentration der angreifenden Stoffe in Expositionsklassen XA1 (schwach angreifend) bis XA3 (stark angreifend) einzustufen. Hinsichtlich weiterer maßgeblicher Einflussfaktoren wird an dieser Stelle nicht näher differenziert, ob und inwieweit die Regelungen für Böden und Grundwässer auch auf andere Bereiche mit chemischem Angriff auf Beton zu übertragen sind, ist stets im Einzelfall zu überprüfen. Ebenfalls sind die zu treffenden Maßnahmen über die Vorgaben der DIN EN 206-1/DIN 1045-2 [R19] hinaus anwendungsspezifisch festzulegen. Der Hauptausschuss Baustofftechnik (HABT) des DBV hat daher den Arbeitskreis "Chemischer Angriff auf Beton" beauftragt, dieses Merkblatt zu erarbeiten, das Hilfestellung bei der Bewertung einer projektspezifischen chemischen Angriffssituation auf Beton sowie bei der Planung und Ausführung von Schutzprinzipien leisten soll.
ln den letzten Jahren wurden diverse Prüfverfahren und Methoden entwickelt, um die Leistungsfähigkeit von Beton bzw. Bindemittel hinsichtlich des Widerstands gegenüber betonaggressiven Einwirkungen beurteilen zu können. Ein wesentliches Ziel von Prüfverfahren zur Beurteilung der Dauerhaftigkeit von Baustoffen ist, die im Laufe der Nutzungsdauer zu erwartenden Einwirkungen auf den Baustoff realitätsnah abzubilden. Dazu sind die Prüfparameter auf die im jeweiligen Anwendungsbereich vorherrschenden Umgebungs- und Randbedingungen anzupassen. Daneben sind auch die Bewertungskriterien individuell unter Berücksichtigung der im Einzelfall geforderten Nutzungsdauer eines Bauwerks festzulegen. Eine systematische Zuordnung von adäquaten Prüfverfahren bzw. Prüfparametem und Bewertungskriterien für die verschiedenen Anwendungsbereiche im Betonbau, in denen betonaggressive Einwirkungen auftreten, ist mit Ausnahme von Einzelfällen bislang nicht vorhanden. Daneben stellt sich in der Praxis immer wieder das Problem, das Angriffspotenzial der Umgebung eines Bauwerks (prüftechnisch) zu erfassen und zu bewerten.
Der Hauptausschuss Baustofftechnik des DBV hat daher den Arbeitskreis „Chemischer Angriff auf Beton“ beauftragt, dieses Merkblatt zu erarbeiten, das auf Basis von einschlägigen Erfahrungen der Baupraxis und wissenschaftlichen Erkenntnissen Grundsätze und bewährte Methoden zur Beurteilung der Einwirkungs- und Widerstandsseite beim chemischen Angriff auf Beton aufzeigt und diesbezüglich Hinweise für verschiedene Anwendungsbereiche im Betonbau liefert.
Tricalcium-silicate (C3S) or Alite is the most important mineral in Portland cement. Since pure tricalcium-silicate is only stable above temperatures of 1250 °C, its decomposition has to be prevented technically by fast cooling after the sintering process. At room temperature, the decomposition velocity is very slow so that metastable tricalcium-silicate is obtained.
Although the mechanisms of clinker phase formation during burning process of Portland cement in a rotary kiln were solved and improved over the years, in view of possible economic and ecological benefits current projects aim to produce clinker phases from metallurgical slags. Recent studies discovered that the mineral phase which remained after a reducing treatment and separation of formed metallic iron from molten Linz-Donawitz (LD-) slags contained about 60 wt.% Alite despite it was cooled slowly. Because the results could be verified using slags from different origins and varying cooling velocities a chemical stabilisation of the Alite can be assumed. First tests in mortars indicate that workability, hardening and solid state properties are comparable with an ordinary Portland cement. An application of the observed phenomenon in cement production requires enhanced knowledge about formation and stabilisation conditions of Alite during crystallisation from melts in contrast to the sintering reactions in conventional Portland cement production. Therefore, this study focuses on the stabilisation mechanisms of Alite in consolidating melts. Samples from different melting experiments are analysed to determine stabilising factors.
The potential release of hazardous substances from polymer-based products is currently in the focus of environmental policy. Environmental simulations are applied to expose such products to selected aging conditions and to investigate release processes. Commonly applied aging exposure types such as solar and UV radiation in combination with water contact, corrosive gases, and soil contact as well as expected general effects on polymers and additional ingredients of polymer-based products are described. The release of substances is based on mass-transfer processes to the material surfaces. Experimental approaches to investigate transport processes that are caused by water contact are presented. For tailoring the tests, relevant aging exposure types and release quantification methods must be combined appropriately. Several studies on the release of hazardous substances such as metals, polyaromatic hydrocarbons, flame retardants, antioxidants, and carbon nanotubes from polymers are summarized exemplarily. Differences between natural and artificial exposure tests are discussed and demonstrated for the release of flame retardants from several polymers and for biocides from paints. Requirements and limitations to apply results from short-term artificial environmental exposure tests to predict long-term environmental behavior of polymers are presented.
The interaction of different charged polymers, namely anionic polycarboxylate
superplasticizer (PCE) and neutral polyethylene glycol (PEG) with potassium ions, and their effect on the yield stress of highly concentrated glass bead suspension (GBS), were studied under different concentrations of potassium ions ([K+]). It was found that, compared to the neutral PEG, the negatively charged PCE can be adsorbed on glass beads (GB), and then decreases the yield stress of GBS. The increasing concentration of free polymer in the interstitial liquid phase with the increased polymer dosage leads to the higher yield stress of GBS, which may be caused by the higher Depletion force. In addition, this effect is also related to the charge density of the polymer and the [K+] in the solution. Along with the increase in [K+], the yield stress of GBS increases significantly with the addition of PCE, but this cannot be observed with PEG, which indicates that potassium ions can interact with negatively charged PCE instead of the neutral PEG. At last, the interparticle Forces between two single GB with adsorbed PCE in solutions containing [K+] and PCE were measured by colloidal probe atomic force microscopy to better understand the interaction of the charged polymer with counterions.
The flowability of cement paste is of great importance in today’s construction industry and is influenced by additives such as superplasticizers (SP). One type of SPs are polycarboxylate ether type SPs. These additives electrostatically bind with the negatively charged carboxylic groups at the backbone to the positively charged clinker phases.
To model positively charged clinker phases with adsorbed SP, silicon Wafers are pre-coated with cationic polyethylenimine (PEI) and SP is adsorbed onto the coated surface (Si/PEI/SP). Two different polycarboxylate ether type (PCE) SP are compared – one for ready-mix concrete and one for precast concrete. In this preliminary study the interaction forces between Si/PEI/SP surface and a silica microsphere (colloidal probe) are investigated under mild physico-chemical conditions (pH *6, ion concentration <10−5 M) using Colloidal Probe Atomic Force Microscopy (CP-AFM).
The interaction force between the model surfaces is attractive for low concentration of SP. The force changes from attractive to repulsive by increasing amount of SP. The force upon approach reveals a biexponential behavior. The exponential decay at large and short surface separations are attributed to electrostatic and steric interactions, respectively. The steric forces of the SP for ready-mix concrete show a steeper onset than the SP for precast concrete.
The quantification of these interaction forces will be compared to rheological measurements of similar systems. Furthermore, the parameters will be changed to better approach the conditions in real systems, i.e. higher pH and ionic strength. This helps to understand how the forces on the nanoscale influence the macroscopic rheology.
Properties of interstitial liquid phase in cement paste, including the species and concentrations of polymers and ion etc., play an important role for the rheological properties of cementitious materials. In order to better understand their effect, an inert model substance, spherical silica beads (SBs) with defined surface and granulometry were used in the presence of electrolytes (CaCl2) and/or different polymers, including polycarboxylate superplasticizer (PCE) and polyethylene glycol (PEG). It was found the presence of Ca2+ greatly increases the viscosity and yield stress of silica beads paste (SBP), which is proportional to the [Ca2+]. For the effect of PCE, the addition of PCE is beneficial to the flowability of SBP, but a high dosage of PCE leads to a reversal effect. Furthermore, the yield stress firstly increases and then decreases with increasing [Ca2+] under the same dosage of PCE. The addition of PEG always increases the yield stress of SBP, regardless of the ion concentration and the presence or not of PCE.
Special applications like pumping, spraying or printing of concrete require the precise adjustment of very specific rheological properties at different time steps during the casting process. Superplasticizers such as polycarboxylate ethers (PCE) can be used to obtain the required flowability, which, possibly in combination with additional rheology modifying admixtures, generate the required specified consistency. However, after the application, the concrete should change the rheological properties immediately in order to avoid deformations at rest. Therefore, the use of accelerators can be effective. Accelerators influence the hydration of cementitious materials, and thus the rheological properties over the course of time and the setting.
In this paper, the influence of different accelerators on the rheology and early hydration of cement paste as well as the interaction of accelerator and PCE are presented. Methods like rheometry, needle penetration tests and practical Tests like spread flow were applied. The used accelerators showed accelerating behavior on the cement pastes without and in the presence of PCE. At the same time an influence on the rheology could be observed. This effect was less in the mixes with PCE, especially at the highest water/cement ratio (w/c).
The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted.
Composition and microstructure stability of cement compound under cyclic hydrothermal condition
(2020)
There have been many researches focused on the performance improvement of ultra-high performance concrete (UHPC) by autoclaving treatment. The goal of autoclaving is to increase the pozzolanic reaction, and to densify the cement stone and the transition zone which originates from the incorporation of supplementary cementitious materials (SCMs), such as silica fume, fly ash and blast furnace slag. Due to the superior properties, UHPC can also be utilized under high mechanical load and aggressive condition, for example, the fabrication of water tanks for thermal storage which is of great significance for saving energy and reducing CO2 emission. It is known that mineral stability of the hydration products of an inorganic binder is highly related to the temperature and pressure of the environment. A certain stable composition at room temperature, however, may undergo a phase transformation at high temperature and the performance decrease under this severe condition will generally be more severe. In this way, the rationale behind this deterioration under long-term hydrothermal condition involving many cycles and long duration has to be clarified, and then appropriate optimizing methods will be performed in order to obtain a kind of construction with high durability under aggressive environment. For this purpose, different types and amounts of SCMs are introduced into the standard mixture of UHPC and the phase compositions after autoclaving at 200 °C and 15.5 bar are determined by combined X-ray diffraction and scanning electron microscope. Mercury intrusion porosimeter is used to characterise the microstructure of the samples. In order to establish the relationship between microstructure and macroscopic properties, compressive and flexural strength are also investigated.
Die Klinkerphasenbildung durch Sinterung in Drehrohröfen bei der Herstellung von Portlandzementklinker (PZK) ist gründlich erforscht und optimiert. Im Hinblick auf mögliche ökonomische und ökologische Vorteile befassen sich aktuelle Forschungsvorhaben darüber hinaus mit der Herstellung von Klinkermineralen aus Stahlwerksschlacken, die eine vergleichbare chemische Zusammensetzung aufweisen.
Neuste Untersuchungen zeigen, dass nach der reduzierenden Behandlung schmelzflüssiger Linz-Donawitz-(LD)-Schlacken und Abscheidung des gebildeten metallischen Eisens eine mineralische Schlacke entsteht, die unabhängig von ihren Abkühlbedingungen ca. 50–60 Gew.% des wichtigsten Klinkerminerals Alit (C3S) enthält und eine hohe hydraulische Reaktivität aufweist.
Die Stabilität des Alits auch nach langsamer Abkühlung deutet auf eine Stabilisierung des Minerals durch Nebenelemente aus den LD-Schlacken hin. Ein sinkender Anteil an LD-Schlacke durch Zusatz synthetischer Schlackemischung, die sich hinsichtlich ihrer Hauptkomponenten wie eine ausreduzierte LD-Schlacke zusammensetzt, führt zu einem Rückgang des Alitgehaltes und dem Zerfall der Schlacke beim Erstarren.
Die Steigerung der Leistung und des thermodynamischen Wirkungsgrades von Verbrennungsmotoren führt zu erhöhten Anforderungen an die Festigkeit abgasführender Komponenten wie z. Bsp. Abgasturbolader. Als Folge erhöhter thermomechanischer Wechselbeanspruchungen (TMF) im Betrieb kommt es an den mechanisch und/oder thermisch höchst beanspruchten Stellen der Bauteile zur Bildung von Rissen, wodurch die Lebensdauer der Komponenten begrenzt wird. Derzeit werden bei Turboladern heißgehende Bauteile mit detektierten Rissen zumeist prophylaktisch ersetzt, da die weitere Ausbreitung der Risse während des Betriebs nicht vorhergesagt werden kann. Um diese aufwändige und un- ökonomische Praxis zu vermeiden, wurde im vorliegenden Forschungsvorhaben eine rechnerische Bewertungsmethode auf Basis der experimentellen und numerischen Bruchmechanik erarbeitet, mit deren Hilfe bereits in der Auslegungsphase oder während des Betriebs die (restliche) Lebensdauer der abgasführenden Komponenten vorhergesagt werden kann. Damit wird erstmalig die quantitative Vorhersage der Rissentwicklung bei TMF-Beanspruchungsbedingungen unter Berücksichtigung großer zyklischer viskoplastischer Verformungen ermöglicht.
Zentrales Ergebnis des Vorhabens ist eine automatisierte Berechnungsprozedur auf der Basis spezieller Finite-Elemente-Techniken (FEM), womit sowohl der Pfad als auch die Größe eines Risses als Funktion der Anzahl der Lastwechsel in Bauteilen unter TMF-Bedingungen berechnet werden kann. Als geeigneter Beanspruchungsparameter zur Bewertung des Rissfortschritts unter TMF wurde die zyklische Rissöffnungsverschiebung ΔCTOD verwendet. Das Werkstoffverhalten des betrachteten austenitischen Gusseisens Ni-Resist D-5S wurde mit einem validierten viskoplastischen, temperaturabhängigen Materialmodell modelliert, das zur Berücksichtigung große Verzerrungen und Rotationen am Riss erweitert wurde. Für die genaue Berechnung des ΔCTOD bei TMF wurden effiziente FEM-Techniken erarbeitet. Zur Simulation der Rissausbreitung wurde ein automatischer FEM-Algorithmus mit inkrementeller adaptiver Neuvernetzung entwickelt, bei dem die Verformungen und inelastischen Zustandsvariablen jeweils vom alten auf das neue Netz übertragen werden. Dieser Algorithmus wurde im Software-Paket ProCrackPlast implementiert, das in Verbindung mit dem kommerziellen FEM-Code Abaqus zur Lösung dreidimensionaler Rissprobleme zur Verfügung steht. Ziel der umfangreichen experimentellen Arbeiten war es, an isothermen LCF und anisothermen TMF-Versuchen mit gekerbten Flachzugproben (SENT) das Risswachstum im Temperaturbereich von 20 °C bis 700 °C zu ermitteln. Mit Hilfe begleitender 2D FEM Simulationen wurden anhand dieser Datenbasis die Rissfortschrittskurven des Werkstoffs unter Anwendung des ΔCTOD-Konzepts bestimmt und in geeigneter, parametrisierter Form den Nutzern zur Verfügung gestellt. Die Versuche an SENT-Proben wurden mit der entwickelten Software ProCrackPlast als 3D Modell simuliert. Der Vergleich der 2D und 3D Simulationen ergab einen systematischen Unterschied im CTOD und CTOD, der mit Hilfe eines Übertragungsfaktors korrigiert wurde. Der Vergleich der 3D Berechnungen mit den Experimenten zeigte eine zufriedenstellende Übereinstimmung der er- reichten Risslänge mit der Zahl der Lastzyklen im gesamten Temperaturbereich, wobei die numerische Prognose meist auf der konservativen / sicheren Seite lag. Die Übertragbarkeit der Ergebnisse der 2D Parameteridentifikation auf 3D Risskonfigurationen mit Mixed-Mode Beanspruchung ist mit zusätzlichen Versagenshypothesen verbunden, die aufgrund fehlender Versuchsdaten im Vorhaben nicht endgültig geklärt werden konnten. Zur Validierung des Gesamtkonzeptes wurden LCF-Proben mit einem bauteil- typischen Oberflächenriss experimentell und numerisch untersucht. In der Simulation konnte die komplexe Form und Größe der Rissentwicklung zufriedenstellend (richtig) vorhergesagt werden. Die Leis- tungsfähigkeit der erarbeiteten rechnerische Bewertungsmethode wurde an weiteren TMF-Beispielen vorgestellt und diskutiert. Die Software ProCrackPlast und die viskoplastische Materialroutine wurden dem Anwenderkreis des Vorhabens zusammen mit einem Nutzer-Handbuch und Verifikationsbeispielen zur Verfügung gestellt.
Das Ziel des Forschungsvorhabens ist erreicht worden.
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.
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.
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.
Die sprunghaft zunehmende Wichtigkeit von FAIR- und Open-Data für die Qualitätssicherung, aber auch für die Nachnutzbarkeit von Daten und den Erkenntnisfortschritt führt zu enormem Flandlungsbedarf in Forschung und Entwicklung. Damit verbunden laufen derzeit vielfältige, ambitionierte Aktionen, z. B. bezüglich der Erstellung von Ontologien und Wissensgraphen. Das Knowhow entwickelt sich rasant, die Ansätze zur Implementation entstehen in verschiedenen Fachwelten bzw. mit
unterschiedlichen Zielsetzungen parallel, so dass recht heterogene Herangehensweisen resultieren.
Diese Veröffentlichung fokussiert auf Arbeiten, die derzeit als möglichst ganzheitlicher Ansatz für Materialdaten im Rahmen der Digitalisierungsinitiative „Plattform MaterialDigital" vorangetrieben werden. Die Autoren bearbeiten baustoffbezogene Aspekte im Verbundprojekt „LeBeDigital - Lebenszyklus von Beton". Zielsetzung ist die digitale Beschreibung des Materialverhaltens von Beton über den kompletten Herstellungsprozess eines Fertigteils mit einer Integration von Daten und Modellen innerhalb eines Workflows zur probabilistischen Material- und Prozessoptimierung.
Es wird über die Vorgehensweise und die dabei gewonnenen Erfahrungen berichtet, nicht ohne den Blick auf die oft unterschätzte Komplexität der Thematik zu lenken.
Two test series were examined using nondestructive measuring methods by six independent laboratories before determining their compressive strength. The nondestructive test methods used were the rebound hammer and ultrasonic pulse velocity measurement. Two types of geometries were investigated: drilled cores and cubes. The measurement procedure for each of these datasets is conditioned to the geometry and is therefore different.
The first series consists of 20 drilled cores (approximately diameter/height = 10 cm/20 cm) from the 55-year-old Lahntal Viaduct near Limburg, Germany. After preparation in the first laboratory, the lateral surface of the drilled cores was tested with the rebound hammer using a given pattern. Every laboratory tested every drilled core at different locations.
Ultrasonic measurements in transmission were performed repeatedly at predefined points on the flat surfaces of the specimen.
The second series consisted of 25 newly manufactured concrete cubes of a mix with a target concrete strength class of C30/37. The edge length was 15 cm. Each laboratory received five specimens of this test series. Thus, contrary to the first series, each specimen was tested by only one laboratory. Two side faces of each cube were tested with the rebound hammer. In addition, ultrasonic measurements were performed by one laboratory. The time of flight was measured between the tested side faces of the rebound hammer at different positions.
For both series, rebound hammers were used to determine the R-value as well as the Q-value. The rebound hammer models within the laboratories were always the same, while they differed between the laboratories. The ultrasonic measurements took place with different measurement systems and couplants. Finally, both specimen series were tested destructively for compressive strength.
The dataset contains the raw data summarized in tabular form. In addition, relevant calculated data are included in some cases. For the ultrasonic measurements, the time of flight has already been converted into the ultrasonic velocity. Besides, in addition to the raw data of the compressive strength test (force, weight, and geometry values), the calculated compressive strengths and densities are also provided.
This data set contains three different data types obtained from concrete specimens. For each specimen, the rebound numbers, ultrasonic data (ultrasonic velocity, time of flight), and destructive concrete strength are given. Two kind of specimen geometries were tested: cubes and drilled cores. The files are labeled according to the specimen geometry as "cube" or "core" and the type of measurement data as "compressive_strength", "rn_R" and "rn_Q" for rebound numbers as well as "us" for ultrasonic data. The ultrasonic data were generated by six independent laboratories, the rebound numbers by five independent laboratories and the destructive tests by one laboratory. The designation of each specimen establishes the relationship between the different data types.
"This data set contains three different data types obtained from concrete specimens. For each specimen, the rebound numbers, ultrasonic data (ultrasonic velocity, time of flight), and destructive concrete strength are given. Two kind of specimen geometries were tested: cubes and drilled cores. The files are labeled according to the specimen geometry as "cube" or "core" and the type of measurement data as "compressive_strength", "rn_R" and "rn_Q" for rebound numbers as well as "us" for ultrasonic data. The ultrasonic data were generated by six independent laboratories, the rebound numbers by five independent laboratories and the destructive tests by one laboratory. The designation of each specimen establishes the relationship between the different data types."
This study uses conventional 87Sr/86Sr and 143Nd/144Nd isotope and interelement ratios of Ca, Sr, K, Mn, Mg and Ti as fingerprints for provenancing ordinary Portland cements (OPC). Herein, the first database of Sr and Nd isotope ratios investigated in OPCs, stemming from 29 cement plants located worldwide, was created. The results show that the Sr isotope ratios of OPCs are higher than those of seawater from the observed geological period. The spread of 143Nd/144Nd in OPCs is not as large as the spread for 87Sr/86Sr isotope ratios. However, the combination of both Sr and Nd isotope ratios provides the potential for distinguishing between cements of different production sites. Most of the OPCs investigated have measurable differences in their 87Sr/86Sr and 143Nd/144Nd isotope ratios, which can be employed as a valuable analytical fingerprinting tool. In the case of equivocal results, divisive hierarchical clustering was employed to help overcome this issue. The construction of geochemical profiles allowed the computing of suitably defined distances between cements and clustering them according to their chemical similarity. By applying this methodology, successful fingerprinting was achieved in 27 out of the 29 ordinary Portland cements that were analysed.
The paper descibes a novel method to detoxify pine wood (Pinus silvestris L.) treated with CCB-, CCF- CC-, and Cu-HDO-type salt preservatives. In the process of biological detoxification organic acids produced by strains of Antrodia vaillantii and other brown rot fungi are used for the dissolution of the previously fixed inorganic compounds. These findings are the basis for applying an acid pulping process (FORMACELL) developed by Nimz and Schone (1992) at the BFH, Hamburg, to detoxify salt impregnated wood waste with a mixture of acetic and formic acid. First results achieved with wood chips from treated poles after approximately 20 years of service life show that the obtained pulp contains less than 100 ppm of Cr and Cu. The pulp properties were neither influenced by the Cr and Cu ions nor by the age of the poles. The extracted quantities of Cr and Cu remain with the lignin whereas the acids are evaporated and recycled in the pulping process.
Two fly ash-based geopolymer concretes with quartz aggregates or with expanded clay (lightweight) aggregates were exposed to the ISO 834-1 standard fire curve in a small-scale fire test set-up. Acoustic emission measurements during fire exposure and subsequent cooling were employed to study spalling events and cracking during the tests. Optical microscopy and additional acoustic measurements were conducted after the testing to better understand the crack propagation in the samples. The testing revealed that neither of the concretes were susceptible to spalling, which is particularly notable for the concrete with quartz aggregates, as it is a high-strength concrete. This behavior is attributed to the relatively high permeability of the concretes and their low amount of chemically bound water. Significant crack formation was detected only around the temperature of the alpha–beta quartz transition (573 °C) and on cooling. Because of aggregate deformations at the quartz transition temperature, deterioration after heating was more significant in the geopolymer concrete with quartz aggregates. Crack formation also occurred in the concrete with expanded clay aggregates, caused by shrinkage of the geopolymer paste on cooling. Acoustic emission measurements proved to be a valuable tool to investigate processes during high temperature exposure.
Mixed ionic electronic conducting ceramics Nd6-yWO12-d (d is the Oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost-efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6-yWO12-d, the ionic/electronic transport mechanism in Nd6-yWO12-d is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12-d and molybdenum-substituted Nd5.7W0.75Mo0.25O12-d prepared by the citrate complexation route. High-resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12-d and Nd5.7W0.75Mo0.25O12-d. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit-cell parameter due to cation ordering. Mo replacesWat bothWyckoff sites 4a and 48h and is evenly distributed, in contrast with La6-yWO12-d. X-ray absorption spectroscopy as a function of partial pressure pO2 in the near-edge regions excludes oxidation state changes of Nd (Nd3+) and W(W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo-substituted Nd6-yWO12-d is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies.