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Im Rahmen des europäischen Forschungsprojekts Microcon wurden wirtschaftliche und ökologische Ansätze zur Verwendung von Feinstfüllstoffen so genannten Microfillern in Bauprodukten, die auf zementgebundenen Systemen basieren, untersucht. Hauptzielsetzung war die Entwicklung von modifizierten Bindemitteln und Zusätzen für die Transportbeton- und Fertigteilindustrie bis hin zur Marktreife. Eine der Neuentwicklungen war eine leicht handhabbare Werktrockenmischung für selbstverdichtenden Beton (SVB), die alle Schlüsselkomponenten bis auf das Bindemittel und die grobe Gesteinskörnung enthält und eine hohe Robustheit in der Anwendung gewährleistet.
Varying ambient temperatures in plants or on construction sites during casting of SCC can cause serious problems affecting the fresh concrete performances, such as rheological properties and setting time, with consequences for the hardened properties in the structure. By sensible choices of the components, the robustness of SCC mixtures against temperature variations can be improved. However, this aspect has not been the focus of intensive research yet. In this study the effects of varied ambient temperatures on the early performance of differently composed SCC mixtures are investigated, with emphasis on changes in rheology, early deformations, heat evolution and setting. Focus is placed on the study of the influence of the polycarboxylate ether molecule type as well as different viscositymodifying agents on the temperature robustness. Effects on the relevance for practical concrete applications are evaluated, which will provide a reliable framework of possible actions on the appropriate use of admixtures for SCC.
Stabilising admixtures are commonly used additives in repair mortars and grouts. Beyond this, such type of admixture is increasingly used in concrete and other cementitious materials. In particular when fresh mortar or concrete properties have to be adjusted reliably, stabilising agents can be beneficially used to improve workability and robustness of the mixture. The mode of operation of these admixtures varies, rather affecting either the liquid phase or the solid particles in the dispersion, both causing strong interactions with the mortar or concrete system, and significant changes in their rheological behaviour. Furthermore, these are strongly affected by the environmental temperature during the casting process. In the paper the effect of temperature on the performance of stabilising agents in cementitious systems is presented and how performance changes affect fresh and hardening mortar or concrete properties. Particular attention is placed on interactions between stabilising agents and superplasticizers. Results are discussed with special focus on self-compacting concrete.
Today polycarboxylate ether based superplasticizer (PCE) is commonly used in concrete technology when high flow properties and water reduction are specified. The ionic strength of the polymers’ backbones determines the adsorption behaviour of polymers on clinker and early hydration products. The amount of required polymers for specified flow properties and the performance over the time of casting is thus determined by the molecular structure of the superplasticizer. The time depending consumption of polycarboxylate ether polymers strongly affects the reaction of aluminates and sulphate ions as well as the hydration process in general. Hence, the choice of polymers for particular flow properties greatly affects the very early properties of cementitious materials such as setting, heat evolution and autogenous deformations.
In order to better understand how PCEs influence the early properties, mixes from cement, limestone filler, viscosity modifying agent and water were varied with a high and a low charge density superplasticizer in differing amounts. Results are presented from measurements with an automatic Vicat device, an isothermal heat flow calorimeter, and shrinkage cones. Tests were conducted at 5, 20, and 30 °C.
It is shown that in presence of PCE the final set correlates well with the inflexion point of the heat flow curve, which emphasises the interrelation between C-S-H formation and setting. No such clear correlation can be found for the initial set, which is attributed to the fact that the initial set is rather a rheological than a structural phenomenon, so that other effects overlap with C-S-H formation. The results demonstrate that for a given polymer concentration low charge density polymers yield earlier setting than high charge polymers. However, this influence is overridden by the influence of the total amount of polymers in a cementitious system. Since PCE is typically added according to rheological specifications, and low charge PCE typically requires higher amounts of polymers than high charge PCE for comparable flow performance, low charge PCE retards setting more than high charge PCE.
The paper furthermore points out that there is no significant influence of the polymer type or amount on the early deformations. Since type and amount strongly affect the hydration, it is demonstrated that early setting causes higher strain after the final set. It is hence concluded that higher PCE solid contents reduce the risk of early cracks that occur at time of setting, when a solid structure has already been formed but without resistance against cracks yet.
Since its invention in the early 1990’s, self-consolidating concrete has never become well established in the ready-mix sectors worldwide. The reason for this can be mainly found in the fact that the sophisticated compositions are sensitive against changing environments. This lack of robustness can be attributed to the interaction between cement hydration reaction and high range water reducing agent (HRWRA). Understanding the relevant mechanisms that control the initial flow performance as well as the flow retention helps optimizing SCC mixtures that perform either steadily in one specific environment or that perform largely similarly at steadily changing environments.
This paper depicts how HRWRAs interact with clinker and hydration phases and discusses the important role of the charge density of a polycarboxylic HRWRA in the way the rheology is affected. Based on rheometric results and observations of the Vicat setting times, it is shown that increasing charge densities of the HRWRA and decreasing water to powder ratios (w/p) reduce the flow retention and have lesser retarding effect on the setting. Based on the discussion, optimization procedures for the mixture composition and the HRWRA modification are suggested to achieve optimized performance for varying environmental situations or highest robustness for specific conditions.
ln order to observe the influence of stabilising agents (STA) based on starch and diutan gum, rheometric experiments and setting tests were conducted on cement pastes with and without PCE superpiasticizers. The results show that with regard to yield stress both STAs show differing behaviours in Systems without PCE. In presence of PCE, yield stress infiuences of the STAs retreat into the background. The Vicat results exhibit that STAs can reduce the retard ing effect of PCE.
Todays superplasticizers for self-compacting concrete and high Performance cementitious materials are very versatile. Typically superplasticizers are composed of a polycarboxylic backbone equipped with polyethylene oxide graft chains of variable length and grafting degree. The mode of operation of these admixtures is based on the steric repulsion of the particles upon adsorption. The adsorption is strongly depending upon the charge density of a superplasticizer and the time dependent Adsorption processes control the retention of the flow performance – an important issue particularly for ready-mix and construction site concrete. However, the properties of polycarboxylic superplasticizers typically remain a black box for users. The paper suggests a simple and rapid test method, which can be conducted without sophisticated equipment, to qualitatively distinguish between two types of superplasticizers based on the adsorption mechanism. Interpreting the results in the right way provides a powerful tool to choose the right admixture for individual time dependent flow specifications.
Innovative admixture technology has significantly widened up the ränge of possibilities of concrete engineers. For many decades the water to cement ratio (w/c) was the major influencing factor for the performance of concrete. Due to the need to adjust a consistency, which still allowed reasonable workability, the w/c was typically significantly higher than technologically reasonable. Rheology modifying admixtures Support adjusting the concrete consistency largely independent of the w/c. It was only after the invention of the first superplasticizers that modern concrete technology significantly evolved in terms of flowability, strength, and durability, and only due to the steady evolution of the technology modern innovations, such as Self-Compacting Concrete, Ultra-High-Performance Concrete, or Engineered Cementitious Composites were made possible. Today’s superplasticizers are extremely versatile and can be adjusted to individual technological specifications. However, the other side of the coin of versatility is that cementitious Systems incorporating superplasticizers have become more sensitive against environmental influences, such as the environmental temperature, which may cause unwanted effects or demand for supplementary admixture use such as stabilizing admixtures. Hence, concrete mixture composition with admixtures demands for a high level of expertise and offen there is lack of awareness about the mode of Operation of rheology modifying admixtures among concrete technologists. The paper gives a comprehensive overview about rheology modifying admixtures such as superplasticizers or stabilizing agents, and how they can be used depending upon the application in the most favourable way. Based on experiences with the sub-Saharan African concreting boundary conditions, which exhibit many challenges in terms of environmental boundary conditions and construction site logistics, conclusions are finally drawn, how admixtures can be used in the most beneficial way to improve the concrete casting Situation.
The fresh behaviour of self-compacting concrete (SCC) at varying temperatures differs from that of normal vibrated concrete. This is because the rheology of SCC depends not only on degree of cement hydration, but also on the adsorption of superplasticizers – mostly polycarboxylate based polymers (PCE) -, which is affected by the time and hydration progress. Due to the variety of PCEs and mixture compositions for SCC a prediction of the rheology at varying temperatures is complicated. The charge densities of PCEs as well as the water to solid ratio in the paste are identified to be the main decisive parameters for robust fresh concrete properties.
Rheometric concrete investigations with different SCC mixture compositions and varied anionic charge densities of the PCE were conducted. SCC which is rich in powder components showed robust performance at low temperatures while SCC with low powder content was favourable at high temperatures. High charge density PCE pointed out to be very robust at low temperatures but at high temperatures it significantly reduced the flow retention. Low charge density PCE could not generate self-compacting properties at low temperatures but retained the flow performance over sufficiently long time. Based on considerations about particle interactions and adsorption mechanisms of PCEs, the relevant processes are explained and options for the development of robust mixture compositions for individual temperature ranges are itemised.
To design robust self-consolidating concrete (SCC) for various environmental conditions, it is essential to understand the relevant mechanisms that control the flow performance. This paper depicts how high range water reducing agents (HRWRAs) interact with clinker and hydration phases, and it discusses the important role of the charge density of polycarboxylic HRWRAs in the way the rheology is affected. Based on the rheometric investigations on SCC mixture compositions with different water to powder ratios (w/p) and observations of their pastes' Vicat setting times, the study shows that increasing charge densities of the HRWRA and decreasing w/p reduce the flow retention and have lesser retarding effect on the setting. Based on the test results and discussions optimization procedures for the mixture composition and the HRWRA modification are suggested to achieve optimized performance for varying environmental situations and highest robustness for specific conditions.
Polysaccharides provide high potential to be used as rheology modifying admixtures in mineral binder systems for the construction industry such as concrete or mortar. Since superplasticizers have become state of technology, today, concrete is more and more adjusted to flowable consistencies. This often goes along with the risk of segregation, which can be effectively avoided by adding stabilising agents supplementary to superplasticizers. Stabilising agents are typically based on polysaccharides such as cellulose, sphingan gum, or starch. Starch clearly distinguishes in its effect on rheology from other polysaccharides, mainly due to the strong influence of amylopectin on the dispersion and stabilisation of particles. Based on rheometric investigations on cementitious and limestone based dispersions with different volumetric water to solid ratios, the mode of operation of modified potato starch is explained in comparison to a sphingan gum. It is shown that the stabilising effect of starch in a coarsely dispersed system is mainly depending upon the water to solid ratio and that above a certain particle volume threshold starch mainly affects the dynamic yield stress of dispersions, while plastic viscosity is affected only to a minor degree. Sphingans operate more independent of the particle volume in a coarsely dispersed system and show significantly higher effect on the plastic viscosity than on the yield stress. In systems incorporating superplasticizers, influences of both stabilising agents on yield stress retreat into the background, while both observed polysaccharides maintain their effect on the plastic viscosity.
Innovative admixture technology has significantly widened up the ränge of possibilities of concrete engineers. For many decades the water to cement ratio (w/c) was the major influencing factor for the performance of concrete. Due to the need to adjust a consistency, which still allowed reasonable workability, the w/c was typically significantly higher than technologically reasonable. Rheology modifying admixtures Support adjusting the concrete consistency largely independent of the w/c. It was only after the invention of the first superplasticizers that modern concrete technology significantly evolved in terms of flowability, strength, and durability, and only due to the steady evolution of the technology modern innovations, such as Self-Compacting Concrete, Ultra-High-Performance Concrete, or Engineered Cementitious Composites were made possible. Today’s superplasticizers are extremely versatile and can be adjusted to individual technologicalspecifications. However, the other side of the coin of versatility is that cementitious Systems incorporating superplasticizers have become more sensitive against environmental influences, such as the environmental temperature, which may cause unwanted effects or demand for supplementary admixture use such as stabilizing admixtures. Hence, concrete mixture composition with admixtures demands for a high level of expertise and offen there is lack of awareness about the mode of Operation of rheology modifying admixtures among concrete technologists. The paper gives a comprehensive overview about rheology modifying admixtures such as superplasticizers or stabilizing agents, and how they can be used depending upon the application in the most favourable way. Based on experiences with the sub-Saharan African concreting boundary conditions, which exhibit many challenges in terms of environmental boundary conditions and construction site logistics, conclusions are finally drawn, how admixtures can be used in the most beneficial way to improve the concrete casting Situation.
Pathway of a damaging mechanism - Analyzing chloride attack by synchrotron based X-ray diffraction
(2015)
Typically, the changes of the phase compositions due to the chemical attack are studied in-situ only by chemical analysis or microscopy. In this study, the chloride transport and binding in the cement matrix in different cementitious materials was analyzed by synchrotron based X-ray diffraction (SyXRD) and energy dispersive X-ray spectroscopy (EDX). Sample materials consisting of cement paste were embedded in high concentrated sodium chloride solution over different time spans. Afterwards, the phase and chemical compositions were determined. The high spatial resolution and the information about the chloride distribution offer a detailed view of chloride binding in the cement matrix and allow the conclusions about the degradation mechanisms. The results are discussed related to the influence of different supplementary cementitious materials on the damaging mechanism.
Einfluss einer druckschwellinduzierten Degradation von Fahrbahndeckenbeton auf die schädigende AKR
(2020)
In den letzten Jahren sind im deutschen Bundesautobahnnetz verstärkt Schäden an vor 2005 errichteten Betonfahrbahndecken aufgetreten, die mit einer Alkali-Kieselsäure-Reaktion (AKR) in Verbindung gebracht werden. Neben dem AKR-fördernden Einfluss von alkalihaltigen Taumitteln werden Fahrbahndecken zyklischen mechanischen Belastungen infolge des Verkehrs und Zwangsspannungen durch klimatische Einwirkungen ausgesetzt. Solche mechanischen Belastungen werden bisher in keinem AKR-Prüfverfahren berücksichtigt. Die zyklischen Belastungen können zu einer Degradation des Betongefüges führen, die ggf. einen AKR-fördernden Einfluss hat. Dieser Beitrag stellt Untersuchungen vor, die zur Beantwortung der Frage nach dem Einfluss einer zyklischen mechanischen Belastung auf den AKR-Schadensprozess beitragen. Dabei wird der Hypothese nachgegangen, dass die ermüdungsinduzierte Degradation zu einer Erhöhung des Stofftransports führt.
Dieser hat einen Einfluss auf die AKR-Schadensentwicklung, da die Reaktionspartner zunächst zum Reaktionsort transportiert werden müssen. Daher wird angenommen, dass sich mit dem Stofftransport auch die AKR-Schädigung verstärkt. Es werden Betonproben aus typischen Fahrbahndeckenbetonen einer vorgeschalteten zyklischen Druckschwellbelastung ausgesetzt.
Die Degradation infolge der Vorbelastung wird simultan mittels ZfP-Verfahren charakterisiert. Anschließend werden die Auswirkungen der zyklischen Vorschädigung auf den Stofftransport sowie auf die AKR vergleichend an Prüfkörpern ohne und mit Vorschädigung untersucht. Die Ergebnisse lassen den Schluss zu, dass die zyklische Vorschädigung sowohl den Stofftransport als auch die AKR fördert.
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.
Ultra high performance concrete (UHPC) is known for its high compressive strength of more than 150 MPa and its high durability. Thermal treatment at 90°C can accelerate the strength development so that the 28-days-strength can be achieved immediately after the treatment and an additional increase up to 30 % in some cases. The reason for the strength development is an accelerated hydration of the clinker minerals and an intensified pozzolanic reaction leading to a denser microstructure.
In previous research inhomogeneities in form of a zonation after unprotected thermal treatment were observed and analysed in respect to changes in the microstructure. This zonation is defined by a different microstructure in the core compared to the outer zone in the matter of porosity, mineral phase composition and a significant change in the potassium and sulphur concentration of the zones is measurable.
To isolate different transport mechanisms responsible for these element distributions UHPC samples were thermally treated at 90 °C and the microstructure was investigated under dry conditions and after immersion in water to investigate the influence of dehydration during and rehydration after the thermal treatment on the microstructure. Through durability testing via water absorption, water vapour diffusion, permeability testing and sulfuric acid resistance transport mechanisms like diffusion, migration, capillary suction are under investigation in correlation with the microstructure analysis. For the microstructure analysis measurements with µXRF, mercury intrusion porosity, XRD and SEM were conducted.
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.
Several studies show that thermal and hydrothermal treatment can further improve the excellent properties of UHPC in terms of mechanical strength and durability. While for the thermal treatment the increase in strength is attributed to an intensified pozzolanic and hydraulic reaction, for the hydrothermal treatment previous studies accredited it mostly to the formation of tobermorite. In the presented study thermal and hydrothermal treatment of UHPC samples was systematically varied and the phase formation analysed related to the strength development of a reference sample cured for 28 days in water. For the thermal treatment the results show that the strength increase depends on the protection against desiccation and can be ascribed to an improved pozzolanic reaction of the siliceous fillers. To achieve a significant enhancement of strength, a pre-storage time of few days and a long dwell time at elevated temperature/pressure are required. For the hydrothermal treatment already heating the specimens up to 185 °C in saturated steam followed by an immediate cooling leads to a substantial increase in compressive strength. Pre-storage time did not affect the result as far as a minimum of several hours is guaranteed. The improved performance is due to an increase in the pozzolanic and hydraulic reaction. Surprisingly, tobermorite was only found within a very thin layer at the surface of the sample, but not in the bulk. Sulphate and aluminium stemming from the decomposition of the ettringite are bound in the newly formed phases hydroxylellestadite and hydrogarnet.
ln most of the ASR-test procedures, the expansion of concrete or mortar specimens is used as an indicator to assess the ASR-potential of an aggregate or a specific concrete mix. For these tests, the specimens are stored in an ASR-provoking environment, where the reaction is accelerated by elevated temperature and humidity. To measure the length change, the storage must be interrupted for at least a few minutes. Düring the 60 °C Concrete Prism Test (60 °C-CPT), the specimens are cooled down to 20 °C for 24 hours, to ensure the same hygrothermal conditions for every measurement. This limits the number of measurements during the test period and may lead to additional effects, that probably influence the expansion development.
With a recently developed device, it is possible to continuously monitor the expansion ofprisms without interrupting the ASR-provoking storage. Due to the dense database of this automated test, the results can contribute to a better understanding of the ASR-process. This study compares results of the automated and conventional 60 °C-CPT. Tests of different aggregates showed, that the results of the automated and conventional test are consistent, but the expansions during the conventional test are generally higher. Preliminary results led to the conclusion, that the cooling for the measurements leads to additional expansions. Therefore, a modified threshold should be discussed for the automated 60 °C-CPT.
If the amount of sulfate within the mix design for concrete is not balanced, ettringite formation which first controls solidification continues while the concrete is hardening. Ettringite forms by reaction of sulfate contained in the cement or in some admixture with calcium aluminate (C3A) as cement component. The “late primary ettringite formation” promotes an increase in volume within the hardened concrete leading to cracks. To analyze the effect of substituting part of ordinary Portland cement (OPC) by a treated brown coal fly ash mortar bars were tested according to ASTM C452. This test method was originally developed to extrapolate from the internal to external sulfate attack and is based on the idea that by testing a concrete mixture containing sulfate the process of deterioration is accelerated because it does not have to diffuse into the concrete before reaction first. In addition to the samples prescribed in ASTM C452 further samples in the size of the German SVA procedure were tested also designed for accessing the external sulfate resistance. The results show that while the replacement of 25 % of cement by brown coal fly ash leads to length changes around the limit defined by ASTM, the substitution of 50 % cement exceeded the limit by a multiple. The progress of expansion is the very similar for the two geometries tested. In-situ XRD measurements confirmed that while for pastes made of OPC the formation of ettringite is completed after 20 hours, this is not true for the mixtures containing the brown coal fly ash.
In a different study the effect of hydrothermal treatment on the phase composition of ultra-high-performance concrete was analyzed. The results show that the sulfate and aluminate resulting from the decomposition of ettringite are bound into new phases.
If this binding is permanent this might allow the larger use of sulfate bearing raw materials.
The adaption of the set-up for gas permeability measurements for ultra-high performance concrete
(2022)
In the framework of this project, a steam pressure vessel was to be developed from ultra-high perfor-mance concrete (UHPC) to withstand process temperatures of 200 °C and the respective steam pressure of 15,5 bar. To guarantee the long-term water vapour tightness of the system, the permeability of two UHPC mixtures were tested after long-term cyclic autoclaving. As UPHC shows a high density and therefore low permeability, measurements after the RILEM-Recommendation (TC 116-PCD) reached their detection limit. Therefore, the measurement set-up was adapted to measure the permeability of highly dense UHPC more reliably and quickly. This adaption includes measurements in a higher pres-sure range, the change of sample size thickness and the usage of Ar as a medium compared with the RILEM Recommendation. Additionally, the system was equipped with two pressure sensors and Ar-flowmeters to guarantee a continuous record of the experimental parameters. The new system was tested and evaluated by comparing measurements with the RILEM recommended system. Preliminary results show that the adapted system is capable to provide efficient and reliable results of concrete with low permeability.
Der 60 °C-Betonversuch ist eine in Deutschland und international verbreitete Methode um die Empfindlichkeit von Gesteinskörnungen und Betonen hinsichtlich einer Alkali-Kieselsäure Reaktion (AKR) zu prüfen. Dieser Beitrag stellt eine neuentwickelte automatisierte Variante der Prüfmethode in einem Minireaktor vor. Dabei werden die Dehnungen von Betonprismen nicht, wie beim konventionellen Test manuell, sondern automatisch in entsprechend ausgerüsteten Prüfbehältern gemessen. Neben einer Reduzierung des Messaufwands bringt die automatisierte Prüfung im Minireaktor weitere Vorteile. Die Dehnungssignale werden, anders als bei der konventionellen Messung, quasi-kontinuierlich aufgezeichnet und bilden das Expansionsverhalten der Prismen detailliert ab. Außerdem bleiben Unterbrechungen der AKR-provozierenden Lagerung aus, die bei der konventionellen Prüfung notwendig sind. Im Beitrag werden die automatisierte und konventionelle Prüfung anhand der Dehnungen von Prismen zweier Gesteinskörnungen verglichen. In Übereinstimmung mit vorhergehenden Untersuchungen sind im Minireaktor gemessene Dehnungen systematisch kleiner als manuell gemessene. Als mögliche Ursache werden Unterschiede im Auslaugverhalten experimentell untersucht. Zur Überprüfung der Einstufung der zwei Gesteinskörnungen erfolgen außerdem Referenzprüfungen in der Nebelkammerlagerung bei 40 °C.
Im Gegensatz zur Druckfestigkeit weisen zementgebundene Werkstoffe i. a. nur geringe Zugfestigkeiten auf. Ein Weg, Zugfestigkeiten zementgebundener Werkstoffe zu erhöhen und Rissbildung aufgrund von Zugspannungen zu verringern, besteht in der Einarbeitung von Fasern, die diese Spannungen aufnehmen. Häufig eingesetzt werden Stahlfasern, obwohl synthetische Polymerfasern leichter und meist beständiger gegenüber chemischen Angriffen und Korrosion sind. Die Polymerfasern zeigen allerdings meist einen deutlich schwächeren Haftverbund, was an der hydrophoben Faseroberfläche liegt. Um nun eine Anbindung der Fasern an die mineralische Matrix zu erreichen, müssen die Faseroberflächen modifiziert werden, ohne dass die mechanischen Eigenschaften negativ beeinflusst werden. Eine Herausforderung besteht somit in einer Oberflächenmodifikation durch eine schonende Behandlung der Fasern zur Erzeugung von anbindungsfähigen Gruppen.
Durch eine Behandlung von modifizierten Fasern mit geeigneten Polymerlösungen werden die Oberflächeneigenschaften verändert und erlauben eine Anbindung an die Zementsteinmatrix. Der Einsatz von Tensiden als grenzflächenaktive Verbindungen ermöglicht in diesem Zusammenhang eine Vermittlung zwischen Polymeroberflächen und mineralischen Werkstoffen.
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.
Im Gegensatz zur Druckfestigkeit weisen zementgebundene Werkstoffe i. a. nur geringe Zugfestigkeiten auf. Ein Weg, Zugfestigkeiten zementgebundener Werkstoffe zu erhöhen und Rissbildung aufgrund von Zugspannungen zu verringern, besteht in der Einarbeitung von Fasern, die diese Spannungen aufnehmen. Häufig eingesetzt werden Stahlfasern, obwohl synthetische Polymerfasern leichter und meist beständiger gegenüber chemischen Angriffen und Korrosion sind. Die Polymerfasern zeigen allerdings meist einen deutlich schwächeren Haftverbund, was an der hydrophoben Faseroberfläche liegt. Um nun eine Anbindung der Fasern an die mineralische Matrix zu erreichen, müssen die Faseroberflächen modifiziert werden, ohne dass die mechanischen Eigenschaften negativ beeinflusst werden. Eine Herausforderung besteht somit in einer Oberflächenmodifikation durch eine schonende Behandlung der Fasern zur Erzeugung von anbindungsfähigen Gruppen. Durch eine Behandlung von modifizierten Fasern mit geeigneten Polymerlösungen werden die Oberflächeneigenschaften verändert und erlauben eine Anbindung an die Zementsteinmatrix. Der Einsatz von Tensiden als grenzflächenaktive Verbindungen ermöglicht in diesem Zusammenhang eine Vermittlung zwischen Polymeroberflächen und mineralischen Werkstoffen.
Baustoffe im Betonbau
(2019)
In dem Kap. „Baustoffe im Betonbau“ werden zunächst die Baustoffe vorgestellt, die für die Herstellung von Stahlbeton- und Spannbetonbauwerken erforderlich sind (im Wesentlichen Beton, Betonstahl und Spannstahl). Herstellungsbedingte, typische Eigenschaftsprofile der Baustoffe werden aufgezeigt und ein Bezug zu entsprechenden Anwendungsgebieten hergestellt.
Die geringe Zugfestigkeit von zementgebundenen Materialien kann durch die Zugabe von Fasern maßgeblich verbessert werden. Ziel eines gemeinsamen Verbundprojekts mit einem Industriepartner war die Erhöhung der Leistungsfähigkeit von kurzen Polymer- und Carbonfasern durch eine Verbesserung des Verbundes zwischen Faseroberfläche und Zementsteinmatrix.
Von der IONYS AG wurde dazu eine spezielle Funktionalisierung entwickelt, die über eine Hydrophilisierung der Faseroberfläche eine chemische Anbindung an die Zementsteinmatrix gewährleistet. Aufgabe der BAM war es, die Effizienz der neuen Beschichtung bezüglich der Erhöhung der Nachrissbiegezugfestigkeit und der Reduzierung der Schwindrissbildung während der Erhärtungsphase zu quantifizieren. Die Ergebnisse zeigen, dass die Funktionalisierung die Neigung zur Schwindrissbildung für die Carbonfasern und in noch stärkerem Maße für die Polymerfasern reduziert.
Eine Erhöhung der Nachrissbiegezugfestigkeit konnte dagegen nur für die deutlich steiferen Carbonfasern nachgewiesen werden.
Composite Facade Elements with Self-Cleaning Surface made of Ultra-High-Performance Concrete (UHPC)
(2020)
In the framework of the European project H-House various concrete façade elements were developed with the aim to ensure a long service life by combining a very durable material with self-cleaning properties. The façade elements presented are made of a shell of UHPC filled with blocks of aerated autoclaved concrete as insulating material. Self-cleaning properties were realized amongst others by imprinting a microstructure into the surface during casting. The paper focuses on selected technological aspects of the manufacturing process of prototypes which had to be performed in two concreting sections. Furthermore the challenges faced when upscaling the self-cleaning properties are addressed and the strategy to assess the self-cleaning properties by measuring the contact and the roll-off angel is presented. The results show that a successfull upscalaing process requires detailed planning and that the best results can often be achieved with a moderate work effort or material use.
Composite UHPC facade elements with self-cleaning surface: Aspects of technological manufacturing
(2020)
In the framework of the European collaborative project H-House, which was finished in 2017, large façade elements were developed consisting of a box shaped external shell of ultra-high-performance concrete (UHPC) with a functionalized surface and an insulation of autoclaved aerated concrete (AAC). The exposed concrete of the elements was further refined by adding self-cleaning properties to the surface through imprinting a microstructure in combination with chemical agents directly in the casting process. The paper focuses on selected technological aspects of the manufacturing process of large-scale prototypes. Presented are results of the upscaling process of functionalized surfaces from small specimen up to large UHPC composite facade elements produced for the construction of a demonstrator.
Die vorstehend dargestellten Untersuchungen lassen sich wie folgt zusammenfassen:
• Mit dem für die mechanische Vorschädigung entwickelten Versuchsstand und gewählten Prüfregime können die für die ermüdungsinduzierte Schadensevolution typische stabilisierende und stabile Phase in der auf Zug beanspruchten Betonrandzone gut abgebildet werden. So wurde dort zum Beispiel, ausgehend von dem hier gewählten praxisnahen Belastungsregime, mit Ultraschall in der Ruhephase durch das Trockenschwingen ein maximaler Abfall des relativen dynamischen E-Moduls von ca. 8 - 10 % ermittelt.
• Mit aufbauenden kapillaren Aufsaugversuchen wurde gezeigt, dass die erzeugte Betondegradation zu einer moderaten Erhöhung der Aufnahme des Prüfmediums führt.
• Zur Bewertung der Auswirkungen einer alleinigen Vorschädigung (Trockenschwingen) auf die schädigende AKR mittels Performance-Prüfung ist die Klimawechsellagerung aufgrund der einseitigen Tausalzbeaufschlagung am besten geeignet. Die hier ermittelten Dehnungsverläufe lassen auf einen moderaten Einfluss der mechanischen Vorschädigung auf die AKR schließen.
• Die zusätzlich im Kontext der Nasschwingversuche durchgeführten 60°C Betonversuche zeigen, dass die zyklische Beanspruchung vor und nach dem Aufbringen der Tausalzlösung die schädigende AKR gleichfalls moderat erhöht.
In derzeit laufenden ergänzenden Untersuchungen wird der separate Einfluss der ermüdungsinduzierten Rissbildung auf die schädigende AKR an homogen, stärker geschädigten Prüfkörpern mit einem hohen inneren AKR-Schädigungspotenzial im 60°C Betonversuch grundhaft analysiert. Zusätzlich wird gegenwärtig der Einfluss der degradierten Betonrandzone auf die Dehnungsverteilung an großformatigen Prüfkörpern
über die Höhe im 40°C Betonversuch vertiefend für die makroskopische Modellierung untersucht.
UHPC (engl. ultra-high-performance concrete) bietet außergewöhnliche Eigenschaften, die sich durch eine optimierte Wärmebehandlung weiter verbessern lassen. Wie bei normalen Beton beschleunigt eine Wärmebehandlung den Aushärteprozess und reduziert das Schrumpfen. Durch Ausbildung eines dichteren Gefüges wird weiterhin die Druckfestigkeit und die Resistenz gegenüber Umwelteinflüssen erhöht.
Die Art der Wärmebehandlung wird durch die Parameter: Temperatur, Druck, Wasserdampfsättigung und Dauer definiert und hat einen entscheiden Einfluss auf die Phasenentwicklung und damit auf die makro- und mikroskopischen Eigenschaften des UHPCs. Auch die Dauer und Art der Vorlagerung des UHPCs vor der thermischen Behandlung sind von Bedeutung.
Ziel der vorgestellten Untersuchung war der Vergleich und die Optimierung verschiedener Wärmebehandlungsarten mit Blick auf die Druckfestigkeits- und Phasenentwicklung. Dafür wurden UHPC-Zylinder und Prismen hergestellt und ungeschützt bzw. in Folie eingeschweißt bei 90 °C im Ofen, im Heißwasserbad, sowie alternativ bei 185 °C und 1.1 MPa im Autoklaven wärmebehandelt. Zusätzlich wurde die Vorlagerungs- und die Behandlungszeit systematisch variiert.
Die Ergebnisse zeigen, dass eine praxisnahe Wärmebehandlung im Ofen (kurze Vorlagerungs- und Behandlungszeit, Verdunstungsschutz durch Einschweißen in Folie) zwar zu einer stark erhöhten Frühfestigkeit führt, aber die Langzeitfestigkeit wird nicht signifikant erhöht. Erst längere Behandlungszeiten verbunden mit intensiviertem Schutz gegen das Austrocknen führen darüber hinaus zu deutlich erhöhten Langzeitfestigkeiten. Nach der Autoklavierung dagegen wurden Festigkeitszuwächse von bis zu 30 % gemessen.
Die röntgenographisch nachgewiesene Phasenentwicklung wird in beiden Behandlungsarten durch die Limitierung des zur Verfügung stehenden Wassers bestimmt. Bei der Wärmebehandlung im Ofen wird das durch den Ettringitzerfall freigesetzte Wasser für die puzzolanische Reaktion der Mikrosilika verbraucht, reicht aber für eine weitere Reaktion der Klinkerphasen nicht aus. Bei der hydrothermalen Behandlung dagegen zeigen die Veränderungen im Phasenbestand sowohl eine Intensivierung der puzzolanischen als auch der hydraulischen Reaktion. Der für autoklavierte Baustoffe charakteristische Tobermorit konnte jedoch nicht im Probeninneren, sondern nur als Belag auf der Probenoberfläche nachgewiesen werden. Ursächlich hierfür ist vermutlich wiederum das zu geringe Wasserangebot im Gefüge des UHPC.
Fatigue induced degradation in pavement concrete and its effect on the alkali-silica reaction
(2018)
In recent years the German motorway network has seen an increase in the occurrence of damage to concrete road surfaces that can be attributed to the alkali-silica reaction (ASR). In view of the often drastically reduced service life of road surfaces due to ASR, research activity in this field has notably increased. Alongside preventative measures in concrete technology i.e. the usage of low-alkali cements, the main research focus up to now has been on the development of performance-oriented testing procedures for ASR prevention. The effects of mechanicallyinduced damage resulting from cyclic traffic and climatic loading have previously not been taken into consideration.
The assessment of the myriad degradation and transport processes necessary for an understanding of these effects requires close interaction between experiments and corresponding multi-scale models. This contribution is focused on the experiments utilizing innovative testing techniques. The research is founded on a series of fatigue tests performed on large-scale beams with simultaneous tracking of the degradation process using non-destructive evaluation methods. Subsequently, smaller test specimens were extracted from the predamaged beams for further experiments. These experiments included investigation of the influence of fatigue-induced cracks on moisture and alkali transport. Subsequent storage of the small-scale test specimens, with and without cyclic pre-damage, in an ASR-conducive environment then provided initial findings on the influence of fatigue-induced degradation on the ASR.
The results show that the degradation process can be well observed with the test Setup developed for the fatigue experiments. Further, a small but noticeable increase of mass Transport due to fatigue-induced degradation was measured, which correspondingly indicated an increased ASR damage potential.
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.
Alkali-Kieselsäure-Reaktion in Betonfahrbahndecken unter Berücksichtigung von Verkehr und Taumitteln
(2019)
In Betonfahrbahndecken treten häufig Schäden auf, welche mit einer Alkali-Kieselsäure-Reaktion (AKR) in Verbindung gebracht werden. Obwohl die Hintergründe einer solchen AKR intensiv untersucht wurden, gibt es bei Betonfahrbahndecken besondere Randbedingungen, welche die Schadreaktion signifikant erhöhen können. Diese sind vor allem die Überlagerung der mikrostrukturellen Degradation durch Verkehrsbeanspruchung mit externer Alkali-Zufuhr durch Taumittel. Bisherige Untersuchungen der AKR beschränkten sich auf die Ausgangsstoffe (Gesteinskörnung, Zement, Bewertung des Betons), wobei die besonderen Randbedingungen außer Acht gelassen wurden. Betonfahrbahndecken sind zyklischen Belastungen aus Verkehr und Witterungsbedingungen ausgesetzt.
In einem gemeinschaftlichen Forschungsprojekt wurden die verschiedenen, gegenseitig voneinander abhängigen, Einflussfaktoren auf eine schädigende AKR in Betonfahrbahndecken sowohl experimentell untersucht als auch numerisch modelliert. Auf Mikro-Ebene wurden die AKR-bezogenen Transportprozesse innerhalb der Gesteinskörnung, sowie die Gelbildung und der Ionen-Transport, untersucht. Auf Meso-Ebene fokussierte das Projekt auf die Charakterisierung der durch zyklische Belastung induzierten Schädigung im Mikrogefüge des Betons. Des Weiteren wurde das Transportverhalten in ein derart geschädigtes Betongefüge mit und ohne Berücksichtigung des zusätzlichen Einflusses überrollender Reifen beschrieben und dessen Auswirkung auf eine AKR analysiert. Schließlich wurde auf Makro-Ebene das Risiko eines AKR-bedingten Schadens bewertet. Einige ausgewählte Ergebnisse werden in diesem Beitrag dargestellt.
Severe mechanical fatigue conditions for worldwide proliferating windfarms are a Major challenge for high-performance concrete in towers, connecting joints and foundations of wind turbines. High-performance concrete offers potential for the application in offshore windfarms, not only regarding its good mechanical, but also chemical resistivity due to low diffusivity in the highly densified microstructure. For a more reliable fatigue assessment, monitoring based on nondestructive testing can be a valuable complement to design rules. Both approaches demand reliable experimental data, information about scalability and the development of standardized testing methods. This article presents results of an ongoing research program of BAM (Bundesanstalt für Materialforschung und -prüfung), which is a part of a joint national project (WinConFat) funded by the German Federal Ministry for Economic Affairs and Energy. The subproject implemented by BAM examines the fatigue behavior in dependence of size and slenderness for varying concrete strength at different stress levels. Besides fatigue strength, nondestructive testing is carried out additionally.
Methods used are strain measurement and ultrasonic testing. The change of strain, stiffness and ultrasonic pulse velocity in the fatigue process is discussed. Results disclose a deeper insight into the damage process under cyclic loading of high-performance concrete and contribute to improve nondestructive monitoring.
Ultra high performance concrete (UHPC) is characterised by its high compressive strength of more than 150 MPa and its high durability. Due to thermal treatment at 90°C a strength comparable to the 28-days-strength can be achieved immediately after the treatment and in some cases can be even further increased up to 30 %. The explanations for the increase in strength are the accelerated hydration of the clinker minerals and the intensified pozzolanic reaction contributing to a denser microstructure and hence, a high performance in compressive strength.
Former research shows that thermal treatment can lead to inhomogeneities in form of a visible zonation within the cross-section. The width of the margin increases with shorter pre-storage time before the thermal treatment and with omitting protective measures against desiccation during the treatment. Specimens exhibiting a zonation typically show a lower compressive strength compared to the undisturbed reference whereas changes in chemistry, mineral content and microstructure were not reported in detail.
In this study the zonation of thermally treated UHPC is investigated with respect to its chemistry, mineral composition and microstructure to allow predictions on durability and strength development. Measurements show a change in pore sizes, minerals phase composition and element distribution leading to the visible zonation and weaker bending tensile strength compared to the reference.
The low tensile strength of cement-based materials can be improved by the addition of fibres. In a joint research project, an industrial partner designed special coatings for polymer and carbon fibres by integrating surfactants and hydrophilic compounds. Aim of the developed functionalization was to ensure an even coverage of the fibre surfaces and to anchor them chemically in the cement-based matrix. Task of the BAM was to quantify the effect of the improved bond. In a first step a workable mortar adjusted to the strength of the tested fibres was developed and the fibre distribution assessed by light microscopy and computed tomography. To test the new coating for its efficiency to prevent cracking during hardening and to improve the loadbearing behaviour new test setups were developed or existing methods were adjusted.
The experiments showed that the functionalization leads to a reduction of the crack area measured after the exposure of the wet mortar to strong drying conditions in the wind channel. Regarding the Efficiency to mitigate shrinkage cracks the functionalisation turned out to be more efficient for fibres made from polyacrylonitrile (PAN) than for carbon fibres. An improvement of the tensile strength after cracking of the cementitious matrix could only be documented for the coated carbon fibres. It could be quantified, however, only in the three-point bending tests because the fibres turned out to be too brittle for the applied single fibre pull-through test.
The advantages of treating prefabricated components made of Ultra-High-Performance Concrete (UCPC) at 90 °C are largely recognized, while hydrothermal treatment at 185 °C and the corresponding saturation pressure of 1.1 MPa, in contrast, is not applied in building practice so far and was studied only by a few researchers.
In the research presented, the parameters pre-storage-time before treatment and dwell time in the autoclave were systematically varied. The results illustrate in which way compressive strength increases with the duration of treatment. Already samples which were only heated up and immediately cooled down show an increase in strength compared to the 28-day reference of about 10 %. After 20 h the maximum increase of about 25 % is reached. Interestingly the compressive strength of samples treated very long hardly decreases. It can be therefore concluded that for the composition investigated the achievable mechanical strength is not severely sensitive regarding the duration of the treatment.
Also, pre-storage times before autoclaving longer than 0.5 days showed no significant impact on strength development.
The phase composition measured by XRD exhibits significant changes compared to the reference. The amount of ettringite and portlandite have vanished, the cement clinker phases are substantially decreased and hydroxylellestadite and hydrogarnet are formed as new phases. The increase in strength can be assigned to an improved pozzolanic and hydraulic reaction. Contradictory to literature, there was found no tobermorite, a mineral which is known to be susceptible for disintegration at Long autoclaving duration. This explains why no significant strength loss appeared.
Alkali silica reaction (ASR) is a major concrete durability problem resulting in significant maintenance and reconstruction costs for concrete infrastructures all over the world. To determine whether an aggregate is potentially reactive, accelerated concrete tests are used. Aim of this study is the chemical and microstructural characterization of ASR-products formed under the performance conditions of motorway pavements and during subsequent tests on the remaining ASR susceptibility. Samples were taken from concrete motorway pavements. Some of the samples already showed first indications for beginning damages whereas others showed deteriorations only after applying a performance testing procedure for the estimation of future risk of ASR damage. In a first step ASR-products were identified by polarized light microscopy in thin sections. The reaction products where then analyzed by Raman Spectroscopy and finally the chemical composition of the ASR-products was identified by SEM with EDX.
The results indicate that most reaction products show an increasing Ca/Si-ratio with progressive crack length. If an ASR-product develops inside an aggregate and moves through the cement paste, it has a high (Na+K)/Si-ratio at the beginning which decreases with increasing distance from its place of origin. The Raman spectra of the ASR-products are characterized by two broad bands indicating specific Q-species of different amorphous gel networks. Within the scope of the analysis distinctions in the microstructure and the chemical composition of the ASR-gels were detected relating to various conditions of accelerated testing.
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.
Beton ist weltweit einer der wichtigsten Konstruktionswerkstoffe und zeichnet sich durch eine enorme Anpassungsfähigkeit an sich verändernde Anforderungen aus. Damit verbunden ist eine hohe und kontinuierlich zunehmende Komplexität hinsichtlich der Ausgangsstoffe, Rezepturen und des Herstellungsprozesses. Folglich setzt eine Ausschöpfung des technischen und umweltbezogenen Potenzials der Betonbauweise höchste Expertise bei den Einzelakteuren der Bauindustrie voraus.