TY - JOUR A1 - Priebe, Nsesheye Susan A1 - Schmidt, Wolfram A1 - Mota, Berta A1 - Leinitz, Sarah A1 - Kühne, Hans-Carsten A1 - Rogge, Andreas T1 - The effect of superplasticizers on rheology and early hydration kinetics of rice husk ash-blended cementitious systems N2 - Superplasticizers (SPs) have been employed in concrete technology for decades to improve the workability of concrete in its fresh state. The addition of SPs in cement-based systems affects the early properties. Although the interaction of the cement particles with various SPs has been extensively researched, there still exists limited research on the interaction of SPs with supplementary cementitious materials such as rice husk ash (RHA). This paper investigates the rheological properties and early hydration kinetics of RHA-blended systems with three types of SPs, a polycarboxylate ether (PCE) and two lignosulphonates (LS-acc and LS-ret). In rheological properties, the addition of SP causes an initial improvement of workability as the yield stress is significantly reduced. The pastes with PCE and LS-acc show a slight increase of yield stress over time whereas pastes with LS-ret tend to lower the yield stress slightly over time, further improving the workability. Without SP, pastes with RHA show a lower yield stress but an increase in plastic viscosity as cement is further replaced with RHA. The addition of the LS SPs is observed to lower the plastic viscosity but remains constant with further replacement of cement with RHA. This indicates that LS SPs further adsorbs on RHA particles and hydration products produced causing dispersion of the particles within the system. In early hydration kinetics, pastes with PCE retard hydration and the degree of retardation is further increased with LS SPs. In the presence of RHA, the retardation of LS SP systems is significantly reduced. The pastes with PCE show more ettringite in the SEM micrographs, but is observed to be shorter needles. This indicates an initial good workability for PCE. However, C-S-H and CH were observed to be low in quantity, whereby the pastes with LS show more nucleation sites for C-S-H and CH. The ettringite needles in the LS systems were similar in quantity and more elongated in some cases but not abundant as in the PCE systems. KW - Plastic viscosity KW - Cement KW - CO2 reduction KW - Supplementary cementitious materials KW - Rice husk ash KW - Superplasticizers KW - Hydration KW - Rheology KW - Yield stress KW - Slump flow PY - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0950061817310978?via%3Dihub DO - https://doi.org/10.1016/j.conbuildmat.2017.05.197 SN - 0950-0618 SN - 1879-0526 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. VL - 150 SP - 511 EP - 519 PB - Elsevier Ltd. AN - OPUS4-41036 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Promising bio-based material solutions for more sustainable concrete N2 - Today, concrete engineers can vary consistencies between very stiff and self-compacting. At the same time engineers can opt for a vast variety of binders. The possibility to use optimised mineral binders and to tailor rheological properties of concrete eventually opened up the path to multiple new technologies, where design criteria are no longer limited to the Young’s modulus and the compressive strength, but often comprise additional added value. It can therefore be concluded that the capability to control the rheology and the interactions particles can be considered as the catalyst for concrete innovations such as polymer modified cementitious composites (PCC) self-compacting concrete (SCC), high-performance concrete (HPC), ultra-high performance concrete (UHPC) or strain hardening cement based composites (SHCC). In the same way rheology modifying additions, SCMs and admixtures will become key parameters in mastering the challenges of the next decades such as: - Additive manufacturing/3D-printing - Overcoming pumping height limitations - Casting at extreme temperatures - Tailored rheology at delivery In many regions in the Southern hemisphere the effective use of SCMs, additions and chemical admixtures for concrete could significantly contribute to solve problems induced by the challenging climatic conditions, but particularly in many countries with challenging climatic conditions, it is difficult to use them, due to lacking local supply and supply infrastructure, and often the awareness of the value of local mineral resources is missing. However, the long distance transportation of mineral resources and chemicals is not very environmentally friendly and the economic consequences are dramatic. However, bio-based constituents and chemicals have been used in construction for ages effectively. Due to the enormous relevance of binders, fillers and rheology modifying admixtures it is worthwhile to recollect that nature provides an enormous variety of products that can be used readily or with low processing. Today, the use of petrol based polycarboxylate ether superplasticizers has become quite common in concrete technology due to their versatility, but their uncomplicated and cost efficient availability is limited in many countries in the world. However, alternatives are available, which can be found locally. In addition many agricultural wastes today are dumped, although they could be converted to reactive ashes easily. Plant extracts have been used to modify the properties of concrete for long time. These plants are typically regionally abundantly available, cheap, and they are environmental friendly. They do not require special caring for seedlings, weeding or manuring to grow since they grow wildly. The talk will present an overview of various options for binders, fillers and rheology modifying admixtures, that can be found in nature, and that may become a real alternative, once their interaction within the complex cementitious system is well understood. T2 - Peak Forum on Sustainable Civil Engineering Materials CY - Shanghai, China DA - 18.05.2017 KW - Cement KW - Concrete KW - Sustainability KW - Bio-based materials KW - Polysaccharides KW - Supplementary cementitious materials PY - 2017 AN - OPUS4-41031 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Influence of nano scale effects on the macroscopic rheology N2 - Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The present study discusses fundamental mechanisms at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation, and links these effects to macroscopic flow phenomena. Based on the observations of the nano scale effects, it seems that higher sensitivity against variations in the constituents, the handling, or the boundary condition are the inevitable price for higher performances. However, eventually a very effective method is introduced that helps to maintain stable processes regardless of the root cause for performance changes based on an efficient in-situ process control scheme and superplasticizer and stabilising agents as counter actions. T2 - International Workshop on Nano-Engineered Meta-materials for Civil Infrastructures CY - Jinan, China DA - 20.5.2017 KW - Rheology KW - Meta materials KW - Nano engineering KW - Admixtures KW - Cement KW - Ettringite PY - 2017 AN - OPUS4-41032 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Barthel, Maria A1 - Vogler, Nico A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten T1 - Outdoor performance tests of self-cooling concrete paving stones for the mitigation of urban heat island effect N2 - Rising temperatures worldwide pose an increasing challenge for safe and healthy living conditions. Particularly inner cities have been affected by these environmental changes because of the materials used to build houses, streets and infrastructure. The most common building material is concrete. It shows a specific heat capacity, while the heat conductivity for Standard concrete is low. Thus, the use of concrete generates a high capacity of heat storage. In addition, extensive soil sealing also contributes to the temperature rise of inner city areas compared to their surroundings. To mitigate this so-called urban heat island effect, a self-cooling concrete paver was developed. This paver is able to store water. The evaporation of the water at elevated temperatures provides a cooling effect. This paper focuses on determination of this new paver’s capability to cool the surface and the surrounding. The new paver’s cooling Qualities were analysed in a series of laboratory tests. To prove the results outside of laboratory conditions, two fields (12 m × 8 m) with self-cooling and reference pavers were installed in Spain. This paper presents and discusses the results of the tests. Correlation between reduced surface temperature of the self-cooling concrete pavers and the air temperature is examined. KW - Urban heat island KW - Concrete paving stone KW - Self-cooling KW - Performance tests KW - Hitzeinsel KW - Betonpflasterstein KW - Selbstkühlend KW - Nachweis der Wirksamkeit PY - 2017 DO - https://doi.org/10.1080/14680629.2016.1163282 SN - 1468-0629 SN - 2164-7402 VL - 18 IS - 2 SP - 453 EP - 463 AN - OPUS4-35741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - RPRT A1 - Schmidt, Wolfram A1 - Tchetgnia Ngassam, Ines Leana ED - Schmidt, Wolfram ED - Tchetgnia Ngassam, Ines Leana T1 - Cement proficiency testing scheme 2016/2017 - Final report N2 - The cement proficiency testing (PT) scheme was set up by the German Metrology Institute (PTB) and the Federal Institute for Materials Research and Testing (BAM) in 2012. The PT scheme was a spin-off from a European Commission and African, Caribbean and Pacific-Group of States funded project entitled SPIN – Spearhead Network for Innovative, Clean and Safe Cement and Concrete Technologies (www.spin.bam.de). The SPIN project aimed at crosslinking experts in industry and policy making bodies, with the prospect of establishing a sustainable cement and concrete construction capacity in Africa. After a successful first pan-African proficiency testing scheme in 2012/2013, it was decided to establish the scheme permanently and independent of the SPIN project. The main focus of setting up a testing scheme was to enable all cement testing laboratories in Africa to evaluate their competence and efficiency in cement testing and further enhance their capacity to obtain better quality products according to their environment. The acronym developed for the PT scheme is PACE-PTS (Pan-African Cement Proficiency Testing Scheme). The framework for the PT scheme was set up jointly among the organisers and the first participants. The first PT scheme was initiated in Dar Es Salaam in 2012 followed by a final workshop in Berlin in 2013. The second PT scheme began in 2014. A final workshop was organised in Dar es Salaam in 2015. The third and current scheme was started in 2016 and the final workshop is held in Yaoundé. KW - PACE-PTS KW - Round Robin KW - Proficiency testing KW - Cement KW - Quality infrastructure PY - 2017 VL - 3 SP - 1 EP - 74 PB - BAM CY - Berlin AN - OPUS4-43546 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Bio-adhesives and bio-chemicals from bio-mass N2 - After a brief introduction into past and modern concrete, the relevance of sustainable concrete technologies is emphasised from a global perspective. In order to minimise the environmental impact of cement and concrete in the world, solutions for alternative binder materials as well as rheology and performance modifying additives are presented based on local bio-based resources. However, the perception of bio-based constituents is typically rather negative in construction materials and its application is often limited to low-end construction. In order to show that this is not inevitable, the lecture ends with a number of case studies for the use of bio-based materials for high performance concrete applications. T2 - Sustainable Adhesives from Bio-Mass (SAB) Symposium CY - Greensboro, North Carolina, USA DA - 26.01.2017 KW - Starch KW - Bio-based materials KW - Superplasticizer KW - Ash KW - Concrete KW - Cement PY - 2017 AN - OPUS4-43544 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Challenges of the growing African cement market – Environmental issues, regulative framework and quality infrastructure requirements N2 - The African cement, concrete and construction business are growing at rapid pace. The cement sales are expected to grow tremendously until 2050. The number of newly built cement plants increases dramatically and in addition more cements are being imported from outside the continent, e.g. from Turkey, Pakistan, Indonesia, and China, driven by overcapacities in the countries of origin. This causes a high number of potentials and challenges at the same time. New cement plants can operate directly at best technological state of the art and thus incorporate more sustainable technologies as well as produce new and more sustainable products such as cements blended with sustainable supplementary cementitious materials such as calcined clays, and industrial or agricultural by products. At the same time the new variety of binding agent as well as the international imports, which are driven by price considerations, make the cement market prone to quality scatter. This puts pressure on the quality control regulations and institutions to ensure safety of construction, healthy application, and environmental safety for the population. The paper presents possible solutions to build up the rapidly increasing African cement production more sustainably than in the rest of the world as well as the related challenges and obstacles that need to be overcome. Based on experiences with a series of pan-African cement testing laboratory proficiency schemes conclusions are made on technical, regulative and political level. T2 - 2nd International Congress on Materials & Structural Stability CY - Rabat, Morocco DA - 21.11.2017 KW - Quality infrastructure KW - Round Robin KW - Proficiency testing KW - Cement KW - Africa PY - 2017 AN - OPUS4-43543 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Govin, Alexandre A1 - Schmidt, Wolfram A1 - Bartholin, M. C. A1 - Grosseau, P. ED - Amziane, Sofiane ED - Sonebi, Mohammed ED - Charlet, Karine T1 - Effect of Guar gum derivatives combined with superplasticizers on properties of Portland cement pastes N2 - Chemical admixtures allow to create a variety of fresh and hardened state properties in cementitious materials. In the case of self-compacting concrete, plasticizers or superplasticizers are introduced with the aim to decrease the yield stress and the viscosity of the materials. However, in order to prevent segregation and bleeding, and to improve the water retention of cement-based system, stabilizing agents or viscosity agents are often introduced in addition. Among these admixtures, polysaccharides are most commonly used. The aim of this study is to provide an understanding of competitive or synergetic effects induced by the combination of hydroxypropyl guar stabilizing agents (HPG) and superplasticizers on cement pastes. Two polycarboxylate superplasticizers (PCE) exhibiting different charge densities and one HPG were studied. It was found that the combination of HPG with PCE superplasticizer strongly affects the rheological behavior of cement pastes. Despite the presence of HPG, the viscosity of the pastes strongly decreased with increasing dosage of PCE until it became close to the viscosity of a cement paste with PCE only. However, the use of HPG in combination with PCE allows maintaining a significant yield stress in the cement paste compared to PCE alone. The increase in the charge density of the PCE seemed to amplify the drop of the viscosity and to reduce the gain on the yield stress induced by HPG. The results also highlight a delay in the setting-time of the cement paste by adding HPG and PCE. The delay induced by HPG is significantly lower than that generated by PCEs. However, the combination of the both kind of admixtures leads to a slightly shorter setting-time compared to the PCE alone. T2 - Second International RILEM Conference on Bio-based Building Materials, 21-23 June 2017 CY - Clermont-Ferrand, France DA - 21.06.2017 KW - Rheology KW - Cement KW - Guar Gum KW - Polysaccharide KW - Superplasticizer PY - 2017 SN - 978-2-35158-192-6 SP - 55 EP - 61 PB - RILEM Publications S.A.R.L. CY - Paris, France AN - OPUS4-43547 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram ED - Priebe, Nsesheye Susan T1 - Future civil engineering challenges - Skill requirements, new professional profiles and implementation N2 - Urbanisation, habitat, environment, infrastructure and sustainability are major global challenges of the 21st century. By planning, exploiting of resources, building, and maintaining, civil engineers and relevant adjacent disciplines have been carrying a large responsibility for the existing environmental problems. Civil engineers are responsible for 70% of all material uses in the world, and civil construction has been dominating the growth of the developing world for the next decades, with enormous impact on the global climate as well as the distribution of wealth and quality of living in the world. Today a variety of sustainable construction concepts have been developed and discussed. Recently a UNEP report was published, which provides a comprehensive overview of the challenges and potentials in the future from a scientific and industrial point of view. Sustainable solutions based on abundantly available resources (pozzolana and clay) or on renewable instead of limited industrial by-products (e.g. agricultural waste ashes) and new construction echnologies do exist. By applying, promoting and developing the implementation of the existing knowledge into real life constructions, civil engineers also hold the key for the mitigation of the global challenges. Using best practice sustainable construction solutions is particularly of highest importance in the developing world, since the implementation at an early stage creates the highest leverage for positive effects. T2 - 3rd Symposium on Knowledge Exchange for Young Scientists (KEYS) CY - Johannesburg, South Africa DA - 26.6.2017 KW - Civil Engineering KW - Cement KW - Concrete KW - Global engineering KW - Nano engineered materials KW - Sustainability PY - 2017 SN - 978-3-9818270-7-1 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. VL - 3 SP - 9 EP - 14 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-40975 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram T1 - Concrete casting robustness improvement due to active rheology control N2 - With ongoing innovation in process technology, the challenges of concrete technology are more and more focused on the rheological optimisation for these processes, since improper mixture stability or poor compaction ability negatively affect the concrete homogeneity and quality. However, along with the increasing complexity of today’s concrete mixture compositions, concrete becomes more prone to failure regarding the casting process. Variable properties of the raw materials typically cause changing workability. The reasons can be found among others in scattering water contents, physical or chemical properties of the cement or varying environmental temperatures. Robustness in the delicately adjusted rheology, however, is of utmost importance for modern and future process technology, from sprayed concrete over pumpable concrete towards 3D-printing, with regard to the long-term strength, the function and the durability. Typically, material induced changes cannot be identified easily due to the complex interactions of concrete constituents. Therefore, a precise and prompt counteraction is impossible. However, it is known that the yield stress can be controlled by addition of supplementary superplasticizer or stabilising agent. In combination with computerized process observation tools that can rapidly interpret and react on changes in the rheology, it is therefore thinkable, that only these two admixture types can adjust the rheology steadily and permanently, regardless of the actual root cause for observed macroscopic rheology change. The presentation will firstly give a comprehensive overview of effects at the interface between pore solution, particles and hydrates, which affect the rheology of fresh concrete. Secondly, ways are recommended how the rheology can be actively manipulated before eventually computerized methods are demonstrated that help to actively and rapidly assess and counteract performance scatter during steady casting processes. T2 - 2nd International Congress on Materials & Structural Stability CY - Rabat, Morocco DA - 21.11.2017 KW - Rheology KW - Control charts KW - Cusum KW - Additive manufacturing KW - Online quality control PY - 2017 AN - OPUS4-43542 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -