TY - CONF A1 - Schmidt, Wolfram A1 - Weimann, Christiane A1 - Chaves Weba, Luciana ED - Schmidt, Wolfram ED - Priebe, Nsesheye Susan T1 - Influences of hydration effects on the flow phenomena of concrete with admixtures 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 such as self-compacting concrete. Today, admixture addition has become common practice in concrete technology, but the understanding of their highly complex mode of operation is extremely difficult and demands for understanding of processes within the range between nanometres and centimetres. 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. Methods are discussed that appear promising interdisciplinary tools for enhancement of the understanding of the relevant interactions that are responsible for the macroscopic flow of flowable concrete. T2 - 2nd International Conference on Advances in Cement and Concrete Technology in Africa CY - Dar es Salaam, Tanzania DA - 27.01.2016 KW - Cement hydration KW - Polymer adsorption KW - Rheology KW - Superplasticizer KW - Self-compacting concrete PY - 2016 SN - 978-3-9817502-3-2 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 79 EP - 88 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-36875 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Akindahunsi, A. A. A1 - Uzoegbo, H. Ch. A1 - Schmidt, Wolfram ED - Schmidt, Wolfram ED - Priebe, Nsesheye Susan T1 - Effect of Cassava Starch on Shrinkage Characteristics of Concrete N2 - The use of starch and its derivatives in concrete as an admixture to modify relevant properties of concrete is on the increase in recent times. It is known to modify the rheology, to affect the hydration kinetics of cement, and influence on initial and final setting time of cement. This paper examines the effect of cassava starch on concrete. shrinkage properties of concrete, with and without starch addition, were studied. Various percentages (0, 0.5, 1.0, 1.5 and 2 %) of starches by weight of cement were added to concrete mixes prepared in the laboratory. Shrinkage tests were conducted for duration of up to one year. The result show that concretes with starch additions exhibit lower shrinkage, which is an indication the addition of starch as admixture in concrete improves the ability of the concrete reduce shrinkage problems. T2 - 2nd International Conference on Advances in Cement and Concrete Technology in Africa CY - Dar es Salaam, Tanzania DA - 27.01.2016 KW - Cassava KW - Starch KW - Cement KW - Concrete KW - Shrinkage PY - 2016 SN - 978-3-9817502-3-2 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. VL - 187 SP - 196 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-36880 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram ED - Priebe, Nsesheye Susan ED - Schmidt, Wolfram T1 - Parameters controlling superplasticizer cement interactions during the casting and hardening of cement based systems N2 - Concrete of today has only little in common with the traditional concrete used a few decades ago. It has become a high performance material, which can be adjusted for high performance applications and according to ultimate user specifications. The reason for the rapid evolvement was the increasing awareness about how the rheology of concrete can be improved without negatively affecting the mechanical properties of concrete by chemical admixtures. T2 - KEYS 2015 - 1st Symposium Knowledge Exchange for Young Scientists CY - Dar es Salaam, Tanzania DA - 09.06.2015 KW - Superplasticizers KW - Rheology KW - Cement hydration KW - Setting PY - 2015 SN - 978-3-9817149-3-7 N1 - Geburtsname von Priebe, Nsesheye Susan: Msinjili, N. S. - Birth name of Priebe, Nsesheye Susan: Msinjili, N. S. SP - 31 EP - 35 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-33578 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram ED - Beushausen, Hans T1 - Application of a cusum control system for enhanced robustness of the flow properties of self-compacting concrete N2 - Control chart systems are used in quality management systems to keep production processes stable. In concrete production they are often applied for the control of the compressive strength. The most efficient control chart systems are cumulated sums (cusum), which help to observe deviations from a targeted value. Unlike alternative observation chart systems that focus on process data evaluation, cusum observations react very rapidly on systematic process changes in processes. Therefore, the cusum method is particularly suitable if immediate counteractions have to be taken, like in the case of fresh concrete properties of self-compacting concrete (SCC), which can have severe influences on the durability and mechanical strength of concrete. The rheology of SCC can be affected by an enormous variety of influencing factors, from raw material properties to handling or environmental temperature. The present study shows that regardless of the material based influencing parameter for a rheology change, a steady slump flow can be achieved only by adding supplementary superplasticizer in case of loss of flow and adding stabilising agent (ST) in case of increased flow if the respective V-mask indicates a systematic change. A reference SCC was artificially manipulated in order to achieve realistic experimental data for flowability and flowability changes due to changes in the raw material properties. The results point out that productions with applied cusum methods were capable of keeping the target slump flow deviation within approximately 1% only, while productions without applied cusum method deviated up to 14% and more from the target. T2 - fib Symposium 2016. Performance-Based Approaches for Concrete Structures. CY - Cape Town, South Africa DA - 21.11.2016 KW - Concrete KW - Self-compacting concrete KW - cusum KW - control chart KW - quality control KW - robustness PY - 2016 SN - 978-2-88394-121-2 SP - 106-1 EP - 106-10 PB - Fédération internationale du béton ( fib) CY - Lausanne, Switzerland AN - OPUS4-40976 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bessaies-Bey, H. A1 - Khayat, K. H. A1 - Palacios, M. A1 - Schmidt, Wolfram A1 - Roussel, N. T1 - Viscosity modifying agents: Key components of advanced cement-based materials with adapted rheology N2 - Viscosity modifying agents (VMAs) are essential ingredients for the production of flowable cement-based materials. This paper presents an overview of commonly used VMAs and attempts to shed some light on the underlying physics at the origin of their mechanisms of action. The main molecular parameters of VMA controlling the rheological properties of the cement pore solution are highlighted. As the mechanisms of action of VMAs in cement-based materials are closely related to their affinity with the surface of cement particles, the adsorption of the main VMA types is discussed. The effect of VMAs on flow properties and stability of cement-based materials is presented for VMAs added without any superplasticizer, and then in systems incorporating both VMAs and superplasticizers. Finally, the effect of VMAs in enhancing concrete properties to secure adequate performance of different construction applications, and perspectives for future developments of novel cement-based materials made with VMAs are showcased. KW - Viscosity modifying agents KW - Cement KW - Stability KW - Rheology KW - Working mechanism KW - Compatibility PY - 2022 DO - https://doi.org/10.1016/j.cemconres.2021.106646 VL - 152 SP - 1 EP - 20 PB - Elsevier AN - OPUS4-58396 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Paul, S. C. A1 - Ebell, Gino A1 - Van Zijl, G. P. A. G. A1 - Schmidt, Wolfram ED - Schlangen, E. ED - Sierra Beltran, M.G. ED - Lukovic, M. ED - Ye, G. T1 - Cracked and uncracked SHCC specimens under different exposure conditions N2 - This paper describes the fibre-reinforced strain hardening cement-based composite (SHCC) performance under various exposure conditions. Cracked and uncracked SHCC beam specimens were subjected to cyclic wetting and drying under chloride exposure to observe the time of depassivation and corrosion potential of the imbedded reinforcement. Two reference mortars, one of the same strength class as the SHCC (Mortar 1) and the other of high strength class (Mortar 2) were used under the same conditions. Finally, tests for determining the rapid chloride migration coefficient, electrical resistivity, capillary water absorption and freezethaw were also performed to observe the corrosion probability and diffusion rate in uncracked SHCC and mortars. T2 - SHCC3 - 3rd International RILEM conference on strain hardening cementitious composites CY - Dordrecht, The Netherlands DA - 03.11.2014 KW - Depassivation KW - SHCC corrosion crack KW - Lochkorrosion KW - Betonstahl PY - 2014 SN - 978-2-35158-150-6 SN - 978-2-35158-151-3 SP - 25 EP - 32 AN - OPUS4-32462 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Wend, Dirk A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - The influence of superplasticiser modifications on early hydration processes N2 - Self-compacting concrete (SCC) differs substantially from normal concrete as regards the quantity of superplasticiser dosage. The functionality of superplasticisers, based on the polycarboxylate ether (PCE) superplasticiser customary with SCC, is nowadays very well understood at construction material research level. However, knowledge concerning pertinent correlations does not always permeate practice to an equal extent. PCEs are extremely polymorphic as opposed to earlier superplasticiser groups, which still possess a considerable proportion of the superplasticiser market. The geometry of polymers can be adjusted individually to performance characteristics required for certain uses. Yet, in selecting a superplasticiser for its specified rheological properties, a very strong influence can equally be exerted simultaneously on the subsequent hydration process. The charge density of the PCE employed also plays a key role in connection with both rheology and early hydration. KW - Rheology KW - Early cement hydration KW - Polycarboxylate ether vicat KW - Shrinkage PY - 2012 SN - 1437-9023 VL - 4 SP - 64 EP - 69 PB - ad-media-Verl. CY - Köln AN - OPUS4-26355 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Shamsuddoha, Md A1 - Hüsken, Götz A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Baeßler, Matthias ED - Alexander, M.G. ED - Beushausen, H. ED - Dehn, F. ED - Moyo, P. T1 - Workability and mechanical properties of ultrafine cement based grout for structural rehabilitation: A parametric study on the partial replacement with SCMs N2 - Grouting is a universal repair and strengthening technique, which is constantly used for structural remediation of concrete components, trenches, mine subsidence, dam joints, restoration of masonry structures, and geological stabilizations. Having an extremely small particle size of only few microns, ultrafine cements are ideal for grouting applications due to their superior permeability and compressive strength properties of the hardened cement paste compared to that of the less-expensive, but coarser ordinary Portland cements. Supplementary cementitious materials (SCMs) are often used to replace ultrafine cement in order to modify certain properties and to reduce costs. The aim of this experimental study is to investigate the effect of three supplementary materials: microsilica (MS), fly ash (FA), and metakaolin (MK) on the workability, and mechanical properties of an ultrafine cement based grout with a constant water-binder ratio and constant superplasticizer content. Maximum percentages of replacement with ultrafine cement were 6% by volume of cement for MS and 16% for FA, and MK. In general, results suggest that the workability is improved by addition of FA, whereas is reduced, when modified with MS and MK. The compressive strength of grout after cement replacement remains comparable to that of pure cement grout. However, there is a tendency of the MS to positively affect the compressive strength opposite to FA, whereas flexural strength is positively affected by FA. Based on the results, it is evident that grouts with Hägerman cone flow more than 500 mm and compressive strength of more than 90 MPa after 28 days can be produced. T2 - International Conference on Concrete Repair, Rehabilitation and Retrofitting (ICCRRR 2018) CY - Cape Town, South Africa DA - 19.11.2018 KW - Grouting KW - Repair KW - Box-Behnken KW - Supplementary cementitious materials KW - Analysis of variance PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-464769 DO - https://doi.org/10.1051/matecconf/201819907006 SN - 2261-236X VL - 199 SP - 07006-1 EP - 07006-7 PB - MATEC Web of Conferences AN - OPUS4-46476 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zhang, K. A1 - Schmidt, Wolfram A1 - Mezhov, Alexander T1 - Influence of the hydroxypropylation of starch on its performance as viscosity modifying agent N2 - Synopsis: Starch is a commonly used viscosity modifying agent (VMA). The performance of starch as VMA depends on its origin (e.g. potato, corn, cassava, etc.) and corresponding molecular properties, such as molecular weight, ratio between amylose and amylopectin etc. Depending upon the application, the efficiency of starch can be enhanced by hydroxypropylation. The maximum degree of substitution (DoS) cannot be greater than 3.0, which is the number of hydroxy groups per glucose monomer in the polymer. In the current research three potato starches exhibiting the DoS of 0.4, 0.6 and 0.8 were utilised. The influence of the modified starch on the rheological properties and hydration of cement paste, as well as the viscosity of the pore solution were investigated. Our findings show that the starch with the highest DoS increases the dynamic yield stress the most, while the plastic viscosity is less dependent on the DoS. Additionally, starch with the highest DoS retards hydration to lower degree than other starches. T2 - 13th International Conference on Superplasticizers and Other Chemical Admixtures in Concrete CY - Milan, Italy DA - 10.07.2022 KW - Potato starch KW - Rheological KW - Cement hydration KW - Pore solutions PY - 2022 DO - https://doi.org/10.14359/51736074 VL - 354 SP - 209 EP - 218 PB - ACI Special Publications AN - OPUS4-58320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Sturm, Patrick A1 - Gluth, Gregor A1 - Schmidt, Wolfram A1 - Astorg, Adéle A1 - Kühne, Hans-Carsten A1 - Brouwers, H.J.H. T1 - Rheological properties of microsilica and sodium aluminate based one-part geopolymers compared to ordinary Portland cement T2 - 5th International Conference Non-Traditional Cement & Concrete CY - Brno, Czech Republic DA - 2014-06-16 KW - Alkali-activated binders KW - One-part geopolymers KW - Rheology PY - 2014 SN - 978-80-214-4867-4 SP - 71 EP - 74 AN - OPUS4-31159 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -