TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Interactions of polysaccharide stabilising agents with early cement hydration without and in the presence of superplasticizers JF - Construction and Building Materials N2 - Polysaccharides are incorporated into cement based Systems in order to modify the rheological properties. Typically, cellulose ethers, sphingan gums, guar gum or starch ethers are applied. Depending upon their chemistry, molecular architecture, and adsorption tendency, polysaccharides interact differently with the entire cementitious system. Some stabilising agents like diutan gum mainly affect the cementitious paste; other stabilising agents like starch tend to interact with the sand fraction and even with the coarse aggregates. Cellulose and guar gum shows more diverse performances. Typically stabilising admixtures like polysaccharides are used, when sophisticated rheological properties are adjusted. Therefore, polysaccharides are often used in combination with superplasticisers, which are added to reduce the yield stress of concrete. This can cause interactions, particularly when the stabilising Agent shows a strong tendency to adsorb on particle surfaces. Adsorptive stabilising agents may reduce the amount of adsorbed superplasticisers, thus affecting both viscosity and yield stress, while non-adsorptive stabilising agents mainly affect the plastic viscosity independently of the superplasticiser. Due to the strong influence of superplasticisers on the yield stress, influences of the stabilising agent on the yield stress retreat into the background, so that their major effect is an increase of the plastic viscosity. The paper provides a comprehensive overview of how different polysaccharide superplasticisers affect cementitious flowable systems and points out the challenges of the combined use of polysaccharides and superplasticisers. Based on rheometric experiments and observations of the hydration process, time dependent effects on the workability as well as of the hydration of cement are presented and discussed. KW - Concrete KW - Polysaccharides KW - Rheology KW - Stabilising agents KW - Starch KW - Sphingan PY - 2017 DO - https://doi.org/10.1016/j.conbuildmat.2016.11.022 SN - 0950-0618 SN - 1879-0526 VL - 139 SP - 584 EP - 593 PB - Elsevier AN - OPUS4-40597 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 (Proceedings) 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 - TY - JOUR A1 - Schmidt, Wolfram A1 - Sonebi, M. A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Rheology modifying admixtures: The key to innovation in concrete technology - a general overview and implications for Africa JF - Chemistry and Materials Research N2 - 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. KW - Rheology KW - Admixtures KW - Concrete KW - Superplasticizers KW - Polycarboxylate ether KW - Viscosity modifying agents PY - 2013 SN - 2224-3224 SN - 2225-0956 VL - 5 SP - 115 EP - 120 PB - International Institute for Conservation of Historic and Artistic Works CY - New York, NY, USA AN - OPUS4-30948 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Influences of superplasticizer modification and mixture composition on the performance of self-compacting concrete at varied ambient temperatures JF - Cement & concrete composites N2 - 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. KW - Polycarboxylate ether KW - Temperature KW - Rheology KW - Mixture composition KW - Self-compacting concrete PY - 2014 DO - https://doi.org/10.1016/j.cemconcomp.2013.12.004 SN - 0958-9465 SN - 1873-393X VL - 49 SP - 111 EP - 126 PB - Elsevier CY - Barking, Essex AN - OPUS4-30552 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Effects of the characteristics of high range water reducing agents and the water to powder ratio on rheological and setting behavior of self-consolidating concrete JF - Advances in civil engineering materials N2 - 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. KW - Polycarboxylate KW - HRWRA KW - Robustness KW - Rheology KW - Self-consolidating concrete PY - 2014 DO - https://doi.org/10.1520/ACEM20130094 SN - 2165-3984 VL - 3 IS - 2 SP - 1 EP - 15 PB - ASTM International CY - West Conshohocken, Pa., USA AN - OPUS4-30388 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Sonebi, M. A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit ED - Diouri, A. ED - Khachani, N. ED - Alami Talbi, M. ED - Ait Brahim, L. ED - Bahi, L. T1 - Rheology modifying admixtures: The key to innovation in concrete technology - a general overview and implications for Africa T2 - CMSS 2013 - International congress on materials & structural stability - Building up sustainable materials & constructions (Proceedings) N2 - 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. T2 - CMSS 2013 - International congress on materials & structural stability - Building up sustainable materials & constructions CY - Rabat, Morocco DA - 27.11.2013 KW - Rheology KW - Superplasticizers KW - Stabilising agents PY - 2013 SN - 978-9954-32-689-3 SP - 1 EP - 6 AN - OPUS4-30040 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - The working mechanism of starch and diutan gum in cementitious and limestone dispersions in presence of polycarboxylate ether superplasticizers JF - Applied rheology N2 - 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. KW - Cement KW - Limestone KW - Rheology KW - Stabilising agent KW - Coarsely dispersed systems KW - Diutan gum KW - Starch ether PY - 2013 DO - https://doi.org/10.3933/ApplRheol-23-52903 SN - 1430-6395 SN - 0939-5059 VL - 23 IS - 5 SP - 52903-1 EP - 52903-12 PB - Kerschensteiner CY - Lappersdorf AN - OPUS4-29932 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit ED - Roussel, N. ED - Bessaies-Bey, H. T1 - A simple test method to assess the influence of PCEs on the rheology of flowable cementitious systems T2 - 1st international RILEM conference on rheology and processing of construction materials and 7th RILEM conference on self-compacting concrete (Proceedings) N2 - Today’s 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. T2 - 1st international RILEM conference on rheology and processing of construction materials and 7th RILEM conference on self-compacting concrete CY - Paris, France DA - 02.09.2013 KW - Adsorption KW - Polycarboxylate ether KW - Rheology KW - Slump flow PY - 2013 SN - 978-2-35158-137-7 IS - Chapter 2.1.1 SP - 1 EP - 8 AN - OPUS4-29929 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Brouwers, H.J.H. A1 - Kühne, Hans-Carsten A1 - Meng, Birgit T1 - Influence of environmental temperatures on the performance of polymeric stabilising agent in fresh cementitious materials JF - Key engineering materials N2 - 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. KW - Biopolymers KW - Cementitious materials KW - Polycarboxylate ether KW - Rheology KW - Setting KW - Stabilising agent KW - Starch ether KW - Self-compacting concrete KW - Superplasticizer PY - 2011 DO - https://doi.org/10.4028/www.scientific.net/KEM.466.97 SN - 1013-9826 VL - 466 SP - 97 EP - 104 PB - Trans Tech Publ. CY - Aedermannsdorf AN - OPUS4-22853 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Meng, Birgit A1 - Brouwers, H.J.H. ED - Aguiar, J. B. ED - Jalali, S. ED - Camoes, A. ED - Ferreira, R.M. T1 - Influence of ambient temperature conditions on the effect of stabilising polymers in cementitious building materials T2 - ICPIC 2010 - 13th International Congress on polymers in concrete (Proceedings) T2 - 13th International Congress on polymers in concrete - ICPIC 2010 CY - Funchal-Madeira, Portugal DA - 2010-02-11 KW - Stabilising agent KW - Polycarboxylate ether KW - Polysaccharides KW - Starch ether KW - Biopolymers KW - Rheology KW - Setting PY - 2010 SN - 978-972-99179-4-3 SP - 241 EP - 248 CY - Funchal-Madeira, Portugal AN - OPUS4-21971 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -