TY - JOUR A1 - Schmidt, Wolfram A1 - Mota, Berta A1 - Ramirez Caro, Alejandra T1 - The action of aggregates on concrete rheology N2 - Most factors acting on concrete rheology work at an extremely small-scale level. Influencing factors in the millimetre or centimetre area are essentially restricted to sand and aggregates. The latter, however, make up 50 to 70% of the total volume of most concretes – a fact often ignored in research on controlling concrete processing properties. Whereas suitably chosen concrete admixtures and additives can influence rheology in a very targeted manner, sand and aggregates are less suitable for controlling rheology but nonetheless contribute to the rheology of the Overall system. The actions of sand and aggregate can impose themselves upon the actions of admixtures and additives and, in unfavourable circumstances, even render them redundant. For this reason, any results concerning the processability of binding agent systems can only be transferred to concrete with great care. It is important to better understand the action of sand and aggregates in order to be able to harmonise them in such a way that they complement the action of superplasticisers positively, instead of working against them. Savings on costs can also be made by this targeted fine-tuning. KW - Rheology KW - Aggregates KW - Viscosity KW - Yield stress KW - Concrete PY - 2018 VL - 3 SP - 42 EP - 49 PB - ad-media GmbH CY - Cologne AN - OPUS4-47045 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Wolfram A1 - Tchetgnia Ngassam, Ines Leana A1 - Olonade, K. A. A1 - Mbugua, R. A1 - Kühne, Hans-Carsten T1 - Plant based chemical admixtures – potentials and effects on the performance of cementitious materials N2 - While today, engineers can choose from a wide range of rheology modifying admixtures, in some parts of the world, these are difficult to access, due to their complex processing. However, alternatives can be bio‐based polymers such as polysaccharides from various sources. These are easily accessible all over the world, do not demand for complicated processing, and typically they are more sustainable than many established materials, which are crude oil‐based. The paper presents the effects of acacia gum, cassava starch and the gum of triumfetta pendrata A. Rich on the rheological performance of cementitious systems. It is shown that acacia gum can be as efficient as polycarboxylate based superplasticisers, cassava starch can reduce the yield stress slightly with little effect on the plastic viscosity, and the gum of triumfet ta pendrata A. Rich increases the thixotropy of cement pastes with plasticizing polymers significantly. KW - Polysaccharides KW - Rheology KW - Cement KW - Chemical admixtures KW - Bio-based concrete PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-476748 DO - https://doi.org/10.21809/rilemtechlett.2018.83 VL - 3 SP - 124 EP - 128 PB - RILEM S.A.R.L. CY - Paris AN - OPUS4-47674 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shamsuddoha, Md A1 - Hüsken, Götz A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Baeßler, Matthias T1 - Ternary mix design of grout material for structural repair using statistical tools N2 - Repair is an indispensable part of the maintenance of structures over their lifetimes. Structural grouting is a widely used remediation technique for concrete components, trenches, mine subsidence, dam joints, restoration of masonry structures, and geological stabilizations. A structural grout system should be injectable in narrow spaces and hence include ingredients with finer particles. Ultrafine cements are ideal for these type of demanding grouts due to their superior properties compared to that of the less expensive, but coarser ordinary Portland cement (OPC). Supplementary cementitious materials (SCMs) are often used to replace OPC clinker based binder in order to modify certain properties and to reduce costs. The most commonly used SCMs are fly ash (FA), and ground granulated blast furnace slag (GGBS). For various special applications microsilica (MS), and metakaolin (MK) are also used. Identifying the optimum replacement contents of OPC by SCMs are a challenge during the design of such grouts. The aim of this experimental study is to investigate the effect of the selected SCMs (FA, MS and MK) on the slump flow, time of efflux, viscosity, shrinkage, and compressive and flexural strength of ultrafine cement based grouts with constant water-binder ratio and superplasticizer content. The test program was formulated using Box-Behnken design principles. Maximum percentages of replacement with ultrafine cement was 6% by volume of cement for MS and 16% for FA, and MK. The results suggest that most investigated grouts have the potential to be used for structural applications. The appropriate quadratic models are then formulated through statistical tools and presented as response surfaces. The trends indicate that fly ash improves the rheological properties, whereas microsilica and metakaolin positively affect shrinkage and mechanical properties to some extent. Based on the influence of SCMs and priorities among the properties, Decision Matrix Analysis (DMA) is carried out to select the most suitable ones among the SCMs. The analysis suggests that microsilica and fly ash are more suitable as SCMs than metakaolin without affecting the properties. KW - Grouting KW - Microsilica KW - Fly ash KW - Metakaolin KW - Workability KW - Viscosity KW - Strength KW - Mix design KW - Box-Behnken KW - Decision matrix analysis PY - 2018 DO - https://doi.org/10.1016/j.conbuildmat.2018.08.156 SN - 0950-0618 SN - 1879-0526 VL - 189 SP - 170 EP - 180 PB - Elsevier Ltd. AN - OPUS4-45922 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shamsuddoha, Md A1 - Hüsken, Götz A1 - Schmidt, Wolfram A1 - Kühne, Hans-Carsten A1 - Baeßler, Matthias T1 - Long-term mechanical and shrinkage properties of cementitious grouts for structural repair N2 - Grouts have numerous applications in construction industry such as joint sealing, structural repair, and connections in precast elements. They are particularly favoured in rehabilitation of structures due to penetrability and convenience of application. Grouts for repair applications typically require high-performance properties such as rapid strength development and superior shrinkage characteristics. Sometimes industrial by-products referred as supplementary cementitious materials (SCM) are used with neat cement due to their capabilities to provide binding properties at delayed stage. Micro silica, fly ash and metakaolin are such SCMs, those can modify and improve properties of cement products. This study aims at investigating long-term mass loss and linear shrinkage along with long-term compressive and flexural strength for grouts produced from ultrafine cement and SCMs. A series of mixtures were formulated to observe the effect of SCMs on these grout properties. Properties were determined after 365 days of curing at 23oC and 55% relative humidity. The effect of SCMs on the properties are characterised by statistical models. Response surfaces were constructed to quantify these properties in relation to SCMs replacement. The results suggested that shrinkage was reduced by metakaolin, while micro silica and fly ash had positive effects on compressive and flexural strength, respectively. T2 - International Conference on Sustainable Materials, Systems and Structures (SMSS 2019) CY - Rovinj, Croatia DA - 20.03.2019 KW - Grout KW - Long-term shrinkage KW - Micro silica KW - Fly ash KW - Metakaolin PY - 2019 DO - https://doi.org/10.21809/rilemtechlett.2019.82 SN - 2518-0231 VL - 4 SP - 9 EP - 15 PB - RILEM Publications SARL CY - 4 avenue du Recteur Poincaré, 75016 Paris, France AN - OPUS4-48712 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thiedeitz, M. A1 - Schmidt, Wolfram A1 - Härder, M. A1 - Kränkel, T. T1 - Performance of rice husk ash as supplementary cementitious material after production in the field and in the lab N2 - Supplementary cementitious materials (SCM) can reduce the total amount of Portland cement clinker in concrete production. Rice husk ashes (RHA) can be converted from an agricultural by-product to a high-performance concrete constituent due to a high amount of reactive silica with pozzolanic properties if they are burnt under controlled conditions. The way and duration of combustion, the cooling process as well as the temperature have an effect on the silica form and thus, the chemical and physical performance of the RHA. Various studies on the best combustion technique have been published to investigate the ideal combustion techniques. Yet, the process mostly took place under laboratory conditions. Investigating the difference between the performance of RHA produced in a rural environment and laboratory conditions is useful for the assessment and future enhancement of RHA production, and its application both as building material, for example in rural areas where it is sourced in large quantities, and as additive for high performance concrete. Thus, the paper presents a comparison between RHA produced under rudimentary conditions in a self-made furnace in the rural Bagamoyo, Tanzania and under controlled laboratory conditions at the Technical University of Munich, Germany, with different combustion methods and temperatures. In a second step, RHA was ground to reach particle size distributions comparable to cement. In a third step, cement pastes were prepared with 10%, 20% and 40% of cement replacement, and compared to the performance of plain and fly ash blended cement pastes. The results show that controlled burning conditions around 650 °C lead to high reactivity of silica and, therefore, to good performance as SCM. However, also the RHA burnt under less controlled conditions in the field provided reasonably good properties, if the process took place with proper burning parameters and adequate grinding. The knowledge can be implemented in the field to improve the final RHA performance as SCM in concrete. KW - Rice husk ash KW - Agricultural by-product KW - Supplementary cementitious material KW - Waste management KW - Carbon dioxide emissions PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-568953 DO - https://doi.org/10.3390/ma13194319 SN - 1996-1944 VL - 13 SP - 1 EP - 17 PB - MDPI CY - Basel AN - OPUS4-56895 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, K. A1 - Mezhov, Alexander A1 - Schmidt, Wolfram T1 - Effect of Polycarboxylate Superplasticizer in Ordinary Portland Cement and Sulfate Resistant Cement N2 - Polycarboxylate superplasticizers (PCE) are the most widely used admixtures in today’s cementitious construction materials. The molecular structure has a decisive influence on the effectiveness of PCE, which also can be tailored to serve in a different cementitious system. The current study investigates the influence of the backbone charge density of PCE on the rheology, hydration kinetics, and adsorption behavior of ordinary Portland cement (OPC) and sulfate-resistant cement (SRC). The results indicate that regardless of the PCE type, OPC requires a higher amount of PCE to be adsorbed to induce changing of rheological parameters and hydration kinetics. Regardless of the cement type, the PCE with a higher charge density exhibits higher adsorption behavior, corresponding to lower viscosity measurement. Compared to OPC, SRC is more sensitive to the introduction of both PCEs and has a lower saturation dosage, indicating that SRC generally provides better workability properties regardless of the PCE. KW - Polycarboxylate superplasticizers (PCE) KW - Sulfate resistant cement (SRC) KW - Rheological KW - Adsorption KW - Cement hydration PY - 2023 DO - https://doi.org/10.1061/JMCEE7.MTENG-15033 SN - 0899-1561 VL - 35 IS - 6 SP - 1 EP - 12 PB - ASCE Libary AN - OPUS4-58244 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, K. A1 - Mezhov, Alexander A1 - Schmidt, Wolfram T1 - Chemical and thixotropic contribution to the structural build-up of cementitious materials N2 - The structural build-up of fresh cement paste is often considered as a purely thixotropic phenomenon in literature even though cementitious materials undergo a non-reversible hydration process that can have an influence on the structuration process. In the current paper a method is proposed to validate the impact of the non-reversible structural build-up. It is shown that fresh cement paste samples lose their structural gain almost completely due to thixotropy while the structural build-up due to hydration can be observed but occurs in a significantly lower order of magnitude over the course of the first hours of hydration. In addition, it is shown, that the chemical component of the structural build-up accelerates with the onset of the acceleration period of hydration, while its contribution in the entire structural build-up remains constant. KW - Thixotropy KW - Structural build-up KW - Penetration test KW - Rheological properties PY - 2022 DO - https://doi.org/10.1016/j.conbuildmat.2022.128307 SN - 0950-0618 VL - 345 IS - 128307 SP - 1 EP - 10 PB - Elsevier Ltd. AN - OPUS4-58248 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -