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In order to improve dimensional stability of cementitious materials, synergistic effect of shrinkage reducing admixtures (mixture of glycol ethers and siloxane, SRA) and MgO-based expansive agent (MEA) burned at 850, 950, 1050 and 1200°C (1560, 1740, 1920, and 2190°F) for 1 h on the deformation of cement paste cured in water and sealed by polyethylene sheet at 20, 40 and 60°C (68, 104, and 140°F) was investigated. The results illustrated that combined use of MEA(850~950) and SRA could compensate the shrinkage of cement paste effectively, MEA also could make up for the shortage of SRA whose shrinkage-reducing ratio decreased at later age. Then hydration of MEA in the present of SRA was examined by DSC/TG and gravimetry. The results indicated that the presence of SRA retarded the hydration of MEA because SRA decreased the polarity of solvent and adsorbed on the surface of MEA, but with prolonged curing, the hydration degree of MEA with or without SRA tended to be the same.

The implementation of cement materials is improved by the addition of a polymer called a superplasticizer. In this presentation, we look for the impact of the polymer architecture on the physico-chemistry properties of cement slurries. Initially, we focus on the adsorption of sodium polymethacrylate grafted by poly(ethylene oxide) chains on different types of cement using macroscopic and microscopic techniques. Finally, we measure the fluidity of different cement slurries with the use of new tools such as helicoidal ribbon geometry to explain how polymer architecture controls the performance concrete formulations.

Ultra-high-performance concrete (UHPC) possesses a very low watercement ratio (< 0.25). Additionally, a large amount of fines, such as silica fume, are used to achieve optimum packing density. Because of its specific surface chemistry and higher surface area, silica fume is more difficult to disperse than cement. Previously, it was found that methacrylic acid-MPEG methacrylate ester type PCEs disperse cement effectively whereas allylether-maleic anhydride-based PCEs work better with silica fume. Apparently, PCEs with different molecular architectures are required to achieve optimum coverage of the different surfaces of cement and silica fume. Thus, a blend of methacrylate- and allylether-based PCEs used at approx. 0.5% by weight of cement is more effective than when they are utilized individually. To further enhance the performance of the formulation, sodium gluconate was introduced as a "supplemental" agent. The combination of PCE with gluconate allowed a reduction of approximately 50% in the dosage of PCE. The final blend contained 0.28% of allylether-based PCE and 0.10% of gluconate by weight of cement. A mechanistic study established that sodium gluconate adsorbs very strong on cement and to a less extent also on silica fume, whereas the allylether PCE almost exclusively adsorbs on the silica surface. Thus, the surface of cement is covered by gluconate molecules whereas the silica surface shows concomitant adsorption of both PCE and sodium gluconate molecules. The small gluconate molecules fill the space between the huge PCE molecules on the silica fume surface.

Self-consolidated concrete (SCC) is increasingly being used for both precast and ready mixed concrete applications. For ready mixed concrete, slump flow retention becomes a concern when the concrete is transported for long distance, and when delays in placing the concrete occur due to unexpected traffic problems or incomplete jobsite preparations. In this study, the performance of a special multifunctional superplasticizer is discussed that can enable SCC mixtures to have slump flow retention up to two hours without any significant extended setting properties and delay in strength gain. Furthermore, during the period of extended slump-flow, the SCC demonstrates rheological properties adequate to ensure segregation resistance once the concrete has been placed, as well as good moisture tolerance. This capability provided by the special superplasticizer formulation is expected to significantly reduce quality control operations and facilitate the successful production and placement of self-consolidating ready mixed concrete by imparting an appropriate amount of thixotropy to the SCC mixture without compromising suitable flow properties.

The combination of different type of blending materials with portland cement such as natural pozzolans, fly ashes, and slags provides high flexibility in designing concrete mixtures with several technical advantages and low cost. However, their addition influences the properties of fresh concrete and causes problems of compatibility in blended cement systems containing superplasticizers that are usually used either for reduction of water demand or for increase of workability. In this study, two of the widely used type of superplasticizers, one based on sulphonated naphthalene formaldehyde condensate (SNF) and another based on polycarboxylate polymers (PC), were tested with ten blended cement mixtures containing 20, 30, 50, or 80% portland cement replacement with one or more of the above-mentioned supplementary cementitious materials. The action of superplasticizer on cement pastes was monitored by making zeta potential, pH, and temperature measurements as well as by using DTA-TG method for determining the hydration and hardening process. Porosity and strength development were also measured at different ages. The aim of the research work was to find which type of superplasticizer was more suitable for each type of binder system. The highest reduction of water demand was achieved with polycarboxylate polymer superplasticizer. Results show that compared to the plain portland cement system, the decrease of water/binder ratio with superplasticizer addition was lower in blended cements.