In this paper, the flowability, compressive strength, hydration heat, porosity and calcium hydroxide content of cement–silica fume–fly ash-based ultra-high-strength concrete (UHSC) incorporating either nano-silica (SiO2) or nano-calcium carbonate (CaCO3) were investigated. Test results showed that the flowability of UHSC was reduced by incorporating nano-silica and nano-calcium carbonate. After incorporating nano-silica, the hydration heat flow of UHSC increased, and the hydration heat of UHSC increased at first but decreased later. For UHSC with nano-calcium carbonate, the hydration heat flow increased and the hydration heat decreased. With the increase of both nano-silica and nano-calcium carbonate content, the compressive strength of UHSC increased at first and then decreased. The porosity decreased at first and increased later with the increase of nano-silica and nano-calcium carbonate content. As regards the calcium hydroxide content, this decreased with the increase of nano-silica content, but increased with the increase of nano-calcium carbonate content.
In this research, two kinds of polycarboxylate (M-PCE and O-PCE) with the same degree of polymerization in side chains but different main chains were synthesized via a radical polymerization reaction at room temperature. Along with two commercial polycarboxylates (C-PCE-1 and C-PCE-2), their properties on adsorption, hydration, zeta potential, liquid surface tension, and flowability of cement pastes were investigated. The results showed that the adsorption of M-PCE on the surface of cement particles increased 14.1% and the adsorption rate increased 24% compared with C-PCEs. Furthermore, three polycarboxylates (O-PCE, C-PCE-1, and C-PCE-2) exhibited a delayed effect on the hydration of cement due to the shielding effect of their chain alkyl groups, meanwhile the hydration of the cementitious materials by the M-PCE was not delayed but promoted because of its incomplete hydrolysis of the siloxane. As a result of the higher adsorption amount, M-PCE with siloxane groups exhibited favorable effects in terms of zeta potential, liquid surface tension, and flowability of cement pastes.
Modified polyurethane prepolymer was prepared using the segmental synthesis method. Then, pectiniform polycarboxylate was synthesized at normal temperature in the complex initiation system of H2O2, APS, sodium bisulfite, Vc, and Rongalit according to the free radical polymerization reaction mechanism, using TPEG, AA, and PEG as raw materials and TGA as the chain transfer agent. Compared with commercial Sika polycarboxylate, its flowability, strength, drying shrinkage, and auto-shrinkage were studied. The experimental results show that the synthesized polycarboxylate could be better dispersed. Adding silica fume can enhance the compressive strength of ultra-high performance concrete (UHPC), while slag may decline its strength. By incorporating slag and silica fume, the drying shrinkage of UHPC was reduced, but its auto-shrinkage was increased.
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