Abstract
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.
Highlights
Multifunctional polycarboxylate has been developed rapidly over the decades
The auto-shrinkage of ultra-high performance concrete (UHPC) prepared with mother liquor of polycarboxylate (M-PCE) or Sika is relatively smaller than that of UHPC prepared with pure Portland cement
Polyurethane-modified polycarboxylate was synthesized at indoor temperature and its applications in UHPC, including water reduction rate of mortar, flowability, strength, drying shrinkage, and autogenous shrinkage, were investigated
Summary
Multifunctional polycarboxylate has been developed rapidly over the decades. Polycarboxylate has functions such as slump protection, coagulation control, and shrinkage reduction. With the birth of polycarboxylate, preparing concrete mixtures with low water-to-binder ratio and high flowability becomes possible. Polyurethane-modified polycarboxylate was prepared at indoor temperature by controlling the molar ratio of acrylic acid to macromonomer. The content of polycarboxylate is 2% (mass ratio) of cementitious components, the water-to-binder ratio of ultra-high performance concrete is 0.18, and the sand-to-binder ratio is 1.0. According to the standard GB/T2419-2005 “Method for Measuring Fluidity of Cement Mortar,” fine sand below 2.36 mm was selected, the mass of cementitious material was 200 g, the sand-to-cement ratio was 1:1, the water-to-binder ratio was 0.18, and the polycarboxylate mother liquor content was 2%, the flowability of mortar was tested. In view of JC/T603-2004 “Test Method for Drying Shrinkage of Cement Mortar,” a group of 25 × 25 × 280 mm specimens should be formed in the drying shrinkage test of cement mortar, and the specimens should be demolded after being cured for 24 ± 1 h
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