Abstract
In this paper, modified polyurethane prepolymer was synthesized by the segmental synthesis method using isophorone diisocyanate (IPDI), hydroxyl-terminated silicone, and polyether glycol dimethylolpropionic acid as raw materials. After that, pectiniform polycarboxylate, of which side chains were in roughly the same polymerization degree and main chains were in different lengths, was synthesized at normal temperature in the complex initiation system of H2O2, APS, sodium bisulfite, and Vc. Then, compared with commercial Sika polycarboxylate, their applications in ultrahigh-performance concrete (HUPC), including flowability, strength, drying shrinkage, and autogenous shrinkage, were investigated. The results showed that, due to the molecular structure of polyorganosiloxane, the synthesized polycarboxylate could be better dispersed. Dosage of silica fume could effectively improve the compressive strength of UHPC, while slag had a certain negative impact on its strength. Incorporation of slag and silica fume could effectively reduce the dry shrinkage of UHPC.
Highlights
In recent years, polycarboxylate (PCE) had developed rapidly
Under the cementitious system of cement-silica fume-slag-fly ash, UHPC was prepared by using Modified PCE (M-PCE) and Sika, respectively, and the autogenous shrinkage changes in prepared UHPC are shown in Figures 10 and 11
We found that adding silica fume alone would increase the autogenous shrinkage of UHPC, which was consistent with the results in [23]. e main reasons could be listed as follows: (1) silica fume fineness was large, and its unique filling effect could refine the pore structure of cement-based materials; (2) Ca(OH)2 generated in the early stage was not well grown and very small in particle size
Summary
By changing the chemical structure of main chain, branch chain, and carboxylic acid group in polycarboxylate molecules, polycarboxylate became capable of protecting the collapse, controlling condensation, and reducing shrinkage. Polycarboxylate was commonly synthesized by the heating synthesis method, in which synthesis temperature was required to be between 60°C and 90°C or even higher and the content of synthesized polycarboxylate was relatively low, resulting in increased synthesis and marketing costs. On this basis, synthesis of polycarboxylate at room temperature had become a trend of development. By controlling the molar ratio of acrylic acid and large monomer, polyurethane-modified polycarboxylate (MPCE) was synthesized at room temperature in this work, and its application in ultrahigh-performance concrete was studied by comparing Sika high-performance polycarboxylate
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