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.
In this article, a new kind of polycarboxylate (M‐PCE) was synthesized at room temperature in the complex initiation system of hydrogen peroxide (H2O2), ascorbic acid (Vc) and ammonium persulfate (APS), by using polyoxyethylene allyl methyl ether (TPEG), acrylic acid (AA), polyethylene glycol (PEG) as raw materials and thioglycolic acid (TGA) as chain transfer agent. Effect of different composite initiation systems and raw material ratios were fully explored. Along with three other polycarboxylates (O‐PCE, C‐PCE‐1, and C‐PCE‐2), their properties on water reduction rate, strength, drying shrinkage and autogenous shrinkage of cement mortar were investigated. The results showed that the average performance of the prepared M‐PCE was the best when the molar ratio of AA to TPEG was 2:1 in the same situation. When the water cement ratio was 0.3 and the dosage of M‐PCE was 1%, the strength increased by 24.5%(with 10% slag), the lowest drying shrinkage and autogenous shrinkage were reduced by 21.9%(with 10% fly ash) and 60.1%(with 10% metakaolin), respectively.
In order to improve the performance of concrete, it is of great significance to have a better understanding the mechanism and main influencing factors of concrete bubble evolution under the action of polycarboxylate and air-entraining agents. In the present review, with respect to the generation, growth, stability, and rupture of concrete bubbles under the action of polycarboxylate and air-entraining agents, this paper discusses the influence of bubble characteristics on concrete performance and studies bubble regulation by air-entraining agents and polycarboxylate (PCE) superplasticizer. The results show that the acid-to-ether ratio, sulfonic acid group, ester group, and the type of air entraining agent of the polycarboxylate acid structure have a significant impact on the bubbles. The bubble size, specific area, spacing factor, and bubble content have a significant impact on the rheological properties and related mechanical properties of fresh concrete and also affect the appearance quality of concrete. The problems with the experimental methods and theoretical models of concrete bubble research were analyzed, and future research ideas were put forward.
According to the principle of radical polymerization reaction, different polycarboxylates with comb structures were synthesized. With the other two commercial polycarboxylates (C-PCE-1 and C-PCE-2), the effects of all the polycarboxylates on adsorption, hydration, zeta potential, liquid surface tension, and flowability in Portland cement were determined. Compared to O-PCE and C-PCEs, the adsorption value of M-PCE increased by 14.1% and the adsorption rate increased by 24% maximum. O-PCE, C-PCE-1, and C-PCE-2 have a delayed effect on the hydration of the cementitious materials, but M-PCE does not. Due to higher adsorption amount, M-PCE with siloxane groups has an excellent comprehensive performance of zeta potential, liquid surface tension, and flowability in cementitious materials.
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