Research progress in synthesis technology of polycarboxylate superplasticizer
Polycarboxylate water reducer (PCE) has high blending capacity and high water reduction rate (>40%), which can significantly improve the workability, mechanical properties and durability of concrete. It has become high performance or ultra high performance. One of the essential components in the design of concrete mix ratio. PCE usually consists of a main chain containing an anionic group (such as a carboxyl group, a sulfonic acid group, a phosphate group, etc.) and a side chain of a neutral graft charge. The anion is mainly adsorbed on the positively charged cement particles as an adsorption group. The surface provides electrostatic repulsion, and the side chain provides spatial repulsive force. The synergistic action of the two breaks the flocculation state between the cement particles and improves the dispersibility of the cement slurry. A variety of modified PCEs (such as side chains, grafting densities, anchoring functional groups, and backbone lengths) exhibit different effects and can be used for concretes with different performance requirements. As the quality of concrete raw materials continues to decrease and performance requirements continue to increase, PCE is more sensitive to concrete mix ratio parameters and production conditions such as cement type, water-cement ratio, operating temperature, mixing time. The incompatibility of PCE and gelling materials consisting of carboxyl and polyethylene oxide (PEO) side chains is becoming more and more prominent. Ultra-high performance concrete has higher and higher requirements for PCE performance, and a series of shrinkage and viscosity reduction PCE with high performance and high performance has emerged. PCE is mainly divided into two categories: one is a polyester type PCE synthesized by α-methoxy poly(ethylene glycol) methacrylate (MPEG-MA) by aqueous solution copolymerization or esterification/transesterification; The other type is the free radical copolymerization of α-allyl-α-methoxy or β-hydroxypolyethylene glycol ether and maleic anhydride as key monomers through bulk or aqueous solution, or isoprene oxidation. Polyether type PCE is synthesized by copolymerization of diol, acrylic acid and α-methacryloyl-α-methoxy or α-hydroxypolyethylene glycol ether. Different functional groups in PCE have different effects: the carboxylic acid group acts as a water-reducing and retarding, the sulfonic acid group acts as a dispersion, the -OH hydroxyl group acts as a retarding and impregnation wetting, while the polyethoxylated group remains in the flow. Sexual effect. The water-reducing rate of ester PCE and the ability to inhibit cement hydration are slightly lower than that of ether PCE. The free radical polymerization process is simple and the synthesis conditions are mild, but the polymerization degree is reduced due to the irreversible reaction, and the synthesis product is difficult to control. The living radical polymerization (RAFT) can prepare the block PCE with controlled molecular weight and narrow molecular weight distribution.