Study On Preparation And Properties Of Low Air-entraining Polycarboxylate Superplasticizer

Since the conventional polycarboxylic acid water reducing agent contains a long polyether structure,the air-entraining property of the water-reducing agent tends to be too large,and the problem of high air content and low strength of the concrete is easily caused.In practice,people often use mandatory measures to disperse insoluble defoamers into water-reducing agents,which brings problems of cost increase and complicated operation.In this study,we designed and synthesized a macromonomer component with a defoaming function by means of the molecular design theory of macromolecule materials and macromonomer preparation techniques,and then copolymerized with other monomers to obtain a low storage stability index.Air-based polyanhydride water reducer,and at the same time solve the problem of high air-entraining capacity and low hardening strength of the polycarboxylic acid water-reducing agent.According to the guiding ideology of the molecular design theory,the low-air-inducing polycarboxylic acid water reducer was prepared by polymerizing the defoaming functional monomer SP into the water-reducing agent molecular structure by means of the polymerization after esterification.The optimum conditions for the synthesis of low air-entraining polycarboxylic acid water reducer were as follows:the ratio of acid to alcohol was 4:1,the amount of functional monomer was 2.5%,the amount of initiator was 2%,and the temperature was 35-40°C.The SP monomer in the low air-entrained polycarboxylic acid water reducer contains hydrophobic alkyl side chains,which can reduce the surface tension of the water-reducing agent and can effectively eliminate bulky and unstable bubbles in the concrete and make the air-entraining property smaller.The test results show that the concrete air content is not more than 2%,and the compressive strength of the concrete samples at 3 days,7 days,and 28 days is higher than that of ordinary polycarboxylate water reducer without hydrophobic alkyl side chains.The principle of the low air-entraining polycarboxylic water reducer is as follows:the hydrophobic alkyl side chain in the water reducer acts on the gas-liquid interface on the one hand,eliminates unstable large bubbles in the system,reduces the gas content of the system,and bleeds air On the other hand,it acts on the solid-liquid interface and adsorbs on the surface of the cement particles.The entropy driving force increases the free water of the system,and the cement particles are further dispersed,which improves the dispersion ability of the water reducing agent.The production process of low air-entraining polycarboxylic acid water-reducing agent has mild conditions,and the raw materials used are non-toxic,harmless,and not suitable for volatilization,so it will not cause environmental pollution and conform to the national sustainable development strategy.