Polycarboxylic Superplasticizers And Their Mechanism

Polycarboxylic superplasticizers had been increasingly widespread concern because of their high water reducing rate, high security collapse, high increase, cement adaptability, safety and environmental protection. In this paper a kind of macromer, methoxy poly (ethylene glycol) methacrylate (MPEGMA) was synthesized with methoxy poly(ethylene glycol) (MPEG) which molecular weight was1100 or 600. A kind of Polycarboxylic superplasticizer had been synthesized with MPEGMA, AA, MAA and AMPS, and their structure, properties and adsorption characteristics were investigated in details.The MPEGMA was prepared through transesterification with methyl methacrylate and methoxy poly(ethylene glycol). Comb-type Polycarboxylic superplasticizers (PC) were synthesized by solution copolymerization with MPEGMA and other monomers. The structure of MPEGMA and PC were characterized by mean of FTIR. A series of influence on the fluidity of cement paste, such as copolymer structure, macromer addition, initiator dosage, neutralization degree of AA, MPEGMA1100/MPEGMA600 ratio, AA/MAA ratio and neutralization agents, was studied. The influence of side chain composition on the strength of cement mortar and hydration process had been researched as well.It indicated that, there was a synergetic effect between long MPEG graft chains and the short ones like MPEG1100 and MPEG600, respectively. Short chains increased the adsorption capacity and adsorption stability of superplasticizer on the cement and long chains provided great steric hindrance. The combination could ensure absorption and the steric hindrance. When the molar ratio between MPEGMA1100 and MPEGMA600 was 1/0.2, it showed high dispersion efficiency. When the mole dosage of initiator was 5%, the mole ratio of AA/MAA was 1/1 and using ethanolamine as neutralization agents, at a water/ cement ratio (w/c) of 0.29 with the PC dosage of 0.30mass% (as solid component), the fluidity of cement paste could attain as high as 330mm. After 120 minutes, the fluidity of cement could retain 220mm.PC on the hydration process of cement mortar was discussed by ultrasonic test signal of continuous mortar. The results showed that the superplasticizer with length and short PEG side chains could be better able to extend the initial setting and final setting time of cement mortar. PC could better guarantee the cement mortar 3d, 7d, 28d of compressive strength and flexural strength, which were much better than superplasticizer with a single PEG side chain and SNF. On the other hand, it also showed good dispersion on the aluminate cement.Light scattering determined the hydrodynamic and average gyration radii in saline conditions were 256.4 nm and 116.0nm, respectively. It indicated that, on cement particle surface, the superplasticizer might form a kind of stable dense aggregate similar to core-shell, and the steric hindrance played an important role in controlling slump loss. The limit adsorption amount of superplasticizers on the cement was 2mg/g by using TOC. The soft matter characters of polycarboxylic superplasticizers of the pronounced responses to the weak influences were discussed through the studing of the size of the aggregates at different ionic strength and adsorption entropy on cement particles.