Preparation And Properties Of Polycarboxylic-Type Superplasticizers

Compare to the traditional water reducer, polycarboxylic superplasticizers exhibit the advantages of strong dispersing ability, high water-reducing rate, low slump loss and abroad applicability in at low base water cement ratio (w/c). On the basis of molecular design and performance design, methoxypoly(ethylene glycol) methacrylate (MPEGMA), AA-MAA-MPEGMA-SAS copolymer and AA-MAA-MPEGMA- AMPS copolymer were synthesized. Their structure, properties, applied performances and the mechanism were investigated in detail.MPEGMA is prepared through ester-interchange reaction, and the influences of catalyst, inhibitor, reaction time and the reaction temperature on the esterification are discussed. In the optimized conditions, the esterification ratio reached 92.3 %.A series of polycarboxylic-type superplasticizers(PCS), like AA-MAA-MPEGMA-SAS and AA-MAA-MPEGMA- AMPS, were synthesized through aqueous copolymerization. The factors influencing on performance of PCS, such as the dosage of initiator, the kind and dosage of chain transfer agent and sulphonate, the dosage of acrylic acid (AA) and mathacrylic acid (MAA), the class of neutralization agent and the reactive time are discussed comprehensively. The result showed that the copolymer of AA-MPEGMA-AMPS (2.93:1:1.2), prepared with 2-mercaptopropionic acid as chain-transfer agent at 85°C for 5.5h, possesses preferable properties.At the dosage of 0.3mass% and the water/cement ratio of 0.29, the original fluidity of cement paste can attain 280mm, and the setting fluidity retain as high as 260mm and 240mm after 90min and 120min, respectively. The water-reducing rate is 31.2%.The testing result of ζ, electrical potential and surface tension showed that the mechanism of polycarboxylate-type water reducer is different from that of naphthalene-type. The mostly working mechanism of polycarboxylate-type water reducer is stereo hindrance, but for naphthalene-type water reducer, it is static repulsion.