Synthesis And Performance Of Polycarboxylic Superplasticizers

Compare to the traditional water reducer, polycarboxylic superplasticizers were attracted much attention because of their small dosage, excellent ability of water reducing, and preventing the slump loss of concrete. On the basis of molecular design, methoxypoly(ethylene glycol) methacrylate (MPEGMA) macromer, and the copolymer of AA/MAA/AMPS/MPEGMA/EA/DEM have been synthesized in this paper. Their dispersing performance and the mechanism were investigated in details.The MPEGMA was prepared through transesterification with methyl methacrylate(MMA) and MPEG, and the structure of MPEGMA was characterized by mean of FTIR. The influences of catalyst, inhibitor, reaction temperature and reaction time on the transesterification yield were discussed in details. At the inhibitor dosage of 0.27wt% and the MPEG/catalyst mole ratio of 4, conducted for 6h at 87℃, the yield of MPEGMA was 98.8%.The high-performance water reducing agent was prepared through solution copolymerization with acrylic acid (AA),α-methylacrylic acid (MAA), 2-acrylamido-2-methyl propane sulfonic (AMPS), diethyl maleate(DEM) and MPEGMA, and its structure was characterized by mean of FTIR. The influences of initiator, sulphnate, acrylic acid and diethyl maleate on dispersing performance were discussed in details. It indicated that diethyl maleate help to reduce the slump loss. The results show that the copolymer of AA/MAA/AMPS/MPEGMA/EA/DEM mole ratio of 4.16:2.08:1:1.88:0.66:0.82, the APS dosage of 6.4w%, the mercaptopropionic dosage of 0.22wt%, possesses preferable properties. On cement grout, the fluidity of cement grout can reach as high as 275mm by adding the neat copolymer 0.3% and used water/cement ratio 0.29, which there was not slump loss within 120 minutes.The dispersion mechanism of polycarboxylic superplasticizers was investigated. Results indicate that for naphthalene-type water reducer,electrostatic repulsion plays an important part. But for polycarboxylic superplasticizer, with the action of electrostatic repulsion and steric hindrance, the steric hindrance plays the important part.