低温合成保坍型聚羧酸减水剂及性能研究

Synthesis and properties of slump-retaining polycarboxylate superplasticizer at low temperature

本文以新型聚氧乙烯基醚大单体GPEG、丙烯酸(AA)、以过氧化氢-抗坏血酸(H_(2)O_(2)/Vc)为氧化还原引发体系,以巯基丙酸(MPA)为链转移剂,通过自由基共聚合成了一种保坍型聚羧酸减水剂.研究了酸醚比和合成温度对减水剂分散性能的影响.研究结果得出,聚羧酸减水剂的最佳合成工艺为:n(AA)∶n(GPEG)=4∶1,H_(2)O_(2)和MPA分别占GPEG大单体总质量的0.83%和0.42%,Vc占GPEG大单体总质量的0.41%,滴加时间为40 min,反应初始温度为15℃.合成的减水剂在水灰比0.29,折固掺量0.2%时,水泥初始净浆流动度达到了320 mm,2 h后流动度可以保持在298 mm,减水率可达到25%.掺减水剂后,3 h混凝土塌落度损失仅为7.4%,表现出优异的保坍性能.

A slump retaining polycarboxylate superplasticizer was synthesized by free radicalcopolymerization with a new polyoxyethylene ether macromonomer(GPEG),acrylic acid(AA),hydrogen peroxide/ascorbic acid(H_(2)O_(2)/VC)as redox initiator and mercaptopropionic acid(MPA)as chain transferagent.The effects of acid ether ratio,synthesis temperatureon the dispersion of water reducing agent were studied.The results show that the best synthesis process of polycarboxylate superplasticizer is:n(AA)∶n(GPEG)=4∶1,H_(2)O_(2) and MPA account for 0.83%and0.42%of the total mass of GPEG macromonomer,respectively,Vc accounts for 0.41%of the total mass of GPEG macromonomer,the dropping time is 40 min,and the initial reaction temperature is 15℃.When the water cement ratio is 0.29 and the content of water reducing agent is 0.2%,the initial fluidity ofcement paste reaches 320 mm,the fluidity can be maintained at 298 mm after 2 h,and the water reducing agent rate can reach 25%.After adding water reducing agent,compared with the commercial group,the compressive and flexural strength of mortar in 28 d are increased by 12%and 7%,respectively.Moreover,the slump loss of concrete in 3 h is only 5.6%,showing excellent slump retention performance.