Effects of Chain Transfer Agent on the Performances of Branched Polycarboxylate Superplasticizer
A branched polycarboxylate superplasticizer (BPCE) was synthesized via copolymerization of polymerizable active center, isobutenyl polyethylene glycol (IPEG) and acrylic acid (AA). To investigate the effects of chain transfer agent on the performances of BPCE, a series of BPCEs with different molecular weights were further synthesized by changing the addition amount of chain transfer agent, i.e., thioglycolic acid (TGA). The characteristic molecular structures of BPCEs were determined by Infrared Spectroscopy (IR) and viscosity method. Furthermore, the dispersing capacities and adsorption behaviors of BPCEs in cement pastes were probed. The result showed that, the paste fluidity and adsorption amount both presented a trend of first increase and then decrease with the increase of TGA/IPEG proportion, and the maximum appeared at the TGA/IPEG proportion of 0.15 (M = 96314 g/mol). The hydration products of cement pastes containing BPCEs at different curing ages were measured by X-Ray Diffraction (XRD), showing that the introduction of BPCE caused the delay of initial hydration which presented some retardation, and this trend was shown most significantly at the TGA/IPEG proportion of 0.15. The aim of this study is to suggest that moderate dosage of chain transfer agent for the synthesis of BPCE is beneficial to achieve good dispersing and adsorption effectiveness.
KeywordsBranched structure Polycarboxylate superplasticizer Effectiveness Characterization Chain transfer agent
The authors would like to acknowledge the National Natural Science Foundation of China (Grant number: 51578025), Beijing Natural Science Foundation (Grant number: 2162007), Project of Science and Technology Plan of Beijing Municipal Commission of Education (Grant number: KM201510005003) and Rixin Talent Development Project of Beijing University of Technology (Grant number: 2015-RX-L09) for financing this research work.
- 6.GB/T 8077-2012, Method for testing uniformity of concrete admixture, 2012. http://cx.spsp.gov.cn/