Affiliation: | 1. Tianjin University, School of Chemical Engineering and Technology, Tianjin, China Chongqing Fupu New Material Co., Ltd., Chongqing, China;2. Tianjin University, School of Chemical Engineering and Technology, Tianjin, China;3. Chongqing Fupu New Material Co., Ltd., Chongqing, China Contribution: Resources;4. Tianjin University, School of Chemical Engineering and Technology, Tianjin, China Contribution: Investigation |
Abstract: | Two types of slump-retention polycarboxylate superplasticizers (PC-M and PC-S) were synthesized by using 3-mercaptopropionic acid or sodium hypophosphite as chain transfer agents, the effects of polycarboxylate superplasticizers on slump-retention of cement and concrete were investigated, and the mechanism of action and the structure of polycarboxylate superplasticizers were investigated by using conductivity, complexing Ca2+ concentration, gel permeation chromatography (GPC), nuclear magnetic resonance hydrogen spectroscopy (1H-NMR), and nuclear magnetic resonance phosphorus spectroscopy (31P-NMR). The results indicated that the slump flow of cement paste mixed with PC-M was increased quickly within 60 min and then lost gradually, while PC-S increased slowly and evenly within 240 min. The slump flow of concrete mixed with PC-S reached 405 mm after 150 min, but the concrete mixed with PC-M was almost no fluidity after 150 min. The conductivity of the PC-M aqueous solution decreased quickly within 45 min, then slowly decreased, while the conductivity of the PC-S aqueous solution decreased slowly within 180 min. PC-M had a much greater complexation ability of Ca2+ than PC-S. The composition and structure of the two slump-retention polycarboxylate superplasticizers were altered by different chain transfer agents, and the hydrolysis-adsorption capacity of each component was different. The rate of hydrolyzation-adsorption of each component was PC-M3 ≈ PC-S3>PC-M1>PC-M2 ≈ PC-S1>PC-S2. The faster the adsorption rate, the faster the slump flow loss of concrete. |