Effect of chain transfer agents in polycarboxylate superplasticizer on slump‐retention of concrete

Abstract

AbstractTwo 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.