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Effect of Carboxylic Density on Sulfate Sensitivity of Polycarboxylate Superplasticizers
Yan He,Xiong Zhang,Tao Ji,Liangliang Shui 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.12
Effect of carboxylic density on sulfate sensitivity of polycarboxylate superplasticizers (PCEs) was analyzed. PCEs with different carboxylic densities were synthesized by changing molar ratio of isopropyl oxy polyethylene glycol (TPEG) macro-monomer to acrylic acid. The compositions of the self-synthesized PCEs were tested by 1H nuclear magnetic resonance spectroscopy (1H NMR), and the molecular weight was tested by size exclusion chromatography (SEC). Effects of sulfates on the adsorption-dispersing properties of PCEs and the surface charge of cement system in function of PCEs were investigated through total organic carbon (TOC) analyzer, mini-slump cone, and Zeta potential analyzer. Influence mechanisms of sulfates on the dispersing force of PCEs were evaluated through the competitive adsorption of sulfates, the aggregation of PCEs and the calcium ion concentration in pore solution. The results show that the competitive adsorption between PCE and SO42− impairs the dispersing capability of PCEs. In comparison with calcium sulfate, sodium sulfate has higher negative effects on the dispersing capability of PCEs. High amount of sulfate ions leads to the aggregation of PCEs, which further impairs the dispersing capability of PCEs. PCE with higher carboxylic density is less sensitive to the impact of sulfates.