Effect of Sulfates on Dispersity of Polycarboxylate Superplasticizer and Its Mechanism

Abstract:

In order to investigate the effect of sulfates on the dispersibility of polycarboxylate superplasticizer and its mechanism, different kinds of sulfates with various contents were added into cement paste mixed with polycarboxylate superplasticizer. By fluidity test and Marsh time test, the effect of sulfates on the flowability of cement paste was studied. Furthermore, the rheological properties of cement paste were investigated through the rheometer, the zeta potential of cement paste was investigated through the zeta potential measurement analyzer, the competitive adsorption between sulfates and polycarboxylate superplasticizer was investigated through ultraviolet spectrophotometry, and the flocculent structure of cement paste was observed through optical microscope, respectively. The results indicate that alkali sulfates (Na2SO4 and K2SO4) have great influence on the dispersibility and retentivity of polycarboxylate superplasticizer; with the increase of dissolution of alkali ions, the competitive adsorption of sulfate ions enhances. Meanwhile, the absolute value of zeta potential decreases due to the destroyed double electrode layer. In this way, the electrostatic repulsion of cement particles is weakened and the flocculation structure becomes stronger. At a certain shearing rate, less degree of flocculation structure is damaged, leading to the decrease of rheological properties in cement paste.

Key words:polycarboxylate superplasticizer; sulfates; zeta potential; competitive adsorption; flocculent structure