Effect of polyacrylic acid emulsion on fluidity of cement paste

Abstract

Polymer-modified cement-based materials (PMC) have been widely applied in civil construction and municipal projects. In order to obtain deeper insight into the workability of PMC, the effect of polyacrylic acid emulsion (PAE) on fluidity of cement paste was investigated in this study. The fluidity was assessed with mini slump, and the change of Ca2+ concentration in pore solution was tested with inductive coupled plasma emission spectrometer. Zeta potential and adsorption behavior were characterized to reveal the mechanism behind the fluidity results. The results show that the effect of PAE on fluidity depends on the added dosage: dosage less than 5.0% reduces the fluidity, while the opposite is true with dosage more than 5%, which can also be indicated from the change of Ca2+ concentration in pore solution. Conductivity and X-ray photoelectron spectrometer (XPS) results demonstrate the chemical adsorption of PAE on the surface of cement particles. Dynamic light scattering (DLS) results strongly prove that the surface group of the PAE used is SO3− rather than COO−. Finally, the dispersion model was proposed to illustrate mechanism behind: with a small amount of PAE, the decline in zeta potential caused by adsorption of negatively charged PAE and the agglomeration of cement particles caused by electrostatic attraction of PAE are responsible for the reduced fluidity; while with a great amount of PAE, the negatively increased zeta potential, lubrication effect provided by non-adsorbed PAE, and filling effect of PAE are the main reason for the increased fluidity. Such results would give deeper understanding about the effect of polymer emulsion on rheology of cement paste.