Effect of styrene-butadiene rubber latex on the rheological behavior and pore structure of cement paste

Styrene-butadiene rubber (SBR) latex is beneficial to the workability of cement-based materials, but the mechanism remains unclear. This study aims to investigate the effect of SBR latex on the rheological property and pore structure of cement paste. The results showed that the fluidity of the modified cement-based material was improved, and a significant linear relation was obtained between the air content and the fluidity of the cement paste. The yield stress and viscosity of the paste decreased with increasing SBR latex content, and the modified cement paste exhibited shear-thinning behavior. In addition, the SBR latex can deteriorate the pore structure of the hardened cement paste at 3 days due to the hydrophobic groups easily trapping the air into the paste. Compared with that of the ordinary Portland cement paste, the number of pores (size range of 0.1 mu m-1 mu m and 10 mu m-200 mu m) in the SBR-modified cement paste was clearly increased. However, the lowest porosity was achieved at 28 days, when 2% SBR was used due to the filling effect of the hydration products and polymer particles. The throat/pore ratio and fractal dimension increased with the SBR latex content, illustrating the increasing of ink-bottle pores with a rough surface.