Effect of nano-silica on material properties, pore structure, and hydration of polyacrylate/cement composite paste

Abstract

Nanomaterials and polymer emulsions have their own advantages and disadvantages on the properties of cement-based materials. The innovative point of the research is the synergistic effect of nano-silica (NS) and polyacrylate (PA) in materials and the improvement of the properties triggered by the addition of NS into PA/cement composite paste. To investigate the effect of the NS dosage on the material properties of PA/cement composite paste and to find out the micro-mechanism of action of cementitious composites containing NS and PA, experimental tests of rheology, apparent bulk density, compressive strength, splitting tensile strength, capillary water absorption, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetry (TG), and mercury intrusion porosimetry (MIP) were performed. The main conclusions drawn from the experimental results are as follows: With the NS dosage increasing from 0 % to 3 %, it results in a decrease in the fluidity and an increase of both the plastic viscosity and the yield stress of the PA/cement composite paste. The addition of NS strongly reduces the porosity and improves the apparent bulk density of the PA/cement composite paste. This is consistent with the experimental findings that the compressive strength and the splitting tensile strength gradually increase with increasing NS dosage, while the capillary water absorption gradually decreases. NS expedites the heat release rate of the PA/cement composite paste during the acceleration period of the hydration process, pushes the second heat-releasing peak, and increases the peak value from 1.71 mW/g to 2.71 mW/g. And NS also elevates the cumulative heat release 120 h after mixing. Thus, it increases the production of the C-S-H gel, of calcium sulfoaluminate hydrates, and of calcium hydroxide. This can be explained by the nucleation and pozzolanic effect of NS.