Effects of aggregate volume content on sulfate resistance properties of cement based materials with supplementary cementitious materials

The degradation of cement-based materials with different aggregate volume contents and additions, was analyzed when they were exposed to 5 and 50 g/L Na₂SO₄ at 20 ℃. The microstructures of the corresponding cement-based materials was determined by mercury intrusion porosimetry (MIP), scanning electron microscopy backscattered electron (SEM-BSE) image, and energy dispersive spectrum (EDS) analysis. The influence mechanism of the mineral addition and the aggregate volume content on the sulfate resistance properties of cement-based materials was investigated. Results show that the addition of limestone powder (LP) causes an increase in the porosity of hardened paste, exerting an adverse effect on the sulfate-resistance ability of cement-based materials. The incorporation of high amount of slag increases the total porosity, but refines the slurry pore structure from coarse pore to finer one (>10 nm). Moreover, the addition of slag strengthens the sulfate-resistance ability of cement-based materials significantly. After corrosion by Na₂SO₄, the degradation of cement-based materials prepared with pure Portland cement or Portland cement-limestone powder binary binders is more severe as the aggregate volume content increases. However, this negative effect caused by the aggregate is less remarkable in case of the slag blended system. From the BSE image and EDS analysis, the preferable deposition of gypsum in the region close to the aggregate is the main reason for the expanded degradation of specimens with a relative high amount of aggregate.