含白云石微粉水泥砂浆的抗硫酸盐侵蚀性能

To evaluate the effect of dolomite powder on the sulfate resistance of Portland cement, a comparative study was performed on the sulfate resistance of Portland cement mortars containing dolomite powder (limestone powder as a reference). The expansion and strength change of mortars with various replacements of dolomite powder (i.e., 10%, 20% and 30%, mass fraction) were investigated in 5% sodium sulfate solution. A method based on sulfate-resisting index for evaluating the sulfate resistance of cement with the carbonate mineral powders was proposed as well. Results indicate that the process of mortars expansion can be divided into three stages, i.e., stable period, slow period and accelerate period. The mortars with carbonate mineral powders except for the specimens with 10% dolomite powder give larger expansion than that of PC. Compared to the mortars with limestone powder, dolomite-containing mortars show a delayed start in expansion and develop a lower expansion at the same age. The difference in expansion is more pronounced with prolonging immersed immersion in Na₂SO₄ solution and the increase of the powder dosages. The mortars with carbonate mineral powders in either water or sodium sulfate solution develop a similar trend with PC, but have lower compressive and flexural strengths. The greater replacement of carbonate powders in mortars, the lower values in the strength. The strength of mortars immersed in water increases, but the strength of mortars in sulfate solution firstly increases and then decreases. Compared to the mortars with limestone powder, the mortars with dolomite powder achieve the maximum strength for a longer time and have a greater strength at later period. The sulfate resistant index at 28 d K₂₈ specified in the standard can not accurately reflect the sulfate resistance of the cement with carbonate mineral powders. The sulfate resistance index at the age of starting expansion or reducing attaining peak strength could be applied to improve the accuracy and reliability.