Deterioration of cement asphalt pastes with polymer latexes and expansive agent under sulfate attack and wetting-drying cycles

The deterioration mechanism of cement asphalt (CA) pastes used in CRTS II slab track under sulfate attack and wetting-drying cycles was investigated in this study. Two types of polymer latexes and one expansive agent were employed to discuss their effects on the sulfate attack of CA pastes. Compressive strength of CA pastes before and after corrosion was measured and an anticorrosion coefficient was calculated. Mercury intrusion porosimetry, thermogravimetric analysis and scanning electron microscopy were used to investigate the changes of corrosion products and microstructure of CA pastes. The results indicate that the sulfate attack of CA pastes under drying-wetting cycles begins from the reaction with portlandite, accompanying with the depositions of expansion products and the decalcifications of C-S-H gel. The incorporation of polymer latexes and expansive agent shows an obvious impact on the resistance of CA pastes against sulfate attack under wetting-drying cycles. At an A/C of 0.2, latex I and expansive agent both visibly reduce the anti-corrosion coefficients due to their effects on pore structure of CA pastes. By contrast, latex II decreases the coefficients at low dosages but slightly increases them at high dosages. At an A/C of 0.6, the addition of latexes and expansive agent both effectively increases the anti-corrosion coefficients. Compared to latex I, latex II brings about better resistance of CA pastes to sulfate attack. It is believed that the depositions of expansion products during corrosion in a compacted structure produce expansion stress and even microcracks, thereby decreasing anti-corrosion coefficients of CA pastes at low A/C values. In the case of high A/C values, the paste structure is difficult to be damaged due to the binding effects of asphalt membranes. Hence, the anti-corrosion coefficients are increased by adding polymer latexes and expansive agent.