Effect of Dry-Wet Cycles on the Transport and Mechanical Properties of Cement Mortar Subjected to Sulfate Attack

Abstract

This study deals with the analysis of the detrimental effects of a "sulfate attack" on cement mortar for different dry-wet cycles. The mass loss, tensile strength, and gas permeability coefficient were determined and analyzed under different exposure conditions. At the same time, nitrogen adsorption (NAD), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques were used to analyze the corresponding variations in the microstructure and the corrosion products. The results show that certain properties of the cement mortar evolve differently according to the durations of the dry-wet cycles and that some damage is caused to the mortars in aqueous solution. The pores fill with corrosion products, increasing the mortar specimen mass and tensile strength while reducing the permeability coefficient and pore size distribution. As corrosion proceeds, the crystallization pressure of the corrosion products increases, resulting in a 16% reduction in tensile strength from the initial value and a 2.6-factor increase in the permeability coefficient, indicating sensitivity to sulfate attack damage. Furthermore, the main corrosion products generated in the experiment are gypsum and ettringite. Application of osmotic pressure and extension of the immersion time can accelerate the erosion process.