Durability of cement mortar under sulphate partial immersion based on a novel hydrophobic agent

In this paper, a hydrophobic mortar using the ordinary Portland cement and new hydrophobic agent was tested, which could be applied in the coastal engineering, bridge engineering, salt lake or underground engineering to improve the durability in harsh environments. A series of experiments were conducted to investigate the effects of the mass fraction of hydrophobic agent on the durability of the mortar under partial sulfate immersion. The mass loss rate, the linear expansion rate, the compressive performance, and the microstructure of the mortar specimen were evaluated. In addition, the X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) were applied to further analyze the modification mechanisms of the hydrophobic agent on the resistance of mortar to sulfate attack. According to the analytical results, the optimal hydrophobic agent mass fraction wass 5 %, the hydrophobic agents slightly prolonged the setting time and mildly increased the standard consistency water consumption. As the hydrophobic agent mass fraction increased from 0 % to 5 %, the water absorption and loss decreased by 68.6 % and 27.3 %, the mass loss rate of the specimen decreased from 1.79 % to 0.27 %, and the linear expansion rate decreased from 0.019 % to 0.005 %. The hydrophobic agent played a role in reducing the rate of the water absorption and desorption, resulting in a weak entry of sulfate and erosion product generation. Finally, an empirical prediction model for the relationship between compressive strength of the mortar and hydrophobic agent was proposed. The empirical model showed a linear law of first increasing and then decreasing, and the fourth month was the inflection point of the model.