Effects of incorporated silane on mechanical and water absorption properties of sulphoaluminate cement mortar

In this paper, the hydrophobic modification of sulphoaluminate cement (SAC) mortar was carried out by adding silane to improve its durability in harsh environments such as the ocean. Firstly, the setting time and hydration exothermic behavior of SAC paste with different saturation of silane were analyzed, and the influence of silane content on the mechanical and water absorption properties of SAC mortar at different ages was systematically investigated. The mechanical and water absorption evolution mechanism of silane-doped SAC mortar was further discussed based on the results of Mercury Intrusion Porosimetry, scanning electron microscope, X-ray diffraction and surface moisture contact angle tests. Finally, the evolution law of interface shear strength between SAC mortar with different silane contents and old mortar substrates with different water saturation was investigated. The results show that the SAC pastes with different silane contents still possess quick-setting characteristics, and its rapid exothermic stage is concentrated within 2 hours after water mixing. The incorporation of silane (0.5%~2% of cement in mass) has a certain negative effect on the compressive strength of SAC mortar, but can improve its flexural strength at the age of 28 d. The capillary water absorption coefficients of SAC mortar specimens incorporated with silane are reduced by 71.0%~94.2% compared with specimens without silane at the age of 1~28 d. The incorporation of silane does not cause a significant increase in the porosity of SAC mortar, but increases the volume fraction of capillary pores with a diameter greater than 50 nm and the content of hydration products. The increase of silane content in SAC mortar leads to the increase of its surface water contact angle and further reduces its capillary water absorption properties. At the age of 3d, the interface shear strength between SAC mortar and substrates increases with the increase of silane content, and decreases with the increase of the saturation of substrates. The SAC mortar with silane still have low water absorption properties after bonding to substrates with different saturation.