The mechanical and microstructural study on the cement pastes adding various cementitious capillary crystalline waterproof materials

Cementitious capillary crystalline waterproof materials (CCCW) have been used sto improve the water-resistance properties of concrete. However, different kinds of CCCW affect concrete properties differently due to varying reaction mechanisms. In this study, the effects of four kinds of CCCWs—LD (Loudun), KE (Kelite), YST (Yuanshuitong), and SC (Schomburg)—on the microstructure and compressive strength of cement paste were investigated. The pastes were characterized using a combination of techniques including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Mercury intrusion porosimetry. The results show that LD was mainly composed of silica fume, where the active silica can improve the microstructure and compressive strength of cement paste. The addition of 0.5 % LD increased the 28-d compressive strength by 7.5 %. In contrast, SC contained organic species, which was not beneficial to cement paste's mechanical properties. The addition of SC caused higher porosity despite the low 0.5 % dose, decreasing the 28-d compressive strength from 29.5 MPa to 20.2 MPa. KE contained high levels of amorphous species with large loss on ignition values, which acted as active materials to optimize the microstructure of cement pastes. YST possessed large volumes of CaO and SiO₂, possessing a similar mineralogical phase composition to cement. The high content of Si-species in KE and YST also contributed to the improved compressive strength of cement pastes. This study demonstrated that the type of CCCW used and their dosage affected the microstructure and the mechanical properties of cement paste due to the different chemical composition and reaction mechanisms. The CCCW should be well chosen based on the application scenario by considering the balance of mechanical properties and other properties like waterproof properties.