The Effect of Cementitious Capillary Crystalline Waterproof Materials on the Hydration, Microstructure, and Mechanical Properties of Cement Pastes

To apply the cementitious capillary crystalline waterproof materials (CCCWs) in real engineering practice, the mechanical properties and related mechanism of cement after adding CCCW are investigated in this study. By using a combination of techniques including X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry, the effect of Penetron (PNC, a kind of CCCW) content on the microstructure and compressive strength of cement with different water-to-bind (w/b) ratio were studied. The results show that the high-water content definitely decreased the mechanical properties of cement pastes. The addition of PNC appeared to play a detrimental role in the 7 d compressive strength due to the lower reactivity of PNC than cement. As the PNC content increased from 0% to 1.5%, the 28 d compressive strength of cement pastes increased despite the w/b ratio. For cement pastes with a w/b ratio of 0.50, its 28 d compressive strength increased from 24.6 MPa to 32.9 MPa. This can be attributed to the sulfate/carbonate-containing species in PNC to react with cement to form suitable ettringite. Consequently, the microstructure became denser, and porosity decreased. As PNC content increased to a further 2.5%, the compressive strength of cement pastes decreased gradually. The excessive PNC caused the excess ettringite, which destroyed the microstructure and increased the porosity of cement pastes. This study demonstrated that the PNC and its dosage affected the microstructure and the mechanical properties of cement paste. Suitable content, normally 1.5%, is recommended to apply in cement paste considering the mechanical properties despite the w/b ratio.