Experimental analysis on water penetration resistance and micro properties of concrete: Effect of supplementary cementitious materials, seawater, sea-sand and water-binder ratio

To evaluate the water penetration resistance of seawater and sea-sand concrete (SSC), this study conducts water penetration test and capillary water absorption test. And scanning electron microscope (SEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), Thermogravimetric analysis and derivative thermogravimetry (TGA-DGA) were used to reveal the micro morphology, pore size distribution, porosity and hydration products of SSC. The effects of water-binder (w/b) ratio, supplementary cementitious materials (SCMs) (fly ash (FA) and limestone and calcined clay (LC2)), and curing age on the resistance to water penetration and micro performance of SSC were studied. The results show that with the smaller the w/b ratio and the increasing of curing age, the more is C–S–H gel and the denser SSC matrix, which is beneficial to resist water diffusion. With the addition of FA, the water penetration resistance of SSC tends to decrease overall. The addition of LC2 can reduce the macro pores obviously and promote cement hydration to generate denser hydration products (C-A-S-H, monosulfate (AFm)) to fill the macropores and free water channels of the matrix and improve the water permeability of SSC. Especially, when the replacement rate of LC2 is 25%, the water penetration depth (WPD) decreases by 55.81%, 51.08%, 48.91% during the curing age of 28 d, 56 d, and 120 d, respectively. With the higher the design compressive strength of SSC, the better is the water penetration resistance. Using the data regression analysis method, the relationship between the compressive strength and the WPD of SSC was established, and the capillary water absorption with time and w/b ratio/FA content has a good non-linear function relationship, and the correlation coefficients are greater than 0.95.