Experimental and mechanism study on the impermeability and thermal insulation of foam concrete regulated by nano-silica and fluorine-free foam

Abstract

To address the problems of the higher thermal conductivity and the lower impermeability of the existing foam concrete, the nano-silica (NS) and fluorine-free foam were introduced to regulate the foam concrete. Through a series of experiments, the compounding design of fluorine-free foam concrete (FFFC) with different NS admixtures was carried out, and the parameters such as dry density, thermal conductivity, impermeability, compressive strength, and pore structure were measured. The results show that the dry density and thermal conductivity decreased firstly and then increased with the increase of NS admixture, and the lowest dry density and thermal conductivity were 387 kg/m3 and 0.1310 W/(m·K) when the NS admixture was 1.5%. The penetration depth of water decreases in a stepwise manner overall with the increase of NS admixture, and the penetration depth of water was lowest at its admixture of 3.5%. Through the black and red binarization analysis of FFFC, it was found that when the NS admixture was less than 1.5%, the percentage of 1∼2 mm pores and porosity increased with its admixture. Analysis by SEM indicated that NS could reduce the tiny pores inside the foam concrete, increase its compactness, and contribute to the formation of a water-resistant barrier layer with more nucleated hydration sites and interwoven C–S–H structure. The synergistic effect of the proper amount of NS and fluorine-free foam can block the infiltration of external moisture and harmful ions, which improves the impermeability and thermal insulation performance of FFFC.