Effects of silicate impurities on fracture behavior and microstructure of calcium aluminate cement concrete

Abstract

In this paper, to accurately evaluate the effect of the variation of the silica content in Calcium aluminate cement concrete, the fracture parameters of concrete made with this cement were investigated at different substitution levels of rice husk ash (RHA), as a material containing the amorphous silica content of more than 90%. The three-point bending test was conducted on 150 notched beams with water to cement ratios (W/Cs) of 0.4 and 0.5 based on the RILEM code specifications. For all of the mix designs, the fracture parameters were determined via two different methods, i.e., the work of fracture method (WFM) and the size effect method (SEM). At W/C of 0.5, substituting RHA led to improved fracture parameters, with the maximum values seen in the mix with a substitution level of 5%. However, at W/C of 0.4, as the substitution level of RHA increased, the fracture parameters decreased. The pozzolanic property, higher specific surface area, and greater water demand of RHA relative to cement at the W/C of 0.5 (due to more free water relative to W/C of 0.4) improved the integrity, hydration, microstructure, and fracture properties of the concrete. Further, the results demonstrated that there was a significant correlation between GF and Gf (GF/Gf=2.38).