Effect of high temperature and additions of silica on the microstructure and properties of calcium aluminate cement pastes

In this study different formulations of calcium aluminate cement pastes (CACP) with 51 wt% (wt% -percentage by weight) of Al2O3 (CACP 51) were made at 0.4 water to cement ratio (W/C) with additions of 0 wt%, 10 wt% and 20 wt% silica (CACP 51-0 wt%, CACP 51-10 wt% and CACP 51-20 wt%, respectively). All samples were exposed to oxidative environment for 4 h at T = 1000˚C, in a furnace under an air atmosphere. The behavior of the constituent phases according to the temperature was also studied through TGA and DTG. The characterization was done using SEM, XRF, XRD, the Williamson-Hall Model (WHM)) and FTIR. Compression, absorption, density and porosity tests were done. It is observed that: C12A7 decreases between T = 800 °C and T = 1000 °C while the quantity CA and CA2 increases, silica improves compression strength at T = 20 °C and T = 1000 °C, Silica favors the formation of C2ASH8 and avoids the conversion process of the CAC pastes. Knowledge of the behavior of the CACP added with silica between the temperatures of 20 °C and 1000 °C, is essential to understand its behavior at higher temperatures. A review of the state of the art shows an incipient literature in this aspect, for this reason this research is relevant for the refractory industry based on CACP with silica.