Influence of calcium aluminate cement (CAC) on alkaline activation of red clay brick waste (RCBW)

In this paper, the effect of calcium aluminate cement (CAC) additions on the alkali activation of red clay brick waste (RCBW) was studied at room temperature and at 65 °C. RCBW was partially replaced with CAC (0–50 wt.%) and blends were activated with NaOH and sodium silicate solutions. The compressive strength evolution was tested on mortars and the nature of the reaction products was analysed by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, microscopic studies and pH measurements. The results show that the use of CAC accelerates the activation process of RCBW so that 50 MPa were obtained in the blended mortars containing 40 wt.% CAC cured for 3 days at room temperature. CAC did not undergo normal hydration and only the C3AH6 phase was identified in the pastes blended with more than 30 wt.% CAC and cured at 65 °C, while the main reaction product was a cementitious gel containing Ca and Al from CAC.