Cement reinforcing and toughening agent microcrystalline brownmillerite: preparation and hydration

As one of the basement phases of cement, the performance of microcrystalline brownmillerite (MB) has attracted attention for a long time. Brownmillerite and MB were prepared using different raw meals and the effects of MB on the mechanical and hydration properties of cement after replacing cement with MB at 0%, 2%, 4%, 6%, 8% and 10% by weight at a constant water/binder ratio of 0·44 (25°C) were investigated. The results showed that the optimum temperature for the preparation of brownmillerite was 1350°C (held for 100 min). The addition of MB improved the compressive strength of cement. Specimens with 4 wt% MB (M4) had the highest compressive strength and the tensile strength and toughness of M4 specimens were better than those of specimens without MB (M0). In addition, MB prepared using calcium carbonate (CCMB; elastic modulus 3150 MPa) showed better mechanical properties than MB prepared with calcium hydroxide (CHMB; elastic modulus 4002 MPa) and calcium oxide (COMB; elastic modulus 3765 MPa). A model of the strength enhancement effect of MB on a cement matrix was established. Heat of hydration test results showed that the normalised heat flow of M4 was smaller than that of M0 and the cumulative heat of mortars was in the order M0 (160·29 J) > M4 (154·07 J, COMB) > M4 (152·25 J, CHMB) > M4 (151·98 J, CCMB).