Fast-Hardening Production of High-Strength BOFS Aggregates by High-Temperature Carbonation Curing

Accelerated carbonation is an effective means to solidify fresh granulated basic oxygen furnace slag (BOFS) aggregates while simultaneously mineralizing a considerable amount of CO2. However, accelerated carbonation of BOFS aggregates at room temperature may require a curing time of up to several days. To address this long carbonation curing time, the present work aims to utilize the high temperature of flue gas (20 wt % CO2) to shorten the curing time. Relative humidity (RH) was also optimized at different high temperatures to examine the microstructure development and mechanical properties of the BOFS aggregates. The results show that the use of elevated temperatures of 60-80 degrees C accompanied by a RH of similar to 10% was effective in enhancing the carbonation reactivity, attaining an individual aggregate strength of 3.24 MPa and a CO2 uptake of 11%. The aggregate properties cured under such optimized temperature and RH conditions for 2 h showed even better results than 4 days of carbonation at ambient temperature reported in the literature. The carbonation-induced calcium carbonate (calcite and vaterite) effectively promoted the formation of calcium silicate hydrates (C-S-H), allowing further strength improvement, attaining 4.52 MPa at 7 days. Besides that, the lower embodied CO2 (CO2 emission associated with every 1 MPa increase in aggregate strength) confirms that elevated-temperature carbonation represents a more environmentally friendly alternative to ambient-temperature carbonation.