Flue gas carbonation curing of steel slag blocks: Effects of residual heat and water vapor

To make full use of residual heat (temperature) and water vapor (relative humidity, RH) retained in flue gas, the compound effects of temperature (60–140 °C) and RH (2–60 %) of 2-hour CO2 curing on the compressive strength and CO2 fixation of basic oxygen furnace slag (BOFS) blocks were systematically investigated. The results indicated that, in general, an increase of curing temperature increased the compressive strength of the blocks. The high early compressive strength gain (31.3 MPa) at 2-hour for carbonated BOFS blocks was directly related to the microstructure densification and pore refinement due to rich formation of calcite. It should be noted that the supply of sufficient water vapor (≥40 % RH) is particularly important at high temperature (e.g. ≥ 120 °C) to offset the water loss due to water evaporation. Furthermore, under an extremely dry environment (2 % RH), the continuous flow-through of CO2 gas at high temperature not only resulted in no carbonation reaction at the outer layer of the freshly pressed blocks, but may also deteriorate the integrity of the pore structure matrix.