The potential application of cement kiln dust-red clay brick waste-silica fume composites as unfired building bricks with outstanding properties and high ability to CO2-capture

In this paper, a simple eco-sustainable approach was applied to synthesize unfired building bricks, in which cement kiln dust (CKD), red clay brick waste (RCBW), and silica fume (SF) were the main ingredients. The CKD-RCBW-SF composite was adjusted at different weight ratios of 50-50-0, 50-40-10, 50-30-20, and 50-20-30 wt%. The fabrication process included three main stages, i.e. dry blending, water mixing, and casting. Different curing conditions were applied (water, air, and CO2-gas) to assess the effect of curing type on the performance of the prepared bricks. The results demonstrated that increasing SF content caused an increase in compressive strength escorted by a significant decrease in bulk density of the hardened bricks, regardless of curing type. All over of the curing media, the hardened samples cured in water showed the highest performance. The highest 28-days compressive strength value (47 MPa) was achieved by hardened CKD-RCBW-SF composite (at a weight ratio of 50-20-30 wt%, respectively) cured in water. Unlike its effect on the physical and mechanical performances, increasing SF content negatively influenced the capability of the hardened bricks to CO2-sequestration. Specifically, the hardened bricks with no SF cured in CO2 gas for 28-days can sequestrate higher CO2 content (~75 kg/ton) compared to the hardened samples containing 30 wt% SF (~59 kg/tonne). The proposed method is not only considered as an innovative approach for mitigating CO2 emission resulted from the traditional bricks industry, but also strongly contributed to waste disposal, the conservation of the reserve of natural materials, the decrease of energy demand and processing cost, and the enhancement of the ability of the hardened bricks to CO2-capture.