Optimizing carbon sequestration and performance of concrete masonry blocks containing alkaline industrial waste

This study aims to optimize the carbon sequestration, compressive strength, and water transport properties (i.e., water absorption and volume of permeable voids) of concrete masonry blocks incorporating calcium carbide residue (CCR) as a partial cement replacement. The Taguchi design of experiments was utilized to study the influence of CCR replacement percentage, initial air curing duration, carbonation duration, and CO₂ gas pressure on the performance responses. These response criteria include CO₂ uptake, carbonation depth, compressive strength, water absorption, and volume of permeable voids. The concrete mixture proportions were then optimized for superior performance. The results highlight that a CCR replacement level of 10 % was required for optimum carbon sequestration potential, while only 5 % was optimum for superior strength and water transport properties. To maximize each performance criterion, the carbonation process parameters comprised an initial air curing duration of 20 h, a carbonation curing duration of 20 h, and a CO₂ pressure of 5 bars. Analysis of variance showed that the initial air curing duration was the most contributing factor to the CO₂ sequestration potential. In contrast, the CCR content was decisive for strength and water transport properties. Microstructural analysis unveiled that calcite formed abundantly in optimum mixes with the consumption of calcium hydroxide. Compared to a hydrated counterpart, using the optimum mix containing 10 % CCR in concrete masonry applications would emit a 31 % lower carbon footprint, sequester 50 million tons of CO₂, consume 10 % less cement, and valorize up to 23 million tons of CCR industrial waste.