Lightweight masonry units using carbon-activated steel slag and recycled wood aggregates

The incorporation of recycled wood aggregates, whether to reduce the dead load or to contribute towards sustainability, significantly affects the overall mechanical properties and results in a concrete suitable for non-load-bearing applications. To this end, this study investigated the effect of carbonation curing on the development of sustainable, load-bearing, and lightweight steel slag masonry units (SMUs) incorporating recycled wood aggregates. Masonry units were prepared with steel slag as an exclusive binder to replace cement, and with recycled wood aggregates replacing 35% and 50% by volume of crushed granite sand. Temperature and relative humidity inside the CO₂ curing chamber were monitored throughout the experiments. Compared to conventional SMUs, the carbonation of wood-SMUs is deeper and more homogeneous. Experimental results revealed that the incorporation of wood increased the CO₂ uptake potential of wood-SMUs; thereby achieving a higher degree of carbonation. The incorporation of wood resulted in reduced compressive strength; however, extended carbonation curing partially mitigated this effect. BSE-SEM tests revealed that the interfacial transition zone (ITZ) of hydrated wood-steel slag samples was highly cracked and poorly packed with hydration products, whereas the ITZ of carbonated wood-steel slag samples was devoid of cracks and densely packed with a C–S–H gel of low Ca/Si ratio and calcium carbonate precipitates.