Enhancement of engineering properties of cement mortars with masonry construction and demolition fines via carbon dioxide utilization, storage and chemical treatment

Shortage of natural sand is severely affecting the global construction industry. The construction sector also generates a substantial amount of construction and demolition (C &D) waste of which masonry wastes constitute a major fraction. Using a circular economy approach, this article explores the feasibility of using treated masonry waste fines (MWF) to replace 75 % of natural sand in Portland cement-based mortars. The treatment consists of a combination of acid washing and CO 2 curing to improve the engineering properties of MWF-cement mortars. 0.1 mol/L and 0.5 mol/L (M) H 2 SO 4 were used for chemical treatment of the MWF followed by CO 2 curing at 50,000 ppm for 4 hours. Mortars containing treated MWF (MWF-0.1 M-C and MWF-0.5 M-C) were subject to conventional curing (moist curing followed by dry curing at 30 degrees C and 65 % RH) and carbon sequestration via accelerated carbonation curing. Experimental findings suggest that combined treatment with acid and CO 2 reduces the pore volume by 13 - 27 % in the pore size range of 10 - 100 nm in MWF. Consequently, mortars with MWF-0.1 M-C and MWF-0.5 M-C show 29 - 30.50 % higher compressive strength at 28-d age and a 29 - 36 % reduction in total shrinkage compared to mortars with similar dosages of as-received MWF. This ensures statistically similar strength and shrinkage as that of the plain mortar (with 100 % natural sand), demonstrating the potential for 75 % sand replacement using treated MWF. Furthermore, carbon sequestration of 16.40 - 19 % by mass of Portland cement is achieved, which contributes to a 15 % enhancement in early strength and reduces the mesoporous volume and shrinkage by up to 43 % and 15-19 % respectively. In summary, the research offers a pathway to recover a "new sand" from C &D wastes , which could be used to manufacture masonry construction products with reduced demand for natural sand.