Resistance of red clay brick waste/phosphorus slag-based geopolymer mortar to acid solutions of mild concentration

This work is devoted to the investigation of the resistance of geopolymer cement (GC) mortar based on mixture of red clay brick waste (RCBW) and phosphorus slag (PHS) in exposure to HCl and H2SO4 solutions of mild concentration. For this purpose, the GC mortar specimens were exposed to pH = 3 of each acid solution for 24 months. To prepare GC mortar, blend of RCBW and PHS was activated by water glass and NaOH and then hydrothermally cured. For comparison purpose, reference specimens were also prepared using high alumina and Portland cements. The durability of mortar specimens was evaluated by measuring the changes in compressive strength and mass as key parameters at predetermined time intervals. The structural and compositional changes of the reaction products were studied using appropriate characterization techniques. The obtained results disclosed that GC mortar exhibited an excellent acid resistance compared to reference mortars exhibiting significantly lower durability properties. The exposure to H2SO4 caused more deterioration in all specimens than the exposure to HCl owning to the adverse effect of gypsum formation, which results in the expansion and cracking of the paste matrix.