Eco-friendly construction mortars for heavy metals immobilization – Effect of partial PC replacement by lignite-based fly ash and prolonged high humidity curing on physical and chemical parameters

Abstract

The study presented in this manuscript concerns the safe immobilization of heavy metals (HMs) present in fly ash (FA) from lignite combustion in Portland cement- (PC-) based blended mortars with an emphasis on the influence of prolonged high humidity curing on material properties. The performed experiments covered both the aspect of the FA-PC replacement ratio as well as the changes in structural, hygric, chemical, and mechanical parameters of the prepared composites after 28, 90, and 180 days of curing. It was shown, that the used FA shows a high pozzolanic activity, which strongly contributed to the mechanical parameters of the developed blended mortars, namely the strength activity index in the range of 0.94–1.06 for 180-day samples. The blended mortars were cautiously studied concerning the HM immobilization efficiency. The immobilization efficiency was analyzed through the HM leaching test, showing that HMs present in the leachates manifested concentrations well below the prescribed limits. In addition, the immobilization effectiveness was found to be higher with a longer curing time. As FA-PC replacement has recently become a highly researched topic, this study adds a significant point of view in terms of the safety and environmental efficiency of the designed composites. Furthermore, the proposed safe handling of hazardous HM-containing FA through their implementation in construction mortars while ensuring high HM-immobilization effectiveness represents the next step in the ongoing research into the decarbonization of the construction industry and minimization of the depletion of natural resources.