Performance of sustainable mortar using calcined clay, fly ash, limestone powder and reinforced with hybrid fibers

Green mortar (GM) is a mortar that at least one of its components uses waste materials or materials that do not cause environmental destruction throughout their production. This research aims to design a mortar with the highest possible cement and sand substitutions with acceptable fresh and hardened properties. The experimental work was conduct in three phases. In phase one, calcined clay replaced cement by 20%, 25%, 30%, 35%, and 40% in mortar mixes. Then, the cement replacement raises to 50% by substituting cement with a combination of calcined clay (CC) and fly ash (FA) in different percentages in other mortar mixes. In phase two, limestone powder (LP) partially replaced sand by 20% and 30% (by weight) in two of the chosen mixes from phase one that contained high cement replacement and fairly good fresh and hardened properties. Then environmental impacts of GM mixes have been evaluated by estimating the reductions of CO2 emissions from producing such mixes. Phase three involved the effects of incorporating 0.5% fibers (by volume) on the properties of GM using two types of steel fibers with different aspect ratios. Ultra steel fibers (USF) with an aspect ratio of 65 and steel nail fibers (SNF) with an aspect ratio of 20. The inclusion of hybrid fibers was by combining USF and SNF in different percentages while maintaining the same volumetric fraction of 0.5%. The fresh and hardened properties have been determined in phase three also. The results show that replacing OPC with 25% CC provides the best increment on compressive strength by increasing the compressive strength by about 21% at 28 days. The use of 20% LD as sand replacement increases the flow and 28 days-compressive strength by about 55% and 13%, respectively, for the mortar that contains 35% CC+ 15% FA. The test results of reinforced mixes show that the hybridization of 0.175% USF and 0.325% SNF affords the best enhancements on the mechanical properties. The results obtained from the estimated reduction of CO2 emissions study reveal that incorporating 30% CC + 20% FA as cement replacements and 30% LP as a sand replacement reduces the CO2 emissions by approximately 41%. Therefore, adopting the concept of green mortar is a promising approach for mitigating CO2 emissions and preserving natural resources.