Sustainable eco-mortar development using industrial by-products and recycled aggregates: an experimental and predictive study

Abstract

This study evaluates the performance of sustainable mortar incorporating fly ash (FA) and limestone (LS) powder as partial binder replacements and construction and demolition waste (CDW) as an alternative fine aggregate. Cement was replaced by fly ash and limestone powder up to 24%, while natural sand was substituted with CDW up to 100%, maintaining a constant water-to-binder ratio of 0.45 and coconut fibre content of 0.3%. Experimental results indicate that the optimised mix containing 6% fly ash, 6% limestone powder, and 25% CDW exhibited superior performance. This mix achieved the highest dry density of 793.55 kg/m³ at 28 days, along with maximum ultrasonic pulse velocity, indicating improved internal compactness. Rebound hammer strength and compressive strength also peaked at this composition, confirming enhanced surface hardness and load-carrying capacity due to improved particle packing and pozzolanic activity. Beyond the optimum level, higher CDW content resulted in increased porosity and reduced mechanical performance. Machine learning models, particularly Gradient Boosting (GB) and Random Forest (RF), demonstrated excellent predictive accuracy with R² values exceeding 0.95 for all properties. The results confirm that controlled use of industrial and construction wastes can produce high-performance, low-carbon mortar systems.