Sustainable Utilization of Volcanic Pumice Powder and Recycled Nylon Fiber in Concrete Production: Experimental Assessments and Machine Learning Modeling

This study explores the combined use of volcanic pumice powder (VPP) and recycled nylon fiber (RNF), sourced from discarded fishing nets, in developing sustainable concrete. Ten mixtures were designed using 10–20% VPP as a partial cement replacement alongside 0–2% RNF. Fresh-state behavior, mechanical performance (compressive, tensile, and flexural strength), and non-destructive testing (rebound hammer and ultrasonic pulse velocity) were assessed, while SEM-based microstructural analysis confirmed pore refinement and enhanced C–S–H gel formation. The 10% VPP–1% RNF mixture achieved the highest compressive strength, exceeding the control by about 18%, while 10% VPP–2% RNF delivered the best tensile and flexural results, improving by roughly 35% and 34%, respectively. Environmentally, 20% VPP replacement reduced CO2 emissions by nearly 20%, highlighting the mixture’s sustainability benefits. Machine learning models were also applied to predict mechanical properties, with the Gradient Boosting Regressor outperforming Random Forest and XGBoost, achieving a test R2 of 0.924 and MAE of 6.75 MPa. Feature importance analysis identified curing age, supplementary cementitious materials, and cement content as the most influential parameters. Overall, the VPP–RNF combination enhances concrete’s strength, durability, and environmental performance, while machine learning provides reliable, interpretable tools for optimizing sustainable concrete mix design.