Multi-response optimization of red mud and sand proportions in paving block production via response surface methodology (RSM)

Rising cement and natural aggregate prices have intensified the need for sustainable and optimized paving block mixtures incorporating industrial by-products. This study investigates the multi-response optimization of red mud and stone content in paving block production using response surface methodology (RSM). Red mud, an alkaline by-product of the bauxite refining industry, was utilized as a partial cement replacement to reduce material consumption and environmental impact. The objective was to determine the optimal proportions that satisfy the performance requirements of SNI 03-0691-1996. An RSM-based experimental design evaluated the interactive effects of red mud substitution (0–20% by cement weight) and stone proportion on compressive strength, bulk density, water absorption, and abrasion resistance. Specimens were produced using portland composite cement, sand, stone, water, and pre-treated red mud. Regression models and response surface plots were developed for prediction and optimization. Results indicate that approximately 18.79% red mud replacement with an optimized aggregate proportion yields the best overall performance. The optimized mix achieved a 28-day compressive strength of 22.91 MPa, satisfying SNI class B criteria, while demonstrating reduced water absorption and abrasion loss. This study introduces a statistically robust multi-response RSM approach for sustainable paving block mix design.