Response Surface Methodology and Life Cycle Assessment of self-compacting mortars incorporating olive pomace bottom ash

Olive pomace bottom ash (OPBA) is a locally available biomass residue that could reduce cement consumption while providing a practical route for agricultural-waste valorisation. This study combined Response Surface Methodology (RSM) with cradle-to-gate Life Cycle Assessment (LCA) to examine the effects of OPBA replacement (0–20%), limestone filler content (10–20%), and water-to-binder ratio (0.45–0.50) on the mechanical, physical and life cycle assessment properties of self-compacting mortars. Seventeen mixtures were evaluated using a central composite design, and quadratic models were developed for compressive strength, water absorption, and four LCA indicators. OPBA was the main factor controlling compressive strength, accounting for 71.20% of the modelled response, followed by the water-to-binder ratio at 17.44%. Increasing OPBA generally reduced strength because of cement dilution and its limited pozzolanic contribution at 28 days. Water absorption was jointly influenced by OPBA, limestone filler, and the water-to-binder ratio, with contributions of 34.74%, 23.50%, and 21.26%, respectively. The compressive-strength model showed good fitting performance and moderate cross-validated predictability (R2 = 0.950, R2pred = 0.606), whereas the water-absorption model showed weaker predictive stability (R2 = 0.902, R2pred = 0.245). Lack-of-fit was not significant for either response. Under the adopted cut-off allocation approach, OPBA was also the dominant factor governing the environmental indicators, accounting for approximately 95.7–99.9% of their modelled variation. Multi-objective optimisation identified a formulation containing 20% limestone filler, 20% OPBA, and a water-to-binder ratio of 0.453, with predicted compressive strength of 40.0 MPa, water absorption of 12.9%, and climate-change impact of 294.7 kg CO2-eq/m3.