Optimization of self-compacting mortars with olive pomace bottom ash using central composite design approach

Abstract This study investigates the potential use of Olive Pomace Bottom Ash (OPBA) as a partial cement replacement in self-compacting mortars (SCMs) to enhance sustainability in construction while addressing environmental concerns. A Central Composite Design (CCD) approach was used to investigate the effect of OPBA content (0–20%), limestone filler content (10–20%), and water-to-binder (W/B) ratio (0.4–0.5) on fresh properties, mechanical behavior, and water absorption potential of SCM. The results indicate that increasing the OPBA content typically decreased workability and strength while at the same time increasing water absorption potential. However, this effect can be mitigated by optimizing the filler content and W/B ratio. With low additions of OPBA (up to 10%), incorporating limestone filler showed a regular increase in strength. Statistical analyses using the central composite design method confirm that complex non-linear relationships among variables exist and that advanced optimization techniques are needed in mix design. An optimal mix was found to have 6.66% OPBA, 20% filler, and a W/B ratio of 0.42, with a desirability value of 0.927. This optimal mixture recorded a slump of 26.3 cm, flow time of 11.85 s, compressive strength of 48.66 MPa, flexural strength of 5.47 MPa, and water absorption of 11%. The above study indicates that OPBA is feasible in SCMs and could improve sustainability in the construction industry without compromising performance. These findings highlight OPBA feasibility in SCMs, promoting waste valorization and reducing cement consumption without compromising performance.