This study addresses the development and improvement of foam concrete using a hybrid lightweight aggregate that includes natural lightweight aggregate (locally called Ponza), expanded clay (Leca), and expanded polystyrene (EPS), aiming to achieve a balance between mechanical properties and thermal performance while maintaining low density. The RSM and CCD were adopted to analyze the effect of different aggregate ratios and to develop predictive models. The results showed that the density ranged between 990–1295 kg/m³, compressive strength between 5.80–16.40 MPa, flexural strength between 1.27–3.81 MPa, and thermal conductivity between 0.382–0.595W/m·K. The statistical models showed acceptable agreement with the experimental results, with R² values ranging from 73.95% to approximately 88%. The thermal conductivity model exhibited the lowest R² value (73.95%), indicating relatively lower predictive accuracy compared with the other models. The results also indicated that Ponza is the most effective in improving mechanical properties. Leca contributed to reducing density and thermal conductivity. In contrast, expanded polystyrene led to improved thermal insulation at the expense of strength. The optimization process showed that the optimal mix consists of (17.85%) Ponza and (4.22%) Leca with no use of expanded polystyrene, achieving an optimal balance between strength, density, and thermal insulation. The study confirms the efficiency of using hybrid lightweight aggregates with the RSM to produce foam LWA concrete mixes with density range of (990–1295 kg/m³) and compressive strength from 5.80 to 16.40 MPa which, according to ACI 213R-14, are suitable for semi-structural engineering applications.
