Thermo-Mechanical Performance of Macro-Polymer Modified Sustainable Rigid Pavement Concrete for Urban Heat Island Mitigation

Abstract

The urban heat island effect, driven largely by heat absorption and retention by paved surfaces, remains a major challenge in sustainable urban development. This study presents a systematic three-stage experimental program to assess supplementary materials in rigid pavement concrete for improving mechanical performance and reducing surface temperature. Stage I examined single-material replacements of 5–35%, including natural zeolite and hydrated lime as partial Ordinary Portland Cement replacements, steel slag as fine aggregate replacement, and recycled plastic aggregate (RPA) as coarse aggregate replacement. Stage II identified optimum levels of cementitious modifiers and RPA, while Stage III evaluated triple-modified mixes with simultaneous cementitious, fine aggregate, and coarse aggregate substitutions. The surface temperature of the specimens was measured using infrared thermometry. The Jonckheere–Terpstra test confirmed statistically significant trends for zeolite, steel slag, and RPA replacements (p ≤ 0.042).  Stage I optimum levels were 15% zeolite, 10% lime, and 20% steel slag, yielding compressive strength improvements of 10.9%, 4.5%, and 12.5%, respectively, over the control, whereas RPA caused progressive strength reduction. The optimum triple-modified mix, Z15R5S20, achieved a 28-day compressive strength of 50.5 MPa, a 14.8% increase over the control, and a 7.5 °C surface temperature reduction. Taguchi S/N analysis confirmed this optimum mix with a prediction error of 0.62%. A strong negative Pearson correlation between compressive strength and surface temperature (r = −0.83, p < 0.001) demonstrated the potential to balance structural performance and thermal mitigation. The findings indicate a technically viable and environmentally sustainable approach for UHI mitigation in urban pavements.