Empirical Optimization of Combined Effects on Moisture Resistance of Hydrated Lime-Modified Densely Graded Asphalt Concrete under Medium Traffic: A Central Composite Design Approach

This study explored the main and interaction effects of hydrated lime (HL), granite, sand, and bitumen on the durability of hydrated lime-modified densely graded asphalt concrete (HL-DGAC), focusing on moisture resistance as measured by the Tensile Strength Ratio (TSR). Despite HL’s established benefits in asphalt modification, its combined influence with other components remains inadequately understood. Using a Central Composite Design and Analysis of Variance (ANOVA), the research varied binder content, aggregate gradation, and HL dosage to assess their effects on TSR. Results showed TSR values between 80.24% and 90.88%, all surpassing the AASHTO minimum of 80%, confirming satisfactory moisture resistance. HL was identified as the most significant factor, boosting TSR by up to 10.26%, with optimal content between 1.815% and 2.013%. Notably, interaction effects revealed that sand–bitumen and granite–bitumen combinations significantly improved durability, yielding peak TSR values of 87.5% and 90.0%, respectively. Contour analysis indicated optimal TSR performance (86–88%) occurred when bitumen content was >6.418% or <6.33%, granite content fell outside the 57.34–57.82% range, HL exceeded 2.013%, and sand content was >35%. The optimized HL-DGAC blend, comprising 55.221% granite, 35.177% sand, 6.297% bitumen, and 3.304% HL, achieved a peak TSR of 90.343% with a high desirability of 95.34%. These findings highlight that maximizing durability in HL-DGAC requires a multi-variable optimization approach, as critical interactions between fine aggregates and binder play a pivotal role. The study emphasized the importance of considering interactive effects among mix components to design asphalt mixtures capable of withstanding moisture damage, especially in humid environments.