Response Surface Methodology for Evaluating Voids In Metakaolin Modified Granite-Granular Sand Densely Graded Asphalt Concrete

This study investigates the optimization of void properties in Metakaolin-Modified Densely Graded Asphalt Concrete (MK-DGAC) using Response Surface Methodology (RSM). The mix includes granite, granular sand, bitumen, and metakaolin (MK) as a pozzolanic additive. Void parameters analyzed are Voids in Mineral Aggregate (VMA), Voids in Total Mix (VTM), and Voids Filled with Bitumen (VFB), which critically influence pavement durability, moisture resistance, and load capacity.Results show that increasing MK content reduces VMA by up to 17.92% (15.67% to 19.09%) and decreases VTM by 61.68% (2.06% to 5.37%), while raising VFB by 21.39% (71.88% to 87.25%). These changes improve binder distribution and moisture resistance but may elevate rutting risk if overdosed. RSM models for VMA and VTM achieved high predictive accuracy with R² values of 88.98% and 83.96%, respectively, confirming reliability in capturing void behavior based on granite, sand, bitumen, and MK proportions.Statistical analysis highlights MK as the most influential factor in reducing voids and enhancing bitumen filling, followed by granular sand and bitumen, with granite having minimal impact. The optimized mix proportions identified are approximately 57.3% granite, 32.7% sand, 6.4% bitumen, and 3.63% metakaolin. This formulation yields a VMA of 15.9% (above the 14% minimum), a VTM of 2.03% (slightly below the 3–5% guideline), and a VFB of 86.9% (exceeding typical upper limits), achieving a composite desirability of 96.95%.Overall, the study confirms that carefully dosed metakaolin enhances asphalt concrete void properties, offering a durable, moisture-resistant, and structurally sound pavement mix optimized through RSM coupled with desirability functions.