Evaluation of the effects of asphalt paving block thickness and crumb rubber size on buton rock asphalt-modified paving blocks using response surface methodology

Abstract The use of Buton rock asphalt paving blocks as alternative surface layers of road structures can be a solution. As construction materials, paving blocks come in various sizes and shapes, as well as different constituent materials. This study aims to evaluate the effects of crumb rubber size and paving block thickness on the flexural strength, volumetric characteristics, and immersion resistance of asphalt concrete materials used as road surface layers. Flexural strength and volumetric tests were conducted on paving blocks with thicknesses of 60, 80, and 100 mm using three-point flexural tests and Marshall tests. Data analysis used an exponential model, response surface methodology, and ANOVA. The results revealed that variations in crumb rubber particle size decrease penetration by 10–11% and increase the softening point by 9–10%, as described by a quadratic model (R² = 0.94–0.99). This change affects volumetric characteristics: as the crumb rubber granule size decreases, the voids in the mix and the voids in the mineral aggregate decrease, whereas the voids filled with asphalt and the density increase (R² = 0.94–0.95). The flexural strength increases by 5–10% as the crumb rubber decreases. The residual flexural strength index is influenced by the CR particle size: the smaller the CR particle size is, the greater the resistance to immersion. Increasing the thickness of the paving block increases flexural strength.