Mixture Design-Based Performance Optimization via Response Surface Methodology and Moisture Durability Study for Palm Oil Clinker Fine Modified Bitumen Asphalt Mixtures

With the increase in asphalt mixtures sustainability, the application of waste as a bitumen modifier has been encouraged. In addition, the asphalt mixtures produced considering only the engineering properties show degradation due to repetitive traffic loading and not the performance properties. Thus, necessitate the use of an alternative mix design considering various properties and considering alternative modifiers. Also, there are limited studies on the impact of long-term water immersion on the strength of asphalt mixtures, particularly the effects of both immersion-drying (I-D) cycles on Palm oil clinker fine-modified bitumen (POCF-MB). Thus, this study employed palm oil clinker fine (POCF) as a bitumen modifier. Response surface methodology (RSM) was used to evaluate an alternative engineering and performance mix design technique for asphalt mixtures was examined. Subsequently, the durability and strength of the optimized POCF-MB asphalt mixture for both I-D cycles were evaluated. Samples were vacuum saturated and immersed for 0 (dry) 1, 3, 5, and 7 days. Then assessed in terms of Marshall quotient (MQ), retained Marshall stability (RMS), swelling index (SI), indirect tensile strength (IDT), Indirect tensile strength ratio (ITSR), and subsequently redried at ambient temperature to evaluate the retained durability and strength. The RSM findings show that the synergetic effects of POCF dosage and bitumen significantly impact performance. Based on the high coefficients of determination (R²) values (> 0.95), high adequate precision values (> 4), and low p-values for all responses, the statistical models were determined to be significant and well-fitted. The optimum values of numerical optimization were 5.86% POCF dosage and 4.65% bitumen content. The validation test shows an error margin of < 5% for all responses indicating that the model and experimental values agree well and are closely aligned. With increasing conditioning time, all samples showed increased SI, flow, and a decline in MQ, RMS, IDT, and ITSR. However, POCF-MB samples showed minimal moisture durability reduction, which can be attributed to the hydration process of the POCF, making the mixtures stiffer. After redrying POCF-MB samples show a higher recovery of their initial durability, revealing that the durability and strength properties of the asphalt mixture are recoverable.