Document Type : Research Paper
Authors
1
Ph.D. Candidate, Department of Transportation Engineering, Faculty of Civil Engineering, Semnan University, Semnan, Iran
2
Faculty of Civil Engineering, Semnan University, Semnan, Iran
3
Assistant Professor, Department of Transportation Engineering, Faculty of Civil Engineering, Semnan University, Semnan, Iran
Abstract
Hot Mix Asphalt (HMA), although widely used in pavement construction due to its favorable mechanical properties, is highly affected by environmental and chemical conditions of surface runoff. The aim of this study is to investigate the effect of runoff pH variations (4, 7, and 9) on the adhesion between bitumen and aggregates and the mechanical failure parameters of asphalt mixtures. To this end, a series of laboratory tests, including Indirect Tensile Strength and moisture sensitivity (ITS/TSR), Semi-Circular Bending (SCB) at low temperature, Indirect Tensile Fatigue Test (ITFT), and contact angle measurements for Surface Free Energy (SFE) analysis were performed. The results indicated that acidification of the environment (pH = 4) significantly increased the contact angle and reduced the total surface free energy of bitumen from about 46.14 to 52.12 (ergs/cm²), reflecting a decline in wettability and adhesion. TSR values decreased markedly under acidic conditions, while a relative improvement was observed in alkaline conditions. In addition, the Indirect Tensile Strength and SCB indices (peak load and fracture energy) were considerably reduced in the acidic environment; for example, the maximum load of the samples dropped by more than 20% compared to the neutral condition. Fatigue tests showed that fatigue life decreased sharply in acidic conditions, whereas alkaline conditions provided a relative improvement compared to neutral conditions, although still lower than that of the dry state. Overall, the findings demonstrate that acidic runoff has the most detrimental effect on the adhesion and mechanical durability of HMA, while alkaline conditions may partially compensate for moisture-induced damage. These results highlight the importance of considering environmental chemical conditions in the design and maintenance of pavements, particularly in urban and industrial areas with a high probability of acidic runoff
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