Evaluation of moisture resistance of cold mix asphalt and binder using Tensile strength ratio and Surface Free energy approach

Cold Mix Asphalt (CMA), while offering environmental benefits such as reduced energy consumption and emissions, is often limited by inadequate moisture resistance due to weak binder-aggregate adhesion. Conventional evaluation methods like the Tensile Strength Ratio (TSR) do not fully capture the underlying mechanisms of moisture-induced damage. To address this gap, the present study integrates Surface Free Energy (SFE) analysis with TSR testing to comprehensively evaluate the moisture susceptibility of CMA and its binders. Dense graded CMA and Hot Mix Asphalt (HMA) specimens were prepared using two slow-setting emulsions (SSE10, SSE30) and two virgin binders (VG10, VG30), respectively. TSR results indicated that SSE30 and SSE10 surpassed the standard threshold by 4.16% and 1.59%, while VG30 marginally met the requirement and VG10 fell short by 5.11%. SFE analysis showed that SSE30 exhibited 131.57% higher total SFE and 115.26% greater nonpolar component than SSE10, while VG30 exceeded VG10 by 195.22% and 142.57%, respectively. SSE30 and VG30 also demonstrated significantly higher cohesive energy and lower debonding energy, confirming better moisture resistance. Energy Ratios (ER1 and ER2) further established the superior performance of VG30 and SSE30. This study provides a novel framework for binder evaluation in CMA using SFE-derived indicators, supplementing traditional mechanical tests. The findings establish that dense graded CMA with SSE30 can offer moisture resistance comparable to HMA, thus enhancing its applicability in moisture-prone conditions.