Evaluation of low-temperature behaviour of additive-modified cold mix asphalt for cold region applications

This study evaluated the low-temperature performance of cold mix asphalt (CMA) modified with hydrated lime (HL) and calcium chloride (CaCl₂) to enhance durability in cold regions. A dense-graded CMA was produced using basalt aggregates and a cationic slow-setting emulsion in accordance with Indian Roads Congress and Asphalt Institute specifications. Optimum pre-wetting water (2%) and emulsion content (8.5%) were determined from standard volumetric and Marshall criteria. HL was incorporated as a constant 2% filler replacement, while CaCl₂ was varied between 0.5% and 2.5%. The calcium-to-silica (Ca/Si) ratio obtained from energy dispersive spectroscopy (EDS) served as a microstructural indicator of hydration and pozzolanic reactivity. CMA-2.0 reached the highest Ca/Si ratio (0.70), indicating favourable C–S–H development and a denser microstructure, which was also reflected in the peak Marshall stability of 8.21 kN. Freeze–thaw ITS results showed nearly double the strength of the control, which was supported by improved TSR values. Resilient modulus testing at 5°C, 15°C and 25°C confirmed consistent stiffness gains, while IDEAL-CT data demonstrated enhanced cracking resistance with increasing temperature. Correlation and statistical assessments reinforced these findings, showing that the Ca/Si ratio strongly governs mechanical and moisture-related responses. High determination coefficients (R 2 = 0.80–0.97) and highly significant t-test and ANOVA results (p < 0.001) confirmed that calcium-driven hydration directly influences stability, moisture tolerance, stiffness and cracking performance. Overall, combined HL–CaCl₂ modification markedly improves the structural and durability characteristics of CMA, establishing Ca/Si as a reliable mechanistic parameter for designing chemically optimised cold-mix materials suited for cold-climate pavements.