Evaluating mechanical and thermodynamic properties of asphalt mixtures containing anti freezing agents against low temperature cracking.

In cold climates, hot-mix asphalt (HMA) is vulnerable to surface freezing, leading to reduced pavement performance. This study examined the effects of aqueous solutions containing sodium acetate (NaOAc) and sodium chloride (NaCl), which are commonly used in cold climates, on the low-temperature performance of hot-mix asphalt (HMA) using surface free energy (SFE) analysis and semi-circular bending (SCB) tests. To mitigate adverse effects, Zeolite was incorporated at 1% and 2% by bitumen weight due to its strong absorption properties. Two aggregate types (granite and limestone) and two performance grade bitumens (PG 58-22 and PG 64-16) were used. SCB testing was performed at -12 °C and -22 °C to assess temperature sensitivity. The SFE results showed that the aqueous solutions containing anti-freezing agents decreased the bitumen-aggregate debonding energy (DE) by up to 8.5%. The anti-freezing agents increased the bitumen-water adhesion free energy (AFE) and the bitumen-aggregate AFE by approximately 10-13%, thereby increasing the samples' adhesive failure potential. The SCB test revealed that anti-freezing agents diminished the HMA's performance at low temperatures by decreasing the peak load (up to 21%), fracture energy (FE) (up to 17%), and fracture toughness (FT) (up to 17%). The results of both methods indicated that NaOAc had a more significant impact on reducing the low-temperature resistance of HMAs and bitumen-aggregate adhesion compared to NaCl. Statistical analysis revealed that adding 2% zeolite to the bitumen significantly increased FE by nearly 10%, FT by 14%, and DE by 18% in HMAs exposed to anti-freezing agents. The combination of PG 58-22 and limestone had the best performance against thermal cracking under moisture conditions caused by anti-freezing agents due to the better adhesion properties.