Investigation the effect of short term aging on thermodynamic parameters and thermal cracking of asphalt mixtures modified with nanomaterials

Abstract

Thermal or low temperature cracking is among the most common distresses in asphalt pavements, occurring in cold regions and exerting a detrimental effect on the quality and life of the pavement. Hardening or aging of asphalt binder in the process of production and service life of asphalt mixtures is known as a major factor impacting the durability of asphalt mixtures. This study investigated the effect of asphalt binder modification with two types of mineral nanomaterials, nano calcium carbonate (NCC) and nano hydrated lime (NHL), on the aging and thermal cracking of asphalt mixtures using thermodynamic and mechanical methods. To this end, 24 asphalt mixtures were prepared using limestone and granite aggregates with different mineralogical properties, two types of asphalt binder with PG of 64–16 and 58-22, and two types of nanomaterials, including NHL and NCC. Thermal cracking of asphalt mixtures was evaluated by mechanical semicircular bending (SCB) test based on AASHTO TP105, and thermodynamic tests of sessile drop and universal sorption device based on surface free energy (SFE) methods. The results of the SCB test indicated that aging significantly affected the values of maximum load, fracture energy, and fracture toughness. In addition, asphalt binder modification using NCC and NHL significantly increased the values of all three parameters mentioned above in both the control and aged samples. On the other hand, the results of thermodynamic tests demonstrated that the free energy of cohesion of PG 64–16 in both control and aged states was higher than that of PG 58-22. Accordingly, aging and modification of the control and aged asphalt binder using nanomaterials increased the cohesion energy of asphalt binder. Results also indicated that mixtures made with granite aggregates, in both aged and control states, had higher values of free energy of adhesion compared to mixtures made with limestone aggregates. Aging caused a decrease in the free energy of adhesion, which was much lower in the nano material modified samples in comparison with the control samples. The results of ANOVA and linear regression analysis also revealed that there was a significant and strong correlation between thermodynamic parameters of cohesion and adhesion energy and the maximum load, fracture energy, and fracture toughness parameters in examining the effects of aging and additives on thermal cracking. This indicates the high potential of thermodynamic methods in thermal cracking examination in asphalt mixtures.