Effect of Long-Term Aging on Low-Temperature Cracking of Asphalt Mixtures using Mechanical and Thermodynamic Methods

Document Type : Research Article

Authors

1 Faculty of Niroo Research Institute (NRI), Tehran, Iran

2 Electric Power Structural Research Group, Niroo Research Institute (NRI), Tehran, Iran

Abstract

One of the common phenomena in the cracking of asphalt pavements is thermal cracks or cracks due to low temperature, which occur in cold regions and accelerate the distresses of road structures. Numerous different factors can affect the behavior of asphalt mixtures at low temperatures. The factors affecting heat cracking in asphalt concrete pavements are generally divided into three categories: materials, environment, and geometry of the pavement structure. Factors related to materials in the occurrence of thermal cracks include bitumen, type and aggregate granulation, percentage of bitumen, and percentage of air pores. One of the most important factors affecting the occurrence of thermal cracks in bitumen is its aging or the age of pavement. As a result, bitumen aging has a direct effect on pavement performance. In most existing studies to investigate the aging performance of asphalt mixes, the results of mechanical tests are used to investigate the thermal cracking potential of an asphalt mix and less attention is paid to the basic properties of materials that are important in the event of this cracking. Accordingly, the present study investigates the effect of aging on thermal cracking of 12 different compositions of asphalt mixtures through mechanical methods and surface free energy (SFE), which is based on the main properties of the material. Thermal cracking of asphalt mixtures has been evaluated by performing semi-circular bending mechanical tests and thermodynamic tests by determining the SFE components of bitumen and aggregates. The results showed that the parameters of fracture energy and fracture toughness, which are known as indicators of sensitivity of asphalt mix to thermal cracking, for aged asphalt mixtures between 6.3-13.7% and between 6.5-10.7%, respectively. The results of SFE tests showed that aging causes an increase in the non-polar component between 1.3-1.5% and a decrease in the acidic and basic free energy components of bitumen between 41.1-53.4% and between 334.2-349.6%, respectively. These results have increased the amount of free cohesive energy from 0.63 to 1.03 (ergs/cm2). Also, aging reduces the free energy of bitumen-aggregate adhesion with a maximum reduction of 2.61 (ergs/cm2). This means that aging reduces the cover-ability of bitumen on the aggregate surface and the resistance to fracture at the bitumen-aggregate interface.

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