Adhesive and Cohesive Cracking Analysis of Asphalt Mastics in Contact with Steel Substrates Using an Energy-Based Crack Initiation Criterion

Abstract

Adhesive and cohesive properties play a vital role in the durability of asphalt mixtures. As a result of the lack of models characterizing adhesive and cohesive cracking, the occurrence of adhesive and cohesive failure has not been fully formulated by using an explicit mechanical approach. Strain energy density in intact mastics is transformed into adhesive and cohesive surface energies as cracks initiate. This study developed an energy-based crack initiation criterion based on the Griffith model and differentiated adhesive and cohesive cracking. The onset of cracking was identified by the deviation of the measured stress from the linear viscoelastic stress. The released strain energy at the crack initiation balanced the increase in surface energies, thus creating a new adhesive and cohesive surface. Several fracture parameters such as initial crack size, cracking stress, and tensile strength were proposed to analyze the effects of sample thickness, strain rate, temperature, and filler concentration in mastics. Results indicate that the adhesive energy, cohesive energy and strain energy density significantly depend on filler concentration in mastic and test temperature but is independent from sample thickness and strain rate. In particular, the variation of the strain energy density from 20 °C to 35 °C reaches 127.4%, and its decrease is up to 46.9% as the filler concentration in the mastic varies from 0 to 60%. The increase in the sample thickness from 160 μm to 1000 μm results in the 150.0% growth of the initial crack size and 74.4% reduction of the cracking stress. Therefore, increasing the adhesive and cohesive energy can essentially improve the toughness to resist the cracking, and decreasing the mastic thickness enhances the loading capacity. It provides a deep understanding of the mixture cracking from a perspective of adhesive and cohesive surface energies.