Predicting crack growth of paving materials under indirect tensile fatigue loads

Abstract

Cracking of paving materials affects the reliability and safety of pavement structures, and indirect tension (IDT) test is commonly used to investigate the cracking behavior of the paving materials. However, the existing studies usually adopted a reduced modulus or strength to indirectly quantify cracking damage under the IDT fatigue loads. A direct analysis method for the crack growth under the IDT fatigue loads is still missing. The objective of this study is to propose a crack growth prediction model under the IDT fatigue loads based on continuum damage mechanics (CDM), which can directly quantify and predict the crack growth of the paving materials. Two types of paving materials, cement-treated aggregates and asphalt mixtures, were investigated. A damage density model based on CDM was proposed to quantify the crack growth under the IDT fatigue loads. The model coefficients are obtained by the IDT horizontal tensile stress, material surface energy, resilient modulus, and the size of the IDT specimen. The surface crack length of the IDT specimen is obtained using the solved damage density with introducing a crack depth ratio. Results show that the cement-treated aggregates show relatively more brittle cracking where the cracks are penetrative and going through the whole thickness of the IDT specimen. In contrast, the asphalt mixtures exhibit more ductile cracking where multiple cracks present and are nonpenetrative. The cracks of the asphalt mixture penetrate only 48% and 46% of the specimen thickness when the IDT fatigue loads are 540 kPa (1 Hz) and 700 kPa (10 Hz), respectively. The damage density calculated by the CDM-based model can accurately predict the crack lengths for both the cement treated aggregates and the asphalt mixtures, which are found consistent with the measured crack lengths from the IDT tests. This study provides a mechanics model for determining the crack growth under the IDT fatigue loads that can serve as a tool for evaluating the fatigue crack resistance of the paving materials like the asphalt mixtures and cement treated aggregates.