Investigation into the crack propagation behaviors of asphalt mixture containing recycled concrete aggregates using digital image correlation

Abstract

Recycled concrete aggregates (RCAs) produced by crushing the demolished concrete from construction and demolition waste (C&DW) are potential raw materials for sustainable asphalt pavement, providing an alternative method to facilitate the efficient use of C&DW. However, the deterioration of RCAs brings risks to the load-bearing capacity of the aggregate skeleton of asphalt mixture. This study aims to investigate the mechanical properties, especially the crack propagation behaviors of asphalt mixtures containing RCAs (AM-RCAs). For this purpose, dense graded asphalt mixtures with RCAs replacement proportions of 0, 17, 37, and 56.7 % were designed and prepared for performance tests, including high-temperature rutting tests, low-temperature small beam tests, water immersion Marshall tests, freeze-thaw splitting tests, uniaxial penetration tests, indirect tensile asphalt-cracking tests, semi-circular bending tests, and dynamic creep tests. Digital image correlation (DIC) was synchronized with the semi-circular bending test to record the entire crack propagation process of the AM-RCAs. Depending on the replacement proportions of RCA, AM-RCAs exhibit a higher asphalt-aggregate ratio and improved high-temperature stability and water stability, but sharply decreased cracking resistance. With the increase of the RCAs replacement proportions, the CT_Index values decrease by 32.9, 31.6, and 38.4 %, respectively; the W_fb values decrease by 6.95, 9.75, and 11.28 %, respectively; the $G_f$ values decrease by 22.4, 23.1, and 30.5 %, respectively; and the FI values decrease by 16.6, 17.5, and 42.9 %, respectively. DIC analysis indicates that the areas prone to cracking along the crack propagation paths of the specimens are the RCAs-adhered mortars and their interfaces with asphalt binders, emphasizing the necessity of strengthening treatments of RCAs. The average crack-propagation rate of AM-RCAs increases by more than 7.3 %, and the fracture toughness decreases by more than 3.9 %, indicating that AM-RCAs are more prone to cracking than asphalt mixtures using natural aggregates (AM-NAs). These findings provide a visual and quantitative method for evaluating the crack propagation behavior of AM-RCAs.