Review on the mesoscale characterization of cement-stabilized macadam materials

The base layer constructed by cement-stabilized macadam (CSM) has been widely used in highway construction due to its low elasticity deformation and high carrying capacity. As a bearing layer, the CSM base is not exempt from fatigue cracking under cyclic loading in the service process. Cracks in the base will create irreversible structural and functional deficiencies, such as the potential for reflective cracking of subsequently placed asphalt concrete overlays. The fracture of the base will shorten the service life of the pavement. The quality of the CSM base is directly related to the bearing capacity and integrity of the whole pavement structure. It is of practical significance to further study the fatigue failure behavior of CSM material for the long-term performance of the pavement. The CSM material is a typical heterogeneous multiphase composite. On the mesoscale, CSM consists of aggregate, cement mortar, pores, and the interface transitional zone (ITZ). On the microscale, the hardened mortar contains a large number of capillary pores, unhydrated particles, hydrated crystals, etc., which makes the spatial distribution of its material properties stochastic. In addition, cement hydration, dry shrinkage, and temperature shrinkage can also produce micro-crack defects in cement mortar. These microcracks will have cross- scale evolution under load, resulting in structural fracture. Macroscopic complex deformation and mechanical response are the reflections of its microscopic and even mesoscale composition and structure. This study summarized the existing studies on the mesoscopic properties of CSM materials, respectively from the three aspects of mesostructure, structural characterization, and mesoscale fatigue damage analysis, to help the development of long-life pavement. The future research direction is to explore the mesoscale characteristics of CSM using multi- scale representation and analysis methods, to establish the connection between mesoscale characteristics and macroscopic mechanical properties.