Multiscale performance of composite modified cold patch asphalt mixture for pothole repair

Cold patch asphalt mixture (CPAM) has become primary material for pothole repair of asphalt pavement due to its advantages of convenient storage, strong seasonal adaptability and timely repair, as well as green mainte-nance feature. However, insufficient adhesion of CPAM due to the asphalt binder diluted by diesel may lead to secondary distress in a short term. In this paper, composite modified CPAM is developed and its multiscale interfacial morphology and mechanical properties are explored. Three kinds of CPAM with different gradations are designed. Based on indirect tensile test, scanning electron microscope and nanoindentation experiment, the multiscale interface morphology characteristics and mechanical properties are analyzed. The results showed that elastic modulus of CPAM increases with the increase of aged time because of the evaporation of light diesel; with the optimal cold patch asphalt (CPA) content 4.3%, the aggerates are all coated and the mixture is loose; with redundant CPA content 5.0%, too thick asphalt film and agglomerate CPA paste can also be observed; with insufficient CPA content 3.5%, aggregates are not completely coated by CPA. By comparing interface micro-structure, with the optimal CPA content 4.3%, redundant CPA content 5.0% and insufficient CPA content 3.5%, smooth morphology, redundant CPA spilling and inadequate asphalt attachment are observed in the interface of CPAM, respectively. In addition, the evaporation of light diesel, age of asphalt polymer and composite additive cause microcracks and micro-holes in the interface between CPA mortar and aggregates.