Long-term performance and microstructure of asphalt emulsion cold recycled mixture with different gradations

Abstract

This work investigated the long-term performance and microstructure of asphalt emulsion cold recycled mixture (CRME) with different gradations. Three gradations were selected by varying the passing rate of 4.75 mm critical sieve. CRME samples were firstly treated by an accelerated aging test, and the aging conditions were aging temperatures of 60 °C and 75 °C and aging times of 0 day, 5 days and 10 days. Then the indirect tensile strength (ITS) test, freeze-thaw ITS test and low-temperature ITS test were conducted. The results show that, among the selected three gradations, the CRME with finer gradation has the higher optimum water content and optimum asphalt emulsion content and the denser structure, which in turn leads to the better mechanical property, moisture stability and low-temperature cracking resistance after different aging conditions. Moreover, after long-term aging, the effect of gradation on mechanical property of CRME becomes more and more significant. As the aging time increases, the ITS and freeze-thaw ITS ratio of all CRMEs firstly increase rapidly and then increase slowly or even decrease, and the low-temperature cracking resistance gradually worsens. Compared with 75 °C aging temperature, the CRME under 60 °C aging temperature has the better moisture stability and low-temperature cracking resistance, and the aging effect of 75 °C aging temperature on asphalt binder in CRME is more serious than that of 60 °C aging temperature. Environmental scanning electron microscopy results indicate that, after 10 days aging at 60 °C or 5 days aging at 75 °C, the CRME can form a continuous and close-grained microstructure composed by cement hydration products and asphalt binders.