Effect of cement on the strength and microcosmic characteristics of cold recycled mixtures using foamed asphalt

Abstract This paper investigates the influence of cement on the strength and microcosmic properties of cold recycled mixtures using foamed asphalt (CRMF). An indirect tensile strength (ITS) test and simple triaxial test (STT) were used to evaluate mixtures properties with and without cement. A repeated loading deformation-strength test (RLDST) was conducted to discern the difference of resistance to permanent deformation between the two kinds of mixture. An X-ray computed tomography (CT) test and scanning electron microscope (SEM) test were used to identify the air voids distribution and micromorphology characteristics of CRMF. Strength formation mechanism was revealed by analyze the micro-structure and air voids distribution of CRMF. Test results indicated that cement had a significant influence on ITS and resistance to moisture damage. Moreover, micro-structure and air voids distribution was obviously changed due to the addition of cement, as shown by SEM and CT test. STT results showed that internal friction increased significantly, while cohesion had little difference with addition of cement. The fracture energy of the mixture increased remarkably, but failure strain decreased obviously with the addition of cement. Thus, the brittleness of CRMF was enhanced, therefore flexibility was reduced. Results of RLDST indicated that resistance to permanent deformation was distinctly improved with addition of cement. The X-ray CT test indicated that the weak interface was destroyed as the freeze-thawing process continued, which resulted in several voids connecting to form a large voids. Consequently, air void distribution varied after freeze-thaw processes.