Investigation of early-stage strength for cold recycled asphalt mixture using foamed asphalt

This papers aims at investigating the strength properties of cold recycled mixtures using foamed asphalt (CRMF) at its early-stage of curing. Indirect tensile strength (ITS) and deformation-strength test were used to figure out the early-stage strength development law of the CRMF. Through image processing and analysis the fracture interface characteristics of CRMF were identified. Statistical methods were used to analyze the amounts of air voids in the CRMF specimens and a two-parameter Weibull model was used to describe the distribution of air voids in the CRMF using X-ray computed tomography (CT) technique. The results indicated that moisture content had a significant effect on the strength of CRMF. Moreover, cement only affected the early strength while the foamed asphalt affected the long-term strength of CRMF. The fracture path was developed along the weak interface where there was moisture membrane especially at 0-3 days curing. The asphalt mastic may be broken off forming the fracture path as the curing continuing after 3 days of curing. The X-ray CT test indicated that a weak hydration products interface was destroyed and two voids were interconnected to become one large void. However, variations of the voids amounts had almost no significant effect to the Weibull distribution of air voids in CRMF. The findings helps us to understand well to the development mechanism of early-stage strength of CRMF and lead us to new approaches to improve the early-stage strength.