Laboratory Investigation of Factors Affecting the Evolution of Curing in Cold In-Place Recycled Materials

Most cold in-place recycling (CIR) construction uses asphalt emulsion or foamed asphalt as stabilizing agent, which requires placing and compacting at optimum moisture or fluid content in the field. To ensure the CIR layer gains appreciable mechanical capacity to support traffic (including that of construction vehicles), the CIR layer must cure. Curing is typically expressed in relation to moisture content in the CIR layer; however, there is need to explore if a direct link exists between the amount of moisture in CIR and the mechanical properties of CIR. Presently, to ensure sufficient curing, construction specifications recommend time estimates with minimal consideration of how various factors such as material variations, climatic inputs, and construction process differences may affect the curing evolution. The objective of this study was to investigate and identify the critical factors that affect the curing evolution of CIR materials. Curing was evaluated in relation to moisture loss (using gravimetric measurements) and gain in mechanical properties (using indirect tensile strength and resilient modulus tests). The results show that there is further gain in mechanical properties after the CIR mixtures have reached an equilibrium moisture condition. Additionally, the following factors were identified to most significantly affect the curing evolution of CIR materials: stabilizer type and amount, active filler type and amount, initial moisture content, curing temperature (when active filler is present), and moisture reintroduction through external sources (e.g., rainfall). On the other hand, density and curing temperature (in the absence of active filler) did not seem to affect the rate of curing.