Minnesota Department of Transportation
Most cold In-place recycled (CIR) construction uses asphalt emulsion or foamed asphalt with or without active fillers as a stabilizing agent. To ensure the CIR layer gains appreciable stiffness and strength to support traffic, the stabilizing agents have to undergo curing (to dry additional moisture). If traffic is allowed on the CIR layer before sufficient strength and structural capacity is gained, premature damage will occur. Lack of a fast and reliable procedure to determine the extent of in-situ curing significantly increases the risk of such damage. Current construction specifications rely on empirically based time recommendations to ensure sufficient curing. Current empirical time estimates do not account for material variations, climatic inputs and construction process differences. This research uses a combination of in-situ testing of actual CIR construction projects and supplementary laboratory tests to develop a model for pavement engineers and practitioners to reliably predict the recommended time (as a function of mechanical property) for placing of overlay on CIR layers. The prediction model incorporates the critical factors that influence curing in CIR including stabilizer type and amount, presence of active filler, initial moisture content, in-situ density and curing temperature. Due to the large number of possible model variables and their interactive effects, rigorous regression analysis is conducted to determine the most significant variables. The model provides an option of defining sufficient curing based on criticality of the project. The major outcome of this research is a user-friendly spreadsheet-based tool with pre-programmed curing model predictive equations.