An application of the Michaelis-Menten model to analyze the curing process of cold recycled bituminous mixtures

In this paper the laboratory curing process of two types of cold recycled mixtures manufactured during the construction of an experimental pavement section along an Italian motorway was investigated. Specifically, a cement-bitumen treated material (CBTM) mixture and a cement treated material (CTM) mixture, produced both on site and in laboratory, were tested. Moisture loss by evaporation (DW), indirect tensile stiffness modulus (ITSM) and indirect tensile strength (ITS) were measured in order to evaluate the curing process. The measured data were analyzed using the nonlinear Michaelis-Menten (MM) model with the aim to characterize the rate at which the mixture properties evolve over time and their values at the long-term cured state. The results showed that the adopted curing variables (DW, ITSM and ITS) gave a comparable description of the curing process, when evaporation was allowed and that the MM model gave an appropriate description of the evolutive behavior of CBTMs and CTMs. Finally, the results showed that in the initial curing stage the effect of cement hydration prevailed on that of emulsion breaking.