Simulation and Validation of Asphalt Foaming Process for Virtual Experiments and Optimization of WMA Production

Abstract

The asphalt foaming process, as one of the major warm mix asphalt (WMA) technologies, can significantly increase the volume of asphalt binder with large surface area in the unit volume and thus generate a strong coating with high shear strength of the mix and improved workability. It allows lower production and construction temperatures and less greenhouse gas and other emissions. Foaming asphalt has generally been achieved by introducing water as a foaming agent into hot asphalt flow before mixing with aggregate at a certain temperature. The water will evaporate and expand the asphalt volume and reduce its viscosity. However, both the formation and decay of the foamed asphalt binder is a highly thermodynamic process, which makes the characterization of the foamed asphalt binder extremely difficult. A high fidelity model to simulate the foaming process will provide a powerful tool to conduct virtual experiments of WMA production and optimize the asphalt foaming process and WMA design. To this end, a numerical model using smooth particle hydrodynamics (SPH) is developed to simulate the asphalt foaming process. A self-developed nozzle-based foamer was used to generate foamed asphalt binder at different water contents. Three primary parameters, i.e., expansion ratio, half-life and foam index, that have been widely applied to evaluate the foaming characteristics of foamed asphalt, have been studied. It was found that the simulation results agree well with the experiments. Parametric studies were further conducted by using the numerical model to evaluate the effects of environmental controlling parameters on the foaming characteristics of the foamed asphalt binder.