Simulation and validation of asphalt foaming process for virtual experiments and optimisation of WMA production

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. Foamed 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 make the asphalt’s volume expanded and its viscosity reduced. However, both the formation and decay of the foamed asphalt binder is a highly thermodynamic process, which makes the characterisation 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 optimise the asphalt foaming process and WMA design. To this end, a numerical model using the smooth particle hydrodynamics is developed to simulate the asphalt foaming processes. A self-developed nozzle-based foamer was used to generate foamed asphalt binder at different water contents. Three primary parameters, expansion ratio, half-life and foam index that are widely applied to evaluate the foaming characteristics of foamed asphalt, have been studied. It was found that 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.