Foamed bitumen decay equation and bitumen foaming characteristics evaluation

The expansion ratio and the half-life are usually utilized to evaluate the characteristics of foamed bitumen at present, but it's hard to determine the optimum foaming parameters due to lack of definite numerical evaluation criteria. Therefore, an index is developed in this study to solve the problem. One of the existing decay equations is chosen as the basic form of the foamed bitumen decay equation. Then the general equation is derived by differential for the actual maximum expansion ratio, and a general decay equation is obtained with corrected boundary conditions of foamed bitumen decay. The foam energy index is defined from the view of energy, and the index formula is derived by integral. The foaming test data of four kinds of bitumen used in actual works are analyzed. The result shows that the foam energy index quantifies the bitumen foaming characteristics with a clear physical meaning, and it can be used to determine the optimum foaming parameters and evaluate the characteristics of different foamed bitumen.