Optimising foamed bitumen performance: an orthogonal testing and response surface methodology approach

The foaming performance of bitumen critically affects its dispersion uniformity in cold recycled mixtures. Expansion Ratio (ER) and Half-Life (HL), two key indicators of foaming performance, show opposite trends as water consumption increases, with ER rising and HL decreasing. This study investigates the combined effects of water consumption and foaming temperature using orthogonal experimental design. Results indicate that bitumen type and water consumption significantly influence ER and HL, while foaming temperature has minimal impact within 140°C – 160°C. To balance the trade-off between ER and HL, the Foam Index (FI) is proposed as a comprehensive metric. A Response Surface Methodology (RSM) model is developed to optimise the interaction of water consumption and temperature for FI. The findings provide practical strategies for improving the quality of cold recycled mixtures through optimised foaming conditions, offering valuable guidance for pavement engineering applications.