A review of the development of asphalt foaming technology

To comprehensively assess the current state-of-art in asphalt foaming technology, the following four key aspects have been reviewed systematically: foaming principles, test methods, evaluation indicators, and influencing factors. Key findings reveal that asphalt foaming was primarily driven by the vaporization of water, with deterioration processes including bubble collapse and liquid film drainage. However, the current understanding of asphalt foaming principles remains limited, primarily due to difficulties in capturing and precisely measuring its microscopic behaviors during asphalt foaming process. Volume changes provided an intuitive means to evaluate the expansion capacity of asphalt and its foaming stability. Bubble evolution characteristics of foamed asphalt offered promising insights into its foaming performance. Traditional ruler and stopwatch-based assessments were being superseded by automated techniques like laser and ultrasonic ranging. Nevertheless, the current measuring equipment still lacks the capability to comprehensively evaluate the foaming effect of asphalt across various dimensions. Asphalt temperature and foaming water consumption significantly affected asphalt foaming performance, and the inclusion of foaming agents typically led to a notable increase in the half life of foamed asphalt. However, the interaction between foaming agents and asphalt, as well as the underlying mechanisms affecting the foaming effect, are still unclear and require further exploration. Future research should primarily focus on the correlation between asphalt foaming effect and mixture performance, aiming to guide the practical engineering application of foamed asphalt mixtures and enlarge the advantages of such low-emission and sustainable mixtures.