A comprehensive review of theory, development, and implementation of warm mix asphalt using foaming techniques

Asphalt foaming techniques have been used over the last couple of decades as an alternative to the traditional method of preparing asphalt mixtures. Various efforts have been initiated to assess the technology and enhance its efficiency during production. In this article, a comprehensive review of foaming warm mix asphalt (WMA) techniques, foaming theory and mechanisms, research and development as well as characterization procedures are presented. This paper also summarized numerous research and paving applications using foaming WMA technologies in Europe, the United States, Canada, China, Australia, New Zealand and some other countries. Findings from laboratory tests and field performance are also presented. Based on several field trials, the performance of foaming WMA is comparable to conventional HMA. The United States was found to be the most active country working on research-based and field trial evaluations on WMA besides two European countries: Germany and Norway. In addition to reducing energy consumption, reductions in fuel usage have significantly reduced the stack emissions of greenhouse gases, such as carbon dioxide, sulfur dioxide, and nitrous oxide. This review concludes with some recommendations in terms of diversifying the foaming agent and selection of test parameters in order to have a better precision and repeatability of test results.