Properties of Foamed Asphalt for Warm Mix Asphalt Applications

This report presents proposed AASHTO standard test methods for measuring performance-related properties of foamed asphalts and designing foamed asphalt mixes with satisfactory aggregate coating and workability. The objectives of this project were to determine key properties of foamed asphalt binders that significantly influence the performance of asphalt mixtures and develop laboratory protocols for foaming of asphalt binders and laboratory mixing procedures. The production and performance-related properties of foamed asphalt were investigated through a series of laboratory and field experiments. A key finding of the research is that the foaming characteristics of an asphalt binder are primarily affected by its source (i.e., its crude oil slate), the production date for a given refinery and crude oil slate, and polymer modification. A laser-based method was developed to measure parameters associated with the expansion and collapse of foamed asphalt. A digital photographic approach was developed to characterize the size, distribution, and surface area of bubbles formed during production of foamed asphalt. Methods were also identified for determining a coatability index for foamed asphalt and the workability of mixes produced with foamed asphalt. A foamed asphalt mixture design procedure was developed to identify the optimum water content for coating and workability. Finally, the utility and effectiveness of these various methods were verified through their application to foamed asphalt binder and mix produced in full-scale asphalt mix plants. This report fully documents the research. Four appendixes are included: Influence of Binder Properties on Binder Foam Expansion; Draft Commentary on Guidelines Proposed for Revising Appendix to AASHTO R 35; AASHTO Style Standards; and Field Foaming Data Acquisition Form.