Novel Testing Procedure for Assessment of Quality of Foamed Warm Mix Asphalt Binders

Abstract

This paper presents an image-based testing system called the asphalt foam collapse test (AFCT) to measure parameters that indicate the quality of foamed warm mix asphalt (WMA) binders. The AFCT was used to measure and evaluate various potential quality indicators such as expansion ratio (ER), half-life (HL), and foam index (FI). In addition, this paper introduces a method to calculate the bubble size distribution (BSD) of the bubbles in the foamed WMA. The BSD is then used to introduce a new parameter called the surface area index (SAI) as an indicator of foamed binder quality. It was shown that the SAI is a strong candidate for evaluating foamed WMA binder for coating and workability. Furthermore, this paper presents the effect of water content and air nozzle pressure on the foam properties. The results revealed that the water content and air pressure have a significant influence on the ER, HL, FI, BSD, and SAI. The low water content and low pressure produced foams with smaller bubbles as compared to foams made with high water content and high pressure, which affected the aggregate coating.