Investigating Foamed Bitumen Viscosity

Abstract

Foamed bitumen is a binder of cold mix road recycling materials. It is necessary to understand the best foamed bitumen properties prior to mixing with aggregate materials. Viscosity is one of the important properties, which facilitate the foam to distribute across the aggregate phase in the mixing process, and form a well coated asphalt mix. Unfortunately, the understanding of foamed bitumen viscosity and its contribution in the development of mixture performance is still poorly understood. This paper discusses foamed bitumen viscosity which was explored based on theoretical studies and a series of laboratory investigation. Foamed bitumen was produced using bitumen Pen 70/100 at temperature of 180°C. The research method was developed in three activities, i.e. (1) the previous studies on the foamed bitumen rheology, (2) investigating flow behavior of foamed bitumen, and (3) estimating foamed bitumen viscosity using Kraynik equation.The research results can be summarized in the following three points. First, foamed bitumen consists of gas content and liquid bitumen, in which the value of foam viscosity increases with the gas content. Second, foam flow can be used to indicate the apparent foam viscosity. Foamed bitumen with a higher foaming water content (FWC) tends to have a decreased flow rate and hence higher apparent viscosity. Third, foamed bitumen viscosity estimated using Kraynik equation is affected by gas content and liquid bitumen viscosity. It was found that an ERm of around 35 (or at FWC of 6%) is the critical area of foam viscosity.