Laboratory testing of rheological behavior of water-foamed bitumen

From the rheological behavior of bitumen, one can understand the physical properties of water-foamed bitumen used in warm mix asphalt. Previously, rheological behaviors of water-foamed bitumen such as apparent viscosity, agitation torque, and shear rate have not been well documented. The objectives of this study are as follows: (1) evaluating the accuracy of the cup-and-bob test with a dynamic shear rheometer to investigate the rheological behavior of water-foamed bitumen, (2) analyzing the rheological behavior of water-foamed bitumen at various temperatures, and (3) proposing an optimum water content that decreases the apparent viscosity and required agitation torque of water-foamed bitumen. Bitumen with various water contents (ranging from 0.0 to 3.0% bitumen content by mass) were prepared for rheological testing. The optimum water content at each of these foaming temperatures was determined based on the testing results. This study concludes that the current cup-and-bob test methods accurately describe the rheological behavior of water-foamed bitumen. Within the accepted water content range, the apparent viscosity and required agitation torque of water-foamed bitumen decrease more dramatically as water content increases.