Decay properties of the foamed bitumens

This paper presents study on decay properties of two foamed bitumens. Foaming tests under various conditions were carried out to investigate decay properties of two types of bitumen: Penetration-grade 60 (PG 60) and Penetration-grade 100 (PG 100). Decay data were recorded and analyzed. It is found that water content has a significant effect on the bitumens’ decay, and the time at which the maximum expansion ratio appears advances with an increase of temperature. PG 60 achieves the maximum expansion ratio at an earlier time than PG 100. The effect of viscosity on the two bitumens’ decay properties was discussed and explained; and the observation of the tests confirms this explanation is rational. For developing the bitumens’ decay functions, a four-parameter power function and a three-parameter exponential function were selected to fit the testing data of PG 60 and PG 100 bitumen, respectively. Two bitumens’ decay functions were established by a two-stage method. Non-linear fitting analysis exhibits that two functions can well fit the data of the foaming tests. Decay functions’ parameters were obtained by using the best subset regression method. Two decay functions can be used to calculate the maximum expansion ratios and half-lives of PG 60 and 100 bitumen under various conditions.