Study of aggregate gradations in foamed bitumen mixes

This paper investigated the influences of aggregate gradation on the mix design and mechanical properties of foamed bitumen mix (FBM). Various gradations with different compositions of the fine aggregate fraction (FAF) and coarse aggregate fraction (CAF) were designed and quantified as gradation shaper factors for the different fractions. The mix design results showed that the optimum foamed bitumen content was mainly determined by the content of fillers (<0.075 mm), but independent of the CAF composition. The indirect tensile strength test and unconfined compressive strength test were used to characterise the mechanical properties of FBM with varying aggregate gradations. The test results indicated that the FAF was the most dominant part in gradations of FBM, while the composition of the CAF had an insignificant impact on FBM. Increasing the density of the FAF and ensuring a rational trend of the blended gradation simultaneously could effectively improve the mechanical properties of FBM. Rational ranges of the shaper factors for the FAF and blended gradation were recommended based on the test results.