Advanced characterisation of flexural fatigue performance of foamed bitumen stabilised pavement materials

This study investigates the flexural fatigue behaviour of FBS mixtures at different temperatures (11℃, 22℃ and 31℃) bitumen contents (2%, 3% and 4%), secondary binders (cement at 2% and hydrated lime at 2% and 4%), densities (2.14 kg/m³, 2.20 kg/m³ and 2.26 kg/m³) and moisture contents (dry and 90% saturation) with a view to developing a rigorous design approach for FBS pavements. The experimental results showed that the flexural fatigue life of the FBS beams increases with increasing density and bitumen content while it decreases with increasing temperature and moisture content. Further, no noticeable difference was seen in the flexural fatigue life of FBS specimens with 2% and 4% hydrated lime contents while the FBS mixtures with 2% cement showed significantly higher fatigue life than those prepared with 2% hydrated lime. The flexural fatigue life of 3% bitumen and 2% lime FBS mixture under strain-controlled mode was found to be around 21 times higher than that under stress-controlled mode for a given initial flexural strain. The normalised modulus degradation master curve in stress-controlled mode appears to demonstrate a characteristic behaviour of FBS materials under cyclic fatigue loading. Using this new concept and the experimental results, suitable analytical models were developed for the prediction of the flexural fatigue life of FBS mixtures under both stress-controlled and strain-controlled modes taking into account the variations in temperature, bitumen content, moisture content and density of the FBS mixtures.