Effect of mixing sequence on asphalt mixtures containing waste tire rubber and warm mix surfactants

Abstract

Crumb rubber modified asphalt mixture (CRMA) has gained rapid-growing interest as a sustainable paving material, because it allows value-added recycling of waste tire into durable and low-noise asphalt pavements. However, the poor workability of CRMA leads to higher construction temperature, which results in more energy consumption and hazardous emission. Surfactant, a typical warm mix asphalt additive, has been proven to be effective in alleviating the workability concern of CRMA without obviously deteriorating its mechanical properties. Nevertheless, performance of CRMA with surfactant may be influenced by the mixing sequence of different components (raw asphalt, crumb rubber, surfactant and aggregates), which unfortunately has not been well investigated yet. This study aims to address this issue by characterizing the engineering performance of warm CRMA prepared by six different mixing sequences. Properties including Marshall stability and flow value, workability, rheological property, rutting resistance, moisture sensitivity and fatigue resistance of prepared mixtures were measured and compared. Analytic hierarchy process (AHP) was employed to determine the optimal mixing sequence of warm CRMA considering the overall engineering performance. Test results showed that the effect of warm CRMA's mixing procedure on its engineering performance is noticeable. Earlier incorporation of surfactant additive had limited negative influence on mechanical properties of warm CRMA but allows for more energy saving during the production of rubberized asphalt binder. The AHP analysis results indicated that among the six mixing sequences, the optimal option is to make rubber absorb surfactant first, then incorporating the rubber-surfactant compound to raw asphalt and finally blending the modified binder to aggregates.