Study on improvement of asphalt adhesion by hydrated lime based on surface free energy method

Abstract

In order to study the improvement of hydrated lime (HL) on asphalt adhesion from mechanism, an asphalt-aggregate adhesion failure model was established based on surface free energy (SFE) method. In the model, the adhesion work Wa was chosen as the main index to evaluate the adhesion between asphalt and aggregate. Adhesion work was studied from two aspects: one was the polarity difference between asphalt and aggregate before and after HL modification, and the other was the variations of asphalt SFE before and after HL modification. The effect of HL on the polarity difference was studied by the changes of the SFE polarity component γap of solid asphalt and contact angle θ between solid asphalt and aggregate, based on SFE theory and sessile drop method respectively. And then, the SFE components between liquid asphalt and aggregate before and after HL modification were measured by improved Wilhelmy plate method. To exclude the effect of binder ageing occurred in the preparation of HL modified asphalt and verify the effectiveness of HL, rolling thin-film oven (RTFO) and pressure ageing vessel (PAV) tests were conducted on asphalt with and without HL modification. The results showed that HL could significantly reduce the polarity difference between asphalt and aggregate and raise the SFE of asphalt. The reduction of polarity difference and the increase of SFE both lead to the raise of adhesion work, resulting in the improvement of the adhesion between asphalt and aggregate. Moreover, the results of RTFO and PAV test illustrated that binder ageing occurred in the whole process of study would have negligible effect on asphalt adhesion. Therefore, it was concluded that SFE method would be a good choice to explain the improvement of asphalt adhesion by HL.