Performance Evaluation of Asphalt Rubber in Porous Asphalt-Concrete Mixtures

The purpose of this study was first to present the laboratory mix design results for porous asphalt concrete (PAC) mixtures blended with high-viscosity-graded cement (AR-80) and asphalt rubber (AR). In addition, the master curves of dynamic modulus were determined for both the unconfined and confined conditions to evaluate the rutting behavior of both PAC mixtures. The mix design results showed that the PAC open-graded mixture consisted of a relatively large percentage of coarse aggregate, with less than 15% of the material passing through a 2.36-mm (No. 8) sieve, which created a sufficient space for water drainage. The target air voids of approximately 20%, as well as the coefficient of permeability greater than ${10}^{-2}\mathrm{cm}/\mathrm{s}$ , were established. Comparing the master curves of dynamic modulus between these two types of PAC mixtures indicated that the asphalt-rubber mixtures exhibited higher dynamic modulus at longer reduced times for both the unconfined and confined conditions. The experimental results of repeated triaxial-loaded and wheel tracking permanent deformation tests confirmed that the asphalt-rubber mixtures have superior performance against rutting. Furthermore, the high void of both PAC mixtures illustrated the validity of the principles of time-temperature superposition in the large strain of the viscoplastic stage during repeated triaxial-loaded permanent deformation tests.