Study On Component Design And Properties Of Fibers Modified Porous Asphalt Mix

Porous asphalt is a type of open-graded asphalt pavement with stone-on-stone and porous skeleton, used to improve friction, minimize hydroplaning, reduce splash and spray, improve visibility, and lower pavement noise levels. On the basis of learning some design processes of porous asphalt abroad, this paper proposes a simpler and quicker design process of fibers modified porous asphalt. The process includes making samples using Superpave Gyratory Compactor (SGC), selecting gradation by the criterion of stone-on-stone contact and certain air voids in the mix and determining the optimal asphalt content limited by draindown test and expected air voids as the main controllability condition. It is suitable to increase the asphalt content of the mix in the range of expected air voids, which can ensure the compatibility of function and durability of porous asphalt.The drainage mechanism of porous asphalt is expatiated, and drainage ability is equal to light and medium rain intensity when the interconnected voids in the mix changes from 8% to 15% through experiments and calculation. Among the mixes with the different gradation types but same maximum normal size, porous asphalt mix has the best friction resistance. Influenced by ice expanding and freezing/thawing cycle, rutting depth of porous asphalt prominently increases, however the dynamic stability slightly decreases.Suffering from different test temperature and loading speed, the mechanics strength between open-graded PA-13 and dense-graded AC-13 was compared. The brittleness point for both mixes was determined respectively. Basing Mohr-Coulomb theory, indirect tension and unconfined compression were used to calculate the cohesion and angle of internal friction of both mixes. As the functional pavement, porous asphalt has weaker strength than dense-graded mix, and destroyed interface of this mix is different with different destroying conditions.At last, the research was conducted to evaluate fiber types on the properties of porous asphalt mixes. High temperature rheology of asphalt added fibers was determined and the evaluation of the rheology on the properties of the mix wasperformed in combination with rutting results. The technologies of scanning electron microscopy and X-ray computerized tomography was adopted to observe the microstructure of the fibers and inner skeleton of porous asphalt. Results indicate that the fibers mainly operate on stabilizing asphalt and thickening asphalt film on aggregates, but lead to minor improvement of the strength characteristics of porous asphalt mixes. In generally, cellulose fibers performed better than polyester fibers in porous asphalt mixes.