Properties Investigation Of Moisture Damage For Gneiss Asphalt Mixtures

The main problems of asphalt pavement are bleeding, cracking, rutting and raveling, and the existence of water can accelerate to form and develop all these problems, what is called water damage to asphalt pavement. Among the controllable factors, the lithology of the aggregate has the greatest effect on the water stability property of asphalt mixture. Acidic aggregates such as gneiss, granite and gritstone are not widely used because of their poor adhesion to bitumen. China is vast in territory and different in geological structure. Blindly pursuing the use of alkaline, neutral stone in some regions rich in acidic stone is bound to raise the project cost and extend construction period. In such circumstances, we should think of ways to use the local materials actively and rationally not only to reduce cost and shorten the construction period, but also to bring the economic development and benefit the local people. Corresponding to the actual project, this paper investigate the preparation of asphalt mixture with acidic aggregate gneiss and its service performance particularly the water stability, which lay a basis to the extensive use of gneiss asphalt mixture.Firstly, the influences of hydrated lime on the rheological properties of bitumen binder were investigated. Results indicates that a appropriate amount of hydrated lime can decrease the penetration and temperature sensitivity, increase the softening point and viscosity; it can also increase the complex modulus of bitumen binder, and the temperature sensitivity area for the influence of hydrated lime on complex modulus is in the range of 30～40℃.Secondly, the effects of different improvement measures to gneiss asphalt mixture performance were determined by Immersing Marshall test, Frozen-thaw Cycle Test, Dynamic Modulus Test and Indirect Tensile Fatigue Test. Results shows that addition of proper hydrated lime and fine aggregate of limestone replace gneiss made together can significantly improve the moisture resistance and high temperature stability of gneiss asphalt mixture, and enhance the mechanic property of dynamic modulus. Its fatigue life is better than limestone asphalt mixture when the stress level is smaller than 1.0 MPa.Thirdly, the influences of moisture treatments water immersing and frozen-thaw cycle on the creep and bending fatigue properties of gneiss asphalt mixture were taken into consideration. Results indicate that after water immersing, the strain and permanent deformation is 1.4 and 1.5 times of normal samples, respectively. And the creep stiffness modulus is decreased by 27 persent. When the strain is smaller than 300με, the fatigue life of samples after water immersing is better than normal asphalt mixture, but take all things into consideration, the water treatments water immersing and frozen-thaw cycle evidently decrease the fatigue life of gneiss asphalt mixture.Finally, according to the actual project application, the conclusion is that addition of proper hydrated lime and fine aggregate of limestone replace gneiss taken together can significantly improve the performance of gneiss asphalt mixture. The proper amount of hydrated lime for application is 1 wt% of the asphalt mixture.