Study On The Resistance Ability To Water Damage Of Hot Mix Asphalt (HMA)

Water damage of hot mixture asphalt (HMA) is a leading mode of premature disease of asphalt pavement. Bleeding, cracking, rutting and raveling are typical diseases of asphalt pavement and the existence of water consequentially accelerate the forming and development of all sorts of diseases, which is called the water damage of asphalt pavement.The main contents included in this paper are ternary. Firstly, to investigate the relationship between aggregate characters such as surface roughness, relative surface area, the number ratio and distribution of pores, the presence of clay fines on the aggregate surface and aggregate-asphalt adhesive strength, because aggregate can greatly influence whether a mixture will be sensitive to water or not. The test method of "Texas Freeze-Thaw Pedestal test" was utilized to investigate the relation between the chemical and mineralogical elements of aggregate and water stability of asphalt mixture. Contact angle test indicated that the surface characteristics would contribute a good preliminary adhesion between asphalt and aggregate. Secondly, two different materials of liquid anti-stripping agent and hydrated lime were utilized as an organic and an inorganic measures to improve the water stability of asphalt mixtures, the dosage of them are 0.4 wt% of asphalt and 1.5 wt% of the aggregate respectively, the effectiveness of the treatments were discussed too; thirdly, the mechanisms of adhesion and rupture model of asphalt film on aggregate surface and how the liquid anti-stripping agent and hydrated lime improve the resistance ability to water were analyzed according to the anterior tests and investigations.Aiming at the subject, numerous laboratory tests have been used to identify moisture-related problems. Micro-tests are mainly aim at the performance of raw materials, and macro-tests, mainly aim at asphalt mixture, these include tests on (a) loose mix to determine coating during water immersion or in boiling water and (b) compacted mix to evaluate the retained strength or stiffness and the amount of rutting or disintegration during wheel-tracking tests immersed in water. All types of tests measure the effects of moisture on adhesion, cohesion, or some combination of others.The tests results indicated that biggish surface area, rough and clean surface condition, proper pore number and size distribution, abundant alkaline-earth metals such as calcium will contribute to a satisfactory adhesion between asphalt andaggregate. Relative to "alkaline" aggregate, the asphalt mixture with "litmusless" or "acid" aggregate will be more sensitive to water because of the weak bond between asphalt and aggregate. The liquid anti-stripping agent and hydrated lime can effectively improve the water sensitivity of asphalt mixture, and relatively, the liquid anti-stripping agent is more expensive but convenient, the hydrated lime, more effective but time-consuming.