Effects of moisture damage on asphalt mixtures

The reduction in the ability of bitumen to bond with the aggregate surface due to the infiltration of moisture has been recognised for years, and this deterioration phenomenon is called moisture damage. In general, the loss of bonding between bitumen and aggregate shortens the service life of the top layer of the pavement. Many investigations have been conducted to understand the mechanisms of moisture damage due to the loss of bonding strength between bitumen and aggregate and to find ways to improve and strengthen the bond to mitigate the effect of moisture. This paper reviews the extensive literature on the loss of bitumen-aggregate bonding strength due to moisture damage in asphalt mixtures. The general description of the theories and mechanisms that explain the effect of the thermodynamic, chemical, physical and mechanical characteristics of the bitumen and aggregate on the bonding phenomenon are discussed in this paper. In addition, the causes of and contributing factors to moisture damage and methods to improve the bond between bitumen and aggregates are also discussed. Moreover, a description of the test methods that can be used to evaluate moisture damage in poorly bonded and compacted mixtures are also presented. Special attention is given to a well-known method, known as the pull-off test, which has been successfully used to evaluate aggregate-binder bond strength, both for laboratory and in-situ tests. This includes the test methods, the factors that affect the bonding strength results and their correlation with other test method. A review of the failure mode of bitumen under the pull-off loading test is discussed in the final section of this paper.