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Highlights • Moisture damage induced by dynamic pore water pressure exhibits a totally different failure mechanism. • Newly proposed dynamic pore water pressure conditioning methods and their applications are reviewed. • Relevant investigations on multiscale numerical simulation and field tests are analyzed. • Challenges on current research and future works are discussed. Abstract Under repeated vehicle loadings, surface runoff and retained water inside asphalt pavement structure will cause dynamic pore water pressure with positive and negative alternations. Such dynamic pore water pressure squeezes and pumps water flow along the inner wall of void channels to strip asphalt film and finally develop into moisture damage. Different from the traditional freeze-thaw and static water immersion mechanisms, dynamic hydraulic scouring induced by vehicle tires demonstrates a more general moisture damage of asphalt pavement in warm seasons or warm regions. This paper reviews extensive research works in the last decade about moisture damage of asphalt pavement induced by dynamic pore water pressure. A field survey of distresses characterization for an asphalt pavement is firstly introduced and analyzed. On the basis of analyzing macro-scale and micro-scale mechanisms of hydraulic scouring, traditional experimental methods for moisture damage evaluation are then discussed. Newly proposed three types of dynamic pore water pressure conditioning systems with their applications, which include pneumatic, piston and other types, are categorized and analyzed. Multiscale experimental investigations considering dynamic pore water pressure are discussed in detail. Numerical simulation on the water-mechanic response, moisture damage characteristics of asphalt pavement and the real-time monitoring of dynamic pore water pressure in field tests are also summarized. Finally, a series of measures to mitigate moisture damage from the perspective of dynamic hydraulic scouring is proposed. [ABSTRACT FROM AUTHOR]

• Stiffness and relaxation modulus similarly declined with water severities. • Master curves of creep compliance moved up, but inversely did relaxation modulus. • A larger size of coarse aggregate skeleton reduced HMA's moisture sensitivity. • Asphalt showed different reaction mechanisms in different water environments. With the degraded service performance induced by the erosion of dynamic water pressure environment in summer, asphalt pavement has to subsequently overcome the challenge of low-temperature environment in winter. Considering the unique phenomenon of the gradual disintegration of asphalt mixtures' components, it is still a lack of systematic research on moisture damage induced by dynamic water pressure environment from the perspective of viscoelastic properties. This study adopted the bending beam rheometer (BBR) method to evaluate the influence of dynamic water pressure environment on viscoelastic mechanical performance for asphalt mixture. The results indicated that both creep stiffness modulus and relaxation modulus of asphalt mixture showed similar downward trends with the increase in severities of different water environments, while values of relaxation modulus were slightly smaller than that of creep stiffness modulus. Master curves of creep compliance gradually moved upward with the increase in severities of dynamic water pressure environments, while master curves of relaxation modulus inversely moved downward. Specially, master curves of both creep compliance and relaxation modulus exhibited irregular trends for the dynamic water pressure environment of 60 ℃ − 0.414 MPa, which implied that significant erosion had been brought into asphalt mixture. A relative larger size of coarse aggregate skeleton could improve the resistance of asphalt mixture to moisture damage. The positive effect on improving resistance of asphalt mixture to moisture damage induced by SBS modified asphalt binder was stronger than the negative effect induced by the gradation with a relatively small nominal maximum aggregate size (NMAS). Differences existed in the reaction mechanisms of different types of asphalt binder subjected to the erosion of different water environments. [ABSTRACT FROM AUTHOR]

• Dynamic response signals showed relatively larger magnitudes in saturated condition than those in dry condition. • Pore water pressure was sensitive to vehicle speed compared with vehicle load. • Vehicle wheels of front and rear axles generated pore water pressure with obvious different magnitudes. • Tread pattern of vehicle wheel would affect the transverse distribution of dynamic pore water pressure. • Prediction model of positive pore water pressure taken both vehicle load and speed into account was proposed. Asphalt pavement exhibits different dynamic responses to vehicle loading in saturated conditions and in dry conditions. It is essential to directly conduct field full-scale tests to systematically investigate comprehensive influence of water on dynamic response of asphalt pavement. However, real vehicles which were often applied in field tests might result in a certain deviation in dynamic responses measured from each field loading test due to the inevitable influence of the driver's subjective operation and the tread pattern on vehicle wheel. This study adopted the full-scale accelerated loading test system to comprehensively characterize dynamic response of asphalt pavement in both dry and saturated conditions based on the strict control of loading vehicle's path. The results indicated that dynamic responses showed relatively larger magnitudes in saturated condition than those in dry condition. Strain and stress respectively showed slowly increasing and decreasing trends with the increase of vehicle load and speed correspondingly. Pore water pressure was apparently sensitive to vehicle speed compared with vehicle load. Pore water pressure generated by the front axle wheels showed obviously larger magnitudes than those produced by the rear axle wheels due to the change in thickness of surface runoff. The transverse distribution of pore water pressure obtained from both field tests and numerical simulation exhibited consistent variation trends. Decline degree of pore water pressure magnitudes was obtained at 86.1% for the two adjacent testing points with a distance of 100 mm under the vehicle wheel, which proved the great influence of the tread pattern of vehicle wheel on the transverse distribution of dynamic pore water pressure. A prediction model of positive pore water pressure that considered vehicle load and speed was proposed. [ABSTRACT FROM AUTHOR]

• FAM's performance greatly affected the moisture sensitivity of HMA induced by dynamic water environment. • Short-term conditioning in a harsh dynamic water environment also exhibited a great erosion effect on asphalt materials. • Softening and emulsifying showed more obvious effects on asphalt binder during dynamic water conditioning. • HMA tended to exhibit more elasticity as the increase of environment severity. Moisture damage induced by dynamic pore water pressure commonly occurs in asphalt pavement located in regions with rich rainfall. This kind of moisture damage illustrates a special and quite different mechanism compared with that induced by static water immersion and freeze-thaw. Fine aggregate mixture (FAM) plays a vital role on the entire resistance of hot mix asphalt (HMA) to moisture damage. However, there is still a lack of systematic research on the evaluation of moisture sensitivity for both HMA and its components such as asphalt binder and FAM at the same scale. This study adopted the bending beam rheometer (BBR) method to assess moisture sensitivity for HMA and its components induced by dynamic water environment. The results indicated that the creep stiffness for both HMA and its components declined after being conditioned in dynamic water environment. FAM was quite easily eroded and its maximum decrease extent of creep stiffness could even up to 54.8%. In this case, it was clearly shown that the moisture sensitivity of HMA was greatly affected by its FAM component's performance. The erosion effect of short-term conditioning in a harsh dynamic water environment was comparable to that of long-term conditioning in a mild environment. Softening and emulsifying showed more obvious effects on both asphalt binder and FAM during dynamic water conditioning, which made them exhibit more viscosity. Specially, after the FAM component on the surface of a HMA sample being scoured away, the retained coarse aggregate skeleton made the entire HMA sample still remain a certain mechanical strength and anti-erosion ability. Based on the analysis of the indicator m/S , HMA showed viscous performance in a mild dynamic water environment but tended to exhibit more elasticity with the increase of environment severity. [ABSTRACT FROM AUTHOR]