Evaluation Method Of Adhesion Between Aggregate And Bitumen And Long-term Moisture Susceptibility Evaluation Of Hydraulic Asphalt Concrete

In this paper,the moisture damage of hydraulic asphalt concrete has been studied from two aspects:the adhesion between aggregate and bitumen and the long-term moisture susceptibility of asphalt concrete.The adhesion between aggregate and bitumen was studied based on the surface energy theory.The static contact angle and Advancing Contact Angle of 5 kinds of probe liquid,such as distilled water,glycol,diiomethane,glycerin and ?-formamide,on the surface of limestone,basalt,granite and bitumen of different grades were measured.Studies have shown that temperature has a great influence on the stability of the contact angle on bitumen.According to the measured contact angle,the surface energy components of different aggregates and bitumen were calculated,and the adhesion work between different aggregates and bitumen was calculated.The results show that for the same bitumen,its adhesion work with limestone is the highest and its adhesion work with granite is the lowest,which is consistent with the test results of boiling test.The adhesion work increases with the decrease of the Lewis alkaline component of the surface energy of the aggregate and the Lewis acid component of the bitumen surface energy.The long-term moisture susceptibility test of limestone and granite asphalt concrete at 20?,40?,60? and 80? was carried out for up to 128 days.During the test,the asphalt concrete specimens did not appear loose and separation between aggregates and bitumen.The compressive strength,splitting strength,and bending strain were used to calculate the moisture susceptibility coefficient after different immersion times.The results show that the compressive strength is less sensitive to moisture damage.The relationship curves between the moisture susceptibility coefficient and the logarithm of immersion time at different temperatures were obtained.Based on the Time-Temperature-Superposition principle,the main curve of moisture susceptibility coefficient versus logarithm immersion time and shift factor at different temperatures was obtained.Based on this,an evaluation model of immersion durability of hydraulic asphalt concrete is established.The two most probable forms of failure of hydraulic asphalt concrete under moisture damage are studied:low temperature fracturing and cracking.The results show that the fracture temperature of asphalt concrete increases first and then decreases with the extension of the immersion time,indicating that moisture damage is unlikely to cause the asphalt facing to eventually crack at low temperature.According to study,the maximum tensile strain that may occur during the operation of the hydraulic asphalt concrete facing is 0.23%.Taking this as the life threshold,the moisture damage life of granite aggregate and limestone aggregate asphalt concrete is infinite.Finally,the influence of the anti-stripping agent to adhesion of aggregate and bitumen and the moisture susceptbility of the asphalt concrete are studied.The calculation results of surface energy and adhesion work show that after adding anti-stripping agent,the Lewis acidic component of bitumen surface energy decreases,the adhesion work of granite aggregate and asphalt is improved,and its moisture susceptibility has reached the same level as that of limestone aggregate.