Water Stability Of Asphalt Mixture With Combined Dynamic Water Scouring And Freeze-Thaw Cycles

Water damage is a common problem in the current use of highway asphalt pavement.Some newly constructed roads have appeared a large number of pits,subsidence,looseness and other diseases even after one or two years of opening,and the performance and service life are far below the design level.Water is a key factor in causing water damage,vehicle loads and temperature factors exacerbate the occurrence of water damage.As a typical porous material,the water exist in the voids of the asphalt mixture forms a dynamic water scouring action under the repeated action of the vehicle load.Under the repeated action of the load,the existence of pore water causes the viscosity of the asphalt and the adhesion to the aggregate to decrease,thereby causing scour fatigue damage.For seasonal frozen soil region,repeated low temperature frost heaving and high temperature melt of the internal moisture of the asphalt mixture in the winter and spring season,which will also accelerate the strip of the asphalt film and water damage is further exacerbated.Carrying out the research of water damage behavior and prevention of asphalt pavement has important theoretical and practical significance for preventing and reducing economic losses caused by water damage.This paper comprehensively considered the dynamic water scouring effect caused by vehicle load and the interaction of freezing and thawing in seasonal frozen soil region based on the basic mechanism of water damage on asphalt pavement.Through the indoor simulated dynamic water scouring freeze-thaw cycle test and combing with micro-structural analysis(CT scan),the water damage mechanism of asphalt mixture under water-temperature-load interaction was analyzed.At the same time,combing the characteristics of road aggregates in Gansu Province and taking the solid anti-stripping agent cement,slaked lime and new anti-stripping agent commonly used in engineering as the research object,the anti-stripping performance of the dynamic water scouring freeze-thaw cycle was evaluated.The results show that the dynamic water scouring effect will aggravate the loss of fine aggregates in the asphalt mixture,which resulting in a decrease in the adhesion of the asphalt film to the aggregate.The decline of mechanical properties is more significant under the effect of low temperature frost heaving,the dynamic water scouring action causes a large amount of micro-opening voids inside the mixture to retain a large amount of moisture,and the frost heaving occurs continuously as the freeze-thaw cycle continues,resulting in a large number of micro-cracks.Under the repeated scouring action of the dynamic water pressure,the micro-cracks gradually penetrate,which resulting in the porosity increases constantly.The freeze-thaw damage of the mixture under the dynamic water scouring mode presents a typical step-like incremental pattern,which can be divided into rapid damage period,stable damage period and accelerated damage period,while the static immersion mode is characterized by a continuous progressive damage mode.The CT scan results show that the mechanical abrasion of the water scouring will accelerate the strip of the asphalt film.At the same time,the dynamic water scouring will accelerate the loss of fine aggregates,resulting in the volume of the surrounding voids increase.Under the action of dynamic water scouring freeze-thaw cycle,the test of splitting tensile strength of asphalt mixture with different types of anti-stripping agents shows that: after multiple freeze-thaw cycles,compared with the asphalt mixture without the anti-stripping agent,the asphalt mixture with high polymer added has the highest splitting tensile strength,the second is slaked lime,and the smallest is cement.The asphalt mixture with cement added is more sensitive to the cumulative effect of freeze-thaw and dynamic water scouring,the porosity and TSR of the mixture change the fastest.The mixture of the high molecular polymer added has the lowest rate of change in porosity and TSR,and the water stability is optimal.