Asphalt And Asphalt Mixture Performance Deterioration Under Action Of Chloride Salt

Bituminous mixes are most used all over the world in pavement construction.Under normal circumstances,bituminous materials if designed and executed properly perform quite satisfactory.Some materials produce a good effect and enhance the strength as well as qualities of bitumen.On the other hand,some are responsible for the adverse on the bitumen.In saline areas like coastal regions,the salts play a significant role in the bituminous pavements.In coastal area,pavement often comes across with saline water.In this area,the salts particularly sodium chloride plays an important role in the stability as well as durability of roads.In this situation,the effect of salts on properties of bitumen is important for proper design and maintenance of the pavements.The objective of this paper is to find out the effects of salt on asphalt and asphalt mixture using different proportions of salt and soaking times.Before being subjected to soaking,44?g of asphalt was made into specimens of similar shape and thickness(10 cm x 10 cm x 2 cm).A lot of samples were soaked in saline water at room temperature and conditioned at predetermined time.After conditioning the specimens were taken out and blow dried for testing.All samples are subjected to different salt concentrations(5%,10% and 15%)with different soaking time(1 day,7days,15 days,30days).We Firstly evaluate the effect of sodium chloride on asphalt binders by using the empirical tests(penetration point,softening point and ductility)to evaluate the properties of different types of asphalt binders after soaking in salt water and it is observed from the laboratory test that the penetration and ductility values are gradually decreased while the softening point increase with increase of salt content in water.Before subject to soaking we also evaluated the original asphalt properties at different salt water concentrations.After that the surface morphology(topography)of each asphalt was evaluated by using Atomic Force Microscopy(AFM)test.The AFM results showed that the roughness of asphalt surface increase while the salt concentration and soaking time increase.Otherwise we used Dynamic Shear Rheometer(DSR)test to evaluate the complex modulus and phase angle master curves of each binder before and after soaking in salt water.The DSR test results indicated that the complex shear modulus of all binders increases while the salt concentration increases in water but the phase angle slightly drops for modified asphalts and increase for conventional asphalts.Secondly the effect of sodium chloride on asphalt mixture performance was tested by using Hirsch Model to calculate asphalt concrete modulus and Asphalt Institute(AI)model for prediction of fatigue cracking of asphalt mixtures.The Hirsch Model indicated that the asphalt concrete modulus increases while the salt concentration increases in water and Asphalt Institute(AI)Model predicted that the fatigue life of asphalt concrete reduces when the salt concentration and soaking time increase.Salt is responsible for the increasing of fatigue damage on asphalt pavement.It should also be noted salt improved high temperature properties of asphalt by reducing rutting damage on asphalt pavement.Finally,we used Abaqus finite element dynamic mechanical response to evaluate the deformations of typical pavement structure under wheel load action with different variation of salt concentration(5%,10% and 15%)and soaking time(7days,15 days,30days)and the simulation test result showed that the pavement deformations decrease with increasing of salt concentration in water and soaking times.The low value of deformation is obtained at high salt concentration with 30 days soaking times.After that we used different Asphalt Institute models to predict the fatigue cracking and rutting damages of asphalt mixture and it is observed that at 15% salt concentration the fatigue life of pavement is small than 5% and 10% of salt concentrations.The increasing of soaking times increases also the fatigue damage on asphalt pavement.But the rutting result showed that higher the salt concentration and soaking time smaller the rutting damage of asphalt pavement.