Study On Degradation Of Mechanical Properties Of Cement-stabilized Base Course Under Acid Rain Environment And Cyclic Loading

With the development of expressways,semi-rigid base,as the first choice for highway construction,has been widely promoted and applied in various places.However,semi-rigid materials have the characteristics of temperature shrinkage and dry shrinkage.Under the influence of external environment,The semi-rigid base course will gradually produce cracks and reflect to asphalt mixture surface course.In the acid rain environment.acid rain will penetrate into the base course along the cracks in the pavement,it will be influence of the cement stabilized base course.And it will reduce the strength and modulus of the cement stabilized base structure and leading to the shortening of pavement structure life.Therefore,it is of great engineering significance to study the degradation of mechanical properties of cement stabilized base course with the influence of environmental factors.Firstly,the micro test analysis of the internal and external components of the cement stabilized base course of the old road is carried out,and investigate local traffic environment data.It is determined that the cement stabilized base course in this area is in a high axle load and closed acid humid and hot environment.The simulated acid rain solution was made to carry out the deterioration test of the cement stabilized base course specimen under the acid solution erosion and the dry wet cycle based on previous research.In addition,the effects of the acid solution concentration and the number of wetting-drying test on its apparent performance were analyzed.The results show that:after 7 cycles of wetting and drying in solutions of different concentrations,the surface of the specimens becomes more compact.Moreover,the test piece continues the wetting-drying test in the acid solution with pH=3,and the surface particle loss becomes more and more serious with the increase of the test cycle.During the test,the precipitated products on the surface of the test piece are gradually reduced from the initial precipitation on the surface of the test piece to the precipitation at the round edge of the test piece,and then to the final precipitation.The phenolphthalein titration area inside the test piece is also from the dark purple that runs through the whole test piece to the light purple that only exists in the middle area.Secondly,through the concentration of acid solution,the number of drying and watering cycle and the number of load fatigue to simulate the impact of real environment on the strength and modulus of cement stabilized base course.The test results show that the strength and modulus of the 90d standard specimen are increased in different concentrations of solutions after 7 times of wetting-drying test,and the increase is the largest in the acid solution with pH=3.And the test piece continues to be tested in the acid solution with pH=3.With the continuous wetting-drying test,the residual strength and modulus of the test piece gradually decrease.The residual strength and modulus of the long-term corroded specimens will decrease with the increase of fatigue times.Under the influence of multi factor interaction,the mechanical properties of the specimens of the with load fatigue test followed by dryingwetting tests are lower than those with drying-wetting tests followed by load fatigue test.With the increase of the number of dry wet cycles,the impact of load test sequence will increase.The mechanical properties of the cement stabilized base course core samples of the third lane in the original road are worse than those of other lanes.Finally,the Weibull distribution theory is applied to analyze the fatigue life of the cement stabilized base course specimens affected by acid solution erosion,drying and watering cycle and loading cyclic,and the fatigue life equations with a guarantee rate of 50%and 95%are matrixing.The differences and trends of each equation are compared,and then the residual fatigue life of the deteriorated specimens under constant stress are deduced from the equations.The results show that the fatigue properties of the specimens are significantly improved after 7 times of wetting-drying test in different concentrations of solution.In addition,the fatigue performance is negatively correlated with the increase of test times when the wetting-drying test is continued in the acid solution with pH 3.At the initial stage of the wetting-drying test,the influence of load factors is small,but with the increase of the number of wetting-drying test,the influence of load factors on the test pieces will be amplified,and the fatigue resistance of the test pieces with load fatigue before wetting-drying test is better than that of the test pieces with load fatigue after wetting-drying test.