Study On Mechanics Evolution Mechanism And Self-healing Properties Of Cement Stabilized Macadam After Early Microcracking

The shrinkage stress of cement stabilized macadam can be reduced through the micro-cracks caused by early microcracking,which can effectively prevent or reduce the shrinkage cracking of road base.In the later period of curing,the micro-cracks were gradually healed or even recovered relying on the self-healing properties of cement stabilized macadam,so it would not have a serious impact on the bearing capacity of pavement structure.Hence,the quantitative characterization of cement stabilized macadam self-healing process after microcracking,and the proficiency in the changing rule of cement stabilized macadam healing properties under different factors are the focus of the research.In this paper,on the basis of discussing the mechanism of cement stabilized macadam after early microcracking,the mechanical characteristics,mesoscopic structural characteristics and durability of cement stabilized macadam during the healing process was studied,and then relying on field test,the self-healing properties of cement stabilized macadam under complex environment and mechanical conditions was analyzed.This paper has completed the following contents:(1)On the basis of discussing the shrinkage cracking regularity of semi-rigid base,the mechanism of microcracking to reduce the shrinkage cracking was studied,and then the microcracking of cement stabilized macadam was simulated according to the indoor shrinkage test,thus the critical point that the shrinkage stress is just less than the tensile strength of material was determined,simultaneously demonstrated the effectiveness of microcracking to reduce the shrinkage stress of semi-rigid base.(2)By introducing the concept of microcracking degree to characterize the change of material properties of cement stabilized macadam after early microcracking,it is expressed as the decrease percentage of compression rebound modulus.The reasonable control of microcracking degree is the key of producing the ideal micro-cracks after microcracking.In order to achieve the effective control of microcracking process,the microcracking degree control model considering the coupling conditions of microcracking load,microcracking time and material characteristics was established based on response surface methodology.(3)Through the test of unconfined compressive strength,splitting strength and compression rebound modulus,the self-healing process and the mechanical strength changing rule of cement stabilized macadam after early microracking were systematically studied,then the effects of different microcracking time and microcracking degree on the healing properties were obtained using the nonlinear fitting,and the critical state of healing degree was obtained from the perspective of material healing.(4)On the basis of the research on macroscopic mechanical properties,use digital explicit crack width monitor KON-FK(B)to detect the micro-cracks width,and then the representative values of micro-cracks width under different working conditions and the change rule of representative values were obtained based on the descriptive statistics of SPSS.Next,use stereo microscope XTZ-05 T to image the healing product,and the coverage rate of healing product to micro-cracks was acquired by image segmentation technology,so the healing process of cement stabilized macadam after early microcracking can be quantitatively characterized through the coverage rate,and the analysis of micro-cracks healing characteristics was achieved from the perspective of meso structure.(5)Through the dry shrinkage test and thermal shrinkage test,the effect of early microcracking on shrinkage characteristics was studied,and the best time to implement microcracking was determined;through the fatigue test,the durability of cement stabilized macadam after early microcracking was evaluated;then,based on the temperature field test of cement stabilized macadam base,the effect of early microcracking on the frost resistance was studied by freeze-thaw cycle test,which provides a comprehensive theoretical basis for the promotion of microcracking technology in practical engineering.(6)The field test was carried out relying on 104 National Road overhaul works,the internal stress,strain and temperature of cement stabilized macadam base were monitored through the laying of sensors,in order to improve the study on the healing characteristics under complex environment and mechanics conditions,finally the healing state of cement stabilized macadam was tested by FWD deflection test.(7)The three-dimensional model of semi-rigid base asphalt pavement was established based on the test results,and rhe semi-rigid base asphalt pavement structure combination research considering early microcracking was carried out.Combined with the study under static and dynamic load,find that the early microcracking of semi-rigid base has a great influence on the tensile stress on the bottom of asphalt pavement,so the tensile stress on the bottom of asphalt pavement should be checked in the design of the pavement structure.