| The cracking of asphalt pavements problem has always been one of the main concerns of the road engineering community.Large-size asphalt mixture(LSAM)is often used as an underlayment for asphalt pavement structures to prevent the upward expansion of reflective cracks in the subgrade.Based on the semi-circular bending(SCB)test,this dissertation designs monotonic SCB tests and fatigue SCB tests under cyclic loading under different test conditions,and records the displacement-load curve and N-a curve during the tests to investigate the influencing factors of monotonic cracking performance and fatigue cracking performance of LSAM,and further analyses the cracking resistance mechanism based on test images.The study of the monotonic cracking resistance of LSAM at different thicknesses,different notch lengths,different loading rates and different temperatures showed that thicker specimens would retain the large grain size structure more completely and the specimens would have better cracking resistance.Excessively long or short cut lengths will affect the quality of the evaluation of the crack resistance of the specimens.Excessive displacement loading rates can make the crack extension process unstable.The peak load of the specimen increases significantly at low temperatures,but the total fracture energy decreases.The crack resistance of LSAM is significantly better than that of fine-grained asphalt mixes at room temperature,but the advantage is not significant at low temperatures.Based on the monotonic SCB test,a suitable specimen size for evaluating the crack resistance of LSAM was derived to be 60 mm thick and 10 mm in cut length.The results of LSAM fatigue tests at different loading frequencies,test temperatures and stress ratios showed that increasing the loading frequency,decreasing the test temperature and decreasing the stress ratio increased the fatigue performance of the specimens based on Paris law.The fatigue crack expansion rate and the stress intensity factor amplitude have a good linear relationship in the logarithmic coordinate system.Observations of cracks,sections and CT images of fatigue specimens show that fatigue cracks at room temperature extend along the edges of large grain size aggregates and fatigue cracks at low temperatures cross large grain size aggregates.Analysis of the fatigue cracking performance of LSAM by the fatigue rupture energy method shows that the single fatigue rupture energy tends to decrease and then increase with the number of loads,and that increasing the frequency,increasing the stress ratio and decreasing the temperature will increase the fatigue rupture energy of the specimen.The fatigue rupture energy and fatigue life showed a good linear relationship in the logarithmic coordinate system.In summary,LSAM has better crack and fatigue resistance due to the higher content of large particle size aggregates,the longer path required for crack expansion and the slower cumulative change in load displacement.With the selection of suitable parameters,the semi-circular bending test can consistently evaluate the cracking and fatigue performance of LSAM,which provides ideas for subsequent studies on LSAM. |
