Study On The Performance Of Recycled Coarse Aggregate Asphalt Mixture And The Microscopic Characteristics Of The Interfacial Transition Zone

Recycled concrete aggregates obtained from waste concrete through specific processing techniques are used to prepare asphalt mixtures,namely recycled concrete aggregate asphalt mixtures to pave different grades asphalt pavements,which can promote the efficient use of waste concrete and reduce the consumption and mining volume of natural sand and gravel.The load borne by the recycled aggregate asphalt mixture is borne by the support of the aggregate and the interfacial bonding effect.Therefore,its bearing capacity is not only related to the constituent materials,but also affected by the interaction of the constituent materials of the phases.The newly introduced coarse aggregate-asphalt mortar interface is particularly likely to cause the attenuation and variation of the bearing capacity of the recycled aggregate asphalt mixture.Proving the characteristics of the transition zone of the two-phase interface is the basis for strengthening and optimizing the design of the recycled aggregate and its asphalt mixture.Firstly,the raw material test and mix design of the recycled coarse aggregate asphalt mixture were carried out in this paper.Taking into account the characteristics of the reduced bulk density of recycled coarse aggregates and the adhesion of cement mortar on the surface,the method of volume correction of the replacement rate of recycled coarse aggregates and combined with natural fine aggregate curve fitting were used to compare the mineral aggregates of recycled coarse aggregate asphalt mixtures.The gradation was adjusted,and the best bitumen-stone ratio of the asphalt mixture was determined through the Marshall test,and the influence of recycled coarse aggregate on the volume parameters of the asphalt mixture and the content of asphalt is analyzed The test results showed that the blending of recycled coarse aggregate increaseed the optimal asphalt content of the asphalt mixture,and had little effect on the VV,VMA and VFA indicators of the asphalt mixture.The effective asphalt content,effective asphalt film thickness and powder-to-battery ratio did not change significantly.Secondly,the rutting test,low temperature bending test,water immersion Marshall test,freeze-thaw splitting test and indirect tensile cracking test were used to evaluate the high temperature stability,low temperature anti-cracking performance,water stability and resistance of cracking performance of recycled coarse aggregate asphalt mixtures.The test results showed that the addition of recycled coarse aggregate increaseed the dynamic stability of the two graded asphalt mixtures,reduced the low-temperature crack resistance performance,and the indirect tensile cracking performance.The water stability of SMA-13 and AC-20decreased.Water stability was enhanced.On this basis,the nano-indenter(NI),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were used to analyze the nano-mechanical parameters,microscopic morphology and characteristics of the transition zone of the recycled coarse aggregate-asphalt mortar interface.The chemical element composition was tested and analyzed,and the corresponding observation sample preparation method was formed.In terms of nanomechanical parameters,the indentation curve,modulus contour map,and modulus frequency map can be used to characterize the modulus and thickness of the interface transition zone.The old interface transition zone is evenly distributed on the surface of the natural aggregate(NA)with a thickness of 25 μm,the average elastic modulus is 24.01GPa,the thickness of the transition zone of the new interface is 26μm,and the average elastic modulus is 28.68GPa.In terms of microscopic morphology and crystal characteristics,the mortar near the surface of the aggregate in the transition zone of the new interface is denser than the mortar at a distance.The structure transitions from compaction to looseness and then to dense mortar layers.The transition zone of the new interface is mainly composed of Asphalt mortar and mineral aggregates;while the transition zone of the old interface has good integrity between the phases,but when the aggregate is far away from the phase interface,due to the weakening of the agglomeration effect,there are uncompacted pores inside.The transition zone of the old interface is mainly composed of calcium oxide composition with fillers.In terms of chemical element composition,the old interface transition zone is dominated by calcium oxide and its derivatives,including a small amount of calcium silicate.The new interface transition zone is mainly composed of asphalt,mineral powder and a small amount of calcium silicate.Different phases can pass calcium,Characteristic elements such as carbon and silicon were screened.The thickness of the new interface transition zone obtained by the line scan was 27μm,and the thickness of the old interface transition was 32μm.This conclusion is consistent with the nanoindentation test resultsThis study realizes the characterization of the multiple interface structure of recycled coarse aggregate-asphalt mortar and the macroscopic performance evaluation of recycled coarse aggregate asphalt mixture.The nano-mechanical parameters and surface morphology characteristics of the transition zone of recycled coarse aggregate-asphalt mortar interface are explored from the micro scale.And chemical composition characteristics,hoping to provide a basis for the reinforcement and optimization of recycled aggregates and their asphalt mixtures.