Research On The Interface Morphology Characteristics Of Composite Cold Recycled Materials And The Strength Of The Mixture

Composite cold recycling not only can use recycled asphalt surface materials,but also use damaged semi-rigid base materials as raw materials,which has extremely high social and economic benefits.However,due to the complexity of its material composition and the lack of system support research,the current material interface morphology characteristics,interface adhesion effects in the recycled mixture are not clear,the strength of the mixture is unstable,it not widely used.In this paper,through a series of experiments,the interface morphology,interface adhesion and macro-mechanical properties of two different mixture materials are studied.The main work content includes the following aspects:First,the microscopic morphology of the interface between each phase material and the cement in the conventionally mixed and formed cement composite cold recycled mixture was observed by SEM electron microscope,and it was found that shrinkage cracks and cement agglomeration appeared on the surface of the three aggregates.Among them,the surface of the recycle base material(RBP)there are old hydrated cement stones,which causes the RBP material to be not closely combined with the new cement hydration products.Therefore,it is proposed to use the vibration mixing method to form the mixture and then observe the interface.The results show that the vibration mixing method causes the old cement stone that is not closely connected to the RBP material surface in the mixture to fall off,the cement coating on the surface of various aggregates is uniform,and the interface strength variability has be reduced.Secondly,research on the cross-sectional composition characteristics of the emulsified asphalt composite cold recycled mixture,the microscopic morphology and microscopic composition of each interface,and the adhesion between materials,the results show that the 50% RAP content causes the thickness spectrum of the binder to concentrate in 4-8 pixels.At the 30% RAP content,the thickness spectrum of the binder is more evenly distributed in 2-23 pixels,and the thickness of the effective binder is wider.There are old hydrated cement stones on the surface of the RBP material,and there are two states in its interface with the CA mortar: If the gap between the cement stone and the raw stone material is large,the CA mortar can invade between the gaps and form a larger mechanical Bite force and chemical adhesion force,the interface strength is high;if the gap is small,CA mortar cannot penetrate between the gaps,and the interface strength is low.In addition,the aged asphalt on the surface of the RAP material is fused with the CA mortar,which reduces the performance of the CA mortar at the interface,the tensile strength is reduced by 0.12 MPa,and the adhesion fatigue failure time is advanced by 5.46 s.Thirdly,the influencing factors of the mechanical properties of the cement composite cold recycled mixture are studied,and the results show that the increase in the strength of the mixture with age conforms to the law of cement strength growth.The increase of cement content can increase the unconfined compressive strength and splitting strength of the mixture,and the increase of the RAP content increases the strength of the mixture first and then decreases.Compared with conventional mixing,vibration mixing can increase the unconfined compressive strength and splitting strength of the mixture by 32.4%and 44.3%,and the coefficient of variation can be reduced by 27.1% and 31.0%,which is the same as the observation results of micro-interface morphology.Finally,the influencing factors of the mechanical properties of the emulsified asphalt composite cold recycled mixture are studied.The results show that the increase of the cement content will increase the Marshall Stability and porosity of the mixture,and the splitting strength will continue to decrease.The best cement content is 1.5%.The increase in the content of emulsified asphalt will first increase the Marshall stability and splitting strength,and then decrease it.The best content of emulsified asphalt is 5%;the increase in the content of RAP will reduce the Marshall stability and the splitting strength of the mixture,but has little effect on the residual stability of the soaked Marshall.The influence of various factors on the strength of the mixture is consistent with the results of the microscopic test analysis,indicating that the interface morphology and adhesion research results can better guide the composition design of the recycled mixture,and have a good optimization effect.