Meso-cracking Mechanism Of Composite Concrete Based On Damage Characteristics

Composite concrete is a kind of pavement material formed by pouring cement-based materials into a large-voidage matrix asphalt mixture.Compared with the ordinary asphalt mixture pavement,the composite concrete pavement significantly improves the high temperature stability,and at the same time,the low temperature crack resistance,fatigue resistance,anti-slip performance,and wear resistance have also been improved.However,in practical engineering applications,it was found that the composite concrete had the problem of easy spalling and cracking in the early stage.At present,the research direction of cracking of composite concrete mainly focuses on improving the material design of composite concrete,especially cement slurry,and its crack resistance is verified by experimental methods,and there is a lack of research on the cracking mechanism of composite concrete.In order to clarify the location law and variation characteristics of micro-cracks in composite concrete,the meso-cracking mechanism of composite concrete was researched.Firstly,the laboratory test of damage cracking of composite concrete was carried out.The results show that under the test condition of accelerated damage of hydro-thermal coupling,the cement stone inside the composite concrete will generate micro-cracks and gradually expand to produce cracks;at the same time,the cement stone and asphalt bond interface damaged and cracked.Therefore,it is necessary to further study the mechanism of compound concrete cracking,especially under the influence of factors such as shrinkage and temperature of cement slurry,the stress distribution characteristics inside the material,and the damage and evolution law of the material bonding interface under different stress conditions.Secondly,based on the meso-structure characteristics of composite concrete,the construction of the meso-structure model of composite concrete is completed in the finite element software;the adhesion of simulated asphalt by adhesive contact;the mechanical model of the adhesive contact pair is characterized by the cohesion model.Then the research on the internal mechanical response characteristics of the composite concrete under the shrinkage of the cement stone was carried out.The results showed that when the cement stone shrinks,the cement stone itself and the cement stone-aggregate bonding interface will generate large stresses,which are easy to generate micro cracks.Under the load,there is a significant stress concentration phenomenon at the bonding part between the aggregates inside the composite concrete.The simulation study of direct tensile and direct shear of composite concrete was carried out to analyze the damage and evolution of the bonding interface inside the composite concrete under the two effects.Thirdly,analyze the characteristics of temperature changes on composite concrete materials,and establish a local contact model of composite concrete.The basic data of asphalt was obtained by DSR test,which was converted into generalized Maxwell model parameters to give viscoelastic properties to asphalt.Using the local contact model,the local interface stress response study under daily temperature changes was carried out to clarify the internal stress distribution characteristics of the composite concrete during heating and cooling,proving that the cement-aggregate bonding interface inside the composite concrete is inside the composite concrete weak parts that are easy to crack.At the same time,the temperature stress study of the composite concrete local contact model at different temperature ranges and different cooling rates is carried out.The results show that the lower the temperature,the faster the cooling rate and the higher the stress level inside the composite concrete.Finally,the internal stress evolution of the composite concrete local contact model under the measured temperature changes and the effect of different asphalt slurries on the composite concrete temperature stress are analyzed.Combined with the measured temperature curve in Harbin,it is found that the stress evolution inside the composite concrete has obvious seasonal characteristics,and the internal tensile stress peaked in November and February.In order to guide the design of the mix ratio of the actual composite concrete asphalt mortar,different asphalts and different fillers are used to mix into the asphalt mortar.The results show that at low temperatures,the temperature stress of the composite concrete is most sensitive to the low-temperature shrinkage coefficient of the asphalt mortar.Based on the research results of this paper,in order to reduce the generation of micro-cracks in composite concrete,the following suggestions are proposed: when selecting cement slurry,its shrinkage rate is strictly controlled,while taking into account the early tensile strength;the bonding interface strength of cement slurry and asphalt is given pay enough attention to develop a set of methods to evaluate the bonding strength of this interface,clarify the corresponding indicators,when the material is selected,the strength level of this bonding interface is included in the evaluation system;when selecting the type of matrix asphalt mixture,the low-temperature shrinkage of asphalt or asphalt mortar is included in the evaluation system,and asphalt with a low-temperature shrinkage coefficient is preferred.