| Matching the mechanical properties of pavement materials with road performance requirements has always been one of the goals of pavement material design.However,due to the limitations of the existing main pavement materials——asphalt mixture and cement concrete,the high and low temperature performance of the pavement is difficult to acquire at the same time.Composite concrete is a pavement material that is filled with cement slurry in a large-void matrix asphalt mixture and has rigid and flexible mechanical properties.Existing research only focuses on the pros and cons of its various road performances,and it has not been deepened.recognize its true mechanical properties,which leads to its application limitations.The viscoelastic properties are precisely the mechanical properties of the material.For this reason,the research on the variation law of the viscoelastic properties of the composite concrete under the influence of multiple factors,and revealing the mesomechanism of the internal material of the material are helpful to clarify the mechanical properties of the material,thus to guide the application of materials,the following research work is carried out.First,conduct a composite concrete composition design study to obtain the target type of composite concrete material.By measuring the technical indicators of raw materials such as mineral materials,asphalt and cement slurry,the "improved volume method" was used to complete the design of the target voidage matrix asphalt mixture,and the actual test proved that the method meets the design requirements.Then a four-step grouting process is used to form composite concrete materials and the basic physical and mechanical parameters such as density,splitting strength and compressive strength are measured.The results show that the basic mechanical properties of the materials can meet the general design requirements of pavement materials.Secondly,according to the composition and structural characteristics of the composite concrete,the effects of the matrix asphalt mixture porosity and the type of asphalt binder on its viscoelastic properties were studied to clarify their macro-mechanical properties.The dynamic modulus test,bending creep test and uniaxial compression creep test were used to study the characteristics of the viscoelastic energy in each state.The results show that the viscoelastic energy of the composite concrete is closely related to the size of the "rigid-flex ratio".At low temperatures,the viscosity characteristics of composite concrete with VV=25% are the most significant.As the temperature increases,the viscoelastic properties of the three porosities are basically the same.Under high temperature conditions,the viscoelastic characteristics of composite concrete vary with the porosity.Increase and decrease,comprehensively demonstrates that 25% voidage composite concrete has excellent high and low temperature road performance;At the same time,the type of asphalt binder has a significant effect on the viscoelastic performance of composite concrete.Compared with SBS modified asphalt,the viscoelastic mechanical properties of high-viscosity asphalt composite concrete can better meet the road performance requirements in various states,so when designing composite concrete materials,high-viscosity asphalt should be selected as a combination material.Thirdly,based on the theory of linear viscoelasticity,the applicable constitutive model of the selected composite concrete is analyzed to quantitatively describe its viscoelastic mechanical behavior.By analyzing the applicability of the existing constitutive model of asphalt mixture,the modified Burgers model and the three-element Kelvin model were used to analyze the creep curve of the composite concrete.The results show that both can well characterize the viscoelasticity of the composite concrete material characteristics,comprehensive fitting accuracy and convenience of parameter solution,and finally selected the modified Burgers model as its constitutive model,and obtained the influence law of the matrix asphalt mixture porosity on its viscoelastic parameters.The analysis results show that the viscoelastic properties of the three types of porosity composite concrete at low temperature and short time are better to meet the road requirements;the performance of 28% porosity composite concrete is better at low temperature and long time;the performance of 25% porosity composite concrete is better at short time and high temperature The performance of 25% and 28% voidage composite concrete at high temperature and long time is better.Finally,based on the discrete element theory,the PFC3 D software was used to establish the discrete concrete model of the composite concrete,and the numerical simulation study of its dynamic modulus test and uniaxial compression creep test was conducted to reveal the mesomechanical composition and stress evolution process of the material.According to the mortar theory,the composite concrete model is discretized into three parts of cement stone,coarse aggregate and asphalt mortar,and the corresponding particles are generated based on the random drop method and adjusted according to the test results;the characteristics of various contact models of PFC3 D are analyzed by specifying the contact type between the units,and use the material performance calibration method to obtain the meso-parameters of each contact type to complete the establishment of the model;and then conduct a numerical simulation test study,the results show that: at the meso level,each component unit in the composite concrete material is under pressure Most of the stress is borne by the mutual contact between the aggregates,and the tensile stress is mainly borne by the internal contact of the asphalt mortar,the internal contact of the cement stone and the contact between the asphalt mortar and the aggregate.At the same time,it is obtained that with the increase of the slurry injection rate,the dynamic modulus value of the composite concrete material continues to increase,and the phase angle is not much different,which proves that the cement slurry injection rate has little effect on the viscoelastic performance of the composite concrete.When subjected to a constant static load,the internal force of the composite concrete material is: aggregate room > cement stone room > asphalt mortar and aggregate room > cement stone and aggregate room > cement stone and asphalt mortar room > asphalt mortar room.At the same time,with the progress of the creep process,the contact force between the aggregates increased slightly;the internal contact force of the cement stone,the contact force between the asphalt mortar and the aggregate,and the contact force between the cement stone and the aggregate decreased slightly;The internal contact force of asphalt mortar and the contact force between cement stone and asphalt mortar decrease rapidly.Through the above research,the change law of the viscoelastic energy of the composite concrete material is clarified,the constitutive model suitable for its viscoelastic energy description is obtained,and the meso-structure mechanism of the viscoelastic energy is revealed,thus providing science for the material and structure design of the composite concrete Guiding significance. |
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