Numerical Simulation Of Cement-stabilized Macadam Base Compressive Strength With Varied Coarse Aggregates

Cement-stabilized macadam base is one of the mainstream materials for pavement base,which consists of cement,gravel and sand.It has the advantages of excellent integrity,high strength and anti-penetration,etc.However,desiccation cracking,temperature shrinkage cracking,and loading crack also exist.It tends to cause micro-cracks to sprout,gradually expand,and reflect on the asphalt pavement,which seriously threatens the road performance.Coarse aggregate is the largest proportion in the cement-stabilized macadam base and has a significant influence on the strength of the cement-stabilized macadam base.In order to optimize the structural design and aggregate matching scheme,it is critical to understand the dynamic evolution process of mesoscopic characteristics as well as the influence of morphological characteristics of coarse aggregate on the strength of cement-stabilized macadam base.In the dissertation,a meso-fracture model for the standard specimens of cement-stabilized macadam base is established based on test results and a cohesion model.The correlation between the morphological characteristics of coarse aggregate and the compressive strength of a cement-stabilized macadam base is studied by Image-Pro Plus and gray correlation analysis.It indicates a correlation between the 12 morphological characteristics of coarse aggregate and the unconfined compressive strength of cement-stabilized macadam base.The key research contents and results are as follows,(1)The compressive strength and splitting strength tests of standard specimens of cement-stabilized macadam base are examined.The coarse aggregate in crushed pebbles is replaced with limestone machine-rolled gravels to study the effect of coarse aggregate on the strength of the cement-stabilized macadam base.By studying the damage process of standard specimens of cement-stabilized macadam base with different morphological characteristics of coarse aggregate,the influence of coarse aggregate morphology on the unconfined compressive strength and splitting strength of cement-stabilized macadam base is elucidated.The results show that the surface texture of limestone machine-rolled gravels is rougher and more rhombic than that of crushed pebbles,resulting in an increase of 16.99%in the unconfined compressive strength for limestone machine-rolled gravels,while there is no significant change in the splitting strength.The coarse aggregate morphology significantly affects the compressive properties of the cement-stabilized macadam base but hardly changes the tensile properties.(2)Based on the theory of fracture mechanics and the cohesion model,the cohesion parameters,such as fracture energy and bond strength,of non-homogeneous specimens of cement-stabilized macadam base are theoretically derived in combination with splitting strength tests.A meso-fracture model is developed based on the standard strength stabilized base specimen containing a three-phase composite of coarse aggregate,mortar and mortar-aggregate interface.The accuracy of the model is verified by the crack expansion,crack morphology and compressive strength of the specimens under the unconfined compressive strength test.In terms of crack extension behavior and final morphology,cracks appear in the middle of both the test and simulation results and develop along the vertical direction.It leads to the dislodgement of the aggregate near the loading surface and the specimen is completely destroyed.The unconfined compressive strengths of the standard specimens obtained from the test and simulation are 4.71 MPa and 4.84 MPa,respectively.The error is maintained within 2.8%.(3)Three coarse aggregates(A,B,and C)with different morphological characteristics are generated by the random aggregate model.Twelve morphological parameters of coarse aggregates(maximum diameter,minimum diameter,Feret’s diameter,perimeter,convex envelope perimeter,equivalent ellipse perimeter,area,roundness,axial coefficient,convexity,roughness and angularity)are extracted by Image-Pro Plus(IPP)software.A non-parametric method is used to normalize each indicator and a comparative analysis of 12 indicators for coarse aggregate is conducted.The results show that three morphological characteristics of coarse aggregate satisfy the normal distribution.The maximum diameter,minimum diameter,Feret’s diameter,perimeter,convex envelope perimeter,equivalent ellipse perimeter and area of the three aggregates increase with aggregate size.Roundness,convexity,roughness,angularity and axial coefficients are almost unchanged with aggregate size.The axial coefficient satisfies A>B>C.Roundness and angularity satisfy A>C>B.The minimum diameter,equivalent ellipse circumference,area,roughness and convexity satisfy C>B>A.The remaining indicators generally satisfy the minimum of B and the closer of A and C.(4)The simulation of the unconfined compressive strength of standard specimens is carried out according to the meso-fracture model of finite element analysis for cement-stabilized macadam base specimens.The gray correlation analysis investigates the relationship between the 12 coarse aggregate morphological characteristics parameters and the unconfined compressive strength of the cement-stabilized macadam base.The results show that the cement-stabilized macadam base specimens exhibit brittle failure characteristics.The unconfined compressive strength of the three coarse aggregate specimens is C>B>A.There is a strong correlation between the morphological characteristics of coarse aggregates and the unconfined compressive strength of cement-stabilized macadam bases.Axial coefficient,convexity,roughness,angularity and minimum diameter have the highest correlation above 0.9.The correlations of Feret’s diameter,perimeter,convex envelope perimeter,equivalent ellipse perimeter and roundness are around 0.7.The correlation between maximum diameter and area is the lowest at 0.35.