Mechanism Of Cement Pavement Microcrack Homogenization Under Impact Of Falling Weight

In the old cement pavement reconstruction project,in order to ensure the quality of the overlay,it is usually necessary to crush the old cement panel.The micro-cracking homogenization technology of the old cement pavement can make the treated old road blocks crack without breaking,effectively prevent the reflection cracks of the overlay layer,and at the same time retain the strength of the old road to a great extent.This technology has been used in the main lines of many provinces.It has been applied in pavement engineering and achieved good results.Henan,Anhui and other places have also issued relevant technical specifications.However,as a new technology independently developed,its theoretical basis is weak,so it is very necessary to carry out mechanism research.Numerical simulation has unique advantages in mechanism research.Through on-site micro-cracking construction and analysis,combined with actual technology,this paper builds a discrete-continuous mechanical model of cement pavement based on PFC5.0Suite and FLAC3 D,performs parameter correction and verifies the reliability of the model Through analyzing the impact acceleration changes,the development of slab cracks,and the overall cracking effect of the cement pavement slab under the impact of the falling hammer,the dynamic interaction mechanism of the falling hammer and the pavement is studied.The development and improvement of construction technology provide basic support,the study found:(1)With the increase of falling height,mass of hammer,plate modulus and plate thickness,the impact acceleration curve presents the trend of " Same width increasing ","widening and decreasing","widening and increasing","widening and increasing" respectively.(2)There is a close relationship between the crack and each stage of the impact acceleration curve.The first and second stage is the main stage of the crack.The crack at the top of the plate is distributed at the hammer edge,and it is transmitted from the surface to the bottom with a certain diffusion angle.The crack at the bottom of the plate is radial,pointing from the center to the four directions.(3)When the plate parameters remain unchanged,the falling height mainly controls the development of cracks at the top of the plate,and the mass of hammer mainly controls the development of cracks at the bottom of the plate.When the parameter of hammer is constant,the greater the plate modulus is,the more serious the plate cracking is;the greater the plate thickness is,the more separated the top crack and the bottom crack are.(4)The square drop hammer tends to break the bottom of the plate,while the circular drop hammer tends to break the top of the plate,and the total number of cracks is the largest.When the ratio of the long side to the short side is greater than 3,the short side cracking is completely limited.When the impact energy is constant,the increase of falling height can not make up for the decrease of plate bottom cracking caused by the decrease of mass of hammer.(5)The method of construction from both sides to center can reduce the risk of lateral cracking of old concrete pavement,and the overall stability is the best.(6)The micro crack index is put forward,which is(bulk modulus before impact-bulk modulus after impact)/ bulk modulus before impact.The reliability of microcrack index is verified by analyzing the distribution of crack number under different micro cracks.