Test And Analysis Of Mixture Modification And Proportioning Of Gravel Pavement Base Course With Super Large Particle Size And Water Stable Breach

The base course of highway pavement is the bearing layer of pavement structure,which should have sufficient strength,water stability,crack resistance and other road performance.The traditional semi-rigid base course of pavement is easy to produce shrinkage cracks when the temperature or humidity changes alternately,forming temperature shrinkage cracks and dry shrinkage cracks,eventually leading to reflection cracks of pavement,causing serious pavement diseases.In this paper,we try to control the low-dose cement,and mix the right amount of fly ash and polypropylene fiber to modify the mixture,so as to form a new semi-rigid road base with the super large size and dense structure of water stable sand gravel,which has good crack resistance.At the same time,new materials for design and construction of semi-rigid pavement base are developed.On the basis of the research on the mechanism of crack generation and crack resistance of semi-rigid base,through the indoor physical property test,mechanical property test and mixture ratio test of water stable sand gravel material with super large particle size inlay structure,a systematic comprehensive test and Analysis on the gravel mixture with super large particle size water stable breach is carried out.By adjusting and controlling the proportion of cementitious materials(cement,fly ash),fine aggregate and polypropylene fiber,the relationship between the compactness,unconfined compressive strength,rebound modulus of the mixture and the addition of different proportion of fly ash,different length of polypropylene fiber and different age is analyzed,so as to effectively improve the compactness structure and crack resistance of the base mixture.The main research results are as follows:(1)On the basis of the proportion of super large size water stable sand gravel mixture,adding a certain amount of fly ash and polypropylene fiber,the structure of the mixture after compaction will be more dense,the unconfined compressive strength will be significantly improved,and the crack resistance will be effectively improved.(2)When the cement content is controlled at 3% and the fly ash content in the modified mixture is 30% of the cement content,the strength increase of each age is the largest;when the fiber length is 12 mm and the content is 1.33% of the cement content,the strength increase of each age is the largest.(3)Considering the maximum dry density,modulus of resilience,compressive strength and crack characteristics after specimen failure,it can be determined that the reasonable range of fly ash content of Modified mixture is 20% ~ 30%;the reasonable range of polypropylene fiber content is about 1.33%,and the reasonable range of length is 9mm ~ 12 mm.In order to solve the common crack problem of semi-rigid pavement base,and to improve the dense structure and anti crack performance of the base mixture,the maximum dry density,unconfined compressive strength and modulus of resilience of the modified mixture with different proportion are compared and analyzed,so as to provide a scientific basis for the application of oversized gravel materials in the road base.