Study On Mechanical Behaviors Of Polypropylene Fiber Reinforced Fly Ash-soil Mixture

Although fly ash reinforced soil can improve the engineering performance of subgrade soil,it can not effectively improve the crack resistance and compressive strength of subgrade soil.It often presents brittle failure,which causes the pavement to form longitudinal and transverse cracks,and further improvement measures are needed.Polypropylene fiber is widely used as a reinforced material in the field of reinforcement.Researchers at home and abroad have applied polypropylene fiber as a reinforced material.Based on the laboratory tests,the shear strength characteristics and unconfined compressive strength of polypropylene fiber reinforced fly ash-soil and the mechanism of fiber reinforcement was discussed.The conclusions are as follows:1.Incorporating fly ash into the clay can effectively improve the shear strength of the soil,wherein the shear strength of the fly ash-soil mixture specimen reaches the maximum when the fly ash content is 30%;With the increase of the fly ash content,the strength loss post the peak value is gradually reduced.2.Fiber reinforced fly ash-soil specimens tends to increase the ultimate shear strength of the specimen compared to the unreinforced counterpart.In addition,the peak stress increases with the increase of fiber content.When the shear strain reaches 15%,the shear stress of the specimen remains basically constant,and there is no tendency to decrease.3.For the unconfined compressive strength values of specimens with fly ash content of 0% and 10%,the influence of fly ash content and curing age is little.The unconfined compressive strength value of the specimen with fly ash content exceeding 20% is not significantly affected by the curing age under the condition of curing for 7 days to 28 days,and the unconfined compressive strength of the specimens with 30% fly ash content increases with the increase of curing age.4.The fly ash-soil mixture with 30% fly ash content shows brittle failure.The specimen will suddenly break when the axial strain is less than 3%.Compared with the unreinforced fly ash-soil mixture,the stress-strain curve of fiber reinforced specimen exhibits ductile failure,and the axial strain at the time of failure of the specimen is between 3% and 4%.At the same time,the stress reduction of fiber reinforced specimen post the peak is smaller than that of the unreinforced counterpart.5.When the fiber length is kept constant,the c value of the polypropylene fiber reinforced fly ash-soil increases with the increase in the fiber content;When the fiber content remains constant,compared with the 6 mm fiber reinforced fly ash-soil specimen,the c value of fly ash-soil specimen reinforced with 12 mm fiber increased obviously,indicating that the c value of fiber reinforced fly ash-soil increased with the increase of fiber length,but the growth trend was within a certain range.