Study On Crack Resistance Of Basalt And Polyvinyl Alcohol Hybrid Fiber Semi-rigid Base

Cement stabilized crushed stone is widely used as road subbase due to its high strength,good stability,wide material sources,and low cost.However,in high-altitude and cold regions with severe temperature and humidity changes,cracking damage of cement stabilized crushed stone subbase is more common and severe than in other areas.Previous studies have shown that fiber addition can improve the crack resistance of cement stabilized crushed stone subbase to a certain extent.Compared with single fiber addition,the synergistic superposition effect of mixed fibers can achieve better performance.Therefore,by mixing basalt fiber(BF)and polyvinyl alcohol(PVA)fiber into cement stabilized crushed stone,the advantages of each fiber can be exerted to further improve the crack resistance of cement stabilized crushed stone.In this study,different ratios of basalt fiber and polyvinyl alcohol fiber with different lengths were mixed into water-stable crushed stone.The optimal fiber length and fiber content were determined by 7 d compressive strength and 7 d flexural strength.Then,four types of water-stable crushed stone,including single basalt fiber addition,single polyvinyl alcohol fiber addition,no fiber addition,and mixed fiber addition,were compared by unconfined compressive strength test,splitting strength test,compressive rebound modulus test,splitting rebound modulus test,freeze-thaw cycle test,drying shrinkage test,and temperature shrinkage test to investigate the effect of mixed fibers on the mechanical and anti-shrinkage cracking properties of water-stable crushed stone.Grey correlation analysis was used to determine the optimal crack resistance evaluation index based on the test results.Finally,a thermal-mechanical coupling model of pavement structure was established according to the climatic characteristics of high-altitude and cold regions to study the temperature and stress spatiotemporal distribution of the four types of water-stable crushed stone subbase.The results showed that fiber addition could improve the mechanical strength of water-stable crushed stone.Basalt fiber length of 24 mm and optimal content of 0.4‰,and polyvinyl alcohol fiber length of 18 mm and optimal content of 0.4‰ were determined by optimal mixing ratio of fiber length and content.Compared with ordinary water-stable crushed stone,the mixed fiber water-stable crushed stone had the largest increase of 10% and13% in 90 d compressive strength and 90 d splitting strength,respectively.The 90 d compressive rebound modulus and 90 d splitting rebound modulus decreased by 12.5% and7.1%,respectively,which were only lower than those of polyvinyl alcohol fiber water-stable crushed stone.The 28 d freeze-thaw compressive strength increased by 14.33%.The average drying shrinkage coefficient and temperature shrinkage coefficient decreased by 10% and25.6%,respectively.Cement stabilized crushed stone has a large temperature change range before surface layer paving,which is prone to temperature shrinkage cracks.Under the same temperature environment,the temperature stress of mixed fiber water-stable crushed stone was lower than that of single fiber water-stable crushed stone and ordinary water-stable crushed stone.At the same time,the stress intensity factor of mixed fiber water-stable crushed stone subbase was the smallest.In conclusion,under the condition of the same total amount of fiber,mixed fiber water-stable crushed stone can further improve the mechanical and crack resistance of water-stable crushed stone compared with single fiber addition,which has reference significance for the application of mixed fiber in water-stable subbase.