Study On Road Performance Of Cotton Straw Fiber Modified Micro-surfacing Mixture

At present,as a common preventive maintenance technology,micro-surfacing is widely used in pavement repair and maintenance engineering.However,with the popularization and application of micro-surfacing technology,the problem that the mixture is easy to appear loose cracking in practical engineering application is gradually exposed,which leads to the short service life of some micro-surfacing pavement and limits the development of this technology.China is a big country of cotton planting,and a large amount of cotton straw will be left after harvest every year.Due to the low economic value of cotton straw,it is often burned,but incineration seriously affects the local air quality and the health of the surrounding people.Therefore,it is an urgent problem to be solved to treat cotton straw greenly and reasonably and make it play a certain economic benefit.In order to effectively and rationally use cotton straw and prolong the service life of micro-surfacing mixture,the main research contents of this thesis are as follows:（1）Cotton straw fiber was modified by sodium hydroxide（Na OH）,silane coupling agent（KH550）and glacial acetic acid（CH₃COOH）.The effects of cotton straw fiber modification on the properties of asphalt mortar were studied by cone penetration,softening point,ductility and dynamic shear rheological test（DSR）.The results showed that the chemical modification destroys the hemicellulose structure in the cotton straw fiber,reduces the impurity debris adhered to the fiber surface,increases the roughness,and improves the basic physical properties of the fiber.The high temperature performance of asphalt mortar increases with the increase of cotton straw fiber content,but the ductility decreases.Considering the high temperature performance and ductility of the mortar,the optimum fiber content is 2%.Under this dosage,the performance of fiber asphalt mortar meets the requirements of technical specifications for road petroleum asphalt.Among them,the asphalt mortar mixed with CH₃COOH modified cotton straw fiber has better comprehensive performance.Compared with matrix asphalt,its shear strength increases by 3.21 times,and the softening point increases by 14.99%.（2）Through the construction workability and road performance test of micro-surfacing mixture,the best mix ratio of micro-surfacing mixture was determined.The results show that the mixing time of micro-surfacing mixture increases with the increase of water consumption,and the cohesion increases first and then decreases with the increase of cement content.Combined with the results of mixing test and cohesion test,it is concluded that the optimum water consumption of non-fiber and fiber micro-surfacing mixture is 7%and 8%respectively,and the optimum cement content is 2%.The range of asphalt-aggregate ratio of mixture determined by 1h wet wheel wear test and load wheel sand adhesion test is:6.15%～7.20%without fiber;6.64%～8.00%without modification;6.44%～7.96%with CH₃COOH modification;6.30%～7.66%with Na OH modification;6.28%～7.72%with KH550modification.KH550 modified cotton straw fiber micro-surfacing mixture shows better water damage resistance,CH₃COOH modified cotton straw fiber micro-surfacing mixture shows better wear resistance and rutting resistance.Combined with the construction workability and road performance test results of micro-surfacing mixture,the optimum asphalt-aggregate ratios of no fiber and fiber micro-surfacing mixture are determined to be 6.8%and 7.2%,respectively.（3）Under the optimum oil-stone ratio,the long-term performance of micro-surfacing mixture in different states and the scanning electron microscope test of mixture before and after freezing and thawing were carried out.The results show that the fibers are evenly distributed in the mixture,and the pores of the mixture become larger after the freeze-thaw cycle,and the fibers and asphalt are peeled off.The fiber micro-surfacing mixture shows better long-term performance.The performance change rate of KH500modified cotton straw fiber micro-surfacing mixture is slow during freeze-thaw cycles.CH₃COOH modified cotton straw fiber micro-surfacing mixture shows better long-term high temperature rutting resistance,skid resistance,wear resistance and shear resistance.