Study On Road Performance Of Cement-Basalt Fiber Composite Modified Gravel Asphalt Mixture

The supply of basalt,limestone and other s tone resources in Lhasa is insufficient,while the floodplains and terraces of the Lhasa River have a large amount of gravel,which is rich in reserves and convenient for mining.However,gravel has too much smooth surface and Si O 2 content,and it is difficult to meet the use standards of pavement materials when directly applied to asphalt pavement surface.Therefore,a scheme of cement-basalt fiber composite modified gravel asphalt mixture is proposed,aiming to improve the road performance of gravel asphalt mixture.In this paper,combined with the project of "Research on Key Technologies of Urban Roads in Lhasa Area",the properties of cement-basalt fiber composite modified gravel asphalt mixture were studied by means of indoor experiment and theoretical analysis.The main research work is as follows:(1)Under the condition of powder-to-rubber ratio of 1.0,the proportion of cement replacing mineral powder was 0%,15%,30%,45% and 60% to modify KLMY90# asphalt,and the basic properties,shear resistance,viscosity-temperature performance and rheological properties of each asphalt sample were analyzed by three index tests,taper penetration test,rotational viscosity test and dynamic shear rheological test.Comprehensive analysis of the improvement effect of cement on the performance of asphalt,it is concluded that the suitable range of cement to replace mineral powder is 15%～45%.(2)Combined with the characteristics of cement and basalt fiber,composite modified gravel asphalt mixture was prepared by c ombining wet process and dry process.The central composite sequential design method(CCC method)in the response surface method was selected to determine the optimal cement content,basalt fiber content and asphalt dosage in the composite modified gravel asphalt mixture.Firstly,the surface experimental design of three factors,five levels and four response values is carried out,and the response surface model is established.Secondly,the analysis of variance,factor interaction analysis and numerical optimization of the model were carried out,and the predicted values of cement content,basalt fiber content and asphalt dosage were 1.2%,0.24% and 4.9%,respectively.Finally,the prediction value of the response surface model is verified by experiment,and the relative error is small,and the CCC method can be used to design,analyze,optimize and predict the mix ratio of composite modified gravel asphalt mixture.(3)On the basis of the CCC method to determine the amount of cement and basalt fiber,the optimal asphalt dosage of matrix gravel asphalt mixture(GAM),cement modified gravel asphalt mixture(CGAM)and basalt fiber modified gravel asphalt mixture(BFGAM)was determined by the OAC method.Under the optimal amount of asphalt,the road performance of GAM,CGAM,BFGAM and CBFGAM four types of gravel asphalt mixtures were compared and analyzed,and the effect of composite modification of cement and basalt fiber on gravel asphalt mixtures was further explored.(4)The adhesion grade of asphalt and cru shed gravel was judged by the peeling area and initial spalling time(SST)of the aggregate surface.The reasons for the poor adhesion of the two were analyzed by analyzing the proportion of smooth surface and chemical composition of gravel.The adhesion t est between asphalt and crushed gravel showed that the adhesion between asphalt and gravel was most significantly improved by the simultaneous addition of cement and basalt fibers.The results of the water damage resistance test of composite modified grave l asphalt mixture show that the composite modification of cement and basalt fiber can significantly improve the water damage resistance and freeze-thaw resistance of gravel asphalt mixture under the coupling of water temperature.(5)The high temperature stability,low temperature crack resistance and fatigue performance of four types of gravel asphalt mixture were analyzed by rutting test,trabecular bending test and indirect tensile test,and it was found that the composite modified gravel asphalt mixtur e had the best improvement effect.