Experimental Study On Pavement Performance Of Basalt Fiber Cement Stabilized Milling Material

The old Cement-Stabilized Macadam(CSM)is reused after milling,it can solve the problem of disposal of waste materials,and reduce the consumption of natural material.However,how to effectively use the milling material and make the use of waste material to achieve the maximum value still need further in-depth study.In this paper,the pavement performance of cement stabilized milling material is improved by adding basalt fiber,the basalt fiber cement stabilized milling material is systematically studied by raw material property test,research on the influencing factors,mechanical properties of the mixture,crack resistance and frost resistance tests.which is the application of basalt fiber cement stabilized milling material in pavement base for reference.Firstly,the physical and mechanical properties of milling coarse and fine aggregates were determined respectively.Compared with the natural aggregate,the results indicate that water absorption,crushing value and the content of needle chip granules of the milled coarse aggregate are high,and the apparent density is reduced.The particle content of the milled fine aggregate less than 0.075 mm increased,and the apparent density and sand equivalent decreased.Through Scanning Electron Microscope(SEM)scanning and Energy Dispersive Spectrometer(EDS)analysis of milling material surface features and components,it can be seen that the presence of micro-cracks,micro-pores and a considerable amount of hardened cement mortar on the surface of milling material is the main reason for the reduction of milling material technical indicators.Secondly,In order to study the mix proportion of basalt fiber cement stabilized macadam milling material,taking 7d compressive strength and 7d dry shrinkage coefficient as evaluation indexes,The fiber dosages of 0.6‰,0.8‰ and 1.0‰,fiber length of 12 mm,18 mm and 25 mm,milling materials blending method of milling fine aggregates and natural coarse aggregates,milling coarse aggregates and natural fine aggregates,full milling materials were taken as levels.The orthogonal test method was used to study the influence order and the best method of fiber dosage,length and milling materials blending method of basalt fiber cement stabilized milling materials,The results show that: the effect of milling materials blending method on the compressive strength and dry shrinkage coefficient of the mixture is the most significant,and the effect of fiber dosage is greater than the fiber length.When the volume dosage of basalt fiber is 0.8‰,the fiber length is 18 mm,and the blending method of milling materials is milling fine aggregates and natural coarse aggregates,the compressive strength of the mixture is the largest and the dry shrinkage coefficient is the smallest.Then,based on the selected design parameters,the compressive strength test,splitting strength test,compressive resilience modulus test,dry shrinkage test,temperature shrinkage test and freeze-thaw test of basalt fiber cement stabilized milling material,cement stabilized milling material and natural aggregate cement stabilized material with different test ages were tested respectively,and compare pavement performances.The results show that the mechanical properties of CSM increase with the addition of milling materials,among them,7d compressive strength,28 d splitting strength and 7d compressive modulus of resilience increased the most significantly,reaching 45%,10.3% and 29.7% respectively;and the cracking resistance and frost resistance decrease,the coefficient of dry shrinkage and temperature shrinkage increased by 16.5% and 22.7% respectively,and the loss rate of compressive strength after freeze-thaw increased by 37.5%;with the addition of basalt fiber,the mechanical properties,crack resistance and frost resistance of cement stabilized milling materials are improved in varying degrees,the mechanical properties were not enhanced obviously,but the coefficient of dry shrinkage and temperature shrinkage were reduced by 11% and 21% respectively,and the strength loss rate after freeze-thaw was reduced by 62.2%.Basalt fiber cement stabilized milling material compared with ordinary cement stabilized macadam,the mechanical properties of basalt fiber cement stabilized milling material shall not be lower than that of ordinary cement stabilized macadam,the compressive strength,splitting strength and compressive modulus of resilience of 90 d are 0.19 MPa,0.12 MPa and 158.22 MPa higher than those of cement stabilized macadam respectively,in terms of crack resistance and frost resistance,it is close to that of ordinary cement stabilized macadam,in which the 90 d dry shrinkage coefficient,90 d temperature shrinkage coefficient and the strength loss rate after 5 freeze-thaw cycles are only 0.05%,0.03% and 3.3% higher than that of ordinary cement stabilized macadam.According to the comprehensive test results,the mechanical properties of cement stabilized milling material with milled fine aggregate instead of natural fine aggregate have not declined,the compressive strength meets the requirements of high-grade highway base,but the crack resistance and frost resistance are decreased.In the severe cold area,the strength loss caused by the use of milling material should be considered;The addition of basalt fiber with the length of 18 mm and volume content of 0.8‰ can not only solve the problem of crack resistance and frost resistance degradation caused by the addition of milling materials,but also effectively improve the mechanical performances of cement stabilized milling material.Comparing the road performances of the new basalt fiber cement stabilized milling material with that of the ordinary cement stabilized macadam,it was found that the mechanical performance of the new basalt fiber cement stabilized milling material is not lower than that of the ordinary cement stabilized macadam,and it was closed to the ordinary cement stabilized macadam in terms of crack resistance and frost resistance.Finally,the interfacial bonding between fiber and matrix were studied by SEM,It was concluded that the fiber can be evenly distributed in the mixture,filling the micro pores and micro cracks in the cement stabilized milling material,and the fiber distribution and the cracks in the mixture can effectively inhibit the extension of the cracks.