| The Lhasa region of Tibet is known as a "Buddhist holy land" and therefore the mountains in the region are also regarded as sacred mountains and restricted from being mined for stone resources.While limestone and basalt are relatively scarce in Lhasa,the Lhasa River is rich in gravel resources and the granite stones excavated from tunnels can also be used.If gravel and other aggregates can be used in road construction,the problem of lack of road construction materials will be solved and the cost of construction will be greatly reduced.Granite and gravel are acidic aggregates with insufficient adhesion to asphalt and poor water stability,and adding anti-spalling agents to their mixes is a more common solution,but their durability is yet to be investigated.In this paper,polyester fibres were added to the gravel and granite asphalt mixes to improve the adhesion of the acidic aggregates to the asphalt and to improve their road performance.Experimental research on polyester fibre asphalt mastic was carried out,and the mix design and road performance of gravel and granite polyester fibre asphalt mixes were investigated,with the following main research work:(1)The chemical composition of the gravel and granite aggregates in Lhasa was analysed,and the adhesion class of the gravel was determined to be class 3 and the adhesion class of the granite was determined to be class 4 through adhesion tests.Performance tests on mineral powder,bitumen and fibres were carried out,and an economic analysis of four commonly used fibres was made,and polyester fibres were selected as the fibre test material for this paper.(2)Softening point,Brinell’s viscosity and cone penetration tests were used to analyse the performance of polyester asphalt mastic as a single factor;a multi-factor interaction analysis based on response surface testing was carried out to determine the effect of each factor on the softening point,cone penetration and Brinell’s viscosity of polyester asphalt mastic in the following order:powder to mastic ratio > polyester fibre admixture > polyester fibre length > preparation Preparation temperature.The best performance of the polyester asphalt paste was obtained at175°C and 9 mm polyester fibre length.(3)Based on the grey correlation method,the effects of powder to glue ratio and polyester fibres on the rheological properties of asphalt slurry at high and low temperatures were investigated,and the effects of the addition of polyester fibres on the rheological properties of asphalt slurry before and after ageing were analysed.The correlation of each factor on the rutting factor G*/sinδ of polyester fiber asphalt slurry was as follows: powder to glue ratio > polyester fiber dosing > polyester fiber length,the larger the powder to glue ratio the stronger the rutting resistance of asphalt slurry,and the rutting factor showed a trend of increasing and then decreasing with the increase of polyester fiber dosing.Powder to glue ratio > 1.0 will affect the low temperature rheological properties of polyester asphalt slurry,it is recommended that the polyester asphalt slurry powder to glue ratio of 0.8 is appropriate.(4)The optimum oil to stone ratio of gravel AC-16 and granite AC-16 gradation and different polyester fibre admixtures were determined.The effect of polyester fibre admixture on the Marshall index and the mechanism of polyester fibre improving the asphalt mixture were also analysed.The addition of polyester fibres increased the gross volume relative density,effective asphalt saturation and stability,and reduced the void ratio and flow value,which in turn improved the mechanical properties of the acidic aggregate asphalt mix.When the polyester fibre dosing is0.4%,the comprehensive performance of the Marshall index is the best,and the water stability is significantly improved.(5)The improvement of the road performance of polyester fibre was analysed by conducting water immersion Marshall test,freeze-thaw splitting test,rutting test and small beam bending test on gravel and granite asphalt mixes with different polyester fibre dosing.The results of the study show that: the optimum dose of polyester fiber in acidic aggregate asphalt mixes range from 0.4%to 0.45%,polyester fiber dose on gravel,granite asphalt mixes resistance to water damage,high temperature performance,low temperature cracking resistance are significantly improved,polyester fiber acidic aggregate asphalt mixes suitable for application in asphalt road subgrade. |
