Study On Pavement Performance Of Cement Stabilized Gravel Base In Lhasa Area

Because of its special geological environment,gravel in Lhasa River is the main stone material for road use.Although the gravel surface is smooth and can be mixed with good gradation type,the mechanical properties of the mixture are poor due to its poor angular property and excessive acid content in the stone.It is difficult to meet the mechanical properties and durability requirements of road base construction in Lhasa area by using this material directly.Based on the project "Research on Key Technologies of Road Surface in Lhasa Area",this paper aims to study the feasibility of gravel as the base material.By means of aggregate replacement,mixing of waste rubber particles and waste plastic fibers,and taking aggregate replacement ratio,rubber and fiber content,and curing age of specimens as the research variables,an experimental study is conducted on the mechanical properties and durability of cement-stabilized gravel materials.The details include:1.The action mechanism of machine-made sand on cement-stabilized gravel material is analyzed,the proportion of machine-made sand replacing the 4# marking material(river sand)is initially adjusted,and the compressive strength of the initial gradations,T30,T60 and T100 at 7d,14 d,28d and 60 d with the cement content of 4%,4.5% and 5% is compared and analyzed.The results show that: The compressive strength growth of T30 grading is the most stable under different cement dosage and different ages,and the stone reserve and compressive strength value select the T30 grading with mechanical sand replacement ratio of 30% for subsequent tests.The splitting strength,flexural strength and compressive resilience modulus of T30 gradation and initial gradation at 7d,14 d,28d and 60 d were compared and analyzed,and the feasibility of 30%replacement rate of machine-made sand was verified.2.Cement stabilized gravel specimens mixed with fiber and rubber were prepared by orthogonal method,and the mixing proportion of waste rubber particles was adjusted from 0.5%,1% and 1.5% to 0.5%,0.7% and 1% according to the forming rate of specimens during demoulding.The initial grade and T30 grade cement stabilized gravel materials were mixed with waste rubber particles and plastic fibers respectively,and their material parameters were orthogonal tests.Based on 28 d strength range analysis,the optimal combination of fiber cement stabilized gravel materials was obtained as follows: cement dosage 5%,fiber length 9mm,fiber content 0.45%;The optimal combination of rubber cement stabilized gravel materials is: cement dosage 5%,rubber mesh number 30,rubber content 0.5%.Through the analysis of the influence of curing age and rubber and fiber content on the compressive resilience modulus,splitting strength and flexural tensile strength of cement stabilized gravel,the results show that: When the curing time increases from7 d to 60 d and the rubber content increases from 0 to 1%,the compressive resilience modulus,splitting strength and bending tensile strength of rubber cement stabilized gravel increase by 108.7,20.7% and 12.2%,respectively.When fiber content increased from 0 to 0.45%,the compressive resilience modulus,splitting strength and bending strength of fiber-cement stabilized gravel increased by 113.7%,81.1% and 51.9%,respectively.The compressive resilience modulus of rubber cement stabilized gravel is better than fiber cement stabilized gravel,while the splitting strength and bending strength of fiber cement stabilized gravel are better than rubber cement stabilized gravel,and fiber cement stabilized gravel is selected for follow-up study.3.The dry shrinkage properties,freeze-thaw properties and fatigue properties of waste plastic fiber cement stabilized gravel materials and ordinary cement stabilized gravel materials were studied.The results show that:(1)Adding 0.30% waste plastic fiber can reduce the dry shrinkage strain and dry shrinkage coefficient of cement stabilized gravel by 20.6% and 14.3%,and controlling the fiber content within 0.30% can effectively improve the shrinkage property of the material.(2)The anti-freezing coefficients of compressive strength and splitting strength increased by 3.2% and 2.8% respectively under three freeze-thaw cycles.The frost resistance coefficients increased by 5.4% and 4.4% respectively under 5 freeze-thaw cycles.(3)Under different stress ratios,the fatigue life of waste plastic fiber cement stabilized gravel material is significantly improved than that of ordinary cement stabilized gravel material,and with the increase of stress level,the fatigue performance of waste plastic fiber on cement stabilized gravel will be improved more obviously.As there are few research results of cement stabilized gravel material at present,the experimental research of this paper can play a certain reference value for pavement base construction in Lhasa area.