Research On The Road Usage Of Cement Stabilized Coral Reef Sand Base

With the implementation of the Belt and Road Initiative,China and many countries along the Silk Road should build a large number of infrastructure construction such as roads and airport runways on the island.The islands are usually far away from the mainland and are short of building material,while it should pay more on transportation from mainland to island,which seriously restricts the construction and development of island.In order to resolve such difficulties,man usually choose to use local material.Using the rich amount of coral sand around the island as the building aggregate can be a solution to make up the shortage of building materials on island.Because of its special biological origin,coral reef sand has the characteristics of low single particle strength,easy to break,and regional differences.As a building aggregate,it will have certain impact on the safety of highway structure,so whether coral reef sand can be used as the grass base.Building aggregates have important engineering significance for the development of island reefs.In this paper,the influencing factors and the influence degree of the mechanical properties of cement stabilized coral reef sand base and the variation trend of the maximum tensile stress at the bottom of different base structures are studied by laboratory test and finite element simulation.The results of the two tests were compared and the optimum mixture ratio of base was selected.The main work carried out in this paper and the corresponding research contents are as follows:（1）To analyze the basic physical and chemical properties of coral reef sand.In terms of chemical ingredient,coral reef sand is mainly composed of CaCO₃ and SiO_2.In terms of physical properties,it has high water absorption,high void ratio and high pressure fraction.（2）Because coral reef sand with high pressure fraction,in this paper adopts the recommended dense-framework gradation and design the ratio of thickness by using the maximum density curve theory‘n’and control the ratio of particles’thickness.Three grades are 65:35,60:40,55:45.Besides,it also comments non-uniform coefficient and curvature coefficient of every gradation.To draw the conclusion:Three aggregates are well gradated,skeleton has significant function,filing effect also with no problem.（3）After incorporating 5%、6%、7%、8%of cement into threes gradations of aggregate and through compaction test,the maximum dry density and optimum moisture content can be easy to know.The aggregate adopts cylindrical and beam testing mold to form by hydrostatic pressure,meanwhile tests the sample with 7d unconfined compressive strength.According to the design requirement of the specification of asphalt pavement to base unconfined compressive strength by road and the civil aviation,only when the dose of cement above 5%,the strength can meet the base design requirement.Do unconfined compressive strength test,split test,flexural-tensile strength test as well as rebound modulus test on test groups that are meet the requirement.Experimental findings:Every mixture of mechanical properties will be increasing by risen of amount of cement or decline the ratio of coarse particle in aggregate;With the age growing,compressive strength and cleavage strength will all increasing;To make compressive strength as reference man can find that mixture can meet Sub-base’s compressive strength requirement,besides 2#and 3#aggregate with8%cement as well as 3#with 7%cement can meet upper base’s compressive strength requirement.（4）Computation using finite element method about the different base modulus,base thickness and the layer bottom tensile stress of the subbase thickness under static load.The results provides that under the static condition,the layer bottom tensile stress is positive correlation with the base modulus as well as the base thickness,while is negative correlation with the subbase thickness.When compared the different impact subject to each elements,the results shows subbase thickness has the largest impact towards the layer bottom tensile stress,while,successively,in base modulus and in base thickness.The highway structure will have the largest layer bottom tensile stress when there have 40cm base thickness and 15cm sub-base thickness.The dynamic analysis about above mentioned highway structure.The results provide that the layer bottom tensile stress is positive correlation with the base modulus.When the moving load is close or away from the observation point,the tension and compression layer bottom tensile stress is appear alternately,however,the amplitude is relatively small.When the moving load is near the observation point,the layer bottom tensile stress showed a rapid increase and reaches the peak.This phenomenon brings an acid test for the base durability.Compared the analysis about the layer bottom tensile stress and the laboratory test,then provide the applicability analysis about each mixtures.Under the road structure of this paper,in addition to material No.16 and No.26,the extreme value of layer bottom tensile stress under other groups of mixtures ratio is much less than the data collected from the laboratory test,thus all meet the base application requirement about highway engineering.Comprehensive consideration under mechanical properties,the material No.37 would be the optimum selection for the base mixture.