| In the construction of islands far away from the mainland,there are some serious problems,such as lack of fresh water,lack of natural aggregate,sea breeze and high temperature,high humidity and high salt fog.The long coastline and rich coral resources in China provide the possibility of using local materials.Due to the disadvantages of natural coral,such as porous,light weight,low strength and so on,the strength and durability of coral aggregate concrete is poor,which is difficult to apply to the actual engineering construction.Therefore,this paper proposes to grind coral into coral powder instead of quartz to prepare ultra-high performance concrete with coral powder(CUHPC).Based on the above research background,this paper has carried out a series of studies on the influence of coral powder content,mixing and curing conditions of seawater and fresh water,cement types on the mechanical properties,volume stability and microstructure of CUHPC(1)Through crushing and grinding the natural coral,the average particle size is10 μ The compressive strength,flexural strength and splitting tensile strength of ultra-high performance concrete with coral powder were 134 mpa,27.5mpa and14.3mpa respectively.(2)The effects of the amount of coral powder,the mixing and curing of seawater and fresh water,and the types of cement on the workability and mechanical properties of coral powder used in ultra-high performance concrete were studied.The test results show that when the content of coral powder is 65%,the mechanical properties of concrete is the best,but it will reduce the fluidity of concrete and accelerate the setting time.The addition of coral powder increases the micro gap structure of filled concrete,greatly improves the compactness,and its porous microstructure will absorb a lot of free water,causing the changes of fluidity and setting time.For the ultra-high performance concrete mixed with coral powder under the condition of sea water and fresh water,sea water mixing and curing can improve the compressive strength,flexural strength and splitting strength of concrete at the early stage,while the compressive strength at the later stage is less than that under the condition of fresh water mixing and curing.For different types of cement mixed with coral powder ultra-high performance concrete,using P·O42.5 cement mix proportion specimens can improve the working performance of concrete,improve the flexural and compressive strength,while using P·O52.5 cement mix proportion specimens can greatly increase the compressive strength of concrete.R·SAC42.5 cement mix proportion can only be used for rush repair and rapid repair engineering construction due to the strength reduction.(3)The volume stability of ultra-high performance concrete with coral powder,i.e.temperature shrinkage and dry shrinkage,is studied.The results show that the drying shrinkage of UHPC with coral powder mainly occurs in the range of 28 days after setting and hardening,and 65% coral powder and sea water can effectively reduce the temperature shrinkage and drying shrinkage of CUHPC.The direct relationship between the shrinkage rate of CUHPC2 and age was studied,and the fitting equation was obtained through nonlinear regression analysis,which directly calculated the shrinkage value of corresponding age.(4)The microstructure and hydration products of ultra-high performance concrete with coral powder are studied.The results show that the main hydration products of ultra-high performance concrete with coral powder are silica,calcite and calcium silicate hydrate.With the increase of coral powder content,calcite content increases,calcium silicate hydrate decreases,and the microstructure of the matrix becomes denser,and the above phenomenon has a peak value of 65%.Under the action of coral powder,the micro structure gap of concrete is reduced,the overall structure is more dense,and the matrix and steel fiber are firmly filled completely,which shows good mechanical properties and volume stability in macro. |
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