Influence And Mechanism Analysis Of Different Lithological Coarse Aggregate On Performance Of High-Fluidity Concrete

Coarse aggregate plays a role in skeleton,filling and restraining shrinkage in concrete,and its physical and chemical properties will have different effects on concrete.In recent years,many scholars have carried out various researches on the influence of coarse aggregate grading,grain shape and water content on concrete performance,and has drawn many valuable conclusions.With the emergence of high-rise buildings,the high-fluidity concrete is more and more used in practical engineering because of its high fluidity and good self compactness.So far,there are few researches on the influence of different lithology coarse aggregate on concrete performance in the large flow concrete.The influence of different lithological coarse aggregate on the performance of the concrete remains controversial.In this paper,the selection of different lithological coarse aggregate with different strength from small to large is: gneiss,limestone,basalt and diabase in order to study the working performance,mechanical properties(compressive strength,flexural strength,splitting tensile strength)of the high-fluidity concrete.The influence of volume stability(dry shrinkage,crack resistance),microstructure(micro morphology,pore distribution)was studied;The influence rules and reasons are summarized and analyzed,which can provide reference for the selection of coarse aggregate lithology in large flow concrete.The results of concrete compressive strength test show that in C30 strength grade,the 28d compressive strength of gneiss and limestone concrete is slightly higher than that of basalt and diabase;the compressive strength of limestone concrete is relatively higher in each age from 7d to 56d.In C50 strength grade,the 28d compressive strength of basalt and diabase concrete is slightly higher than that of gneiss and limestone;the strength increase of limestone concrete is the highest from 7d to 14d,which can reach 21.0%.In C70 and C90 strength grades,the 28d compressive strength of each group of concrete is diabase ≥ basalt >limestone > gneiss.In the strength grade of C90,the strength of concrete prepared by gneiss is low due to its insufficient strength.The results of concrete flexural strength test show that in C30 and C50 strength grades,the flexural strength of gneiss and limestone concrete is relatively high at 28d,and the strength increase of gneiss and limestone concrete is significantly higher than that of basalt and diabase concrete from 14d to 28d.In C70 and C90 high strength concrete,the flexural strength of basalt and diabase concrete is relatively high at the age of 28d;from 14d to 28d,the strength increase of gneiss and limestone is slightly higher than that of basalt and diabase,but the overall flexural strength is still low.The test results of concrete splitting tensile strength show that in C30 and C50 strength grades,the splitting tensile strength of gneiss and limestone concrete at 7d and 14d is lower than that of basalt and diabase;from 14d to 28d,the splitting tensile strength of gneiss and limestone concrete is higher than that of basalt and diabase,and the strength at 28d is higher than that of basalt and diabase.In the strength grades of C70 and C90,due to the large shrinkage and the differences in the strength,water absorption and apparent texture of coarse aggregate,the splitting tensile strength of gneiss and limestone concrete in each age is lower than that of basalt and diabase Although from 14d to 28d,the strength of gneiss and limestone concrete increases relatively high,but the splitting tensile strength is still lower than that of basalt and diabase.The results of concrete volume stability test show that the drying shrinkage of coarse aggregate concrete with different lithology in 28d and 56d was in turn: diabase > basalt >gneiss > limestone.Only basalt and diabase concrete cracked in the crack resistance test of C70 and C90 concrete rings.It shows that the volume stability of limestone concrete is the best,while that of basalt and diabase concrete is relatively poor.In conclusion,the mechanical properties of concrete,in C30 strength grade,the mechanical properties of gneiss and limestone concrete is slightly higher than basalt and diabase;in C50 strength grade,the flexural and splitting tensile strength of gneiss and limestone concrete is higher,the compressive strength is relatively lower;in C70 and C90 high strength concrete,basalt and diabase concrete has better mechanical properties.In terms of concrete volume stability,limestone concrete has better volume stability than the other three kinds of coarse aggregate in each strength grade.