Mixture Design And Performance Calculation Method Of Steel Fiber Reinforced Recycled Concrete

With the development of water conservancy and civil engineering construction in our country,the contradiction between the shortage of natural building materials and the increase of construction waste is more and more prominent.The waste concrete can be crushed and sieved to partly or totally replace the natural aggregate to produce the fresh concrete that is known as recycled concrete.Recycled concrete can reduce the amount of discarded concrete,turn waste into wealth,and also it is an effective way to realize the sustainable development of building materials.In order to make up for the mechanical and durability deficiencies of recycled coarse aggregate concrete(RCAC),in this paper,steel fiber is added into RCAC to make the steel fiber reinforced recycled coarse aggregate concrete(SFRCAC).The mixture design method,the basic mechanical performance,the axial compression constitutive relation and the durable performance of SFRCAC were studied.The main content as follows:(1)The slump and compression and splitting tensile tests of SFRCAC were conducted on 54 cubic specimens of 150mm×150mm×150mm with batching by 9 group mixture proportions based on the orthogonal method,the main influence factors on the performance of SFRCAC were studied.Based on these results,the reinforced effect of steel fiber on the splitting tensile strength and flexural strength of SFRCAC were studied and the calculated formula of steel fiber content was put forward through the compression and splitting tensile tests conducted on 132 cubic specimens of 150mm×150mm×150mm and four-point flexural tests conducted on 66 prism specimens of 100mm×100mm×400mm with batching by 22 group mixture proportions.The influence of water-cement ratio and recycled aggregate replacement ratio on the compressive strength were studied and the calculated formula of water-cement ratio was put forward through the compression tests conducted on 54 cubic specimens of 150mm×150mm×150mm with batching by 18 group mixture proportions.The influence of water content,recycled aggregate replacement ratio and the characteristic coefficient of steel fiber on slump were studied and the calculated formula of water content was put forward through the slump and compression tests conducted on 99 cubic specimens of 150mm×150mm×150mm with batching by 33 group mixture proportions.The calculated formula of sand volume of SFRCAC was put forward based on the principle that the fine aggregate need to fill the void caused by coarse aggregate,and then through the slump and compressive tests conducted on 45 cubic specimens of 150mm×150mm×150mm with batching by 15 group mixture proportions,the influence effect of the sand ratio on slump and compressive strength were compared with the calculated method of sand ratio.The mixture design method of SFRCAC based on the target strength and workability was established.(2)The influence of recycled aggregate replacement ratio and the volume ratio of steel fiber on prism compressive strength,elastic modulus,peak strain,the stress-strain curve and compressive toughness were studied through the prism compression tests conducted on 90 prism specimens of 150mm×150mm×300mm with batching by 10 group mixture proportions.The calculated relationship formulas between prism compressive strength,elastic modulus,peak strain and cubic compressive strength were put forward.The calculated formula and the constitutive model were put forward.(3)The influence of recycled aggregate replacement ratio,the volume ratio of steel fiber and strength on the load-deflection curve,first-peak strength,first-peak deflection,flexural strength,peak deflection,residual flexural strength,flexural toughness were studied through four-point flexural tests conducted on 30 prism specimens of 100mm×100mm×400mm with batching by 10 group mixture proportions.The evaluation indexes of flexural performance derived from ASTM C1609 and JG/T472-2015 were compared,and then the evaluation index of flexural performance suitable for SFRCAC were established.The calculated relationship formula between flexural strength and cubic compressive strength was put forward.(4)The influence of recycled aggregate replacement ratio,the volume ratio of steel fiber and strength on the load-deformation curve,shear strength,shear deformation shear toughness were studied through double-sided direct shear tests conducted on 40 prism specimens of 100mm×100mm×300mm with batching by 10 group mixture proportions.The evaluation index of shear toughness suitable for SFRCAC was established.The calculated relationship formula between shear strength and cubic compressive strength was put forward.(5)The influence of recycled aggregate replacement ratio,the volume ratio of steel fiber and strength on the carbonization depth at different carbonization time,the mass loss ratio and the relative dynamic elastic modulus at different freeze-thaw cycles,the content of water soluble chloride ion at the different depth form the specimen surface were studied through the carbonization tests conducted on 30 specimens of 100mm×100mm×300mm,rapid freeze-thaw cycling tests conducted on 30 prism specimens of 100mm×100mm×400mm,and dry-wet cycling tests conducted on 60 prism specimens of 100mm×100mm×200mm,the specimens were batching by 10 group mixture proportions.The calculated formula of carbonization depth was put forward.