Experimental Study On Shrinkage And Mechanical Properties Of Micro Expansive Self-compacting Steel Fiber Reinforced Concrete

Self-compacting steel fiber reinforced concrete(SFRC),a green high performance concrete,has the advantages of both Self-compacting concrete(SCC)and SFRC.With the premise of ensuring workability on a fresh mixture,however,the greater shrinkage of hardened self-compacting SFRC becomes an issue due to the content of cementitious materials increased with the volume fraction of steel fiber.By using the expansive agent to reduce the shrinkage of self-compacting SFRC,the strength reduction of hardened self-compacting SFRC is another issue.To solve these issues,this paper performed an experimental investigation on the workability,shrinkage,and mechanical properties of micro expansive self-compacting SFRC compared to the self-compacting concrete with or without an expansive agent.The mainly research contents and conclusions are drawn as follows:(1)The mix proportion of micro expanxive self-compacting SFRC can be designed by the direct absolute volume method,of which the steel fibers are considered as the distributed coarse aggregates.The volume fraction of steel fiber was 0.4~1.2%(0.4%,0.8% and 1.2%)and the dosage of calcium-sulfoaluminate expansive agent was 10% mass of binders.Results showed that the rational workability of high filling and passing ability without segregation and bleeding of fresh self-compacting SFRC can be ensured by increasing the binder to coarse-aggregate ratio and the sand ratio.With the increment of 0.4% volume fraction of steel fiber,the sand ratio increased by 0.01 and the binder to coarse-aggregate ratio increased by 0.10.(2)The early age expansion(within 7d)property of micro expansion self compacting SFRC was studied under the volume fraction of steel fiber was 0.4~1.2%(0.4%,0.8% and 1.2%)and the dosage of calcium-sulfoaluminate expansive agent was 10% mass of binders.A self-compacting concrete with or without an expansive agent as reference.The results showed that the expansion rate under moist condition was great than that of under sealed condition.The expansion rate of specimen showed a trend of a continuous increase under moist condition and an initial increase followed by a subsequent decrease under sealed condition.Both the moist cure and sealed curing conditions,the expansion rate decreased with the increase of volume fraction of steel fiber.(3)The shrinkage properties of micro expansion self-compacting SFRC was studied under the calcium-sulfoaluminate expansive agent was 10% mass of binders and the volume fraction of steel fiber was 0.4~1.2%(0.4%,0.8% and 1.2%).A self-compacting concrete with or without an expansive agent as reference.Results showed that the early age shrinkage,autogenous shrinkage and dry shrinkage of self-compacting SFRC decreased by using expansive agent.With the incorporation of an expansive agent of 10% mass of binders and the steel fiber with the volume fraction of 0.8%,the inhibition effect on early shrinkage of micro expansive self-compacting SFRC was optimum.With the increase of a volume fraction of steel fiber from 0.4% to 1.2%,the autogenous shrinkage of self-compacting SFRC reduced by 20.7% at curing age of 270 d and the dry shrinkage of self-compacting SFRC reduced by 18.4%~7% at curing age of 240 d.The autogenous shrinkage of micro expansive self-compacting SFRC increased before 90 d and decreased after 90 d with the increase of volume fraction of steel fiber.An increased drying shrinkage of self-compacting SFRC with the increase of volume fraction of steel fiber due to the expansion of cementitious matrix was reduced with the increase of volume fraction of steel fiber.(4)The mechanical properties of micro expansion self-compacting SFRC was studied under the volume fraction of steel fiber was 0.4~1.2%(0.4%,0.8% and 1.2%)and the dosage of calcium-sulfoaluminate expansive agent was 10% mass of binders.Results showed that the mechanical properties of self-compacting SFRC were improved with the incorporation of expansive agent and steel fiber.With the increase of a volume fraction of steel fiber from 0.4% to 1.2%,the cubic compressive strength,axial compressive strength,splitting tensile strength and modulus of elasticity of micro expansive self-compacting SFRC increased by 3.2%,9.1%,59.8% and 17.0%,respectively.The cubic compressive strength of micro expansive self-compacting SFRC with restrained condition is higher than that of unrestrained condition.The strength improvement rate of micro expansive self-compacting SFRC decreased with the increase of volume fraction of steel fiber under restrained condition.Ther strength increment under the restrained condition increased with free expansion rate under unrestrained condition.