| Reactive Powder Concrete(RPC) is a cementitious material with ultra-high performance, such as ultra-high strength、ultra-high ductility, it obviously have higher strength、higher ductility and higher durability、especially much higher tensile strength and ductility compared to normal strength concrete(NSC).There are many factors which will affect the bending tensile strength of RPC, such as mix proportion、curing condition、fiber volume fraction, while fiber volume fraction play a major role in determining the bending tensile strength of RPC. The reinforcing and toughening effect of steel fiber in the matrix of RPC mainly through the stress transfer taking place across the fiber/matrix interface.This paper based on the fiber pull-out experiment to study the bond slip characteristics between steel fiber and the matrix of RPC. Several parameters were taken into account in this test such as fiber diameter, different fiber distribution and different fiber distance. The influences of fiber distribution and fiber distance on the pullout curves and pullout works are studied. The two-cylinder model for the single-fiber pull-out test was used to analyze the stress transfer between fiber/matrix interface. Then, the influence of bending tensile strength (such as steel fiber volume fraction、curing regimes、fine aggregate diameter )of RPC was systematically analyzed. From the fiber pull-out experiment and flexural test we get the following main conclusions:(1): By means of the fiber pull-out experiment, we found that the effect of fiber distance play a major role in determining the adhesive property and stress transfer of steel fiber/RPC matrix interface. With the increasing of fiber distance, maximum bond strength of fiber/matrix was also increasing firstly and then becoming stable. Mechanical calculation model for the fiber pull-out was established, and also by the use of the model, adhesive property and stress transfer of steel fiber/RPC matrix interface were systematically analyzed. By use of the experimental results, we create fit curves, which can indicate the relationship between the fiber distance and adhesive strength。(2):The increase of steel fiber volume fraction can enhance the bending tensile strength of RPC under uniform distribution of fibers, when the steel fiber volume fraction increases from 0% to 3%, the bending tensile strength increases from 9.0MPa to26.9MPa.But from the economical point of view ,2% steel fiber volume fraction provide the best reinforcing efficiency. RPC is normally heat treated at an early age for 24~48 hours at 80~90℃,because of such treatment can accelerate the pozzolanic reaction of silica fume with Ca(OH)2.This explains the bending tensile strength of the specimens under hot water curing condition for 48 hours at 85℃is a little higher than the specimens under standard curing condition for 28 days. It was found that aggregate diameter will affect the distribution of steel fibers, when the aggregate diameter increases to 5mm, the bending tensile strength will drops significantly.(3): This paper summarizes the theories of fiber reinforced composites, by using of these theories and based on the assumption of uniformly distributed fibres、perfect bonding between the fiber and matrix, a computational formula of flexural strength of RPC was deduced. The flexural strengths estimated based on the computational formula was then compared with the measured flexural strengths. It can be seen that there is little difference in flexural strength between the measured and the predicted values when fibers are uniformly distributed in matrix, nonetheless there is noticeable diffenence while fibers are badly distributed in matrix. |
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