Bond Strength of Deformed Bars and Steel Fibers in High Strength Concrete
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BOND STRENGTH OF DEFORMED BARS AND STEEL FIBERS IN HIGH STRENGTH CONCRETE ** * AND SCHBOcOCEw2iAwiH NE=HI WEC1UAT *Associate Professor of Civil Engineering, New Jersey Institute of Technology, Newark, N.J. 07102 **Graduate Assistant, Department of Civil Engineering, New Jersey Institute of Technology, Newark, N.J. 07102 ABSTRACT In recent years, the means of making high strength concrete are simple by adding microsilica, fly ash, or other types of additives. As the use of high strength concrete increases, the need to clearly understand its prcperties is essentially a necessity for engineering design. While much of the basic properties of high strength concrete such as compressive strength (fc), modulus of elasticity (Ec), and modulus of rupture (f ), etc., has been investigated and reported recently, many remain unavai5 .able. This paper presents the bond strength characteristics of deformed bar, steel fibers, and normal aggregate in high strength concrete matrix. The compressive strength of concrete used in this study is 75-80 MPa (11,00012,000 psi). Bond slip relationships of deformed bars of three different bar diameters were obtained from the pull-cut test. Two types of steel fiber reinforced high strength cemented composites were tested in a directtension, tapered specimen to observe the pulled-out behavior of steel fibers. Fiber reinforced concretes with fiber volume fraction of 0.5, 1.0, 1.5, and 2.0 % were compared to the unreinforced matrix. A direct-tension, dog boned specimen was used to study the bond between aggregate-matrix interface. The results from this study indicate that high strength concrete is generally more brittle, and in essence, allows less microcracking, less slippage, and less pulled-out deformation. This general trend is observed in both the deformed bar and fiber pulled-out as well as in aggregate-matrix interfacial debonding. The maximum slip of deformed bars in high strength concrete is about 0.15 mm.(0.006 in.) which is only one-tenth of that reported for normal concrete as 1.5 to 2.0 mm.(0.06-0.08 in.). A normalized pull-out stress-displacement relationship of high strength fiber reinforced concrete exhibits a unique behavior similar to those reported for normal fiber reinforced matrix. INTRODUCTION The definition of high strength concrete was defined by V.V.Bertero [1] as "concrete with compressive strength higher than 41 MPa(6,000 psi.)". This definition is generally accepted and adopted by ACI Committee 363 high strength concrete [2]. Attempts to properly proportion the matrix compositions and admixtures in order to achieve high strength have been successfully made in recently years [2,3]. One of the most common practices to make high strength concrete is the addition of microsilica, fly ash, and superplasticizer to normal concrete. As the use of high strength concrete increases, the necessity to understand its properties is obvious. Whereas most basic materials properties needed for structural design have already been reported in the literature [2-5], some remain unaccounted fo
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