Tensile Strength of Carbon Fiber Reinforced Cement Composites
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Tensile Strength of Carbon Fiber Reinforced Cement Composites Houssam A. Toutanji, Tahar EI-Korchi, Gary L. Leatherman, R. Nathan Katz Worcester Polytechnic Institute, Worcester, MA. 01609
ABSTRACT The effect of carbon fibers on the uniaxial tensile strength of cement paste matrix is studied. The tensile strength values are obtained using the novel Cementitious Composites Axial Tensile Technique (CCA1TI) described previously [ 1]. The addition of 1.0, 1.5 and 2.0 volume percent of Polyacrylonitrile-based (PAN) carbon fiber results in an increase in tensile strength of 32, 41 and 48 percent respectively, as compared to the unreinforced matrix. A model based on the rule of mixtures is used to predict the tensile strength of the carbon fiber reinforced composites. Results are discussed with respect to fiber, interface bond, and cementitious matrix characteristic.
INTRODUCTION The addition of fibrous reinforcement to cement and concrete composites is generating increased interest in the construction industry. Fibers are added to cement based materials to improve mechanical properties, especially to increase the strain to failure. Numerous types of fibers may be added, including steel, glass, polypropylene, nylon, natural, etc. Carbon fibers are another type of reinforcement for cement based materials which have been gaining increasing interest among researchers. This interest is attributed to the improved qualities of the resulting composite such as high tensile strength, modulus, toughness, durability, chemical inertness, etc. Carbon fiber reinforced cement (CFRC) composites can be produced by placing the carbon fiber either in the tensile zone using continuous aligned fibers [2-51 or in the body of the specimens using chopped strands which are dispersed in a random two or three dimensional orientation [5101. Research involving CFRC was presented in the early 1970's by J. A. Waller [3], S. Sarkar and M. B. Bailey [4] and A. M. Ali and A. J. Majumdar [51. However, their research in determining the tensile strength was conducted using the traditional uniaxial tensile test which pose well known experimental problems which makes it difficult to obtain an accurate value [11]. Misalignment of the specimen grips or misalignment of the specimens within the grips may cause a nonuniform stress distribution which create bending stresses, resulting in fracture of the specimen at stresses below the true calcualted tensile strength. It was shown that the tensile strength may be reduced by as much as 90% because of load eccentricity [1]. The present research has centered on the use of Polyacrylonitrile-based (PAN) carbon fiber to enhance the tensile strength of the cementitious composite. The tensile strength values are obtained using the cementitious composite axial tensile technique (CCATT) [ 1]. This technique minimizes misalignment and stress concentrations at the attachment and produces a uniform stress distribution along the test specimen. Hence, the measured strength will closely represent the intrinsic tensile strength of
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