Chopped Steel Fiber Reinforced Chemically Bonded Ceramic (CBC) Composites
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CROPPED STEEL FIBER REINFORCED CHEMICALLY BONDED CERAMIC (CBC)
Sean Wise, Kevan Jones, Claudio Herzfeld and David D. Double CEMCON Corporation, 10123 Senate Drive, Lanham, Maryland 20706,
COMPOSITES
U.S.A.
ABSTRACT Very high strength castable chemically bonded ceramic (CBC) materials have been prepared which consist of finely chopped steel fibers and steel aggregate in a silica modified portland cement matrix. This paper examines the effect of metal fiber addition on compressive and flexural strengths. The overall chemistry of the matrix is held constant but the morphological form of silica used and the cure conditions are altered to examine their effect. Compressive strengths in excess of 500 MPa and flexural strengths in excess of 80 MPa can be obtained. It is found that flexural strength increases proportionally with fiber content over the range of 0 to 10% by volume. Compressive strengths are not affected. Use of silica fume in the mixes produces higher strengths at low temperatures than mixes which contain only crystalline silica. High temperature curing/drying (400*C), which produces the highest strengths, produces equivalent properties for formulations with and without silica fume. Higher water/cement ratios are found to reduce compressive strengths but have relatively little effect on the flexural properties.
INTRODUCTION Castable cementitious materials are known for their good compressive properties but relatively poor tensile strengths. Polymer modification, such as latex addition or resin impregnation, can improve tensile properties somewhat [1] and ICI* has shown that order of magnitude improvements can be obtained through use of a water soluble polymer [2]. The use of an organic material to improve the tensile strength or toughness of a cementitious composite, ties the stability of the composite to the stability of the organic modifier, however. This can be a severe limitation if the material is exposed to conditions that will degrade the polymer. Fiber reinforcement is a second approach to solving the brittleness problem and the literature contains examples using metal, glass, mineral and organic fibers [3]. The quantities used in castable mortars and concretes are generally small however and their primary function is to reduce cracking. Fiber in high enough volume to provide substantial reinforcement generally makes these systems unworkable. For this reason, most high fiber cementitious systems are made by felting processes, slurry infiltration or spray methods where the fiber is either suspended in dilute solution with the cement and dewatered, or mixed, with a mortar or cement paste as it is placed [3,4]. High strength cement matrices permit the use of a broader range of fibers than previously considered. Improved bonding in these matrices should result in reduction of the aspect ratio necessary for effective reinforcement. Lower aspect ratio fibers in turn can be used in greater quantities in these mixes without serious degradation of mix consistency. This is important as the minimum fiber vo
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