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Properties of steel micro-fiber reinforced cementitious material

University of British Columbia

The addition of micro-fibers improves not only the tensile strain capacity but also the tensile strength of cementitious materials. Among the different types of micro-fibers currently in use, steel micro-fibers which are characterized by high strength, high stiffness and low cost, have great potential to be used in many applications. The fracture properties of steel micro-fiber reinforced cementitious are, however, not well understood and are necessary for optimization. Three aspects of steel micro-fiber reinforced cementitous materials are examined in this thesis: (1) characteristics of bond between steel microfiber and cement paste; (2) properties of steel micro-fiber reinforced mortar (SMFRM) under uniaxial tension; and (3) properties of SMFRM in flexure. Single fiber pull-out tests were used to study the characteristics of bond between steel micro-fiber and cement paste. A feed-back controlled system, which could avoid the sudden fracture of specimens at peak load, was installed in the uniaxial tensile tests. Similarly, crack-opening controlled, four-point flexural tests were performed on beams. Data collected from these tests were analyzed by computer programs written in the FORTRAN language. In pull-out tests, the highest peak pull-out load and the highest total energy absorption were obtained when the micro-fiber was aligned in the loading direction. This suggests that the optimum inclined angle of fiber is 0°. The increase of silica fume content in the matrix increased the strength of bond between steel micro-fiber and the cement-based matrix. The results of the uniaxial tensile tests and the flexural tests show, as expected, that the strength and toughness of SMFRM increases with an increase in the fiber volume fraction. SMFRM with fibers having larger diameters had higher toughness. The addition of longer fibers in SMFRM also yielded higher toughness. But, with longer fibers, the workability of steel micro-fiber mortar mixtures was inadequate. Short thick fibers, on the other hand, were easy to be mixed at high volume fractions (5% or more) without workability problems. While the inclusion of a polymer in cement mortar increased the toughness of SMFRM significantly, an increase in the sand content in cement mortar led to a significant increase in the strength. Overall, the addition of steel micro-fibers improved the properties of cementitious materials dramatically.

Thesis/Dissertation

application/pdf

2009-01-12

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http://hdl.handle.net/2429/3589

Civil Engineering

University of British Columbia

UBCV

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