Hybrid Fibers and the Development of Cracking in Concrete


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Title: Hybrid Fibers and the Development of Cracking in Concrete

Author(s): J. S. Lawler, D. Zampini, and S. P. Shah

Publication: Special Publication

Volume: 209


Appears on pages(s): 791-810

Keywords: concrete; fiber-reinforcement; fracture process; hybrid; microfibers; shrinkage; workability

Date: 9/26/2002

Cracking in concrete is fundamentally altered by the addition of reinforcing fibers. A combination of microfibers (less than 22 pi [0.0oO9 in.] in diameter) and macrofibers (500 p.m 10.0197 in.] in diameter) that contribute in comple- mentary ways to performance, is presented as a means for controlling cracking and improving the lifecycle behavior of concrete. In previous work, a hybrid blend of these fibers in a mortar matrix demonstrated better mechanical performance and lower cracked permeability than was seen with a single fiber type. The research presented in this paper attempts to realize the potential of such blends in concrete. A mixture proportioning method that achieves good workability and cohesion in concretes containing microfibers was used to produce a cast concrete. The mechanical performance and shrinkage cracking resistance of this material were evaluated. In the hybrid reinforced concrete, the microfibers delayed the development of macrocracks and so the composite demonstrated greater strength and cracking resistance than a similar matrix reinforced with macrofibers only. However, this influence was less pronounced than was observed with a mortar matrix and was confined to smaller crack openings.