Hybrid Fibers and the Development of Cracking in Concrete

Abstract

Cracking in concrete is fundamentally altered by the addition of reinforcing fibers. A combination of microfibers and macrofibers that contribute in complementary ways to performance is presented as a means for controlling cracking and improving the life cycle behavior of concrete. In prior work, a hybrid blend of these fibers in a mortar matrix evidenced better mechanical performance and lower cracked permeability than was seen with a single fiber type. The research presented herein 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, thus demonstrating 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.