Mechanism for tensile strain hardening in high performance cement-based fiber reinforced composites

Abstract

The mechanism responsible for the improvement in tensile strain capacity of FRC (fiber reinforced concrete) as a result of the addition of high volume fraction of discontinuous fibers was investigated, using energy changes associated with cracking. The energy terms considered include: matrix fracture energy, matrix strain energy. debonding energy, fiber strain energy and fiber frictional energy. Assuming that the first observed crack is also the failure crack, it was found that multiple cracking occurs in high performance FRC. In such composites the energy needed to open the critical cracks exceeds the energy needed to form a new crack. The analysis predicts that the major energy term determining this behavior is the fiber debonding energy. Multiple cracking was observed in fiber reinforced small densified DSP (particles) containing a high volume fraction (higher than 3%) of fine and short steel fibers. Because crack localization did not occur during multiple cracking, very large increases in total strain capacity were achieved with increasing fiber volume fraction. At 12% fiber volume fraction, a total strain capacity of about 0·2% was measured from flexures tests; an increase of about 15 to 20 times over that of the plain matrix.