Mechanisms of fiber-matrix interface degradation under fatigue loading in steel FRC

Abstract

The present work reports the outcomes of an experimental research on the steel fiber-cement based matrix interface degradation under fatigue loading. The bond degradation was assessed for two distinct fiber types: hooked and straight steel fibers. First, the fiber bond inside the concrete matrix was analyzed through quasi-static pullout tests in accordance with the stablished literature of the topic. Thereafter, fatigue tests were carried on at different load levels (95%, 85%, 70% and 50%) up to 1,000,000 cycles or up to failure. Through the experimental campaign, it was possible to investigate two distinct failure modes: fiber pullout and fiber rupture under fatigue. While the hook is progressively straightened along the fatigue life when the fiber is pulled out under fatigue, no slip takes place when fiber rupture is concerned. Novel models were proposed to estimate slip evolution of steel fibers during the fatigue pullout tests. Although slip is almost constant when fiber rupture takes place, an exponential curve was adopted in terms of the pre-slip level for the fiber pullout failure mode.