Long-term behavior of cracked fiber reinforced concrete under service conditions

Abstract

This paper presents an experimental study on creep behavior of cracked Fiber Reinforced Concrete (FRC). To this end, a conventional strength concrete incorporating hooked-end steel fibers was used. In order to represent service conditions, specimens under low sustained loads with small pre-cracking damage (lower than 0.5 mm) were tested and analyzed. Taking as a reference the residual stress fR,1 determined according to EN 14651:2007, different stress levels for the creep tests were applied: 25%, 35% and 45% of fR,1. For the pre-cracking damage, several initial crack openings were considered: 0.05, 0.1, 0.2, 0.3 and 0.5 mm. The specimens were tested under a four-point bending scheme for 180 days in controlled environmental conditions. The Crack Opening Rate (COR) was used as parameter to characterize the creep behavior of cracked FRC. After the creep tests, conventional flexural tests were carried out to evaluate the residual capacity and to survey the fiber density of each specimen. Both the stress level and the initial crack opening factors affected significantly the creep behavior. In all cases, the measured increases in crack openings resulted compatible with service conditions, and no negative effects on the residual post-creep behavior were observed. An expression to predict Crack Opening Rate values is proposed.