Long-Term Behavior of Cracked Steel Fiber-Reinforced Concrete Beams under Sustained Loading

Abstract

In many cases, fibers are incorporated in concrete in order to improve the service life of the structures, by means of the three-dimensional crack control capacity of this type of reinforcement. In this sense, the residual (i.e. post-cracking) capacity, and long-term (i.e. creep) behavior of fiber-reinforced concrete is of paramount importance. This work presents an experimental study on the behavior of steel fiber reinforced concrete (SFRC) beams, cracked and afterwards subjected to long-term loading. Beams measuring 150´150´600 mm (6´6´24 in.) were cast using a 45 MPa (6525 psi) compressive strength SFRC with self-consolidating characteristics, having 40 kg/m3 (67 lb/yd3), 0.5 % in volume, of hooked-ended steel fibers of 50 mm (2 in.) length and 1 mm (0.04 in.) diameter. Firstly, a group of four beams was tested in flexure according to EN 14651 to establish a performance reference. Subsequently, other 18 nominally identical beams were loaded up to crack openings between 0.2 and 3.5 mm (0.008 and 0.14 in.) using the same test configuration in order to generate different damage levels. The cracked beams were then placed in creep frames and subjected to different levels of load. The crack opening under constant gravity load was electronically measured by means of displacement transducers, over a period of approximately 21 months. The concept of rate of crack-opening under long-term loading is introduced, and conditions for long-term stable response are discussed.