Influence of steel, glass and polymer fibers on the cracking behavior of reinforced concrete beams under flexure

The use of fibers can improve the behavior at serviceability limit states (crack and deflection control) and ultimate limit states (bearing capacity) of reinforced concrete (RC) elements under flexure. Fibers reinforcement provides a postcracking resistance, leading RC element to have a more diffused crack patterns characterized by narrower and more closely spaced cracks. Some doubts are instead related to RC element ductility, which can be affected by crack localization after rebar yielding. However, most of experiments present in literature relate only to elements in steel fiber reinforced concrete with significant residual strengths (fR,1 and fR,3 greater than 3.5-4.0 MPa). This paper aims to evaluate the influence of different fiber type (steel, glass, or polymer macrofibers) on the cracking and strength capacity of RC beams under flexure by using a broad range of Fiber Reinforced Concrete (FRC) toughness (1.6≤fR,1≤5.1 MPa and 0.8≤fR,3≤4.5 MPa). Twenty-one small scale RC beams with a typical value of longitudinal reinforcement ratio (0.87%) were tested under flexure. Crack and deflection control, as well as bearing capacity and crack localization were evaluated as a function of FRC toughness. Finally, results were compared against mean crack spacing and strength capacity predictions of fib Model Code 2010