LONG TERM BEHAVIOUR OF FIBER REINFORCED CONCRETE BEAMS IN BENDING

Many of the properties of Fiber Reinforced Concrete (FRC) may be used to improve performances of concrete flexural members reinforced with conventional steel bars (RC members). It is well known that fibers, embedded into a concrete matrix, increase its tensile performances and enhance its ductility and toughness, acting as crack arrestors. In particular, fibers are effective in modifying crack propagation causing an higher number of cracks and, consequently, lower crack spacing and a smaller crack widths, as compared to the matrix alone. This effect could be exploited to improve durability of reinforced concrete structures, especially of those exposed to aggressive environments. Few results are present in the literature on durability of full scale FRC structural element. A quantitative correlation between the effect of fibers on crack width and deterioration of RC members exposed to aggressive agents, represents an urgent need for designers. Furthermore, the effect of fibers on cracking has generally been studied considering short term loading test; thus, few data are available on cracking behavior of FRC members under long term loading. In the present research, the influence of fibers on durability of ordinary reinforced concrete beams has been investigated. In particular, beams with and without fibers have been exposed for seventeen months to natural weathering, in a coastal zone, under a sustained load. The influence of long term loading on the cracking behavior and, consequently, on structural durability, has been analyzed. An analytical prediction of the crack width according to Eurocode 2, Model Code 2010 and RILEM TC 162, is proposed. A comparison between experimental and theoretical values of crack width is shown.