Long term behaviour of fiber reinforced concrete beams in bending

Many of the properties of Fiber Reinforced Concrete (FRC) may be used to improve the structural response, under service conditions, of conventional concrete beams reinforced with steel bars (RC members). It is well known that fibers embedded into concrete matrix, enhance its ductility and toughness, increase its tensile strength acting as crack arrestors. In particular, fibers are effective in modifying crack propagation causing an higher number of cracks having a lower crack spacing values and narrower crack widths compared to the plain matrix. This effect could be exploited to improve durability of reinforced concrete structures, especially in those buildings 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 in reducing crack widths, and deterioration of RC members exposed to aggressive agents, is still lacking in the literature. Furthermore, the effect of fibers on cracking has generally been studied considering short term loading test; thus few data are available on cracking behaviour of FRC members under sustained loading. In the present research, the influence of steel and polymeric fibers on durability of plain reinforced concrete beams has been investigated. In particular, beams with and without fibers have been exposed for 17 months to natural weathering, in a coastal zone close to industrial plants, under a sustained flexural load in a three point bending scheme. The influence of sustained loading on the cracking behaviour and consequently on durability of the beams, with and without fibers, has been analyzed. After the exposure period, the beams have been tested in laboratory up to failure and their mechanical and cracking behavior has been studied. Durability tests have been conducted on crashed beams to evaluate carbonation depths and chlorides contents after the exposure period.