Size Effects in Flexural Toughness of Fiber Reinforced Concrete

The influence of specimen size on measured flexural toughness of fiber reinforced concrete (FRC) remains largely unknown. Towards this end, an experimental program was carried out where flexural toughness tests were performed on specimens of two different sizes using ASTM C1609/C1609M-07 test procedure. Two specimen sizes of 100x100x350 mm(3) and 150x150x500 mm(3) were tested. A hybrid polymeric fiber at three fiber dosage rates of 3.0, 4.5, and 6.0 kg/m(3) was investigated. Results indicate that the specimen size affects not only the toughness properties but also the variability in data as quantified by the coefficient of variation (COV). Size effect was more pronounced in the early part of the load-deflection curve and decreased with an increase in the fiber volume fraction. At a given fiber volume fraction, the COV, moduli of rupture, and post-crack residual strengths were all higher for the specimens of smaller size. Finally, the small size specimens showed a greater deflection hardening than the large size specimens. The last conclusion is significant in that deflection hardening is now often cited as the required performance characteristic of high performance FRC, and this property may depend more on the size of the specimens than on the composite itself.