Size Effect during Bending Tests of Fiber-Reinforced Concrete Specimens

Abstract—The influence of reinforcement with basalt fibers in an amount of 0.6 vol % on the size effect in concrete made of Portland cement TsEM II/A-K(Sh-I) 42.5N (GOST 31108–2016) is investigated. For this purpose, geometrically similar specimens of length L = 1075, 465, and 215 mm and width D = 40, 93, and 215 mm, respectively, having a central notch of length a0 are subjected to three-point bending tests; the conditions L/D = 5 and a0/D ≈ 0.3 are met for all specimens. The mechanical properties, the acoustic emission parameters, the characteristics of a local deformed state estimated by the digital image correlation method, and the fracture zone size at the notch tip determined by ultrasonic flaw detection are investigated. The stages of fracture are analyzed using the changes in the acoustic emission parameters and the principal strains at the notch tip. The nominal strength decreases with increasing specimen size. In addition, the specimen size is found to affect the acoustic emission parameters, the principal strains, and the fracture zone size. The introduction of basalt fibers into the composition of concrete is shown to decrease its nominal strength, to increase the fracture energy, and to weaken the size effect.