The Effect of Specimen Size on Compressive, Tensile and Flexural Strength of Steel Fiber Reinforced Concrete

Nowadays, concrete is known as one of the most used building materials in the world. Being economical, the availability of constituents, good resistance under the fire and atmospheric factors, the ability to fit in shapes and molds, and also the high compressive strength are factors that have made public acceptance in the use of concrete as a building material. The use of fiber in concrete has increased dramatically over the last few decades. The use of fiber in concrete causes the concrete to become flexible to a considerable extent and the resulting concrete is highly homogeneous. Since the concrete specimens are used worldwide to determine the mechanical properties of concrete, in this study, 160 samples of fiber concrete containing 64 cube samples with dimensions of 5×5×5, 10×10×10, 15×15×15, 20×20×20 cm for testing of compressive strength, 64 cylindrical cylinders with dimensions (diameter × height) of 15 × 30 and 10 × 20 cm for compressive strength and tensile strength tests and 32 samples of beam with dimensions of 10×45×10 and 15×60 ×15 were used for flexural strength testing. Furthermore, in this study, 4 concrete ranges of 20MPa, 25MPa, 30MPa and 35MPa were tested. Of each concrete grade and each dimension, four samples were made; one of which was non-fibrous (as the base sample) and three samples with fibers. The steel fibers used were two-end hooks of 3.5 cm in length and 0.8 mm in thickness, with 0.5% of the volume of concrete used. The results showed that the flexural strength, tensile and compression strength of the concrete increased with the presence of fibers and some new conversion factors were proposed for the fiber-containing specimens.