Issue 42

A. Jadidi et alii, Frattura ed Integrità Strutturale, 42 (2017) 249-262; DOI: 10.3221/IGF-ESIS.42.27 251 test was accomplished at ages 3, 7, and 28 days as per ASTM C496 standard [12]. In this test 300 × 150 mm cylindrical samples were used. Three samples with 0%, 1.5%, 2% and 2.5% fibers are provided. The samples, as shown here, are placed in the trays of pressing machine. Once the press is turned on, the load gradually increases, and the sample fractures under the tension produced by the pressure in a direction perpendicular to the pressure axis. The load increases evenly with a rate of 7 to 14 kgf/cm 2 per minute till the sample fractures. At this time, the maximum load applied by the machine is read and recorded. Now, the fracture tension is calculated by the following equation: 2 P 1000 FSP FCT T π L D        (1) where," T" is fracture tension in MPa," P", maximum pressure applied by the machine in kN, "L", sample length in mm and "D", sample diameter in mm. Figure 1 : Cylindrical sample under sample splitting tensile test (Brazilian test). Bending strength test The bending test is carried out via four-point bending machine as per ASTM C78 standard (Fig. 2). As shown in the picture, four-point bending machine is used in this study to perform bending test [10]. The bending strengths of concrete cubic samples reinforced with steel fibers are compared to each other and the fibreless sample. The samples are 100×100×50 mm. Three samples from each mentioned range were made with 0%, 1.5%, 2% and 2.5% fibers. To investigate bending strength in this study, the samples were tested after 28 days. The tensile strength of concrete while bending is calculated using the following equation: 2 p L 1000 Fr bh    (2) where "Fr" is the fracture module in MPa, "P", maximum pressure applied by the machine in kN, "L" length of the distance between the two bases of the sample in mm, "b" sample's base in mm, and "h" height of the sample in mm. Compressive strength As most properties of concrete such as tensile strength, modulus of elasticity, permeability and abrasion resistance are directly related to its compressive strength, thus, to calculate it becomes of utmost significance. The compressive strength is usually determined using 100 mm or 150 mm cubic samples. In this study, compressive strength is determined as per ASTM C39 standard [11]. The standard necessitates the loading rate to be fixed. For this purpose, cubic samples with dimensions of 150 × 150 × 150 mm were used. To determine compressive strength, a pressing machine with a maximum capacity of 300 tons was used. This is the most common test on the quality of concrete, concerning strength. In this experiment, there are three cubic samples with known dimensions, which are to be converted to the equivalents of cylindrical ones at the end. The experiment is done using pressure test equipment (pressing machine) applying even pressure on the sample through two heavy jaws. The machine applies enough pressure until the sample fractures, showing