مهندسی عمران شریف (Jun 2024)
The effect of fiber length and composition on the compressive and flexural strength of concrete
Abstract
The use of fibers is often aimed at increasing the ductility and load-bearing capacity of the desired concrete, and controlling the spread of cracks by adding fibers to the concrete causes this. The fibers improve the behavior of the concrete after the first crack due to the bridging property on the micro-cracks. In this paper, 15 concrete mixing designs in the form of 90 cubic specimens with dimensions (15 * 15 * 15) cm for the compressive strength test and 42 specimens with dimensions (15 * 15 * 60) cm for the flexural strength test have been made. Three mixing designs were made as a reference with 3 water-to -cement ratios (0.24, 0.29, 0.34) without fibers and with fibers with 3 different lengths of polypropylene fibers with lengths of (6, 12, 18) mm, respectively. A mixing scheme with 40 mm long hook metal fibers and another mixing scheme with a combination of 40 mm hooked metal fibers and 12 mm polypropylene fibers were investigated. Microsilica gel and super-lubricant were used to increase the smoothness and efficiency of concrete. The highest average compressive strength of 28 days was related to samples with composite fibers with a resistance of 72.52 MPa, which was 12.9% higher than the reference sample. The concrete sample with metal fibers with an average bending strength of 12.85 MPa has the highest strength among all the concrete mixing designs of this research and shows a 60% increase in bending strength compared to the sample without fibers. In the concrete samples tested with polypropylene fibers, after the compressive strength test, with the increase in the length of the polypropylene fibers, the workability and compressive strength of the concrete decreased, but the plasticity of the concrete samples increased. After the flexural strength test, the flexural strength and ductility of the concrete samples increased with the increase in the length of the polypropylene fibers, but it led to a decrease in the workability of the concrete.
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