Prediction of Correlation between Compressive Strength and Flexural/Split Tensile Strength of Graded Fiber-Reinforced Concrete

Abstract

Concrete, though the most widely consumed construction material, suffers from inherent limitations such as low tensile strength, brittleness, and poor toughness, which restrict its performance under flexure, torsion, and cracking. Fiber reinforcement has emerged as an effective solution to address these deficiencies. This study investigates the influence of graded glass fibers—of lengths 6 mm, 12 mm, and 20 mm—on the mechanical performance of M25 grade concrete, with a fixed fiber volume fraction of 0.3%. Experimental work involved casting and testing cubes, cylinders, and prisms in accordance with IS 516:1959 and IS 5816:1999 to evaluate compressive, split tensile, and flexural strengths at 7 and 28 days. Results indicate that the inclusion of glass fibers enhances all strength parameters compared to the control mix, with optimum performance observed at shorter fiber lengths (6 mm and 12 mm). The compressive strength increased by up to 26.58%, while split tensile and flexural strengths improved by 18.98% and 26.6%, respectively, at 28 days. Graded fiber mixes demonstrated superior crack resistance compared to long fibers, confirming the synergistic role of multi-length fibers in controlling both micro- and macro-cracks. Empirical correlations were established between compressive strength and split tensile strength (ft=0.0655fck+1.3636)(ft = 0.0655f_{ck} + 1.3636)(ft=0.0655fck+1.3636) as well as flexural strength (fr=0.1182fck+0.3506)(fr=0.1182f{ck} + 0.3506)(fr=0.1182fck+0.3506), providing predictive models suitable for design applications. The findings underscore that glass fiber reinforcement, particularly with graded fiber lengths, enhances the ductility and toughness of concrete and offers practical guidelines for its structural use.