Investigating the Influence of Fiber Content and Geometry on the Flexural Response of Fiber-Reinforced Cementitious Composites

This study investigates fiber-reinforced cementitious composites (FRCCs), concentrating on the geometric features of soft micro- and macro-fibers with a lower elastic modulus and higher aspect ratios than steel fibers. There is no literature predicting the ratio of ultimate flexural strength to the initial cracking strength of FRCC. The composites were made using a cement-to-sand ratio of 1:2.5, with 20% fly ash as a partial substitution and two water-to-binder ratios (0.55 and 0.60). Carbon, polypropylene, and natural sisal fibers were added at quantities ranging from 0.4% to 2.27%, with aspect ratios ranging from 71 to 3750. Flexural strength was determined using 75 × 75 × 380 mm³ prisms, whereas compressive strength was evaluated using 50 mm cubes. Load–deflection curves were created to investigate fracture behavior. The post-cracking behavior was determined using the matrix compressive strength, fiber type, amount, and aspect ratio. Regression analysis of data from this work and previous publications yielded an equation for predicting the ratio of the modulus of rupture (MOR) to the initial fracture strength. After cracking, carbon-fiber-reinforced cementitious composites (CFRCCs) were fragile, but their flexural strength was two to three times higher than that of control specimens. This was because the increased fiber volume and aspect ratio made the materials stronger and better at handling load and deflection.