Synergistic effect of fiber type-length-distribution on mechanical behavior of high-strength synthetic fiber reinforced engineered cementitious composites

The demand for concrete has underscored its limitations, particularly in tensile stress scenarios, where ordinary concrete (OC) exhibits fragility and susceptibility to catastrophic failure. Unlike OC, engineered cementitious composite offers high ductility and damage resistance, making it a viable alternative. This study presents an overview of synthetic fibers in construction and explores the influence of incorporating two polymeric fibers, high-modulus polyethylene (HMPE) and polyethylene terephthalate, known as polyester (PES), of varying lengths into cementitious composites. The tests used two configurations of inserting the fibers: randomly distributed in the matrix or concentrated at the bottom of the specimens. The materials were characterized, and medium (MSC) and high-strength (HSC) composites were produced for testing. Scanning electron microscopy (SEM) was employed to characterize the fibers and to analyze their interaction with the cementitious matrix. The following properties were evaluated: compressive strength (CS), static modulus of elasticity (E), flexural strength (FT), toughness (T), impact resistance (IR), and thermal conductivity (k). The addition of fibers increased CS and IR, with HMPE outperforming PES. For 38 mm, CS improvements were 23.37 % (HMPE) and 12.93 % (PES) in MSC, and 11.03 % and 2.87 % in HSC. In IR, distributed fibers increased MSC by 28.6 % (HMPE) and 10 % (PES), and HSC by about 6 %. Among concentrated fibers, the 38 mm fiber stood out in MSC, reaching increases of 125 % (HMPE) and 81 % (PES). FT and E, in turn, were not significantly influenced. However, concentrated fibers significantly enhances T and deflection of HSC. The concentrated fiber approach surpasses distributed fibers, especially HMPE, offering valuable insights for optimizing the mechanical properties of these materials in practical applications in structures subjected to sudden loads, intense vibrations, and unexpected external forces. Furthermore, k was significantly increased for HMPE composite, while PES demonstrated a reduction when fibers were distributed. These findings suggest the feasibility of reinforcing medium and high-strength cementitious composites with high-performance polymeric fibers.