Study of the Mechanical and Fracture Properties of Lightweight Concrete with Various Combinations of Polypropylene Fibers

This article examines how hybrid polypropylene fibers of three different lengths affect the mechanical and fracture properties of lightweight structural concrete with lightweight ceramic aggregate. Four mixtures were produced: a reference lightweight concrete and three fiber-reinforced variants with total dosages of 3, 6, and 9 kg/m3 in a fixed length ratio of 4:1:1. Standard tests determined the bulk density, cube compressive strength, splitting tensile strength, modulus of elasticity, and fracture parameters using a three-point bend test. Compared to the reference concrete, the fibers did not significantly change the compressive strength but consistently increased the tensile strength and energy absorption after cracking. The highest fracture energy and toughness were obtained at the highest dosage, while excessive fiber content reduced the static compressive modulus.