Material Properties of Synthetic Fiber–Reinforced Concrete under Freeze-Thaw Conditions

For decades, synthetic fibers have been utilized to improve the performance of concrete structures by enhancing the flexural strength, modulus of elasticity, and other mechanical properties of concrete. However, there are uncertainties about how synthetic fibers affect the coefficient of thermal expansion (CTE), dynamic modulus of elasticity, and flexural strength of the concrete under freeze-thaw cycles. This study was an investigation of the effect of temperature change on the mechanical properties of fiber-reinforced concrete, including CTE, dynamic modulus of elasticity, and flexural strength. Two types of synthetic fiber, polypropylene (PP) and polyvinyl alcohol (PVA) fibers, with three dosages for each type, 6, 7, and 9 kg/m3, were studied. The CTE was obtained using the severe temperature range specified by AASHTO specifications for measuring thermal effects in concrete bridge superstructures. Up to 300 freeze-thaw cycles were applied to specimens, while mass loss, dynamic modulus of elasticity, flexural strength, and CTE were measured in accordance with ASTM protocols. Adding fiber to concrete enhanced the flexural strength, increased the flexibility, decreased the dynamic modulus of elasticity, and increased the CTE. Specimens reinforced with PP fiber showed more flexural strength and flexibility than those reinforced with PVA fiber. Polyvinyl alcohol fiber–reinforced specimens exhibited greater CTE values compared with those reinforced with PP fiber. The added synthetic fiber enhanced the concrete's resistance to freeze-thaw cycles. The optimum fiber dosage appears to be 7 kg/m3, which generally had the best performance in terms of flexural strength, dynamic modulus of elasticity, and CTE while best preserving structural integrity under repeated freezing and thawing.