Mechanical performance and interfacial microstructure of concrete reinforced with alkali-treated rice straw fibers

Abstract

This study investigates the effects of alkali-treated rice straw fibers on the mechanical performance and interfacial characteristics of concrete. To address the limited understanding of the combined influence of fiber length and dosage in rice-straw-fiber-reinforced concrete, rice straw fibers with lengths of 1, 2, and 3 cm were pretreated in a 2% sodium hydroxide solution and incorporated into concrete at volume fractions of 0.3%, 0.5%, and 0.7%. Compressive strength was evaluated at 3, 7, and 28 days to characterize early-age strength development and the standard 28-day mechanical performance, whereas splitting tensile strength and flexural strength were measured at 28 days because these tests were intended to assess the mature crack-bridging and toughness-related behavior of the fiber-reinforced concrete. Scanning electron microscopy was used to observe the surface morphology of the fibers and the fiber–matrix interface. The results show that the incorporation of rice straw fibers generally decreased compressive strength, although the trend depended on fiber length and dosage. In contrast, fiber addition improved the tensile and flexural performance of concrete. The maximum increase in splitting tensile strength was about 17.4%, and the flexural strength increased by up to 58% compared with plain concrete. Microscopic observations indicated that alkali treatment roughened the fiber surface and improved mechanical interlocking with hydration products, thereby promoting crack bridging and energy dissipation during fracture. This study clarifies the trade-off between compressive-strength reduction and tensile/flexural toughening in alkali-treated rice straw fiber concrete.