Effect of Coconut Fiber and Wood Chips on the Physical, Mechanical, and Durability Properties of M21 Concrete

The study focused on evaluating the behavior of concrete under sulfate attack in coastal or industrial regions, where concrete is exposed to sulfate solutions that may compromise the durability and safety of structures. Therefore, the objective of this study was to investigate how coconut fibers (CF) influence the physical, mechanical, and durability properties of M21 concrete, incorporating an optimal dosage of wood chips (WC). A total of nine mixtures were analyzed, including a reference mixture designed to meet a minimum compressive strength requirement of 210 kg/cm². The study used WC dosages ranging from 5% to 20% and CF dosages ranging from 1% to 8%, replacing the weight of fine aggregate and addition by weight of cement, respectively. Neither material underwent chemical treatment. In the mixture containing 10% WC and 1% CF, workability improved by 33.33%, unit weight increased by 5.46%, and temperature variation was minimal. Mechanical properties also improved at 28 days, with a 5.09% increase in compressive strength, a 16.97% increase in elastic modulus, a 15.02% increase in flexural strength, and an 11.54% increase in tensile strength. The hybrid combination of 10% WC and 1% CF demonstrated additional enhancements, particularly in flexural strength (23.99%) and tensile strength (20.09%). In terms of durability, the hybrid mixture reduced water absorption by 22.95%, while the mixture containing 10% WC and 5% CF exhibited only a minimal variation in sulfate resistance (0.03%). It was concluded that these combinations improve concrete performance; however, they cannot yet be applied to structural elements due to the need for further long-term studies.