Durability and Mechanical Performance of Sisal-Fiber-Reinforced Cementitious Composites for Permanent Formwork Applications

Reinforced concrete structures must balance immediate structural performance with long-term durability against environmental degradation, particularly carbonation-induced corrosion. While traditional cast-in-place concrete covers serve as the primary barrier, their substitution with prefabricated permanent formworks made of fiber-reinforced cementitious composites often fails to provide the necessary protective qualities required for aggressive environments. This study evaluates the durability and mechanical behavior of sisal-fiber-reinforced cementitious composites specifically engineered for use as permanent formwork. Short sisal fibers, treated by hornification to enhance dimensional stability and fiber–matrix adhesion, were incorporated at dosages of 2%, 4%, and 6% by weight. The experimental program included tests for water absorption, ultrasonic pulse velocity, axial compression, three-point flexural strength, and accelerated carbonation. The results indicated that composites with 2% and 4% of fibers exhibited reduced water absorption, sorptivity, compressive strength, and modulus of elasticity compared to the reference cement matrix. Residual stress values further demonstrated that the composites maintain significant post-cracking strength and stress transfer capacity, confirming their viability for structural elements. Although sisal-fiber-reinforced cementitious composites exhibit higher porosity and water absorption than conventional concrete used as reinforcement cover, they show sufficient resistance to carbonation to ensure a service life exceeding 50 years for reinforced concrete elements.