Vegetable fibers behavior in geopolymers and alkali-activated cement based matrices: A review

Alkali-activated binders (AAB) are materials based mainly on silica, alumina, and/or calcium precursors, activated by an alkaline solution, and have mechanical properties equivalent to Portland cement-based matrices. However, their brittle behavior requires the use of reinforcements to make them suitable for dynamic or tensile load applications. Vegetable fibers (VF) could reinforce fragile construction materials, such as mortar and concrete, improving toughness and post-cracking strength. However, little is known about VF durability when used as a reinforcement of AAB. Thus, this work is a literature review regarding the use of VF as an AAB reinforcement, discussing the durability aspects of these fibers as well as future challenges for consideration of the composite. Mechanism of degradation of vegetable fibers in alkali-activated matrices based on sodium has been introduced. Furthermore, this review concluded that surface protection through direct treatments can be an important factor for the durability of vegetable fibers. The main effects of the degradation of composites observed were the reduction in flexural strength and the reduction of matrix/fiber adhesion.