Effect of Alkali Treatment to Improve Fiber-Matrix Bonding and Mechanical Behavior of Sisal Fiber Reinforced Cementitious Composites

The current use of dispersed fibers in cementitious matrices is focused on the enhancement in structural performance and mitigation of the effects of shrinkage, which results in microcracks in the cementitious matrix. Natural fibers appear as a low cost and eco-friendly alternative. However, these fibers are degradable in alkaline environments, resulting in changes in the mechanical performance of the composite. These fibers are also susceptible to volume variation with moisture presence, which results in interface degradation. Therefore, the main goal of this work is to evaluate the effect of alkali treatment in order to overcome these limitations and successfully utilize these materials in several applications. For this purpose, sisal fibers with 50 mm length were subjected to 1, 5 and 10 wt.% alkali solutions for chemical modification. The effect of the treatment was evaluated by pullout tests on untreated and treated fibers on a free calcium hydroxide matrix. Additionally, the mechanical performance of fiber reinforced concrete was analyzed through three-point bending tests. Treated fibers presented a brittle behavior in the pullout test. The alkali treatment did not contribute to an increase in the flexural performance of the composite. Similar values of residual strength in the post-cracking region were reached for untreated and treated fiber reinforced cementitious composites.