Enhancement of the long-term mechanical performance of flax fiber-reinforced cementitious composites by using alternative binders

Abstract

The primary concern for plant-fiber-reinforced cementitious composites is the durability of fibers in the highly alkaline cement matrix. This paper presents a way to improve the durability of these composites through partial or total replacement of the ordinary Portland cement by alternative binders such as metakaolin (MK), ground granulated blast-furnace slag (GGBS) or calcium sulfo-aluminate cement (CŠA). The fresh-state and the mechanical properties (3-point bending and compressive tests) were investigated after 7, 28, 90 and 320 days. In the hardened state, alternative binders slow down the development of the compressive strength, especially for short-term curing period. However, after 90 days, alternative binders allow to reach strengths equivalent to OPC-based mortars. In addition, alternative binders can delay the plant fiber degradation between 28 and 90 days. In the long term (320 days), CŠA and metakaolin allow to maintain a significant toughness, which is an essential criterion for fiber-reinforced concretes. Thermal analyzes and pH measurements have identified the causes of degradation of flax fibers and those that explain the improvement in the durability of composites.