Using alternative binders for the development of flax fibre reinforced mortars
The primary concern for plant-fibre reinforced cementitious composites is the durability of the fibres in the highly alkaline environment of the cement matrix. The flax fibres reinforced cementitious composites (FFRM) may undergo a reduction in strength and toughness as a result of weakening of the fibres by a combination of alkali attack and mineralisation through the migration of hydration products to the flax fibre lumen. This paper presents a way to improve the durability of FFRMs by a replacement of the ordinary Portland cement matrix by alternative binders such as metakaolin, ground granulated blast-furnace slag or sulfo-aluminous cement. The properties of fresh mortars were first studied (workability, entrapped air, fresh density). The mechanical properties (3-points flexural and compressive tests) were then tested after several cure periods: 7, 28 and 90 days. In fresh state, the use of alternative binders does not significantly affect mortar properties. However, the GGBS improves the fresh mortar workability. The additives influence the compressive strength of the mortars. C A cement results in a significant decrease, regardless of the curing period. With MK and GGBS, the 7-day strengths are lower due to the pozzolanic reaction. However, those at 90 days are equivalent to CEM-100 and even higher with GGBS. The use of alternative binders limit the degradation of the fibers between 28 and 90 days of treatment. The toughness has been improved using some alternative binders, such as calcium sulfo-aluminous cement.