Improved multiple cracking and autogenous healing in cementitious materials by means of chemically-treated natural fibres

• The ‘green’ natural fibres prove to be a useful construction material.
• Chemical treatment of natural fibres reduces the degradation in alkaline environments.
• Chemical treatment of the natural fibres induced multiple cracking.
• Self-healing can ideally prevail in specimens containing natural fibres.

Natural fibres such as flax and hemp fibres are mainly used in the textile industry, but some have outstanding mechanical properties and have a great potential as reinforcement in cementitious composites, as an alternative to synthetic microfibres. However, due to their hydrophilicity the amount of multiple cracking that occurs in cementitious composites reinforced with natural fibres is reduced. Also, natural fibres may degrade in alkaline environments. Therefore, proper mixtures and multiple chemical treatments are required to improve natural fibre characteristics. The application of flax and hemp fibres in cementitious composites was examined, with a focus on inducing multiple cracking under tensile stresses. The mechanical properties were studied for the natural fibres and the cementitious composites. The degradation of the natural fibres in alkaline environments was also studied. Multiple cracking was achieved and further improvements were made by chemically treating the fibres. Mercerisation with a 2% (m/m) [NaOH] resulted in optimal multiple cracking. This multiple cracking resulted in small cracks widths, which allowed optimal autogenous healing when exposed to wet/dry-cycles. Natural fibres were thus found to be a suitable eco-friendly alternative to synthetic microfibres.