Use of flax fibres to reduce plastic shrinkage cracking in concrete

An experimental investigation was performed to measure the restrained and unrestrained plastic shrinkage properties of small mortar specimens containing short flax fibres (10–38 mm in length) in amounts ranging from 0.05% to 0.3% by volume. Based on the number of cracks, total crack area, and maximum crack widths produced within the first 24 h after casting and exposure to hot, dry, and windy conditions, flax fibres were found to be slightly more effective in controlling restrained plastic shrinkage cracking than commercially available polypropylene and glass fibres for the mortar mixture studied. At a flax fibre volume fraction of 0.3%, total crack areas were reduced by at least 99.5% relative to plain mortar specimens and maximum crack widths were reduced by at least 98.5% to less than 0.022 mm. Fibre length did not significantly influence cracking behaviour, nor did the presence of flax fibres significantly influence the free plastic shrinkage strains observed.