Hydration of flax fibre-reinforced cementitious composites: influence of fibre surface treatments

When formulating cementitious composites with plant particles, the cement setting may be disrupted by the compounds extracted from the plant. An experimental programme is proposed to analyse the influence of flax fibres (FBs) on the hydration of Portland cement. Three fibre treatments are studied in order to limit these disturbances: atmospheric-pressure plasma, hydraulic binder and linseed oil coating. Calorimetric measurements have shown that raw flax (RFs) caused a greater delay in the cement setting, with a time difference of 2h. The Vicat test was also used, with an adaptation by mixing cement with water containing fibre soluble free compounds, obtained after leaching. Similar results to the calorimeter were obtained, showing that the Vicat test can be used to assess the setting delay of a bio-based cementitious composite. The sugars of the solution with FB soluble compounds were quantified by spectrophotometry. A relationship between the sugars in the solution and the setting time was highlighted. These sugars seem to be the main cause of setting delay in cementitious composites with flax. Finally, the long-term hydration degrees were also measured. Hydraulic binder treatment seems to be the most effective in reducing this delay. Linseed oil coating also significantly reduced this delay.