Exploring the Impact of Flaxseed Mucilage Admixture Addition Ways on OPC Materials: Insights into Setting and Mechanical Properties

The aim of the work is to investigate the consequences of the addition of the flaxseed mucilage, as a bio-admixture, on Portland cement materials. Flaxseed mucilage (FM) which is highly soluble in water is part of the flaxseed cake, a by-product of the seed-crushing industry. The addition of biobased admixtures plays a crucial role in the optimization of cementitious material properties and thus in the competitiveness of the material. The influence of flaxseed mucilage addition way (anhydrous and in-solution forms) on cement paste hydration has been studied using FTIR, TGA, and calorimetry. Portland cement mortars (W/C = 0.6) are used to evaluate the impact of the mucilage on the mechanical properties and bulk density. When FM is added solubilized, at the studied admixture rate (0.75% w/w), setting is excessively delayed (more than thirteen-times slower compared to standard conditions without admixture). When FM is added anhydrous, few impact is noticed on setting. However, TGA analysis pointed out a heterogeneous dispersion of the anhydrous FM during the mixing process. More, the anhydrous FM causes water deficit in the mixture due to its high hygroscopy, resulting in a 10% decrease in bulk density. Both flexural and compressive strengths are reduced, particularly for the mortars formulated with anhydrous FM (− 45% and − 54% respectively). Data suggest that FM delays the setting process due to a “poisoning effect,” without hindering the hydrate growth nor changing mineralogy confirmed by FTIR.