Evaluation of admixtures from agricultural and aquacultural sources on hydration and mechanical properties of Portland cement based materials

Abstract This study investigates the potential of bio-admixtures derived from Sargassum natans (SN1E, SN2E), Sargassum fluitans (SFE), water hyacinth (WHE), miscanthus grass (ME), and plantain stem (PSE) as sustainable alternatives to polycarboxylic ether (PCE) superplasticizers in cement-based materials. The research examines their effects on rheology, hydration, microstructure, and mechanical properties to assess their suitability for eco-friendly construction applications. Cement pastes and mortars incorporating 0.1% and 1% bio-admixture dosages were analyzed using isothermal calorimetry, thermogravimetric analysis (TGA/DTG), static yield stress measurements, and compressive strength testing at 7 and 28 days. Results indicate that all mixtures containing admixtures exhibited lower initial yield stress values, indicating a liquefying effect initially. At 0.1% dosage, the admixtures exhibited comparable or slightly improved compressive strength relative to the reference (REF), with no significant losses. However, at 1% dosage, PCE, WHE, ME, and PSE showed notable strength reductions, particularly ME, which significantly impaired both 7-day and 28-day strengths. Hydration studies revealed that bio-admixtures exhibited lower retardation effects compared to PCE, with SN1E, SN2E, and SFE promoting early hydration and portlandite (CH) formation. Conversely, ME and PSE exhibited delayed hydration, leading to lower early-age strengths but a more sustained hydration process over time. Thermal analysis further confirmed these trends, with bio-admixture-modified pastes maintaining stable hydration profiles, while PCE exhibited the strongest retardation effect, as evidenced by its lower total weight loss, and reduced CH content. These findings highlight the potential of bio-admixtures as sustainable modifiers in cementitious materials, providing workability benefits while minimizing hydration delay, making them promising candidates for green construction.