Potato starch as a bio-based admixture in cement mortars

This work investigates the potential of potato starch, an agro-industrial waste of natural and renewable origin, as an admixture in traditional cementitious mortars, aiming to contribute to the development of more sustainable and efficient building materials. Five compositions were formulated, maintaining a reference ratio of 1:3:0.6 (cement:sand:water), with partial substitutions of cement by potato starch in proportions of 0.25%, 0.50%, 0.75%, and 1% by mass. The specimens were characterized in the fresh state (consistency, calorimetry, and setting time) and in the hardened state (compressive strength, water absorption, and density) according to standardized test methods after 28 days of curing. Additionally, microstructural analyses by X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to understand the action of the admixture in the cementitious matrix. The results demonstrated that the incorporation of potato starch significantly influences the properties of cementitious mortars. Regarding fresh-state consistency, a non-linear trend was observed, with improved workability at a low dosage (0.25 wt%) followed by a progressive reduction as the starch content increased. This behavior is attributed to the higher water absorption capacity of the starch, which reduces the amount of free water available for lubrication within the cementitious matrix. Water absorption results did not show significant variations among the mixtures. In terms of compressive strength, the reference mortar (0% potato starch) achieved a compressive strength of 18.38 MPa. The incorporation of potato starch promoted a significant increase in strength up to 0.75 wt%, reaching 28.98 MPa, which corresponds to a 57.7% improvement compared with the reference mixture. Beyond this dosage, compressive strength decreased, indicating the existence of an optimum incorporation level. Calorimetry results revealed a retardation effect on cement hydration, while XRD analysis indicated a reduction in portlandite and a relative increase in C-S-H, suggesting microstructural refinement. SEM observations confirmed changes in the microstructure, including increased ettringite formation and higher porosity at elevated dosages. Overall, the results demonstrate that potato starch has considerable potential as a sustainable admixture for cementitious mortars, provided that an appropriate dosage is adopted. Among the investigated contents, 0.75 wt% exhibited the most favorable performance.