Mechanical properties optimization using response surface methodology (RSM) of a bio-mortar manufactured based on sisal fibers

The application of lignocellulosic fibers to reinforce mortars with cementitious matrices was investigated for possible use in non-structural applications. A Box-Behnken design L29 (BBDL29) experimental design, using the response surface method (RSM), was used to obtain the combination that maximizes the bending stress and modulus. Four input parameters were evaluated for this purpose: fiber content percentage in the mortar, fiber length, NaOH concentration percentage, and immersion duration. Subsequently, different bio-mortars were produced and tested after 28 days of drying in compression and 3-point bending mode. The results showed that the reinforcement of mortars with sisal fibers allows reductions or increases in mechanical properties, while in literature it generally decreases. In comparison to the reference mortar, the optimal combination exhibited a substantial enhancement of 66.3% and 82.8% in compressive stress and modulus, respectively, while in bending, the increases were 34.8% and 21.5%. The RSM analysis of the mechanical outcomes facilitated the development of a quadratic regression model exhibiting a high correlation coefficients (𝑅2) value. Furthermore, the desirability function was employed in multi-objective optimization to generate ten ideal combinations, yielding results that closely aligned with those obtained experimentally for compressive and bending stresses.