Sustainable grout for structural repairs incorporating waste master board and fiber: experimental study and RSM-based evaluation

This study develops a novel eco-friendly cementitious grout by incorporating waste-derived materials to enhance sustainability in structural repairs. Crushed master board (MB) was used as a partial cement replacement at 5%, 10%, 15%, and 20% by weight, alongside 1% steel fibers (SF) sourced from electrical wire waste. An extensive experimental program was conducted to evaluate the impact of these waste materials on the grout's density, flowability, compressive strength, and flexural strength. The results demonstrate that the inclusion of 1% SF enhanced the density at both 7 and 28 days, while MB alone slightly reduced its relative to the control mix. Flowability decreased with the addition of SF and increasing MB content, with a maximum reduction of 35.3%, indicating higher mixture cohesion. A significant improvement in compressive strength was observed with 1% SF (up to 14.8%), which was further elevated to a 31.7% gain compared to the reference mix when combined with 10% MB. Flexural strength followed a similar trend, confirming the structural integrity of the modified blends. Statistical analysis via ANOVA and predictive modeling using Response Surface Methodology (RSM) validated the experimental results, showing a strong correlation between predicted and observed values. The study concludes that an optimum mix containing 1% SF and 10% MB offers the best balance of strength and workability. This combination contributes to a denser microstructure, as evidenced by microscopic analysis, which revealed increased formation of calcium silicate hydrate (C-S-H) gel.