Design of Self-Sensing Geopolymer Using Metakaolin and Agro-Waste Ash for Enhanced Structural and Electrical Performance

This study explores the development of metakaolin–agro-waste ash based geopolymer materials with enhanced mechanical, durability, and self-sensing properties. A Taguchi L9 orthogonal design was adopted to systematically evaluate the influence of key parameters, including metakaolin-to-ash ratio, NaOH molarity, sodium silicate-to-sodium hydroxide ratio, and activator-to-binder ratio. The geopolymer mixes (MA1–MA9) were assessed for fresh properties, mechanical performance, durability, and electrical behavior. The results indicate that compressive strength improved from 29.6 MPa to 48.8 MPa, while flexural and split tensile strengths reached 5.8 MPa and 3.6 MPa, respectively. Durability also improved, with water absorption decreasing from 10.8% to 7.1%, acid mass loss reducing from 8.6% to 5.1%, and retained strength increasing to 85.9%. Electrical characterization revealed a reduction in resistivity from 18.6 to 9.6 kΩ·m and an increase in fractional change in resistivity (FCR) from 2.4% to 4.6%, demonstrating enhanced self-sensing capability. A strong inverse relationship between resistivity and FCR confirms improved conductive pathways. Microstructural analysis confirmed the formation of a dense geopolymer matrix with increased amorphous gel content. Overall, the optimized mix (MA9) exhibited superior performance, highlighting the potential of geopolymer materials as sustainable and multifunctional smart construction materials.