Mechanical performance optimization of CaCO₃-modified fly ash-based hybrid geopolymer concrete using Taguchi...

In this experimental study, a fly ash-based hybrid geopolymer concrete improved with calcium carbonate (CaCO₃) was prepared and tested for pavement block applications. The work primarily focused on the effect of four parameters, namely, the fly ash to CaCO₃ ratio, ordinary Portland cement (OPC) content, specimen thickness, and curing period. A Taguchi L16 orthogonal array was used to plan the experiments, and sixteen different combinations were cast and tested. Compressive strength was measured at 14, 28, 56, and 90 days. The test results show that the variation in calcium content and curing duration has a clear effect on strength, while the changes in OPC content and specimen thickness have a lesser influence within the selected range. The highest compressive strength gained in this study was 41.2 MPa at 90 days for the mix with a fly ash to CaCO₃ ratio of 75:25. The Taguchi signal-to-noise analysis and ANOVA results also indicate that the fly ash-CaCO₃ ratio is the principal factor, followed by curing duration. Scanning electron microscopy images show that the mixes with higher strength have a relatively denser and more continuous matrix compared to the low-strength mixes. Based on these results, it can be stated that the addition of CaCO₃ together with adequate curing helps in improving the strength performance of fly ash-based hybrid geopolymer concrete for pavement block use.