Presenting a prediction model for compressive strength of geopolymer made of metakaolin and slag using the response surface method (RSM)

The objective of this study was to investigate the compressive strength of metakaolin-based geopolymers and slag activated with alkaline activators during periods of 3, 7, and 28 days using the response surface method (RSM). X-ray diffraction (XRD) analysis. and Fourier transform infrared spectroscopy (FT-IR) was performed to investigate the effect of each of the independent variables on the compressive strength of geopolymer samples. Geopolymer samples were made in dimensions of 20×20×20 mm, then they were kept at room temperature for periods of 3, 7 and 28 days and were subjected to mechanical evaluation at the end. The results showed that using the RSM method can provide an appropriate estimation of the response so that the R2 value greater than 90% was obtained for each response. The maximum compressive strength of geopolymer samples was measured as 10 MPa for three days and 16.57 and 22 MPa for 7 and 28 days, respectively. By increasing the molar ratio of sodium silicate to sodium hydroxide to the level of 2.5 and decreasing the ratio of metakaolin to slag, the compressive strength of geopolymer samples increased. The FT-IR results showed that when geopolymers are formed, the structure changes compared to the raw materials due to the formation of monomers and compaction. Also, the results of the XRD analysis showed the presence of a peak-like state due to the formation of an amorphous product.