Mechanical and microstructural properties analysis of one-part geopolymer based on burnt coal cinder replaced by metakaolin

The development of traditional geopolymer for cast-in-situ applications has been a relatively challenging issue due to the difficulties in handling, transporting, and storing of highly corrosive and viscous alkali solutions. This study developed a green, economical, and user-friendly one-part geopolymer, which is formed by mixing burnt coal cinder (BCC), metakaolin (MK), and solid alkali activators such as sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) and cured under elevated temperatures. The effects of parameters such as compressive strength, curing time and temperature, thermal stability, and chemical resistance were investigated. To evaluate the microstructural properties of one-part geopolymers, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, an energy-dispersive spectrometer, and thermogravimetric analysis were employed. The results showed that the optimum preparation conditions were 50:50:15:11.64 (g:g:g:g) for BCC:MK:NaOH: Na2SiO3, with a liquid-solid ratio of 0.30, cured at 80 °C for 24 h and 28 days at room temperature. Significant dissolution and shift of one-part geopolymeric precursors onto the production of new crystalline phases were observed, resulting in more N-A-S-H gel binding substances and the development of properties. Furthermore, the pore size distribution was improved by over 60% compared to their counterparts, and more homogeneity, compactness, and meaningful dense crystal compounds were observed. Despite having the highest compressive strength of 56.61 MPa after 28 days, it substantially declined after exposure to several chemical solutions and thermal stability tests. Therefore, a one-part geopolymer can effectively contribute to ensuring the sustainability of solid waste in the construction industry.