RESUMEN
The main objective of this research is to study the influence of partial replacement of calcined red clay by gypsum-bonded casting investment waste (GCIW) from precious metal casting process on geopolymerization reaction of a red clay-based geopolymer. Calcined red clay was partially replaced by GCIW powder with different contents before mixing with sodium-based alkali activator solution to produce the geopolymers. The results indicate that the GCIW significantly impacted the reaction of flesh geopolymers detected by Differential scanning calorimetry (DSC). The reaction products (hydration products and others) of 28-day geopolymers detected by Fourier transform Infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) were employed to support the reaction results. Moreover, the relation between reaction products and compressive strength was discussed. This work concluded that the calcium sulfate compounds contained in GCIW play an important role on geopolymerization reaction, reaction products, and mechanical properties of geopolymer. Furthermore, the results could be employed to propose a reaction mechanism that occurred in geopolymers. The potential use of GCIW as an additive for red clay-based geopolymer bricks preparation was confirmed in this research.
RESUMEN
Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to demonstrate the reaction mechanisms of alkali-activated materials (AAMs) and the early stage of structure formation in the materials. The effects of different types of alkali activator solutions on the structure formation and reaction mechanisms of AAMs were studied. The results revealed that the main peaks of the ATR-FTIR spectra of the AAMs in the 1300-650 cm-1 range shifted to a low wavenumber with changing patterns, depending on the activator solution used, indicating that the dissolution and reorientation of metakaolin had occurred. Silica and alumina monomers were dissolved by the NaOH solution to produce crystalline zeolites. Although the reaction between metakaolin and Na2SiO3 solution is slow, the condensation between the Al-OH from metakaolin and the Si-OH from Na2SiO3 solution bonded the chain to be longer. Therefore, the Na2SiO3 solution acted as a template-bonded monomer, formed long chains of Si-O-Si and Si-O-Al, and produced an amorphous AAM structure. In the mixed solution, when the NaOH in it dissolved the Si and Al monomers, the Na2SiO3 in the solution also bonded with monomers and produced a complex structure. The different reaction that metakaolin had with different alkali activator solutions reflected the different phases, microstructures, and mechanical properties of the AAMs produced.