Title: Synthesis and Microstructural Characterization of Fully-Reacted Potassium-Poly(sialate-Siloxo) Geopolymeric Cement Matrix
Author(s): Zhang Yunsheng, Sun Wei, and Li Zongjin
Publication: Materials Journal
Appears on pages(s): 156-164
Keywords: microstructure; preparation; strength.
In this paper, a total of nine potassium-poly(sialate-siloxo) (K-PSS) geopolymeric cement matrixes, with different molar ratios of SiO2/Al2O3, K2O/Al2O3, and H2O/K2O, is designated to investigate the influence of the three ratios on mechanical properties and microstructure in accordance with the orthogonal design principle. The experimental results show that SiO2/Al2O3 has the most significant effect on compressive strength among the three ratios. The highest compressive strength (5.04 ksi [34.8MPa]) can be achieved when SiO2/Al2O3 = 4.5, K2O/Al2O3 = 0.8 and H2O/K2O = 5.0. Comparing the infrared (IR) spectra of nine K-PSS geopolymeric cement matrixes also indicates that the geopolymeric cement matrix with the highest strength is the most fully-reacted one and possesses the largest amount of geopolymeric products. Subsequently, X-ray powder diffraction (XRD), environment-scanning electron microscope equipped with energy dispersion X-ray analysis (ESEM-EDXA), transmission electron microscopy-electron diffraction spectroscopy (TEM-EDS), and magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) techniques are employed to further characterize the microstructure of the fully-reacted geopolymeric cement matrix. The microscopic analysis reveals that the fully-reacted K-PSS geopolymeric cement matrix possesses structural characteristics similar to glassy or gel substances in having a wide range of Si endowments, but predominantly the framework molecular chains of Si partially replaced by four-coordinated Al tetrahedral. A three-dimensional (3D) molecular structural model is also proposed based on the decomposition of MAS-NMR spectrum of the fully-reacted K-PSS geopolymeric cement matrix synthesized from the optimum mixture proportion.