Preparation and microstructure of K-PSDS geopolymeric binder

In this paper, a total of nine K-PSDS geopolymeric matrices with different molar ratio of SiO2/Al2O3, K2O/Al2O3, H2O/K2O is designated to investigate the influence of the three key ratios on mechanical properties and microstructure in accordance with orthogonal design principle. The experimental results show that K2O/Al2O3 has the most significant effect on compressive strength amongst the three ratios. The highest compressive strength (20.1 MPa) can be achieved when SiO2/Al2O3 = 6.5, K2O/Al2O3 = 0.8 and H2O/K2O = 10.0. Comparing the IR spectra of nine K-PSDS geopolymeric matrices also indicates that geopolymeric matrix with the highest strength is the most fully reacted one and possesses the largest amount of geopolymeric products. Subsequently XRD, ESEM-EDXA and MAS-NMR techniques are employed to further characterize the microstructure of the fully reacted geopolymeric matrix. The microscopic analysis reveals that the fully reacted K-PSDS geopolymeric matrix possesses structural characteristics similar to 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 3D molecular structural model is also proposed based on the decomposition of MAS-NMR spectrum of the fully reacted K-PSDS geopolymeric matrix.