Influence of Sintering Temperature of Kaolin, Slag, and Fly Ash Geopolymers on the Microstructure, Phase Analysis, and Electrical Conductivity

This paper clarified the microstructural element distribution and electrical conductivity changes of kaolin, fly ash, and slag geopolymer at 900 °C. The surface microstructure analysis showed the development in surface densification within the geopolymer when in contact with sintering temperature. It was found that the electrical conductivity was majorly influenced by the existence of the crystalline phase within the geopolymer sample. The highest electrical conductivity (8.3 × 10−4 Ωm−1) was delivered by slag geopolymer due to the crystalline mineral of gehlenite (3Ca2Al2SiO7). Using synchrotron radiation X-ray fluorescence, the high concentration Ca boundaries revealed the appearance of gehlenite crystallisation, which was believed to contribute to development of denser microstructure and electrical conductivity.

Characterizing Granular Material Coarseness and Micromechanical Properties with a Small-Diameter Penetrometer

A micromechanical theory and data from a penetrometer with a small base area were used to characterize the average microstructural and micromechanical properties of snow, a granular material composed of ice. The micromechanical theory also was used to describe penetration in soil and successfully explains the dependence of penetration resistance for granular materials on penetrometer base area. Material coarseness (microstructural element dimension), elastic modulus, and compressive strength were determined by interpreting penetration resistance measurements by the micromechanical theory. Predictions of the macroscale (continuum) mechanical properties for the snow were made by the micromechanical measurements and theory. The average microstructural dimensions for snow were 3.6 mm (coarse grained) and 1.45 mm (fine grained). Micromechanical strength and modulus of elasticity of snow depend on internal structure and bonding at grain boundaries; grain size by itself was not a good indicator of the mechanical properties for snow. The accuracy of determining micromechanical and microstructural properties for individual microstructural elements decreases as the ratio of the penetrometer base area to the microstructural element cross-sectional area increases. Average micro-and macroscale structural and mechanical properties of a granular material can be determined by interpreting penetration resistance data with a micromechanical penetration theory. The resolution of measurement of material properties increases as the size of the penetrometer tip decreases.