Influence of the Activator Concentration and Solid/Liquid Ratio on the Strength and Shrinkage Characteristics of Alkali-Activated Slag Geopolymer Pastes

Geopolymers have distinct advantages such as having energy-saving properties, being an environmentally protective material, and having high mechanical strength and durability. However, the shrinkage of the geopolymer materials is one of the major problems to affect its practical application. In this study, blast furnace slag-based geopolymer pastes were prepared using sodium silicate and sodium hydroxide as activators to investigate the effect of the activator concentration and solid/liquid ratio on strength and shrinkage properties. For a better understanding of the reaction mechanism and microstructure of the geopolymer pastes, a multitechnique approach including scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectra was carried out. The results showed that the geopolymers compressive strength increased significantly as the activator concentration increased. The increase in activator concentration first increased the flexural strength and then decreased and reached the maximum when the activator concentration was 40%. A higher activator concentration, as well as a lower solid/liquid ratio, generally led to serious geopolymers drying shrinkage. These findings are expected to be ascribed from the changes in the content of the alkali-activated product (i.e., hydrate calcium aluminosilicate), which depends on the activator concentration. The increase in C-A-S-H gel (hydrate calcium aluminosilicate) compacts paste densifiers but causes shrinkage fracture concerns. These results provide an appropriate proportion for alkali-activated slag geopolymer pastes with better mechanical strength and antidry-shrinkage cracking properties, which are beneficial for the further applications of geopolymer materials

Ethylene glycol production from glucose over W-Ru catalysts: Maximizing yield by kinetic modeling and simulation

The kinetics of glucose conversion to ethylene glycol (EG) in the presence of ammonium paratungstate and Ru/AC catalysts was studied to model and predict the reaction performance under a range of conditions. A mathematical model was established through the rational simplification of the reaction network on the basis of a continuous stirred-tank model. The kinetic data of six major reactions in the network were experimentally measured, and the analytical expressions of overall reaction kinetics were obtained by introducing the kinetic data to the model. Yields of EG, hexitols and gas were described as functions of the reaction temperature, the concentration of glucose in the feedstock and the feeding rate. The simulation results matched the experimental data of glucose conversion, demonstrating the validity of the model and method for studying the overall kinetics of glucose conversion to EG over W-Ru catalysts. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 2072-2080, 201