Role of aluminous component of fly ash on the durability of Portland cement-fly ash pastes in marine environment

Research Progress and Development Direction of Filling Cementing Materials for Filling Mining in Iron Mines of China

Backfill mining is the only way to realize no-waste mining and create green mines, but complicated backfill mining technology, high mining costs, and low-production capacity greatly restrict its application in low-quality iron mines. To reduce the cost of iron ore backfill mining, a large number of low-cost green backfill cementing materials have been developed in China over the past 10 years. This paper first introduces the research and development of green cementitious materials using solid waste. Then, it points out the key technologies in the development of green filling cementing materials, reveals the hydration mechanism of green cementing materials through microscopic analysis and research, and optimizes the ratio of green cementing materials based on an orthogonal test. Finally, the development direction of green filling cementing materials is put forward: combining technology development with the filling mining method and filling process; taking the development route from technology to products and from products to commodities. To reduce the cost of filling mining and pursue the economic benefits of filling mining, a demonstration mine of tailings and green cementing materials is taken as the breakthrough point to comprehensively promote the development of iron ore full solid-waste filling mining technology and achieve its large-scale promotion and application.

Microstructural changes in a cementitious membrane due to the application of a DC electric field

The use of electromigration techniques to accelerate chloride ions motion is commonly employed to characterise the permeability of cementitious samples to chlorides, a relevant parameter in reinforced concrete corrosion. This paper is devoted to the study of microstructure's changes occurring in mortar samples when submitted to natural diffusion and migration experiments. The application of an electric field reduces testing time in about one order of magnitude with respect to natural diffusion experiments. Nevertheless, the final sample's microstructure differs in both tests. Impedance Spectroscopy is employed for real time monitoring of microstructural changes. During migration experiments the global impedance undergoes important increase in shorter period of time compared to natural diffusion tests. So, the forced motion of ions through the concrete membrane induces significant variations in the porous structure, as confirmed by Mercury Intrusion Porosimetry. After migration experiments, an important increase in the capillary pore size (10-100 nm) was detected. Conversely, no relevant variations are found after natural diffusion tests. Results presented in this work cast doubt on the significance of diffusion coefficient values obtained under accelerated conditions.