Microstructure Of Fly Ash And Hydration Of Cementitious Material With Fly Ash

Developing high technical product with more additional value is the general trendence of integrated utilizing fly ash in the future. Aiming to this, understanding the physical, chemical characteristic and the microstructure of fly ash is needed.Low-limed fly ash with better sphericity was selected for analyzing the physical, chemical characteristic and the microstructure of material, with the aid of Scan Electron Microscope (SEM), energy spectrum, laser granularity analysis and x-diffraction (XRD). It was found that: Micro-beads from fly ash can be classified as sinking beads and floating beads according to the difference in density. The sinking beads comprise magnetic beads and multiple vitreous beads, and the floating beads contain unburnt carbon particles and hollow vitreous beads. The unburnt carbon exists in fly ash as two kinds of form, honeycombed or spongy carbon monomer, and commensal together with silicon and aluminium inside sinking and floating beads. The magnetic beads usually have rough surface with ferrous crystals, which presence as cubo octahedron or fishbone like. Most of magnetic beads are hollow and wrap small spheres. Magnetic beads are mainly composed of magnetite and hematite with the asymmetry of iron distribution. Because most Carbon, magnetic beads and floating beads are coarse, they could be separated from finer sinking beads by cyclone separating, then be refined for utilization. The residual volumes of fine active silicon-aluminium sinking beads could be used for making of high performance cement and concrete.Size reduction is helpful for improving the activity of fly ash. The experiments of grinding fly ash were conducted by making use of ball mill, vibratory mill and roller mill respectively. The result reveals that vibratory mill and roller mill are suitable for grinding fly ash.To make fly ash fully play its role in cementitious material, the hydration process ofcement clinker, fly ash and slag were compared, taking the advantage of SEM. It implies that the hydration of fly ash is more complex than that of slag. The hydration of slag develops from dot to line, then line to surface and from outside to inside. There is great distinction among the hydration process of different beads from fly ash. Blending fly ash and slag into cement synchronously could accelerate the hydration of fly ash and improving the late strength.