Investigating the Role of Fly Ash and Silica Fume in the Cement Hydration Process

This research work investigates the effect of fly ash and silica fume on cement paste hydration. Percentages of each additive were selected to replace the cement by volume to be studied at five different ages using water curing and vacuum curing. These percentages were compared alongside a controlled cement paste without additives. Testing was carried out on 350 samples. Analysis methods utilized Fourier Transfer Infrared Spectroscopy (FTIR) to monitor the hydration with spectra, Scanning Electron Microscope (SEM) to generate images for regional analysis and MTS testing machine for compressive strength. Results demonstrated that silica fume replacement had the highest overall increase in the CSH and thus in the strength of the hardened cement paste that was cured by water curing. Replacement of fly ash exhibited the highest overall strength under vacuum curing. Also, FTIR and SEM testing showed an increase in the change of CSH area with age. SEM testing revealed the formation of pores, CSH and CH in images at all ages. The area of CSH grows most in early ages and diminishes over time. Although it was clear that the method of curing makes a difference in hydration, further research is needed on the method of vacuum sealing hardened cement paste.