Abstract
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.
Highlights
The hydration of cement paste is responsible for the development of essentially every engineering property of cement paste
This study will provide an understanding and insight towards the roles of fly ash or silica fume in the hydration properties of cement paste at various stages of hydration. This experimental study investigated the hydration of Portland cement with fly ash or silica fume compared to cement paste without the replacements
Before placing the specimen or sample onto the Fourier Transfer Infrared Spectroscopy (FTIR) plate, a background check is performed to remove traces of dissolved gases and solvent molecules that can contribute information to the sample that does not exist within the sample
Summary
The hydration of cement paste is responsible for the development of essentially every engineering property of cement paste. Temperature rise and shrinkage which can lead to cracking. The addition of water to dry cement causes the tricalcium aluminate to react with the gypsum producing ettringite and heat. The tricalcium silicate is hydrated to produce the Calcium Silicate Hydrates (CSH), lime and heat. Calcium Silicate Hydrate (CSH) is the main and most important constituent of cement paste. Its hydration forms most of the new solid phases that give hardened cement paste its strength.
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