In developing countries, one of the usual practices is the uncontrolled, open burning of corn stalk (CS) or its utilization as a fuel. It is known that the ash obtained under uncontrolled burning conditions constitutes blackish and unburnt carbon particles as well as whitish and grayish particles (representing crystallization of silica) due to over burning. However, controlling the burning process can improve the quality of ash produced to effectively use it in cement-based materials. Hence, this research was aimed at exploring the pozzolanic properties of corn stalk ash upon calcination and grinding, for it to be used in the manufacturing of sustainable cement-based materials. In order to obtain a suitable corn stalk ash (CSA), which can be used in cement/concrete, a research investigation consisted of two phases. In the first phase, calcination was carried out at 400°C, 500°C, 600°C, 700°C, and 800°C for 2 hours. The tests applied on the resulting ashes were weight loss, XRD, pozzolanic activity index (PAI), Chapelle, Fratini, and consistency. From XRD spectra, it was found that, at lower temperatures, silica remained amorphous, while it crystallized at higher temperature. Ash combusted at a temperature of 500°C possessed largest pozzolanic activity of 96.8%, had a Fratini CaO reduction of 93.2%, and Chapelle activity of 856.3 mg/g. Thus, 500°C was chosen as an optimum calcination temperature. In the second phase, the ash produced at 500°C was grinded for durations of 30, 60, 120, and 240 minutes to ascertain the optimum grinding times. Resulting ashes were examined for hydrometer analysis, Blaine fineness, Chapelle activity, and pozzolanic activity. Experiment outcomes revealed a direct relationship between values of Blaine fineness, surface area, Chapelle activity, PAI, and grinding duration. It was concluded that CSA can be used as a pozzolan, and thus, its utilization in cement/concrete would solve ash disposal problems and aid in production of eco-friendly cement/concrete.
The objective of this research study was to introduce concrete protective coatings which provide maximum resistance against chemical attacks. The admixtures-silica fume and fly ash were also used to enhance the impermeability of concrete to a greater extent. Tests conducted at various stages of the curing process allowed us to study the destructive and non-destructive strengths of the specimens. The mortar samples were coated with three different types of epoxy coatings and bitumen. They were then subjected to different chemical environments by immersing them in 10% standard solutions of each ammonium nitrate, sodium chloride and sulphuric acid. Drop in strength as a result of chemical exposure was considered as a measure of chemical attack. This was achieved by measuring the drop in compressive strength after 14 and 28 days of chemical exposure. The compressive strength results following chemical exposure indicated that the samples containing silica fume and fly ash (5% replacement of each by weight of cement) and the protective coating Epoxy-2 (E-2) proved to be more resistant to attacks. The control sample (without admixtures) showed a much greater degree of deterioration. Therefore, the application of E-2 coating in addition to silica fume and fly ash was invariably much more effective in improving the compressive strength as well as the resistance of concrete against chemical attacks. The results also indicated that among all the aggressive attacks, the sulphate environment has the most adverse effect on concrete in terms of lowering its strength.
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