Abstract
The cement companies have found in natural and artificial pozzolans a very good option for partial replacement of cement in concrete. Fly Ash is a type of artificial pozzolan, which improves the microstructure of hydrated cement and its durability. Because it is a byproduct of coal combustion, it is economical and abundant for use as an addition to mortars and concrete, making this byproduct a recoverable residue, favoring the environment.The main objective of this study was to evaluate the changes of the microstructural and mechanical strength occurring in portland cement mortars when different proportions of fly ash are added, comparing the effects of adding fly ash in its original state of industrial waste with those of adding fly ash with a reduced content of unburned residues. For the preparation and strength determination of the mortars, cubes of 50x50x50mm were cast, using as references standards ASTM C305 and ASTM C109, respectively. Compressive strength was evaluated in curing times of 1, 3, 7, 28, 56, and 118 days. The characteristics of fly ash and Portland cement were evaluated using X-ray Fluorescence (XRF) and X-ray Diffraction (XRD) techniques, and Scanning Electron Microscopy (SEM).Given that unburned residues in fly ash are defined as the sum of the percentages of volatile matter and fixed carbon contained by it, proximate analyses were carried out - as it is for coal (ASTM D 3172) - to determine the percentage of unburned carbon that is eliminated during the process. As a result, better compressive strengths were obtained when ash containing fewer amounts of unburned carbon was added to mixtures. It is also evident that the optimal amount of fly ash that may be added to mixture of mortar without greatly affecting the mechanical strength is 20 percent.
Published Version
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