Abstract
Objecive: To investigate the influences of CaO/SiO2 ratio, % aluminum addition and curing time to the resulting compressive strengths of produced Autoclaved Aerated Concretes (AACs) with fly ash from a coal power plant in Misamis Oriental, Philippines as an initial activity prior to optimization using Response Surface Methodology. Methods: The production of each AAC sample was based on a Box-Behnken experimental design of the Response Surface Methodology using the parameters: CaO/SiO2 ratio, % aluminum addition and curing time. After which, compressive strengths were obtained from these AACs following the ASTM C 109 method. X-ray Diffraction (XRD) was used to determine tobermorite phases in the samples which are the main binding phases in them. Findings: Compressive strengths of the produced AACs ranged from 2.866 to 11.843 MPa which passed the ASTM C 1693 requirement. The presence of tobermorite in all samples was a good indication for these amenable strength values. These values were observed to pass the requirement at all ranges of CaO/SiO2 ratio and lower % aluminum addition and curing time applied. According to the ANOVA for reduced cubic model, among the production parameters, only the curing time had a significant effect to the resulting compressive strengths since p-value < 0.05 but it had an inverse effect since it had a negative coefficient estimate. However, only the CaO/SiO2 ratio had a positive effect as it had a positive coefficient estimate. The interactions between factors AB (CaO/SiO2 ratio-% aluminum addition) and AC (CaO/SiO2 ratio-curing time) had significant positive effects since their p-values were lesser than 0.05 and their coefficient estimates were positive. Improvement: It is recommended to conduct Scanning electron microscopy for the samples to view micrographs and validate the XRD results. The use of other production parameters like fly ash-to-cement ratio, water-to-cementitious materials ratio, curing temperature etc. and the determination of other functional properties such as flexural strength, impact strength, fire- and sound- proof properties among others are also recommended. Keywords: Autoclaved Aerated Concrete, Compressive Strength, Fly Ash, Production, Tobermorite, X-ray Diffraction
Highlights
Coal ashes are wastes from coal power plants
This study focused on utilizing fly ash from a coal power plant in Misamis Oriental, the Philippines as resource materials in making Autoclaved Aerated Concrete (AAC) materials
To verify results that are generated by Box-Behnken thru Response Surface Methodology, the AAC samples were characterized by X-ray Diffraction (XRD) technique to determine the tobermorite phases which are said to be the main binding phases in any AACs
Summary
Coal ashes are wastes from coal power plants. The generation of these wastes would increase day by day as the operation at the plant is continuous. The problem lies heavily with fly ashes than bottom ashes because they would constitute up to 85% of the total coal ash residues generated at the plant per day[3] These wastes would bring problems on disposal, many researchers have been utilizing them as resource materials for construction purposes[4,5,6,7,8,9,10,11,12,13,14] because of their pozzolanic and cementitious values. Preliminary investigation on the influences of CaO/SiO2 ratio, % aluminum addition and curing time to the resulting compressive strengths of produced Autoclaved Aerated Concretes (AACs) with fly ash from a coal power plant in Misamis Oriental, Philippines as an initial activity prior to optimization using Response Surface Methodology
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