Effect of fly ash on sulphate attack in controlled environment
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1989
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Abstract
Sulphate attack of concretes and mortars is a very complex process which is not yet fully understood. It was the purpose of this thesis to evaluate the influence of two western North American fly ashes on sulphate durability. In this work care was taken to eliminate sources of experimental variability by controlling the quality of (a) the attacking environment and (b) the material composition. The attacking environments were (a) combined sulphate solution (0.176 Mol Na2so4 + 0.176 Mol Mgso4·7H20) and (b) water. Both were kept at pH 7, pH 9.5 and pH uncontrolled. Sulphuric acid (H2so4) was added once daily to keep pH constant. Mortar bars were exposed to experimental conditions when they reached (a) constant strength (21 ± MPa) or (b) constant calcium hydroxide content (15% plain mortars,10.5± 0.5% blended mortars). Ordinary Portland cement (Type 10) and sulphate resistant cement (Type 50) were employed. Sundance and Laramie fly ashes (sub-bituminous ashes) were used in two levels of replacement, 35 and 50% by volume. Water/cement ratio by mass of 0.47 was used. The extent of attack was evaluated by linear expansion measurement. At the end of the testing period (6, 9 or 12 months) compressive and tensile strength measurements were performed and micros true ture of mortars was examined by means of x- ray diffraction and thermogravimetric analyses. Laramie fly ash reduced sulphate resistance at both levels of ash replacement. Sundance fly ash improved sulphate durability of ordinary Portland cement as measured by linear expansion. Increased rate of expansion was displayed by bars exposed to sulphate solution at pH 7 after 250 days of immersion. Generally, though, consistent dependency of extent of attack on the pH of the solution was not detected.
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Bibliography: p. 146-153.
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Citation
Konecny, J. (1989). Effect of fly ash on sulphate attack in controlled environment (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/24036