کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1454472 | 1509670 | 2015 | 8 صفحه PDF | دانلود رایگان |
Some fly ashes are used in the concrete industry but some are deemed unsuitable owing to their chemical compositions. This study investigated the use of such a high-calcium fly ash containing large amounts of anhydrite, free lime, and calcite, to produce room-temperature acid-base cements by activation with phosphate sources. Orthophosphoric acid solutions and potassium dihydrogen phosphate were used as activators. Paste microstructures were studied using x-ray diffraction, scanning electron microscopy, isothermal calorimetry, and pH measurements. These findings were related to strength development up to 28 d. Room-temperature cured pastes activated with a 60% H3PO4 solution and a solution-to-powder ratio of 1.0 gave the highest 1-d strength of 15 MPa and 28-d strength of 22 MPa. Partial replacement of the ash with glass powder further increased the 28-d strength. Crystalline calcium phosphates, Brushite and Monetite, were among the products of the solution-activated pastes, as well as some amorphous phases. Potassium salt-activated pastes did not contain the calcium phosphate crystals and gave lower strengths. The ultimate pH of well-reacted mixtures were close to neutral.
Journal: Cement and Concrete Composites - Volume 63, October 2015, Pages 96–103