Phosphate-activated high-calcium fly ash acid-base cements

Date

2015-10-01

Author

Mahyar, Mahdi
Erdoğan, Sinan Turhan

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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.

Subject Keywords

High-calcium, Fly ash, Acid-base cement, Phosphate, Strength, Heat

URI

https://hdl.handle.net/11511/34987

Journal

CEMENT & CONCRETE COMPOSITES

DOI

https://doi.org/10.1016/j.cemconcomp.2015.09.002

Collections

Department of Civil Engineering, Article

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Citation Formats

M. Mahyar and S. T. Erdoğan, “Phosphate-activated high-calcium fly ash acid-base cements,” CEMENT & CONCRETE COMPOSITES, pp. 96–103, 2015, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/34987.