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


Mahyar M., ERDOĞAN S. T.

CEMENT & CONCRETE COMPOSITES, vol.63, pp.96-103, 2015 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 63
  • Publication Date: 2015
  • Doi Number: 10.1016/j.cemconcomp.2015.09.002
  • Title of Journal : CEMENT & CONCRETE COMPOSITES
  • Page Numbers: pp.96-103

Abstract

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. (C) 2015 Elsevier Ltd. All rights reserved.