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

Mahyar M., ERDOĞAN S. T.

CEMENT & CONCRETE COMPOSITES, cilt.63, ss.96-103, 2015 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 63
  • Basım Tarihi: 2015
  • Doi Numarası: 10.1016/j.cemconcomp.2015.09.002
  • Dergi Adı: CEMENT & CONCRETE COMPOSITES
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.96-103
  • Anahtar Kelimeler: High-calcium, Fly ash, Acid-base cement, Phosphate, Strength, Heat, GLASS-CERAMICS, BRUSHITE, CAHPO4-CENTER-DOT-2H(2)O, DECOMPOSITION, MONETITE, STRENGTH, WASTES, MODEL
  • Orta Doğu Teknik Üniversitesi Adresli: Evet

Özet

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.