Influence of the w/c ratio on the hydration process of a magnesium phosphate cement and on its retardation by boric acid
- Laboratoire des Matériaux Céramiques et Procédés Associés (LMCPA), Université de Valenciennes et du Hainaut-Cambrésis, 59600 Maubeuge (France)
- CEA, DEN, DE2D, SEAD, F-30207 Bagnols-sur-Cèze cedex (France)
- Institut de Physique Nucléaire, CNRS, Université Paris-Sud 11, 91406 Orsay Cedex (France)
Magnesium potassium phosphate cements (MKPCs) are prepared using calcined magnesia (MgO) and an acidic solution of potassium dihydrogen phosphate (KH{sub 2}PO{sub 4}). Their fast setting and high heat of hydration can be problematic when large volumes of materials are produced. Boric acid (B(OH){sub 3}) is thus commonly added as a set retarder. This work investigates MKPC hydration in paste (water-to-cement ratio w/c = 1) and its retardation by B(OH){sub 3}. The precipitation of K-struvite (MgKPO{sub 4}·6H{sub 2}O) is preceded by that of phosphorösslerite (MgHPO{sub 4}·7H{sub 2}O) and Mg{sub 2}KH(PO{sub 4}){sub 2}·15H{sub 2}O. Cattiite (Mg{sub 3}(PO{sub 4}){sub 2}·22H{sub 2}O), an end-product in diluted suspension (w/c = 100), is not observed. B(OH){sub 3} slows down the formation of hydrates in two ways: (i) by stabilizing in solution the cations that outbalance the negative charges of the polyborates formed at pH above 6, and (ii) through the precipitation of an amorphous mineral containing borate and orthophosphate. The first process occurs both in diluted suspensions and pastes, the second is specific to pastes.
- OSTI ID:
- 22806505
- Journal Information:
- Cement and Concrete Research, Vol. 109; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0008-8846
- Country of Publication:
- United States
- Language:
- English
Similar Records
Reaction mechanism of magnesium potassium phosphate cement with high magnesium-to-phosphate ratio
Influence of fly ash and metakaolin on the microstructure and compressive strength of magnesium potassium phosphate cement paste