Effects of the secondary minerals of the natural pozzolans on their pozzolanic activity
- LMTG, CNRS/Universite Paul Sabatier, Observatoire Midi-Pyrenees, 14 Av. E. Belin, 31400 Toulouse (France)
- Lafarge Centre de Recherche, 95 rue de Montmurier, BP 15, 38291 St Quentin Fallavier cedex (France)
- LMDC, INSA/Universite Paul Sabatier, 135 Avenue de Rangueuil, 31077 Toulouse Cedex 04 (France)
Natural pozzolans have been widely used as substitutes for Portland cement, because of their binding properties. Some of them are natural volcanic rocks which contain secondary minerals such as clays and zeolites corresponding to products of the alteration of the rock. The objective of this study was to document the potential effect of the secondary minerals on the strength development of pozzolanic mortars. We chose to investigate this effect by thermally destabilising these minerals in three different pozzolanic deposits (poz-1, poz-2 and poz-3). We first did a detailed mineralogical study, to identify the occurrence and the nature of the different secondary minerals. Kaolinite is abundant in poz-1 and different types of zeolite were identified in poz-2 and poz-3. Thermal treatments were monitored by X-ray Diffraction (XRD) analysis, in order to document mineralogical transformations. The effect on the pozzolanic activity has been tested by strength measurements on normalised mortars at 1, 7 and 28 days. Strength of all blended cements is enhanced while destabilising secondary alteration minerals. For kaolinite, we showed that a strength improvement occurs as soon as it is destructured, even if it is not transformed in metakaolin. For zeolites, destabilisation takes place at low temperature (350 deg. C), but as recrystallisation products are easily formed, activation temperature window is narrow. Endly, we have evidence that the presence of calcite in pozzolans has an effect on early strength. Therefore this study is giving new perspectives for a better use of natural pozzolanic materials in the cement industry.
- OSTI ID:
- 21130732
- Journal Information:
- Cement and Concrete Research, Vol. 38, Issue 7; Other Information: DOI: 10.1016/j.cemconres.2008.02.005; PII: S0008-8846(08)00044-6; Copyright (c) 2008 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
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