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Interpretation of the Thermogravimetric Curves of Ancient Pozzolanic Concretes
Author(s) -
Branda F.,
Luciani G.,
Costantini A.,
Piccioli C.
Publication year - 2001
Publication title -
archaeometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.716
H-Index - 67
eISSN - 1475-4754
pISSN - 0003-813X
DOI - 10.1111/1475-4754.00027
Subject(s) - thermogravimetric analysis , pozzolan , materials science , silicate , pozzolanic reaction , thermogravimetry , mineralogy , pozzolanic activity , calcium silicate hydrate , analytical chemistry (journal) , cement , chemistry , composite material , inorganic chemistry , portland cement , organic chemistry
Pozzolanic concretes submitted to thermogravimetric (TG) analysis show a continuous weight loss starting from about 400 °C. In order to reconcile these observations with those from other analytical methods, it is necessary to attribute this weight loss to CO 2 removal. It has been proposed, in the literature, that silicates and CaCO 3 react at lower temperatures, producing calcium silicates and CO 2 . In this paper, the FTIR spectra collected on samples submitted to TG analysis, stopped at conveniently selected temperatures, provide direct evidence that the continuous weight loss recorded with thermogravimetric analysis of the pozzolanic concrete in the temperature range 400–900 °C is to be attributed to the reaction between the silicates and calcite, with the formation of CO 2 and of a silicate that is richer in CaO. Therefore it is justifiable that the whole weight loss, in the temperature range 400–900 °C, should be taken into account in the calculation of the CaCO 3 content of the concrete. Moreover, the described procedure—of recovering small samples (2 mg) from the sample‐holder of the TG apparatus at various steps of the heating rate and comparing the FTIR spectra—can help in identifying the pozzolanic nature of a concrete that, in general, is not easily recognizable from the trend of the thermoanalytical curve.