V. Rahhal UNCPBA Departamento de Ingeniería Civil Facultad de Ingeniería Avda. del Valle 5737 B7400JWI Olavarría Argentina

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R. Talero CSIC Instituto de Ciencias de la Construcción ‘Eduardo Torroja’ Serrano Galvache no. 4 28033 Madrid Spain

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This paper analyzes the effect of fly ash chemical character on early Portland cement hydration and the possible adverse effects generated by the addition of gypsum. Behaviour was analyzed for pure Portland cements with varying mineralogical compositions and two types of fly ash, likewise differing in chemical composition, which were previously characterized under sulphate attack as: silicic-ferric-aluminic or aluminic-silicic ash in chemical character, irrespective if they are in nature, siliceous or siliceous and aluminous materials according to the ASTM C 618-94a. The experimental results showed that water demand for paste with a normal consistency increased with the replacement ratio in fly ash with a more aluminic than silicic chemical character, whereas it declined when silicic-ferric-aluminic ash was used. On the other hand, the differences between the total heat of hydration released at the first valley and the second peak also clearly differentiated the two types of ash. While the relative differences increased in the more aluminic than silicic ash, they declined in the more silicic than aluminic. In another vein, the findings indicate that within a comparable Blaine fineness range, the reactive alumina (Al2O3r−) content in pozzolanic additions has a greater effect on mortar strength than the reactive silica (SiO2r−) content, at least in early ages up to 28 days. Finally, the adverse effect generated in the presence of excess gypsum is due primarily to the chemical interaction between the gypsum and the C3A in the Portland cement and the reactive alumina (Al2O3r−) in the fly ash.

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Journal of Thermal Analysis and Calorimetry
Language English
Size A4
Year of
per Year
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Founder Akadémiai Kiadó
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Publisher Akadémiai Kiadó
Springer Nature Switzerland AG
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
CH-6330 Cham, Switzerland Gewerbestrasse 11.
Chief Executive Officer, Akadémiai Kiadó
ISSN 1388-6150 (Print)
ISSN 1588-2926 (Online)

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