Ceramics-Silikáty 54, (3) 277 - 283 (2010)

The simultaneous occurrence of the delayed ettringite formation mechanism and the alkali-silica reaction in concrete structures is not well understood. The studies have been carried out in order to produce more experimental data that would help to better clarify these problems. Three types of cements, with constant 1.2 % Na₂O_e and different SO₃ contents were prepared from industrial clinkers. The natural siliceous sand was used as an inert aggregate in the mortars, while opal was used as a reactive aggregate to produce the alkali-reactive specimens at a substitution ratio 6 % by total weight of aggregate. One series of samples was steam-cured at temperature of 90°C and the other was examined in accordance with ASTM C 227. The tests showed that the ettringite formation might increase the expansion due to the alkali-silica reaction as well as in the mortars cured at temperature of 38°C, as a result of the delayed ettringite formation on steam-curing of mortars. Irrespectively of the conditions of curing, the samples prepared from cement with very low SO₃ content always reveal the smallest expansion.