Five year monitoring of curing solutions of heat-cured mortars affected by delayed ettringite formation

The work presented in this paper studies the leaching of heat-cured mortars affected by delayed ettringite formation (DEF). For this, the expansion and the leaching of various elements (OH⁻, Ca²⁺, Na⁺ and K⁺) were monitored for more than 5 years in three mortars: a reference mortar and two compositions in which 3·11% of Na₂SO₄ (sodium sulfate) and 1·75% of NaOH (sodium hydroxide) were added to the mixture. The four mortars expanded but with different kinetics. pH, conductivity and leaching of calcium had the same global variation: a fast decrease during the first few days of curing, a strong increase after the beginning of the expansions and, lastly, a plateau of several months followed, or not (depending on the mixtures and the progress of the reaction), by a strong decrease in leaching. Finally, the results suggest that the reasons for DEF are not only related to the leaching of alkalis.