CSA-based ternary binders for a sustainable concrete

The article deals with the evaluation of the effect of a tartaric acid-based set retarding admixture on the properties of environmentally friendly mortars manufactured with CSA, anhydrite, hydrated lime and supplementary cementitious materials (fly ash, metakaolin and slag cement). Results indicated that the tartaric acid, acts as superplasticizer and it is effective to extend the pot-life of mortars up to about 2 hours. On the other hand, the set-retarding admixture determines a strong retardation of binder hydration and, consequently, a reduction of compressive strength at early ages. Mortars without tartaric acid showed an initial expansion during the first 5-7 days as a consequence of ettringite formation than mixtures shrink. When set-retarding admixture is used, the initial free-expansion totally disappears and shrinkage begins immediately after final set has occurred. However, after 270 days shrinkage is substantially the same for mortars with and without tartaric acid.