Abstract
Retarders are widely used in construction materials to control the setting and hardening. The present study focuses on changes in the rheological behavior, the admixture adsorption and the pore solution composition with a controlled addition of sodium gluconate and ethylenediamine tetra(methylene phosphonic acid) (EDTMP) in cement.The adsorption of the sodium gluconate was influenced by time of addition of dosage. Delayed addition induced a depot effect which was reduced by the ongoing hydration whereas the adsorption of EDTMP was not affected by time of dosage. Nearly the complete admixture concentration was directly adsorbed on clinker phases or first hydration products.For sodium gluconate, an interaction with ferrite containing clinker phases and a calcium complexing mechanism were suggested. In contrast, EDTMP seemed to have no significant influence on the calcium concentration. With regard to the sodium concentration a fast adsorption of sodium gluconate was determined. Furthermore, a competitive adsorption between dissolved sulfate and retarder molecules or a complex formation mechanism is supposed.
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