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This study attempts to estimate the relation between the adsorption of the molecules on calcium silicate hydrates (C-S-H) and their ions complexation on their retarding effect on tricalcium silicate hydration.The molecules mainly differ by their stereochemistry, functionality and charge.A set of small polyols with and without ending carboxylate group (D-mannitol, D-glucitol, D-gluconate) and amines with functionalized carboxylate and phosphonate groups (EDTA, EDTMP...) was studied.The calcium complexation constants were determined by simulating the pH, calcium and molecules concentrations at equilibrium with solid portlandite which were experimentally measured.The adsorption of the organics was measured on synthetic C-S-H with the depletion method.The increase of the calcium and silicon concentrations of the solution at equilibrium with C-S-H in presence of the additives was studied in terms of complexation.It results that all these retarding molecules complex calcium ions in solution and adsorb on synthetic C-S-H to different extents.They are particularly sensitive to calcium counter-ions present at the surface of C-S-H at high Ca/Si.Some of the organic compounds also complex silicate ions.The results point out that the retardation induced by the presence of the molecules on tricalcium silicate hydration is not only function of their calcium complexing abilities or of their affinity with C-S-H.