Influence of organoclay structural characteristics on properties and hydration of cement pastes

•Hydration of cement pastes with the addition of organoclay (1 wt%) was studied.•Organomontmorillonites (OMT) with different cation exchange degree were used.•Pozzolanic behaviour of OMT depends on the cation exchange degree of nanoclay.•Considerable decrease of water sorptivity was achieved for cement pastes with OMT. In this study the effect of small amount (1 wt%) of organically modified montmorillonite (OMT) on the hydration peculiarities, strength and water sorptivity of cement pastes was investigated. Three types of OMT with cation exchange degrees 0.6, 0.8 and 1.0 were selected for cement substitution in the paste. Cement hydration was analysed by XRD/Rietveld method, SEM/EDS and thermogravimetric analysis. OMT of lower cation exchange degree (0.6) displayed pozzolanic behaviour after 14 days while the activity of OMT with higher cation exchange degree (0.8–1.0) was observed only after 28 days. The use of OMT with higher cation exchange degree resulted in the extra formation of aluminohydrates in cement pastes. The capillary sorption of the samples decreased with the increase of the cation exchange degree of OMT.