Characterization by Multinuclear High‐Resolution NMR of Hydration Products in Activated Blast‐Furnace Slag Pastes

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Abstract
The effect of activators on the hydration of granulated blast‐furnace slag (gbfs) was studied through compressive strength measurements, 29 Si, 27 Al, and 23 Na high‐resolution nuclear magnetic resonance, and X‐ray diffraction. Four different activations containing sodium hydroxide, sodium silicate, and/or calcium hydroxide (CH) were considered, at fixed amounts of alkali: 5% Na 2 O, 5% Na 2 O‐2.5% CH, 5% Na 2 O‐7.5% SiO 2 , and 5% Na 2 O‐2.5% CH‐7.5% SiO 2 . Silicate‐activated gbfs cements have greater compressive strength than Portland cements over the whole period of study (1 yr). Also, silicate‐free activated gbfs cements have poorer mechanical strength than silicate‐activated cements. In fact, substantial structural differences were observed between hydration products in both kinds of activations. In silicate‐activated pastes there exists an intimate mixture of C‐S‐H layers and AFm‐like arrangements containing Al in octahedral sites bonded to the silicate layers, originated either from phase intergrowths or from a high density of Ca‐Al incorporation in the interlayer spaces of C‐S‐H. In pastes obtained from silicate‐free activation of gbfs there is a better chemical and structural definition among C‐S‐H and calcium aluminate hydrate domains (AFm and hydrogarnet).

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