Journal
CONSTRUCTION AND BUILDING MATERIALS
Volume 23, Issue 2, Pages 775-784Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.conbuildmat.2008.02.022
Keywords
Reactive cement; Metakaolin; Steam curing; Early age; Hydration product; Precast industry
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The paper presents the results of a hydration study performed in order to explain the significant increase in compressive strength at one day of age observed on steam cured mortars when 25% by mass of cement was replaced with a metakaolin. Two CEM 152.5R cements, differing in reactivity, and a metakaolin (MK) were used. By means of XRD and thermal analysis carried out on cement pastes, blended or not with MK, the main results showed that the improvement in strength at one day of age could be explained by the occurrence of a pozzolanic reaction due to MK, thereto-activated by the high curing temperature (55 C). The pozzolanic reaction was observed through the consumption of calcium hydroxide and an increase in the amount of C-S-H and C-S-A-H hydrated phases. This change in the hydration product nature and amount was more pronounced when MK was combined with the less reactive cement, in agreement with the mechanical results on mortars. These results are of great importance for the concrete industry where the current trend is to decrease the clinker content in cements (1 ton of clinker = 1 ton of CO2 released). In particular, the interesting mechanical performance at early ages can be helpful for precast concrete manufacturing. (C) 2008 Elsevier Ltd. All rights reserved.
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