Abstract
The purpose of this study is to investigate the effect of post-curing conditions on hydration behavior of slag blended cement pastes. Pastes of ordinary portland cement (OPC) and blended cement containing 40% ground granulated blast furnace slag (BFS) were cured at 60℃ for 24 hours and subsequently stored in limewater at 20℃ or subjected to atmospheric curing. Microstructure development in the cement pastes was determined by mercury intrusion porosimetry (MIP), the amounts of calcium hydroxide, carbonates and combined water were measured using thermogravimetric / differential thermal analyzer (TG/DTA), hydration products were analyzed and quantified by X-ray diffraction (XRD)/Rietveld method and the reaction ratio of BFS was estimated by selective dissolution method. Three-day strength of the blended cement pastes was higher than that of the OPC pastes when cured in limewater at 20℃ after the high temperature curing. The hydration ratios of C2S and BFS increased when the pastes subjected to high temperatures at early age were post-cured in limewater at 20℃. Theoretical volume changes of hydration products obtained by the XRD/Rietveld analysis were consistent with the compressive strength and microstructure development. Vaterite, a calcium carbonate polymorph, was observed in the BFS blended cement pastes post-cured under the atmospheric conditions. This phenomenon was accompanied by a decrease in Ca/Si molar ratio which was likely due to calcium ion elution from C-S-H gel. It was concluded that physicochemical properties of BFS blended cement pastes would vary significantly depending on the post-curing conditions after the early-age high temperature curing.
