The Effect of Post-Curing Condition on the Hydration of Slag Blended Cement Subjected to a Temperature History at Early Age

Abstract

The purpose of this study is to investigate the effect of post-curing condition on hydration behavior of slag blended cement pastes. Pastes of ordinary portland cement (OPC) and blended cement, containing 40% ground granulated blast furnace slag (GGBFS), were cured at 60°C for 24 hours and subsequently stored in limewater at 20°C. The development of the microstructure in the cement paste was studied by mercury intrusion porosimetry (MIP). The amount of calcium hydroxide, carbonates and combined water was measured by Thermogravimetric/Differential Thermal Analyzer (TG/DTA), and hydration products were analyzed and quantified by using X-ray diffraction (XRD)/ Rietveld method. The reaction ratio of BFS was estimated by selective dissolution method. The strength development after 3 days of BFS blended cement pastes was higher than OPC pastes when pastes cured in limewater at 20°C following the initial high temperature curing period. The reaction rates of C2S and BFS increased for the pastes subjected an initial high temperature curing followed by water curing at 20°C as post-curing. C3S and C3A were almost completely consumed at 28days irrespective of curing conditions. Theoretical volume changes of hydration products calculated from XRD/Rietveld corresponded with the development of compressive strength and MIP. Vaterite, a calcium carbonate polymorph, was observed in BFS blended cement pastes that were exposed to the atmosphere as post-curing condition. This phenomenon corresponds to a decrease in Ca/Si molar ratio which is likely the product of the C-S-H paste giving up a Ca ion. It was concluded that physicochemical properties of BFS blended cement pastes change significantly following the initial curing conditions.