The Effect of Post-Curing Condition on the Hydration of Slag Blended Cement Subjected to a Temperature History at Early Age
Ryuichiro KUGA, Hiroaki MORI and Masami UZAWA
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 60C for 24 hours and subsequently stored in limewater at 20C. 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 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 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. Key Words:Blast furnace slag, Post-curing, Temperature history, Hydration products, XRD/Rietveld method, Porosity, TG/DTA