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Mechanical and hydration properties of ground granulated blastfurnace slag pastes activated with MgO-CaO mixtures


Type

Article

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Authors

Jin, F 
Al-Tabbaa, A 
Shi, B 
Liu, J 

Abstract

Since alkali-activated slag using conventional activators suffers from economical and technical problems, other alternative activators should be explored. This paper reports the results of an investigation into the activation of ground granulated blastfurnace slag by using 10% (by weight) reactive MgO, CaO and their mixtures with various ratios. The mechanical and hydration properties of pastes were examined up to 90 days. It was found that the strength of slag pastes activated with MgO–CaO mixtures decreased with the increasing ratio of MgO to CaO in the early age while a much steeper strength gain was observed in pastes with MgO/CaO higher than 19/1 after 28 days and longer. The addition of small amount of CaO in MgO can greatly accelerate the hydration of slag in the early age by increasing the pH of pore solution. However, pastes showed small difference in strength development at each period when MgO/CaO was less than 1. The main hydration products, analysed by XRD, TGA and SEM/EDS, were C–S–H and hydrotalcite-like phases. While CaO accelerated the formation of C–S–H in the early age, MgO induced more amount of hydrotalcite-like phases, which notably enhanced the strength of slag pastes with high MgO content after 28 days and longer. Calcite, portlandite and residual MgO were also observed, depending on the MgO/CaO ratio and the hydration time. This work indicated that the replacement of MgO by CaO can make the application of reactive MgO in slag activation more economical.

Description

Keywords

Alkali-activated slag, Reactive MgO, CaO, Hydration

Journal Title

Construction and Building Materials

Conference Name

Journal ISSN

0950-0618
1879-0526

Volume Title

69

Publisher

Elsevier BV
Sponsorship
The work presented in this paper was carried out at Department of Engineering, University of Cambridge, where the first author was a visiting researcher. The visit was funded by the China Scholarship Council and the Scientific Research Foundation of the Graduate School of Nanjing University (No.2012CL11). The financial support for the PhD studentship of the second author from the Cambridge Trust and China Scholarship Council was also very much appreciated.