Synthesis and Reaction Mechanism of an Alkali-Activated Metakaolin-Slag Composite System at Room Temperature
Publication: Journal of Materials in Civil Engineering
Volume 31, Issue 1
Abstract
Synthesis of geopolymer using metakaolin (MK) usually requires a relatively high curing temperature, which limits the application of MK-based geopolymers in the practice of civil engineering. With the goal of developing a cementitious composite that can be cured at room temperature, in the present study, ground granulated blast furnace slag powder was incorporated into MK for the synthesis of a geopolymer. With the aid of compressive strength tests, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), the influence of slag’s impact on the consistency, gelling time, and mechanical properties of the gelling system, as well as the reaction mechanism of the composite system, were investigated. The results showed that the incorporation of slag into MK improved the consistency of the slurry and shortened the setting time. A high-strength paste was synthesized successfully using the MK-slag composite system under ambient temperature curing. Results of XRD and FTIR analyses indicated that MK geopolymerization and slag hydration occurred simultaneously in the MK-slag composite system via alkali activation. The structure of hardened paste consists of both C-S-H-type and N-A-S-H-type gels. The activator module and the MK/slag mass ratio were the main factors affecting the strength of the synthesized products: when the slag replacement ratio was no more than 40%, the strength of the reaction products decreased with an increase of the activator module; when the slag replacement ratio reached or exceeded 60%, the strength of the reaction products increased with the increasing activator module.
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Acknowledgments
This research was supported by the National Key Basic Research Program of China (973 Program) (Grant No. 2015CB057701), the National Natural Science Foundation of China (Grant Nos. 51578078 and 51878068), the Louisiana Board of Regents [Contract No. LEQSF(2017-20)-RD-B-02], and the Hunan Science Fund for Distinguished Young Scholars (Grant No. 2017JJ1027). The writers thank their colleagues and other personnel from the Changsha University of Science and Technology and the Louisiana State University for providing support for this project. This extensive investigation was carried out as a result of the input and involvement of many individuals to whom the writers express their sincere thanks and gratitude.
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©2018 American Society of Civil Engineers.
History
Received: Jan 4, 2018
Accepted: Jul 6, 2018
Published online: Oct 26, 2018
Published in print: Jan 1, 2019
Discussion open until: Mar 26, 2019
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