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Open AccessArticle

Effect of the Sodium Silicate Modulus and Slag Content on Fresh and Hardened Properties of Alkali-Activated Fly Ash/Slag

1
Guangzhou University-Tamkang University Joint Research Center for Engineering Structure Disaster Prevention and Control, Guangzhou University, Guangzhou 510006, China
2
Centre for Future Materials, University of Southern Queensland, West Street, Toowoomba, QLD 4350, Australia
3
Department of Materials and Environment (Microlab), Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628CN Delft, The Netherlands
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(1), 15; https://doi.org/10.3390/min10010015
Received: 8 November 2019 / Revised: 17 December 2019 / Accepted: 18 December 2019 / Published: 23 December 2019
(This article belongs to the Special Issue Alkali Activated Materials: Advances, Innovations, Future Trends)
This paper presents the results of an experimental study performed to investigate the effect of activator modulus (SiO2/Na2O) and slag addition on the fresh and hardened properties of alkali-activated fly ash/slag (AAFS) pastes. Four activator moduli (SiO2/Na2O), i.e., 0.0, 1.0, 1.5, and 2.0, and five slag-to-binder ratios, i.e., 0, 0.3, 0.5, 0.7, 1.0, were used to prepare AAFS mixtures. The setting time, flowability, heat evolution, compressive strength, microstructure, and reaction products of AAFS pastes were studied. The results showed that the activator modulus and slag content had a combined effect on the setting behavior and workability of AAFS mixtures. Both the activator modulus and slag content affected the types of reaction products formed in AAFS. The coexistence of N–A–S–H gel and C–A–S–H gel was identified in AAFS activated with high pH but low SiO2 content (low modulus). C–A–S–H gel had a higher space-filling ability than N–A–S–H gel. Thus, AAFS with higher slag content had a finer pore structure and higher heat release (degree of reaction), corresponding to a higher compressive strength. The dissolution of slag was more pronounced when NaOH (modulus of 0.0) was applied as the activator. The use of Na2SiO3 as activator significantly refined the pores in AAFS by incorporating soluble Si in the activator, while further increasing the modulus from 1.5 to 2.0 prohibited the reaction process of AAFS, resulting in a lower heat release, coarser pore structure, and reduced compressive strength. Therefore, in view of the strength and microstructure, the optimum modulus is 1.5. View Full-Text
Keywords: alkali-activated fly ash/slag; activator modulus; slag content; fresh and hardened properties alkali-activated fly ash/slag; activator modulus; slag content; fresh and hardened properties
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Ouyang, X.; Ma, Y.; Liu, Z.; Liang, J.; Ye, G. Effect of the Sodium Silicate Modulus and Slag Content on Fresh and Hardened Properties of Alkali-Activated Fly Ash/Slag. Minerals 2020, 10, 15.

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