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Minerals 2018, 8(4), 137; doi:10.3390/min8040137

Hybrid Alkaline Cements: Bentonite-Opc Binders

1
Department of Material Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK
2
Department of Cement and Recycling Materials, Eduardo Torroja Institute (CSIC), Madrid 28033, Spain
*
Author to whom correspondence should be addressed.
Received: 2 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 29 March 2018
(This article belongs to the Special Issue Geopolymers)
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Abstract

Moderately alkaline activators can be used to formulate cementitious binders with a high Supplemetary Cementitious Materials (SCMs) and a low portland cement content (hybrid alkaline cements). This study aimed to prepare hybrid alkaline cements containing large percentages of dehydroxylated bentonite (BT) and small Portland cement (OPC) fractions, with 5% Na2SO4 as a solid alkaline activator. The hydration kinetics of the pastes hydrated in water in the presence and absence of the solid activator were assessed by isothermal conduction calorimetry, whilst the reaction products were characterised with X-Ray Powder Diffraction (XRD) and Fourier-transform Infrared Spectroscopy (FTIR). The presence of the alkaline activator hastened OPC and BT/OPC hydration: more heat of hydration was released, favouring greater initial bentonite reactivity. The portlandite forming during cement hydration reacted readily with the Na2SO4, raising medium alkalinity and enhancing bentonite dissolution and with it reaction product precipitation (primarily (N,C)-A-S-H-like gels that co-exist with C-S-H- or C-A-S-H-like gels). The presence of sulfate ions favoured the formation of AFm-like phases. Preceding aspects accelerated the hydration reactions, with the formation of more reaction product and matrix densification. As a result, the 28 days Na2SO4 activated systems developed greater mechanical strength than the water-hydrated systems, with the 60% BT/40% OPC blends exhibiting higher compressive strength than the 100% OPC pastes. View Full-Text
Keywords: alkaline activation; geopolymer; hybrid cements; calorimetry; bentonites alkaline activation; geopolymer; hybrid cements; calorimetry; bentonites
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Garcia-Lodeiro, I.; Fernandez-Jimenez, A.; Palomo, A. Hybrid Alkaline Cements: Bentonite-Opc Binders. Minerals 2018, 8, 137.

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