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Title: Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags

Accelerated carbonation is induced in pastes and mortars produced from alkali silicate-activated granulated blast furnace slag (GBFS)-metakaolin (MK) blends, by exposure to CO{sub 2}-rich gas atmospheres. Uncarbonated specimens show compressive strengths of up to 63 MPa after 28 days of curing when GBFS is used as the sole binder, and this decreases by 40-50% upon complete carbonation. The final strength of carbonated samples is largely independent of the extent of metakaolin incorporation up to 20%. Increasing the metakaolin content of the binder leads to a reduction in mechanical strength, more rapid carbonation, and an increase in capillary sorptivity. A higher susceptibility to carbonation is identified when activation is carried out with a lower solution modulus (SiO{sub 2}/Na{sub 2}O ratio) in metakaolin-free samples, but this trend is reversed when metakaolin is added due to the formation of secondary aluminosilicate phases. High-energy synchrotron X-ray diffractometry of uncarbonated paste samples shows that the main reaction products in alkali-activated GBFS/MK blends are C-S-H gels, and aluminosilicates with a zeolitic (gismondine) structure. The main crystalline carbonation products are calcite in all samples and trona only in samples containing no metakaolin, with carbonation taking place in the C-S-H gels of all samples, and involving the freemore » Na{sup +} present in the pore solution of the metakaolin-free samples. Samples containing metakaolin do not appear to have the same availability of Na{sup +} for carbonation, indicating that this is more effectively bound in the presence of a secondary aluminosilicate gel phase. It is clear that claims of exceptional carbonation resistance in alkali-activated binders are not universally true, but by developing a fuller mechanistic understanding of this process, it will certainly be possible to improve performance in this area.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3]
  1. Materials Engineering Department, Composite Materials Group, CENM, Universidad del Valle, Cali (Colombia)
  2. Department of Chemical and Biomolecular Engineering, University of Melbourne, Victoria 3010 (Australia)
  3. Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
Publication Date:
OSTI Identifier:
21344769
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 40; Journal Issue: 6; Other Information: DOI: 10.1016/j.cemconres.2010.02.003; PII: S0008-8846(10)00032-3; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BINDERS; BLAST FURNACES; CALCITE; CARBON DIOXIDE; COMPRESSION STRENGTH; CURING; GELS; MORTARS; PERFORMANCE; PRESSURE RANGE MEGA PA 10-100; SILICATES; SILICON OXIDES; SLAGS; SODIUM IONS; SODIUM OXIDES; TRONA; X-RAY DIFFRACTION; ZEOLITES ALKALI METAL COMPOUNDS; CARBON COMPOUNDS; CARBON OXIDES; CARBONATE MINERALS; CHALCOGENIDES; CHARGED PARTICLES; COHERENT SCATTERING; COLLOIDS; DIFFRACTION; DISPERSIONS; FURNACES; INORGANIC ION EXCHANGERS; ION EXCHANGE MATERIALS; IONS; MATERIALS; MECHANICAL PROPERTIES; MINERALS; OXIDES; OXYGEN COMPOUNDS; PRESSURE RANGE; PRESSURE RANGE MEGA PA; SCATTERING; SILICATE MINERALS; SILICON COMPOUNDS; SODIUM COMPOUNDS