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

Abstract

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

Citation Formats

Bernal, Susan A., E-mail: susana.bernal@gmail.co, Mejia de Gutierrez, Ruby, Provis, John L., E-mail: jprovis@unimelb.edu.a, and Rose, Volker. Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags. United States: N. p., 2010. Web. doi:10.1016/j.cemconres.2010.02.003.
Bernal, Susan A., E-mail: susana.bernal@gmail.co, Mejia de Gutierrez, Ruby, Provis, John L., E-mail: jprovis@unimelb.edu.a, & Rose, Volker. Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags. United States. doi:10.1016/j.cemconres.2010.02.003.
Bernal, Susan A., E-mail: susana.bernal@gmail.co, Mejia de Gutierrez, Ruby, Provis, John L., E-mail: jprovis@unimelb.edu.a, and Rose, Volker. 2010. "Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags". United States. doi:10.1016/j.cemconres.2010.02.003.
@article{osti_21344769,
title = {Effect of silicate modulus and metakaolin incorporation on the carbonation of alkali silicate-activated slags},
author = {Bernal, Susan A., E-mail: susana.bernal@gmail.co and Mejia de Gutierrez, Ruby and Provis, John L., E-mail: jprovis@unimelb.edu.a and Rose, Volker},
abstractNote = {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 free 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.},
doi = {10.1016/j.cemconres.2010.02.003},
journal = {Cement and Concrete Research},
number = 6,
volume = 40,
place = {United States},
year = 2010,
month = 6
}
  • Geopolymers, obtained by chemical reaction between aluminosilicate oxides and silicates under highly alkaline conditions, are studied in this paper. The proposed mechanism of geopolymer setting and hardening or curing consists of a dissolution, a transportation or an orientation, as well as a polycondensation step. The aim of this paper is to investigate the influence of the curing time and temperature, the relative humidity and the reagents temperature on the geopolymerization process in order to obtain a resistant matrix usable for inertization of hazardous wastes. The evolution of the process from the precursors dissolution to final geopolymer matrix hardening has beenmore » followed by FTIR spectroscopy, X-ray diffractometry, SEM/EDS and leaching tests. The results show the significant influence of both curing temperature in the curing stage and of the mould materials on the matrix stability. The easy-to-run preparation procedure for a chemically stable metakaolin geopolymer individuated can be summarized as reagents setting and curing at room temperature and material mould which permits moisture level around 40%. - Graphical abstract: Chemical stability as a function of curing conditions. Highlights: ► Metakaolin in highly alkaline solutions produced solid materials at room temperature. ► Curing time and temperature, relative humidity, reagents temperature were optimized. ► Leaching tests were used to confirm final hardening. ► FTIR spectroscopy, SEM analysis and X-ray diffractometry were used to interpret matrix stability.« less
  • Binders formed through alkali-activation of slags and fly ashes, including ‘fly ash geopolymers’, provide appealing properties as binders for low-emissions concrete production. However, the changes in pH and pore solution chemistry induced during accelerated carbonation testing provide unrealistically low predictions of in-service carbonation resistance. The aluminosilicate gel remaining in an alkali-activated slag system after accelerated carbonation is highly polymerised, consistent with a decalcification mechanism, while fly ash-based binders mainly carbonate through precipitation of alkali salts (bicarbonates at elevated CO{sub 2} concentrations, or carbonates under natural exposure) from the pore solution, with little change in the binder gel identifiable by nuclearmore » magnetic resonance spectroscopy. In activated fly ash/slag blends, two distinct gels (C–A–S–H and N–A–S–H) are formed; under accelerated carbonation, the N–A–S–H gel behaves comparably to fly ash-based systems, while the C–A–S–H gel is decalcified similarly to alkali-activated slag. This provides new scope for durability optimisation, and for developing appropriate testing methodologies. -- Highlights: •C-A-S-H gel in alkali-activated slag decalcifies during accelerated carbonation. •Alkali-activated fly ash gel changes much less under CO{sub 2} exposure. •Blended slag-fly ash binder contains two coexisting gel types. •These two gels respond differently to carbonation. •Understanding of carbonation mechanisms is essential in developing test methods.« less