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

Journal Article · Tue Jun 15 04:00:00 EDT 2010 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2010.02.003· OSTI ID:21344769

Mejia de Gutierrez, Ruby ^[1]; Rose, Volker ^[2]

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1. Materials Engineering Department, Composite Materials Group, CENM, Universidad del Valle, Cali (Colombia)
2. Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

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.

• OSTI ID: 21344769
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 6 Vol. 40; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALI METAL COMPOUNDS
BINDERS
BLAST FURNACES
CALCITE
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CARBONATE MINERALS
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
COLLOIDS
COMPRESSION STRENGTH
CURING
DIFFRACTION
DISPERSIONS
FURNACES
GELS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IONS
MATERIALS
MECHANICAL PROPERTIES
MINERALS
MORTARS
OXIDES
OXYGEN COMPOUNDS
PERFORMANCE
PRESSURE RANGE
PRESSURE RANGE MEGA PA
PRESSURE RANGE MEGA PA 10-100
SCATTERING
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
SLAGS
SODIUM COMPOUNDS
SODIUM IONS
SODIUM OXIDES
TRONA
X-RAY DIFFRACTION
ZEOLITES