Quantitative analysis of phase assemblage and chemical shrinkage of Alkali-activated slag

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Abstract

This paper presents a quantitative analysis of hydrated phase assemblage and chemical shrinkage of alkali-activated slag (AAS) as a function of pH and modulus (n= SiO2/Na2O molar ratio) of activator. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermodynamic modeling, provide a comprehensive characterization of the phase assemblages and distribution in AAS microstructure. The main hydration products in AAS are calcium-alumina-silicate-hydrate (C-A-S-H) and hydrotalcite-type phases, while the formation of other hydrates is activator-dependent. For NaOH-activated slag, hydration products are preferentially formed around slag particles showing a hydrated rim, while for sodium silicate-activated slag, hydration products are initialized at both slag surface and inter-particle spaces simultaneously. However, a dark hydrated rim whose composition is similar to that of alkali-aluminosilicate-hydrate was observed around unhydrated slag in aged AAS. It indicates that the composition and spatial distribution of hydrates in AAS microstructure is heterogeneous, which cannot be predicted by thermodynamic modeling. The chemical shrinkage of AAS was quantified using buoyancy method and backscattered image analysis. The average chemical shrinkage of AAS is about 0.1211 ml/gslag and increases with the increasing modulus and pH of activator. The chemical shrinkage of AAS is about twice larger than that of portland cement, which may be attributed to the limited formation of expansive crystalline phases, such as ettringite and portlandite.

Original languageEnglish (US)
Pages (from-to)245-260
Number of pages16
JournalJournal of Advanced Concrete Technology
Volume14
Issue number5
DOIs
StatePublished - Jan 1 2016

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Alkalies
Slags
Chemical analysis
Hydrates
Hydration
hydrotalcite
Silicates
Thermodynamics
Silicic Acid
Microstructure
Aluminum Oxide
Aluminosilicates
Portland cement
Buoyancy
Image analysis
Spatial distribution
Energy dispersive spectroscopy
Calcium
Alumina
Sodium

All Science Journal Classification (ASJC) codes

  • Building and Construction
  • Materials Science(all)

Cite this

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abstract = "This paper presents a quantitative analysis of hydrated phase assemblage and chemical shrinkage of alkali-activated slag (AAS) as a function of pH and modulus (n= SiO2/Na2O molar ratio) of activator. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermodynamic modeling, provide a comprehensive characterization of the phase assemblages and distribution in AAS microstructure. The main hydration products in AAS are calcium-alumina-silicate-hydrate (C-A-S-H) and hydrotalcite-type phases, while the formation of other hydrates is activator-dependent. For NaOH-activated slag, hydration products are preferentially formed around slag particles showing a hydrated rim, while for sodium silicate-activated slag, hydration products are initialized at both slag surface and inter-particle spaces simultaneously. However, a dark hydrated rim whose composition is similar to that of alkali-aluminosilicate-hydrate was observed around unhydrated slag in aged AAS. It indicates that the composition and spatial distribution of hydrates in AAS microstructure is heterogeneous, which cannot be predicted by thermodynamic modeling. The chemical shrinkage of AAS was quantified using buoyancy method and backscattered image analysis. The average chemical shrinkage of AAS is about 0.1211 ml/gslag and increases with the increasing modulus and pH of activator. The chemical shrinkage of AAS is about twice larger than that of portland cement, which may be attributed to the limited formation of expansive crystalline phases, such as ettringite and portlandite.",
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Quantitative analysis of phase assemblage and chemical shrinkage of Alkali-activated slag. / Ye, Hailong; Radlińska, Aleksandra.

In: Journal of Advanced Concrete Technology, Vol. 14, No. 5, 01.01.2016, p. 245-260.

Research output: Contribution to journalArticle

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