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Mitigation of Volume Changes in Alkali-Activated Slag by Using Metakaolin
Maïté Lacante1, Brice Delsaute1,2, Stéphanie Staquet1
1BATir Department (LGC), Université libre de Bruxelles (ULB), 1050 Brussels, Belgium.
Materials (Basel, Switzerland)
|June 13, 2025
Summary
Metakaolin as a partial substitute in alkali-activated slag cement affects performance based on activator type and concentration. Higher substitution increased strength with NaOH but decreased it with sodium silicate, altering volume stability and thermal expansion.
Area of Science:
- Materials Science
- Civil Engineering
- Geochemistry
Background:
- Alkali-activated slag (AAS) cements offer sustainable alternatives to ordinary Portland cement.
- Controlling volume stability and mechanical properties of AAS is crucial for practical applications.
- Metakaolin is explored as a supplementary cementitious material in AAS.
Purpose of the Study:
- To investigate the efficacy of metakaolin as a partial substitute for slag in alkali-activated systems.
- To evaluate the impact of metakaolin on the volume changes, compressive strength, and thermal properties of AAS.
- To understand the influence of alkaline activator type (NaOH vs. Na2SiO3) and concentration on these properties.
Main Methods:
- Preparation of alkali-activated slag pastes with varying metakaolin substitution rates (0%, 10%, 20%, 30%).
- Activation using different concentrations of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3).
- Assessment of compressive strength, workability, isothermal calorimetry, autogenous strain, and coefficient of thermal expansion (CTE).
Main Results:
- Compressive strength increased with metakaolin substitution using 8 M and 10 M NaOH, but decreased with Na2SiO3.
- Metakaolin exhibited a dilution effect at 10% substitution, with a third reaction peak appearing under NaOH activation.
- Volume changes (swelling/shrinkage) and CTE were significantly influenced by metakaolin content and activator type, with higher substitutions leading to increased shrinkage and CTE under NaOH activation.
Conclusions:
- Metakaolin can mitigate volume changes in alkali-activated slags, but its effect is highly dependent on the activator system.
- NaOH activation with metakaolin substitution can lead to increased strength and altered thermal-mechanical behavior, including potential shrinkage issues at higher substitution rates.
- Na2SiO3 activation showed promise in mitigating shrinkage, highlighting the need for careful selection of activators and mix designs for metakaolin-modified AAS.
Keywords:
autogenous strainblast-furnace slagcoefficient of thermal expansioncompressive strengthmetakaolinMore Related Videos
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