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Monitoring Thermal Properties and Volume Changes of Alkali-Activated Materials by using advanced experimental techniques

par Lacante, Maïté ;Delsaute, Brice ;Staquet, Stéphanie
Référence RILEM 2026 Spring Convention(15-17 April 2026: Gent, Belgium), RILEM Conference on Innovative Construction Materials and Processes for Sustainable Buildings and Infrastructure, RILEM 2026 Spring Convention, page (289)
Publication Publié, 2026-04-14

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As autogenous and thermal strains are significantly high in alkali-activated pastes, it is necessary to investigate ways to reduce these. This research studies how the volume changes of pastes made from slag activated by alkalis can be mitigated by substituting part of the slag with limestone filler or metakaolin and how this impacts the early age behaviour of the material with a particular focus on the autogenous shrinkage and the thermal expansion coefficient by using a customized AutoShrink device developed at ULB for that purpose.When slag is partially substituted by limestone filler at substitution rates of 15% and 30%, a maximal reduction in the compressive strength of 23% has been obtained. Isothermal calorimetry revealed that the limestone filler was not entirely inert and showed the effect of dilution which is linked to the increase in the solution-to-binder ratio when the substitution rate increases. The autogenous shrinkage magnitude decreased when substituting 15% of the slag while higher autogenous shrinkage magnitude was obtained when 30% was substituted. The coefficient of thermal expansion was slightly reduced and delayed when slag was substituted with limestone filler.When slag is partially substituted by metakaolin, its effect on the autogenous shrinkage and the coefficient of thermal expansion were found to depend on both the type and concentration of the alkaline activator. The swelling was increased at 10% substitution followed by constant shrinkage in case of NaOH-activation. Shrinkage was mitigated with Na2SiO3-activation. Higher substitutions with 8 M NaOH resulted in a significant increase in the shrinkage rate and thermal expansion coefficient (CTE). A 10% substitution delayed the CTE increase but resulted in higher later-age values (dilution effect). The 20% substitution led to a similar final CTE value at 300 h, while 30% substitutionresulted in a decrease in CTE after the initial increase.