Mitigation of Volume Changes of Alkali-Activated Materials by Using Limestone Filler

TL;DR

This study explores how adding limestone filler to alkali-activated materials can reduce volume changes caused by autogenous and thermal strains.

Contribution

The paper introduces the use of limestone filler as a method to mitigate volume changes in alkali-activated materials.

Findings

Substituting 15% of slag with limestone filler reduced autogenous shrinkage and slowed its development.

A 30% substitution increased autogenous shrinkage but reduced compressive strength by 23%.

Limestone filler affected thermal expansion, slightly reducing and delaying it.

Abstract

As autogenous and thermal strains are significantly high in alkali-activated pastes, it becomes 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 and how this impacts the properties of the material, including autogenous strains, thermal strains, heat flow, compressive strength, and workability. The first part investigates how the different substitution rates impact the compressive strength and workability. The substitution rates of 15% and 30% emerged as the most optimal with a maximal reduction in the compressive strength of 23%. Five compositions were consequently investigated in the second part of the study. Isothermal calorimetry revealed that the limestone filler was probably 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 decreased when substituting 15% of the slag, while higher autogenous shrinkage was obtained when 30% was substituted. In addition, its rate of development was reduced. Finally, the coefficient of thermal expansion was generally slightly reduced and delayed when slag was substituted.

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