Evaluation of Air Permeability of Alkali-Aggregate Reaction (AAR)-Affected Concrete

In the context of Alkali-Aggregate Reaction (AAR), the presence of water has a significant impact on the chemical reactions involved, making it challenging to predict and evaluate the transport properties of affected concrete. Air permeability is a particularly sensitive indicator of damage induced by AAR, and the characterization of this property is crucial for reducing the risk of interaction between the fluid, the cement paste, and the new products formed during AAR. This paper demonstrates that specimens subjected to AAR undergo swelling in three phases: a latent phase, an acceleration phase, and a deceleration phase. Early swelling leads to significant crack opening, rendering the material permeable to air flow despite its high moisture content. As the expansion continues, permeability increases and is primarily driven by the crack network created, although a small portion is filled by hydration products. This is further highlighted by drying kinetics, which slow down at high expansion rates.