Airvoid

Airvoid, or air void, refers to a cavity within a solid material that contains air. Airvoids can be introduced intentionally, as in concrete with air-entraining agents, or form accidentally during processing, casting, foaming, or natural porosity. They vary in size from micrometers to millimeters and can be open (connected to the surface) or closed (isolated). The presence and distribution of air voids influence mechanical properties, thermal insulation, and permeability by altering density, stiffness, and fluid transport pathways.

In concrete and cementitious composites, air voids are a common mechanism to improve resistance to freeze–thaw damage and reduce permeability. The effectiveness depends on total air content, the size and spacing of voids, and whether the voids form a connected network. Excessive air voids can reduce compressive strength and increase shrinkage.

In engineering ceramics, polymers, and foams, air voids provide lightness and thermal insulation, with open porosity allowing fluid flow and closed porosity aiding insulation and buoyancy. The manufacturing process controls void morphology through foaming agents, additives, and molding or sintering conditions.

Air voids are characterized by microscopy and imaging techniques such as analysis of polished sections, X-ray computed tomography, or porosimetry. Parameters of interest include void size distribution, total porosity, and the spatial arrangement of voids in the material.

Overall, airvoids play a dual role as either a design feature or a defect, depending on material, application, and the balance between reduced weight and preserved strength.