12.4 : コンクリート中の空気量の測定

Air entrainment significantly improves the durability of concrete against freeze-thaw cycles.

The ideal air content protects the concrete, preventing cracks and damage from environmental stresses. On the other hand, excessive air can weaken the structural integrity of the concrete.

Accurate measurement of air content in concrete is carried out by deploying different methods based on the concrete compositions and project requirements.

For example, the pressure method involves placing a concrete sample in a sealed chamber and calculating the air content based on the changes in pressure.

For concretes that are lightweight or contain highly absorbent aggregates, the volumetric method is more suitable.

The volumetric method involves adding alcohol to a concrete sample to help release the air bubbles and then measuring the volume change.

Another method, the gravimetric method, involves measuring the density of the concrete to calculate the air content.

Alternatively, the Chace indicator method offers a quick field test that gives an approximate measure of air content by observing the change in the volume of air in a syringe-like device as it is forced into the concrete.