26.3.3. Air voids percent V v

Air voids V is the percent of air voids by volume in the specimen and is given by:

V = \frac{(G_t - G_m)}{G_t} \times 100

(26.3)

Air voids percentage, denoted as Vv, measures how much space within the specimen is occupied by air, as opposed to other materials like aggregates or bitumen. It is calculated using the theoretical specific gravity (Gt) of the mix and the bulk specific gravity (Gm). The formula indicates that Vv increases as the difference between Gt and Gm increases, meaning a higher number of air voids in the mix.

Think of making a sponge cake. If you whisk air into the batter before baking, the cake rises and has many holes or 'air voids' which makes it lighter and fluffy. Similarly, in asphalt, having the right amount of air voids is essential for ensuring that the pavement remains stable and can withstand loads without cracking.

Where G_t is the theoretical specific gravity of the mix, given by equation 1, and G_m is the bulk or actual specific gravity of the mix given by equation 2.

Knowing the air voids percentage is crucial for project specifications related to asphalt mixtures. The proportion of air voids affects the durability, strength, and performance of the asphalt layer. Higher air voids may lead to instability under traffic loads, while lower percentages can affect how well the bitumen bonds with the aggregates, impacting longevity.

Consider a sponge in water. If the sponge is completely saturated with water and has no air voids, it becomes heavy and dense, similar to how asphalt might fail under heavy weight if it doesn't have the right air void content. Conversely, if the sponge has too many air voids, it won't hold enough water, making it less effective. Asphalt needs to find that balance for optimal performance.

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