What is the formula used to calculate the percentage of air voids in asphalt?

The formula to calculate the percentage of air voids in asphalt is based on the relationship between the specific gravity of the mixture and the specific gravity of the compacted asphalt. The correct formula is:

% = 100 x (gmm - gmb) / gmm

In this formula, "gmm" is the maximum specific gravity of the mixture, which represents the theoretical maximum density of the asphalt material when it is fully compacted without any air voids. On the other hand, "gmb" is the bulk specific gravity, which reflects the density of the actual compacted asphalt that includes both the asphalt binder and the air voids present in the mixture.

By subtracting the bulk specific gravity (gmb) from the maximum specific gravity (gmm), you determine the volume occupied by air voids. Dividing this difference by the maximum specific gravity (gmm) gives the ratio of air voids to the theoretical maximum density, and multiplying by 100 converts this ratio to a percentage.

Thus, the formula correctly helps to understand how much air is occupying the voids in the asphalt mixture, which is critical in evaluating the quality and performance of asphalt pavements. This understanding is essential for ensuring proper compaction and durability