Q. Necessity of air voids in bituminous pavement?
If the presence of air voids is too high, it results in an increase of permeability of bituminous pavement. This enables the frequent circulation of air and water within the pavement structure and leads to premature hardening and weathering of asphalt. So too high an air void content poses detrimental effect to the durability of bituminous pavement.
If the presence of air voids is too low, bleeding, flushing and loss of stability can result under the effect of prolonged traffic loads due to the rearrangement of particles by compaction. Aggregates may become degraded by traffic loads resulting in instability and flushing for such a low air void content. Air void space can be increased by adding more course or fine aggregates to the asphalt mix. Otherwise if asphalt content is above normal level, it can be decrease to increase air voids.