In-place density compares the bulk specific gravity of the compacted mat with the mix's Gmm, so 93 percent density means 7 percent air voids. Specs commonly set a minimum around 92 percent of Gmm for dense-graded mix, with pay incentives in the 93 to 96 range and penalties or removal below the minimum. Each point of density gained is often credited with about a 10 percent gain in fatigue life, which is why density is the number paving crews watch most closely.
Density's 91.4 on the edge, add a pass with the breakdown on the unsupported side or we're eating a penalty.
The unsupported edge loses the most density, so roller operators are told to let the drum hang a few inches past the edge on the first pass.
Also heard as
- in-place density
- percent compaction
Related terms
Gmm
Maximum specific gravity of the mix: the density it would have if every air void were squeezed out.
Air voids
The small pockets of air between binder-coated aggregate in compacted mix, given as a percent of total volume.
Nuclear gauge
A portable instrument with a radioactive source that estimates asphalt density in about a minute without cutting a core.
Core
A cylinder of pavement drilled out of the finished mat and sent to the lab for density and thickness.
Joint density
The density measured at a longitudinal joint, often specified separately because joints compact poorly.