The job
Modelled, not recorded. Every figure here is the answer the Asphalt In-Place Density (Percent of Gmm) Calculator gives for these inputs, written down in both unit systems and re-run whenever the site is built. No job was carried out, so there is no measured overrun on this page.
The job is a new asphalt surface on a parking lot, placed by a paving contractor under a specification that sets a minimum in-place density as a percentage of the mix's maximum theoretical density. Cores are cut from the finished mat at locations chosen by the specification's sampling plan, and one of them was taken near an unsupported edge, where a roller cannot compact as well as in the middle of a pass.
Two figures come back from the laboratory. The core's bulk specific gravity, 2.25, is measured on the core itself by the saturated surface-dry method of AASHTO T 166. The mix's theoretical maximum specific gravity, 2.5 as the table prints it, is measured on loose mix from the same production by AASHTO T 209: the gravity the mix would have with no air in it at all.
The specified minimum is 92 per cent of that maximum, the figure the calculator opens on. The calculator takes whatever minimum the contract states; a different contract, lift thickness or mix type may set a different one.
The inputs, exactly as entered
| Input | Value | Why |
|---|---|---|
| Bulk Specific Gravity of the Core (Gmb) | 2.25 | The core's bulk specific gravity from the laboratory, by the saturated surface-dry method; this core's is low because it came from a poorly compacted edge. |
| Theoretical Maximum Specific Gravity (Gmm) | 2.5 | Left at the calculator's own default. |
| Specified Minimum Density (Percent of Gmm) | 92 | Left at the calculator's own default. |
The working, step by step
1. Air void content
10.07 %
The in-place density is the core's gravity divided by the mix's maximum, as a percentage, and the air voids are what is left of a hundred: 10.07 %. No coefficient is involved, as the calculator's first source points out; both figures follow from the definitions of the two gravities.
2. Specified minimum applied
92 %
The minimum the contract sets is carried into the working, 92 %, so the figure can be read against it on the same page. The calculator does not choose it; it uses the one entered.
3. Margin over the specified minimum
-2.07 %
The in-place density less the minimum gives the margin: -2.07 % on this core. A negative margin means the core is below the specified minimum by that many points of maximum density; a positive one, above it.
In-place density
89.93 %
This core measures 89.93 % against a minimum of 92 %: below it, with air voids of 10.07 %. What follows from that is set by the contract, not the calculator. Many specifications judge a lot on several cores rather than one, and may apply a pay adjustment, ask for more cores, or require corrective work; an edge core below the minimum points first to how the edge was rolled, before the mix is suspected.
What to buy
| Quantity | Figure | What it is for |
|---|---|---|
| In-place density | 89.93 % | Not a purchase: the core's in-place density as a percentage of the mix's maximum, to read against the specification. |
The allowance, and what it does here
There is no allowance in a density check: it is a ratio of two measured gravities, and its uncertainty is the laboratory's, set by the precision statements of the two test methods. The figure that matters is the margin against the minimum. A margin of a fraction of a point either way is within the reach of testing variation, which is one reason specifications judge lots on several cores and not on one.
The common mistake
Using a Gmm from a different mix or day
The in-place density is only as good as the maximum gravity it is divided by. A Gmm taken from the mix design, a different plant run or another day's production can differ from the mix that was actually placed, and a small change in Gmm moves the percentage by more than a careless reader expects, enough to turn a passing core into a failing one or the reverse. Use the Gmm measured on the same day's production, as the specification normally requires, and record which test it came from beside every core result.
Change the job, and see what moves
A core from the well-rolled middle of the same mat
Bulk Specific Gravity of the Core (Gmb): 2.35 → 93.73 %
A core from the middle of the same mat, where every pass of the roller reached it, measures a bulk gravity of 2.35 and an in-place density of 93.73 %: a margin of 1.73 % above the minimum, with 6.27 % air voids. The difference between the two cores is the edge, not the mix.
The same core, under a stricter minimum
Specified Minimum Density (Percent of Gmm): 93 → 89.93 %
Judge the same core against a minimum of 93 per cent and its density is unchanged at 89.93 %, but the margin widens to -3.07 %. The core does not change; only the line it is read against does, which is why the specification's own minimum must be the one entered.
What to run next
- Asphalt Driveway Calculator
The tonnage of the same mix for a paving area and thickness, the quantity the density check is the quality side of.
- Asphalt Tack Coat Calculator
Between lifts, the tack coat that bonds them is ordered from the paved area and an application rate.
- Asphalt Emulsion Prime Coat Calculator
On a new granular base, the prime coat under the first lift is ordered the same way, at its own rate.
Sources
The method and every constant behind these figures belong to the Asphalt In-Place Density (Percent of Gmm) Calculator, version 1.0.0, last verified 2026-08-30. It rests on:
- Percent of Gmm = Gmb ÷ Gmm × 100, and air voids = 100 − percent of Gmm. Both follow from the definitions of the two gravities; no coefficient is involved.
- AASHTO T 166, Bulk Specific Gravity (Gmb) of Compacted Asphalt Mixtures Using Saturated Surface-Dry Specimens — the test the core's Gmb comes from
- AASHTO T 209, Theoretical Maximum Specific Gravity and Density of Asphalt Mixtures (Gmm) — the test the mix's Gmm comes from
This job is one of that calculator’s published test vectors, which the test suite re-runs on every build.
Frequently asked questions
- How is asphalt in-place density calculated?
- As the core's bulk specific gravity divided by the mix's theoretical maximum specific gravity, times a hundred. For this core that is 89.93 %, with air voids of 10.07 %.
- What happens if a core is below the specified minimum?
- The calculator only states the margin, -2.07 % here. What follows, from more cores to a pay adjustment or corrective work, is set by the contract's specification.
- Why are edge cores often lower?
- An unsupported edge cannot be compacted as well as the middle of a pass. A core from the middle of this mat measures 93.73 % against 89.93 % at the edge.