Asphalt Compaction Calculator
Check density and air voids from matching Gmb and Gmm values, or plan loose lift thickness separately.
Asphalt Compaction Calculator
Asphalt compaction results
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Two compaction checks that should stay separate
The density mode is for field or laboratory quality control. It compares measured bulk density (Gmb) with maximum theoretical density (Gmm) for the same asphalt mix.
The loose lift mode solves a different jobsite question: how thick the uncompacted mat must be to reach a specified finished thickness after an assumed thickness reduction. That reduction is not a substitute for a core or density test.
Density and air-void formulas
Percent compaction = Gmb ÷ Gmm × 100. Air voids = (Gmm − Gmb) ÷ Gmm × 100. The same ratio works with density readings when both values use the same units and the reference is theoretical maximum density.
For loose lift planning, required loose thickness = target compacted thickness ÷ (1 − thickness reduction as a decimal). Use the factor in the paving plan, mix guidance, or established field procedure. A generic factor is only a planning assumption.
Use the project target, not a universal pass mark
The optional target field gives a simple above-or-below check. It does not apply agency lot averaging, percent-within-limits rules, pay factors, test-location rules, or measurement uncertainty.
FHWA materials describe asphalt density specifications in terms of Gmb and Gmm, while the Asphalt Institute notes that the reference may instead be a laboratory density or control strip. Match the calculator inputs to the reference named in the contract documents.
Technical references
- FHWA LTPP data guide: gives the Gmb/Gmm air-void equation.
- FHWA asphalt density technical documents: explains why Gmb and Gmm are central to in-place density specifications.
- Asphalt Institute engineering FAQs: discusses density references, air voids, and lift thickness.
- Asphalt Institute testing overview: maps Gmb, Gmm, and air-void measurements to common AASHTO and ASTM methods.
Related quantity checks
FAQ
How do you calculate asphalt percent compaction?
Divide the measured bulk specific gravity or field density by the maximum theoretical specific gravity or density for the same mix, then multiply by 100. Do not mix specific gravity with density units in the same calculation.
How do you calculate asphalt air voids from Gmb and Gmm?
Air voids equal 100 times (Gmm minus Gmb) divided by Gmm. When percent compaction is referenced to Gmm, air voids also equal 100 minus percent compaction.
Is 93% asphalt compaction always the requirement?
No. Agencies and project specifications use different targets, acceptance ranges, test methods, lot rules, and pay factors. Enter 93% only when it matches the current project documents.
Is thickness reduction the same as percent compaction?
No. Thickness reduction is a loose-to-finished placement factor. Percent compaction compares a measured bulk density with a reference density. Keep the two checks separate.
Where do Gmb and Gmm come from?
Gmb usually comes from a compacted specimen or pavement core. Gmm, often called Rice value, comes from the current asphalt mix and represents its maximum theoretical specific gravity without air voids.