Your Asphalt Density Report: What Is That Percentage Measured Against?
An asphalt density percentage is meaningful only when you know its reference value, where the pavement was tested, and which project criteria apply. Before treating a report as a pass or fail, ask the testing provider to connect the results to the installed mixture, pavement layer, and agreed acceptance requirements. A percentage alone is not a complete paving closeout record.
Start with the denominator, not the biggest number
The Asphalt Institute describes several bases for density targets: a laboratory-compacted mixture, a project test strip, or the mixture's theoretical maximum density. These are different reference points. Two reports showing the same percentage are not necessarily describing the same degree of compaction if their reference bases differ.
Ask the report's author to spell out abbreviations and identify the reference used. If the report names Gmm, ask which mixture and production record that value belongs to. FHWA's density demonstration summary discusses using theoretical maximum specific gravity from plant-produced material to calculate percent density. That connection matters more to an owner than memorizing an isolated target number.
Keep the request simple: Please identify the measured result, the reference value, and the criterion used to evaluate it. If the summary only says compaction passed, request the supporting report rather than asking someone to reconstruct the calculation from memory.
Give every result a place on your property
Request a sketch or marked plan connecting test identifiers to recognizable locations. For a Middle Tennessee commercial property, labels such as rear delivery lane, main entrance, and north parking aisle may be easier for the maintenance team to retain than an unexplained list of sample numbers. Keep any formal stationing or coordinates as well; a convenient nickname should not replace the testing provider's identifiers.
Ask which pavement layer was evaluated and when it was placed and tested. If paving occurred over several days, make sure the report distinguishes those work areas. If it covers only one phase, record that boundary instead of filing it as the report for the entire parking lot.
Also ask how the measurements were obtained. A report should identify its test method, not leave you guessing whether the numbers came from cores or field equipment. Let the testing professional explain method limitations and any correlation or supporting laboratory information needed to interpret the results.
Read the individual results alongside the summary
An average can conceal variation. As a simple arithmetic example, two different sets of numbers can have the same average even though one set contains a much lower individual result. Ask to see the underlying results and how the project's acceptance method treats them, rather than assuming a satisfactory average resolves every location.
FHWA's demonstration summary discusses both statistical acceptance and lot-average approaches with individual-result considerations. It is guidance for highway agencies, not an automatic specification for your driveway or private parking lot. Do not borrow a highway threshold from an internet search and apply it retroactively to a different contract.
If a result is flagged, ask who will review it, what additional information is needed, and when a written disposition is expected. Avoid jumping straight from a number to a demand for replacement. Equally, do not let an unexplained flag disappear into a general statement that the job is complete.
Close out the question, not just the document
Create one project folder containing the final report, location plan, applicable acceptance criteria, and the written response to any exceptions. Label preliminary reports clearly and retain the final version. If further testing is proposed, agree on its purpose, access arrangements, responsibility for costs, and how disturbed pavement will be restored before authorizing it.
For future work, discuss testing expectations during proposal review: Is density testing included? Who orders it? Who receives the report? Who interprets acceptance? Milliken's asphalt services include driveways, parking lots, repairs, and overlays. Ask which testing and documentation are included in your particular scope rather than assuming every project receives the same package.
Frequently asked questions
Does a higher percentage always mean a better result?
Do not rank results that way. First confirm the reference basis and the project's applicable acceptance criteria. Ask the testing professional to interpret the result within that framework rather than treating the highest number as the goal.
Can one passing test close out the whole parking lot?
Ask what area and layer the test represents and how the agreed sampling and acceptance plan works. Do not assume one location documents every paving phase or every part of the property.
What if density testing was not included in the proposal?
Discuss the concern with the contractor and an appropriate testing professional before ordering tests. Clarify what question testing could answer, who will interpret it, and how the added work will be authorized.