Asphalt Core Samples: What Should You Know Before Testing Your Parking Lot?
Before authorizing asphalt core sampling, ask what decision the samples will support, where they will be taken, which tests are included, and who will restore the openings. A core is a drilled cylindrical pavement sample, not a complete diagnosis by itself. Its value comes from connecting the sample, its location, and the test results to a specific question about your property.
Start with the question, not the drill
Are you investigating an older parking lot before planning repairs, or checking newly placed asphalt against the project requirements? Write that purpose at the top of the testing request. Ask the evaluator to explain what a result could change: the repair recommendation, the need for additional investigation, or the acceptance review. If nobody can explain the decision, clarify the assignment before scheduling sampling.
FHWA's archived pavement research guide describes examining asphalt cores, measuring their thickness, and identifying individual layers within them. Separately, its density demonstration report describes agencies using cores to evaluate in-place density. Those are different uses of a sample. A request to take cores should therefore name the measurements or tests being purchased, rather than leave you expecting every possible answer from one service.
Make every sample traceable to a place
Ask for a location sketch with a unique identifier for each planned sample. Use those identifiers in the photographs, field notes, and final report. For a Middle Tennessee shopping center, a description such as rear lot may be too broad for a manager who was not present. A marked image showing the entrance, loading area, and sample positions makes the record easier to use later.
Let the testing professional explain the sampling strategy. Ask whether locations target a particular concern or are intended to support a broader evaluation, and what limits that places on the conclusions. Do not quietly relocate a planned sample simply because a car occupies the space; coordinate any change with the person responsible for the investigation.
Share available paving records and identify known patches or additions. Keep uncertain history labeled as uncertain. You can say that the rear section appears different without claiming to know when it was built. Ask the report writer to state which areas the findings address instead of treating one location as an automatic verdict on the whole property.
Request a report you can connect to the decision
For each sample, request its identifier, collection date, reported measurements with units, tests performed, and any condition that limited interpretation. FHWA's research procedure distinguishes the thickness of an entire core from the thicknesses of its individual layers. If the assignment concerns a recent overlay, ask which reported measurement belongs to that work rather than assuming the full core length is the new pavement.
Keep the observations and recommendation separate. Ask the evaluator to identify what was measured, what the result suggests, and what remains unknown. When the report includes a density percentage, request the reference used to calculate it and the applicable project criterion. FHWA's demonstration report describes density comparisons using theoretical maximum specific gravity; the percentage needs its context, not an owner-selected passing number.
The FHWA documents linked below explain testing concepts and research practices. They do not establish acceptance requirements for your private parking lot. Ask the responsible project professional to explain how the actual contract and specified testing methods apply to your results.
Include the holes and the handoff in the assignment
Before the crew arrives, settle who coordinates access, keeps the sampling area unavailable while work is underway, and handles the resulting openings. Ask whether restoration is included in the testing price, who performs it, and who confirms when the area can reopen. Put these answers in the work order so the testing visit does not end with an unresolved maintenance task.
At closeout, keep the location sketch, report, restoration confirmation, and recommended next step together. If further testing is proposed, ask which unanswered question it addresses before authorizing another visit.
Milliken Corporation lists asphalt parking lot repairs, replacements, and overlays among its services. When discussing a repair proposal, provide any existing core report and explain why testing was done. Ask who should coordinate specialized testing for your project; do not assume laboratory services are included in a paving proposal.
Frequently asked questions
Does taking a core mean the asphalt has failed?
No. Cores can be collected for investigation or quality evaluation. Ask why sampling was requested and wait for the interpreted results before drawing a conclusion.
Is core thickness the same as overlay thickness?
Not necessarily. A core can contain multiple layers. Ask the report writer to identify the layer relevant to your project.
Who fills the core holes afterward?
Confirm that responsibility in the testing assignment before work begins, including restoration scope and reopening coordination. Do not assume a separate paving contractor is already scheduled.