Pavement thickness is a structural specification. DOT projects require documentation at every stage — from base course elevation before paving to core sample results after compaction. Deficient thickness triggers pay reductions, corrective action requirements, or rejection. Understanding what documentation is required, when it must be submitted, and how deficiencies are handled protects the contractor's pay and avoids final acceptance disputes.
What documentation is required for pavement thickness on DOT projects?
DOT pavement thickness documentation includes: pre-paving base elevation verification; daily mat thickness checks during paving using a depth probe; core sample results at specified intervals (typically one core per 250-500 ton lot); and a thickness deficiency report with pay adjustment calculation when cores are below minimum. Federal-aid projects require core data retention for minimum 10 years and availability for FHWA review.
Pavement thickness documentation occurs at three distinct stages of construction, each serving a different QC function:
| Stage | Documentation Required | Purpose |
|---|---|---|
| Before paving — base elevation verification | Grid elevation survey; deviation table; QC manager sign-off | Confirms base is at or below design grade — the prerequisite for correct overlay thickness |
| During paving — mat depth checks | Depth probe readings at 25-50 ft intervals; daily log with station, offset, and measured depth | Real-time control to detect spreading issues before compaction locks in a deficient thickness |
| After compaction — core samples | Core logs with station, offset, measured compacted thickness, and diameter; AASHTO T166 density if specified | Final acceptance verification; basis for pay adjustment if deficient |
Core samples are the primary method of final thickness acceptance for asphalt pavement on DOT projects. The core log must document:
When cores show deficient thickness, the DOT specification defines the remedy. Most state DOTs use a tiered approach:
| Deficiency Magnitude | Typical DOT Response | Documentation Required |
|---|---|---|
| 0 to 1/4 inch below design | Full pay; no action required | Core log in QC file; no additional action |
| 1/4 inch to 1/2 inch below design | Reduced pay per pay adjustment formula (typically 5-15% reduction) | Deficiency report; pay adjustment calculation submitted to resident engineer |
| More than 1/2 inch below design | Rejection; contractor options: milling and overlay, additional overlay (if geometry allows), or accept reduced payment with engineer approval | Deficiency report; corrective action plan; approval before remediation; verification cores after correction |
Deficiency documentation must be submitted promptly — most DOT QC plans require notification within 24 hours of receiving deficient core results. Delayed notification after the contractor has already paved additional lots without correcting the root cause is treated as a QC plan violation.
Thickness deficiencies frequently trace back to base course elevation issues. When a core shows deficient thickness, the first question the resident engineer asks is: what did the base elevation verification show at that location? If the base was found to be above design grade at that station and paving was authorized anyway — that is a documentation failure with pay and liability consequences.
Sitemark links base elevation data to pavement records by station and offset, so when a thickness deficiency is investigated, the complete pre-paving condition record is immediately available.
Sitemark links pre-paving base elevation shots to post-compaction core results by station — giving you the complete thickness story for every lot when DOT inspection comes.
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