What is a profilograph?

A profilograph is a wheeled frame that records how far a pavement surface departs from a straight reference line.

How it works

The frame is rigid and has support wheels at each end and one wheel in the centre. The support wheels set a reference line. The centre wheel measures how far the surface moves away from that line. A strip-chart recorder or a computer records the movement. Most units today have a computer. A crew pushes the frame by hand or tows it with a small vehicle.

On the California type, the support wheel systems are 25 feet (7.6 m) apart. The Rainhart type has twelve wheels along a 24.75 foot (7.5 m) frame. Its wheels are offset so that no wheel follows the same path. One South Carolina test method says to operate the California type at 3 miles per hour or less.

Profile index

The trace gives the profile index (PI). A blanking band lies over the trace. The common widths are 0.2 inch (5 mm) and zero. The heights of the scallops above and below the band are measured and added up. A deviation counts only if it is high enough and long enough. FHWA gives 0.6 mm (0.02 inch) and 0.6 m (2 feet). The South Carolina method sets 0.035 inch and 2 feet. The PI is stated per segment. What counts as acceptable depends on the agency and on the blanking band.

Limits

The profilograph is slow and unsuited to network-level data collection. FHWA reports that the California profilograph measures wavelengths of 3 to 4.6 m poorly. It amplifies wavelengths of 6.1 to 12.2 m by up to two times. Many agencies moved to the International Roughness Index (IRI) for a measure closer to ride quality. A computer calculates the IRI from inertial profiler data or other profile data.

Use in airfield construction

FAA AC 150/5370-10H gives a profilograph roughness test as an option in its asphalt (P-401, P-403) and concrete (P-501) items. The test applies to new or reconstructed runways and taxiways longer than 500 feet (150 m). It is not for aprons. The AC advises caution on rehabilitation projects unless they correct existing defects.

The specification asks for these points:

• The equipment meets ASTM E1274, or is a Class I inertial profiler that meets ASTM E950.
• The average profile index is less than 15 inches per mile per 1/10 mile, with a 0.2 inch (5 mm) blanking band.
• The runs are one foot and 15 feet left and right of the project centreline.
• A trained operator runs the unit, and the unit has a calibration before use.
• The contractor corrects bumps flagged “must grind”, and a second run checks the result (P-401).

A change to the limit needs a modification to standards under FAA Order 5300.1. The AC says the airport should keep a copy of the test report in its pavement maintenance programme.

The profilograph checks the smoothness of new work. The AC uses it as an acceptance test and does not describe it as a condition survey of an existing pavement.