Department of Transportation
for Road and Bridge Construction
NJDOT B-4 – Measuring Thickness of HMA Cores
- Scope. This test method is used to measure the individual lift thicknesses of drilled HMA cores.
- Apparatus. Use the following apparatus:
- Caliper device to measure the axial lengths of individual lifts to the nearest 0.001-inch mounted on a support.
- Support designed to hold the specimen with its axis in a horizontal position by 2 metal roller bearings sufficiently rigid and stable to maintain alignment without distortion or deflection.
- Gauge to calibrate and check the zero reference point of the apparatus.
Ensure that the apparatus accommodates specimens from 1/2 to 12 inches in length.
- Procedure. Perform the following steps:
- If the caliper device is electronic, turn it on. Ensure that the caliper device is zeroed and set to the correct units of measure.
- Place the specimen in the measuring apparatus with the smooth end of the core, which is the top or upper surface of the pavement, firmly against the zero reference point.
- Take 4 length measurements approximately 90 degrees apart around the circumference of the specimen using the caliper device to measure the distance from the zero reference point (top of the core) to the bottom of the first lift. If a measuring point is not representative of the plane of the core lift because of a small projection or depression, rotate the specimen slightly about its axis and take the measurement at the nearest representative point.
- Read each of the 4 measurements for the lift to the nearest 0.001 inch. Calculate the average of the 4 measurements for the lift to the nearest 0.01 inch and record.
- Repeat Steps 3 and 4 for each lift to be measured by measuring from the zero reference point (top of the core) to the bottom of the lift being measured.
- Report. Report the following to the nearest 0.01 inch:
- Average thickness of the first lift, which is the average distance for the first lift as determined in Step 4.
- Average thickness of the second lift, which is determined by subtracting the average thickness for the first lift from the distance measured in Step 4 for the second lift.
- Average thickness of subsequent lifts, which is determined by subtracting the average thicknesses for all preceding lifts from the average distance measured in Step 4 for the lift.
Last Document Correction:
December 14, 2007