Thickness and density measurement, verification, and sampling
Thickness
ASTM E605 uses a thickness gauge with pins that penetrate the SFRM to the substrate. Measurements are taken perpendicular to the steel at random, representative locations, and the gauge reading is the distance from the outer surface to the substrate. Record individual readings, the average, and the minimum. The approved design thickness is the acceptance target; confirm the project's frequency, commonly one set per 1,000 ft² per floor, but the specification controls.
Density
Density is a dry unit weight. Take a full-depth core or saw-cut sample, measure its volume (diameter and thickness), dry it to constant weight at the temperature the method specifies, and calculate density = dry mass ÷ volume. Compare with the manufacturer's listed density. A wet or improperly dried sample will read falsely high or low.
Worked example
A 2.0 in. diameter core is 1.00 in. thick. Volume = π(1.0)² × 1.00 = 3.14 in³. The oven-dry mass is 12.5 g. Density = 12.5 ÷ 3.14 = 3.98 g/in³; multiplying by 3.81 gives 15.2 lb/ft³. The product requires 15 lb/ft³ minimum, so the sample passes. The inspector records the location, core dimensions, dry mass, and calculation.
Traps
Taking density from a wet sample; measuring thickness only at the easiest, thickest spot; using a tape measure instead of a pin gauge; forgetting to mark and map test locations; comparing average thickness while ignoring a thin minimum.