7.2 Sample, Bowl Filling, Consolidation, and Strike-Off

Creating a Valid Concrete Volume in the Bowl

A C173 result starts with the sample, not with the first reading in the neck. The concrete placed in the measuring bowl must come from the properly obtained field sample and should be remixed enough to restore uniformity without changing the mixture. If mortar, coarse aggregate, or water has separated in the sample container, the technician must correct the handling problem before filling the rollameter bowl.

The bowl is the measuring chamber. Its known volume is the reference for the percent air reading. That means the technician must fill it using the required layers, consolidation method, and strike-off procedure. The exact current ASTM steps control the details, but the JTA-level concept is simple: fill the bowl completely, consolidate consistently, avoid trapped placement voids, and finish with the concrete level to the rim.

Consolidation is a balance. Too little consolidation leaves large artificial voids that are not the intended air system. Too much or careless consolidation can disturb the concrete, splash material out, or create a nonrepresentative volume. For rodding, the rod should penetrate the layer as required and the sides of the bowl should be tapped enough to close rod holes and release large pockets. For vibration, the vibrator is used only when permitted or required by the concrete consistency and procedure.

The strike-off step is more important than it looks. The final surface represents the exact concrete volume being tested. A high mound increases the concrete volume, while a low surface decreases it. Mortar or aggregate left on the flange can also prevent the upper section from sealing. The candidate should think of strike-off and rim cleaning as measurement controls, not cosmetic work.

A careful technician also watches for concrete that is not workable enough for the chosen consolidation method. Harsh or low-slump concrete can trap large placement voids if handled casually. Very fluid concrete can segregate or splash during rodding. ACI exam questions may ask which step protects the validity of the test; the answer is usually the step that preserves a representative, correctly consolidated, known volume.

Use this quick field checklist:

• Confirm the concrete sample is fresh, protected, and remixed to uniformity.
• Inspect the bowl rim and interior before adding concrete.
• Fill in the required layers for the apparatus and concrete condition.
• Consolidate each layer as specified without loss of material.
• Tap or close voids as required by the method.
• Strike off flush and clean the rim before attaching the top section.

Once the bowl is struck off, the technician should avoid delay. The concrete is already the basis of the test, and evaporation or stiffening can affect the remaining steps. A valid rollameter result depends on carrying this controlled volume into the liquid, alcohol, inversion, rolling, and reading phases without contamination or loss.