7.1 Scope, Equipment, and When the Volumetric Method Fits

Volumetric Air Method Purpose and Equipment

ASTM C173/C173M covers the volumetric air content of freshly mixed concrete. Instead of using pressure to compress air, the rollameter separates air from the concrete and collects that air as a volume shown by liquid movement in the graduated neck. That is why this method is useful when aggregate absorption, lightweight aggregate, or highly porous aggregate could distort a pressure-meter reading.

For ACI Field Testing Technician Grade I, the exam focus is not advanced materials theory. The focus is whether the technician can select sound equipment, prepare the sample, run the water and alcohol sequence correctly, roll until the reading is valid, and record the result with the required correction logic. The method is procedural, but the purpose is quality control: an air result can affect acceptance decisions, durability expectations, and mixture troubleshooting.

A rollameter has a measuring bowl, an upper section with a graduated neck, a clamp or locking system, a funnel, a cap, and accessories used to add liquid and alcohol. The bowl volume and neck scale must match the apparatus calibration. The top and bowl must seal under the rolling action. A leak during rolling is not a small nuisance; it changes the liquid level and destroys confidence in the air reading.

A field mistake often starts before concrete enters the bowl. Dirty threads, worn gaskets, hardened mortar on the flange, missing caps, or an unreadable neck scale can make the test fail even when the technician remembers the sequence. The performance exam rewards a deliberate setup because it shows that the candidate understands that air testing is a measurement, not a demonstration ritual.

The volumetric method also requires a representative sample obtained and controlled according to the sampling practice. Concrete that has segregated, dried, been retempered without authorization, or sat too long is not a reliable basis for an air result. The C173 procedure should be coordinated with slump, temperature, density, and specimen molding so that the shared sample still represents the delivered concrete.

Remember these scope points:

• Use the current ASTM C173/C173M and ACI program references for exact procedural tolerances.
• Know why the volumetric method is selected when the pressure method may be unsuitable.
• Treat the rollameter as calibrated measuring equipment, not just a container.
• Inspect sealing surfaces, clamps, neck readability, funnel, cap, and accessories before filling.
• Protect the sample and equipment from evaporation, contamination, vibration, and delay.

On written questions, the distractor often describes pressure-meter habits. On performance questions, the distractor is rushing into filling the bowl without checking the seal, the scale, or the liquid and alcohol supplies. A technician who knows the method can explain that C173 is valid only when the concrete volume is correct, the liquid system is sealed, and the rolling process releases air into a stable readable column.