IS 9799:1981 is the Indian Standard (BIS) for pressure meter for determination of air content of freshly mixed concrete. This standard lays down the specifications for the design, construction, and calibration of pressure-type meters used for determining the air content of freshly mixed concrete. It covers two main types of meters (Type A and Type B), detailing their constituent parts like the measuring bowl, cover assembly, and pressure gauge to ensure accuracy and consistency in testing.
Specification for pressure meter for determination of air content of freshly mixed concrete
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Method | Pressure (Boyle's law) — Type B air meter | Scope |
| Measures | Air content (%) of FRESH concrete | Scope |
| Strength cost | ≈ every 1% extra air → ~5% strength loss + short yield | Critical |
| Durability | Entrained air needed for freeze–thaw (hill/cold) | Critical |
| Control | A target BAND — wrong in either direction | Concept |
| Calibration | Calibrate + apply aggregate correction factor | Procedure |
| Test | As placed (after pumping/vibration), not as batched | Caution |
| Admixture | Verifies the air-entraining agent dose (IS 9103) | Cross-ref |
IS 9799:1981 is the specification for the pressure meter for determination of air content of freshly mixed concrete — the *Type B (pressure-method) air entrainment meter* used to measure entrained/entrapped air content of fresh concrete on site. Air content is a control parameter on two fronts: freeze–thaw durability (entrained air protects concrete in cold/hill regions) and strength/yield (excess air silently cuts strength and short-yields the mix).
It sits with fresh-concrete control:
The pressure meter applies Boyle's law: a known pressure is applied to a sealed concrete sample and the volume change reveals the % air. Two opposing concerns make it a true control parameter:
The engineering point: air content must be held in a target band — high enough for frost protection where required, low enough not to bleed away strength and yield elsewhere. The meter is how you verify the air-entraining admixture dose is actually delivering the designed air *at the point of placement*, not what the dosage chart promised.
Scenario: freeze–thaw exposure; air-entrained M30 specified with a target air content band.
Step 1 — calibrate the meter: zero/calibrate the IS 9799 pressure meter (and account for the aggregate correction factor) before the pour.
Step 2 — test at placement: fill and compact the bowl per the method, seal, apply pressure, read % air on fresh concrete *as placed* (not as batched — air changes with transport, pumping, vibration).
Step 3 — judge against the band: below target → frost durability at risk (increase AEA dose); above target → strength/yield bleeding away (reduce dose).
Step 4 — adjust & re-verify: tune the air-entraining admixture dosage and re-test until the air sits in the band, then control it through the pour.
Result: durable frost-resistant concrete that still makes strength and yield. Skipping the meter means trusting a dosage chart while pumping/vibration quietly moves the real air content out of the band in either dangerous direction.
1. Not measuring air at all (non-frost jobs). Excess air from over-dosed plasticisers/AEA quietly cuts strength and short-yields — invisible without the meter.
2. Trusting the AEA dosage chart over a measurement. Transport, pumping and vibration change air content; verify as placed.
3. Skipping calibration / aggregate correction. The pressure method needs the meter calibrated and the aggregate correction applied, or the % air is wrong.
4. Testing as-batched, not as-placed. The durability- and strength-relevant air is at the point of placement, after pumping/vibration.
5. One-sided thinking. Treating air as only-a-durability or only-a-strength issue — it is a *band*, wrong in either direction.
IS 9799 is reaffirmed and under-appreciated outside cold regions, but air content is one of the few parameters that is dangerous wrong in either direction: too little and freeze–thaw exposure scales the concrete off; too much and you have silently bought a strength and yield deficit on *every* pour. The Type B pressure meter is how you stop trusting an admixture dosage chart and actually verify the air *as placed*, after pumping and vibration have moved it. For Himalayan/hill and cold-region work, entrained air is a durability lifeline that must be measured and held in band; everywhere else, an unmeasured creeping air content is a quiet thief of strength and cubic metres. Calibrate the meter, apply the aggregate correction, test at the point of placement, and control to the target band.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Container Capacity | 0.005 m³ (5 litres) | 0.20 ft³ (≈ 5.7 litres) | ASTM C231 |
| Tamping Rod Diameter | 16 mm | 5/8 in (15.9 mm) | ASTM C231 |
| Compaction (for standard bowl) | In 2 layers, 'tamped thoroughly' | In 2 layers, 25 strokes per layer | ASTM C231 |
| Pressure Gauge Readability | 0.1% air content divisions | Graduated to 0.1% air content or finer | ASTM C231 |
| Nominal Operating Pressure | Approx. 0.1 N/mm² (≈ 14.5 psi) | Determined by calibration, typically 15 psi (103 kPa) | ASTM C231 |
| Maximum Aggregate Size | Not explicitly stated (typically ≤ 40 mm in practice) | 2 in (50 mm) | ASTM C231 |
| Vibration Frequency (if used) | ≥ 12000 vib/min (from IS 1199) | ≥ 9000 vib/min [150 Hz] | ASTM C231 |