Volumetric Air Meter: How to Accurately Measure Air Content

Have you ever wondered how construction professionals ensure the strength and durability of concrete structures? One essential aspect is accurately measuring air content in freshly mixed concrete. In this blog post, we’ll explore the Volumetric Air Meter, a crucial tool for achieving this goal, and delve into the ASTM C173 Test, a standardized procedure for measuring air content. Get ready to enhance your understanding of this critical aspect of concrete testing!

Key Takeaways

A Volumetric Air Meter is an essential tool for measuring air content in concrete.
ASTM C173 Test requires safety precautions, proper mixing and curing of test specimens.
Calibration frequency should be determined based on the manufacturer’s recommendations to ensure accurate measurements and quality assurance.

Understanding the Volumetric Air Meter

The Volumetric Air Meter serves as a vital tool that measures the volumetric air content in freshly mixed concrete. This air content is vital in predicting the strength and weight of concrete, which directly impacts the quality and safety of construction projects. The ASTM C173 test is a widely accepted method for determining air content and is especially useful for lightweight concrete or concrete with highly porous aggregate.

The meter determines precise air content measurements by confining air in the concrete sample and employing water displacement to ascertain the volume of trapped air. The outcomes of this test can considerably impact and determine the concrete’s capacity to withstand freeze-thaw cycles, a key factor for the long-term durability of structures.

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Components of the Volumetric Air Meter

A Volumetric Air Meter consists of several components, including:

Measuring bowl: serves as a container for the newly blended concrete during the air content examination
The top section: houses various valves and plugs that work together to measure the base volume and air content in the concrete
Additional alcohol: in some cases, more alcohol may be added to the water in the measuring bowl to reduce the surface tension of the water for more accurate air content measurements.

The functionality of a Volumetric Air Meter heavily depends on its top section, which includes a sight tube. It attaches to the bowl, forming a sealed chamber that facilitates the measurement of the air content of the concrete. A funnel may be used to introduce water and alcohol into the top section of the meter during the test. Additionally, the meter includes various valves, such as needle valves, ball valves, and flow control valves, which control and measure the air content.

How the Volumetric Air Meter Works

The working principle of a Volumetric Air Meter is based on the rotation of a multiple-bladed rotor mounted within a pipe perpendicular to the fluid flow, which enables the measurement of air content at the liquid level. Water displacement is utilized to measure the volume of entrapped air in concrete, based on the principle that air can be displaced by water.

Upon submerging a concrete sample in water, the liquid displaces the air within the concrete. By calculating the volume of water displaced, the volume of entrapped air in the concrete can be determined. The compressibility of air enables units of the Volumetric Air Meter to encapsulate it within the concrete.

The Volumetric Air Meter offers reliable and efficient results when measuring air content in concrete, with an accuracy threshold for two tests conducted by different operators at 0.8%.

Performing the ASTM C173 Test with a Volumetric Air Meter

The ASTM C173 Test represents a standardized method that employs a volumetric air meter for measuring the air content of concrete. By following the test steps outlined in the ASTM C173 procedure, construction professionals can accurately measure air content in freshly mixed concrete, part number which plays a crucial role in predicting the concrete’s strength, weight, and resistance to freeze-thaw cycles.

To ensure the accuracy of the results, it is important to follow safety precautions and guidelines specified in the Manual of Aggregate and Concrete Testing, as well as instructions such as those outlined in ASTM C31 for making and curing concrete test specimens in the field. Proper mixing and curing of the concrete test specimens are also essential for obtaining accurate air content measurements.

Preparing the Concrete Sample

In preparation for the ASTM C173 test, it’s vital to obtain a representative sample of fresh concrete as delivered to the construction site. To accomplish this, follow the sampling procedure outlined in ASTM C172, ensuring that the mortar is not disturbed and that the material is properly mixed before testing.

Mixing the material before testing in ASTM C173 is crucial to ensure that air bubbles in the concrete are evenly distributed, incorporating any air-entraining admixtures and preventing the loss of air content during transportation, pumping, and handling of the concrete mix. Proper handling of the sampling receptacle is also critical, as it helps to avoid spilling or disturbing the mortar during concrete sampling for the ASTM C173 Test. Check the Extra guide Concrete Slump Test.

Filling the Measuring Bowl

During the ASTM C173 test, accurately filling the measuring bowl is a critical step that can influence the precision of the air content measurement. The measuring bowl should be filled using a tamping rod that is at least 4 inches greater than the depth of the measuring bowl, ensuring proper filling of the bowl with the concrete sample.

To ensure a watertight seal when filling the measuring bowl with concrete in a Volumetric Air Meter, it is recommended to wet the inside of the top section of the meter, including the gasket, before attaching the top section to the measuring bowl. The sealed meter should be shaken upside down and from side to side for up to 5 seconds to ensure a complete and uniform distribution of the concrete. By following these steps, a watertight seal should be achieved, ensuring accurate air content measurements.

Adding Water and Alcohol

In the ASTM C173 test, water and alcohol are added to the air meter top and bowl to facilitate accurate air content measurements. It is recommended to use 70% isopropyl alcohol for this purpose.

The protocol for incorporating water and isopropyl alcohol into the air meter top and bowl involves introducing at least one pint of water, followed by the designated quantity of isopropyl alcohol. To add water and alcohol correctly, it is crucial to ensure that the correct quantities are introduced, as incorrect amounts can result in inaccurate air content measurements. The amount of alcohol used for concrete can vary. This depends on the type of cement, the quantity of cement, and any admixtures added.

Inversion and Rolling Process

The inversion and rolling process is a vital step in the ASTM C173 Test, as it serves to create and stabilize air pressure inside the volumetric air meter by agitating the concrete mixture and allowing any trapped air bubbles to escape to the surface. This ensures that the air content measurement is accurate and consistent.

To properly execute the inversion and rolling process using a foam rubber mallet, follow these steps:

Invert the sealed meter and shake it from side to side for up to 5 seconds.
Return the meter to its original position.
Repeat the inversion and shaking process for a minimum of 45 seconds or until the concrete has broken free and the aggregate can be heard moving in the meter.

Tilt the meter approximately 45 degrees and vigorously roll and rock the unit. This process helps ensure the unit has an accurate and reliable air content measurement.

Calibrating Your Volumetric Air Meter

To maintain accurate and reliable air content measurements, it’s crucial to regularly calibrate your Volumetric Air Meter. Calibration should be performed at least every three months to ensure accuracy, or as specified by the manufacturer.

Calibration involves determining the volume of the calibrated cup, also known as the air meter bowl, by filling it with water and weighing it. Proper calibration ensures that the meter provides precise measurements of entrained air in fresh concrete, which is crucial for sustaining the quality and safety of the concrete. Using calibrated cups in this process guarantees accuracy and consistency in the measurements.

Calibration Frequency

The regular calibration of a volumetric air meter is crucial for providing accurate and consistent results. A new volumetric air meter should be calibrated on an annual basis, although the frequency may be modified depending on the application, industry regulations, or quality assurance requirements.

It is important to calibrate your volumetric air meter if the dial reading varies by a margin of +/- 0.2% or more from the actual air volume. Adhering to the manufacturer’s recommendations for calibration frequency can help ensure the accuracy and reliability of your meter. Read this blog Glass Thermometer.

Calibration Procedure

Calibrating the volume of the air meter bowl involves the following steps:

Weigh the bowl empty.
Fill the bowl with room temperature water, ensuring the liquid level is accurate.
Weigh the full bowl with the glass plate on top.
Take the temperature of the water to find the density of that water using that temperature.
Subtract the empty weight from the full weight of the water.
Divide the resulting number by the density of the water in lb/ft3 to accurately calculate the volume of the bowl.

Several methods are available for verifying the calibration of a volumetric air meter, such as the gravimetric method and the pressure air meter method. Annual calibration, or as specified by the manufacturer, ensures that your volumetric air meter provides precise measurements of air content in fresh concrete and steel.

Troubleshooting Common Issues

As is the case with any equipment, encountering issues when using a Volumetric Air Meter is not unusual. By troubleshooting these common issues, you can maintain accurate air content measurements and ensure the quality and safety of your concrete projects.

Some common issues include difficulty in dislodging all concrete from the air meter base, clogging of valves due to concrete buildup, pressure gauge failure, and leakage when using the meter cap. In this section, we’ll delve into two of these issues: inconsistent initial meter readings and handling large aggregates.

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Inconsistent Initial Meter Readings

Factors such as improper calibration, scaling of the flow meter signal, or the unsuitability of the measured fluid for the meter could lead to inconsistent initial meter readings in a Volumetric Air Meter. To troubleshoot this issue, you should consider:

Checking the scaling of the flow meter signal
Ensuring that the measured fluid is suitable for the meter
Verifying the proper placement of the initial pressure line on the gauge of the air meter
Checking for any obstructions or blockages in the meter or the air supply line.

If the issue persists, make sure to follow these steps:

Check if the air pressure regulator is functioning correctly and delivering the desired pressure.
Consult the manufacturer’s troubleshooting guide for further assistance.
If necessary, seek professional assistance.

Dealing with Large Aggregates

Large aggregates can impact Volumetric Air Meter readings if aggregate correction factors are not taken into account. This could lead to the air content being reported at a higher percentage than what is actually present in the concrete. It is essential to consider these factors to guarantee precise air content measurements.

When handling large aggregates in a Volumetric Air Meter, it is recommended to:

Ensure that the air meter top has a volume that is at least 20% larger than the aggregate being used.
Listen for the sound of the aggregate sliding in the meter to ensure proper measurement.
Use a strike-off bar to level the concrete surface and remove excess air.

Moreover, the aggregate correction load factor should be taken into account when calculating the air content.

Summary

In conclusion, the Volumetric Air Meter is a vital tool for measuring air content in freshly mixed concrete, ensuring the strength and durability of concrete structures. By understanding the meter’s components and working principle, performing the ASTM C173 Test, calibrating the meter, and troubleshooting common issues, construction professionals can maintain accurate air content measurements and contribute to the quality and safety of their projects. Armed with this knowledge, you are now better equipped to tackle the challenges of concrete testing and construction.

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Frequently Asked Questions

What is the volume of the volumetric air meter?

The volume of the volumetric air meter is 2,200ml, with a sight tube graduated from 0 to 9.0in 0.25% increments. It comes complete with all the necessary accessories for use.

How do you test air content in concrete?

To measure the air content of concrete, a Type B pressure meter is used. It requires placing the measure on a firm level base and filling it to the point of about one-third of its volume before rotating the bottom layer 25. Finally, the air content is read off the dial which is calibrated for each apparatus and then adjusted using the aggregate correction factor.

What is the volumetric method of concrete?

The volumetric method is an ASTM C173 standard test which requires agitating the concrete in a closed water-filled vessel to free the entrained air, measuring it by noting the drop in water level.

What is ASTM C173?

ASTM C173 is a Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method. It is available both as a physical test and an eLearning course.

What is a roll meter?

A roll meter is a device used to accurately measure the air content of concrete mixes, providing reliable results with any mix, especially lightweight aggregate concrete.