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 measures air content. It’s ideal for lightweight or porous aggregate concrete.
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.
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.
A Volumetric Air Meter’s functionality relies on its top section, which has a sight tube. This tube connects to the bowl, creating a sealed chamber. This chamber helps measure concrete’s air content. During tests, a funnel can add water and alcohol to the meter’s top. The meter also has different valves, like needle, ball, and flow control valves. These valves help control and measure the air content.
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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.
When a concrete sample is submerged in water, the water displaces the air inside the concrete. The displaced water volume helps calculate the concrete’s entrapped air volume. The Volumetric Air Meter uses air’s compressibility to measure this air within the concrete.
The Volumetric Air Meter delivers reliable and efficient air content measurements in concrete. It achieves an accuracy threshold of 0.8% across two tests by different operators.
Performing the ASTM C173 Test with a Volumetric Air Meter
The ASTM C173 Test is a standard method that uses a volumetric air meter to measure concrete’s air content. Construction professionals follow the ASTM C173 procedure to accurately gauge air content in freshly mixed concrete. This measurement is vital for predicting the concrete’s strength, weight, and freeze-thaw cycle resistance.
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 get a watertight seal in a Volumetric Air Meter, first wet the inside of the top section and the gasket. Then attach the top to the measuring bowl filled with concrete. Shake the sealed meter upside down and side to side for 5 seconds for uniform concrete distribution. These steps ensure a watertight seal for accurate air content measurements.
Adding Water and Alcohol
In the ASTM C173 test, water and alcohol are mixed in the air meter’s top and bowl for precise air content measurements. Using 70% isopropyl alcohol is recommended.
The protocol involves adding at least one pint of water and a designated quantity of isopropyl alcohol to the air meter top and bowl. It’s crucial to use the correct amounts. Incorrect quantities can lead to 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.
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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
It’s crucial to calibrate your Volumetric Air Meter regularly for accurate air content measurements. Perform calibration at least every three months. Follow the manufacturer’s guidelines for the best results.
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
Regular calibration of a volumetric air meter is essential for accuracy and consistency. A new meter should be calibrated annually. The frequency may vary based on the application, industry regulations, or quality assurance needs.
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 can verify a volumetric air meter’s calibration, including the gravimetric and pressure air meter methods. Calibrating annually or as the manufacturer specifies ensures precise air content measurements 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 affect Volumetric Air Meter readings. If aggregate correction factors are ignored, the air content may appear higher than it really is in the concrete. Considering these factors is crucial for accurate 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, you should take the aggregate correction load factor into account when calculating the air content.
Summary
The Volumetric Air Meter is crucial for measuring air in fresh concrete, key to the strength and durability of structures. Understanding its components, working principle, and performing the ASTM C173 Test are vital. Calibrating the meter and solving common problems help maintain accurate air measurements. This ensures project quality and safety. Armed with this knowledge, you are now better equipped to tackle the challenges of concrete testing and construction.
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?
A Type B pressure meter measures the air content in concrete. First, place the meter on a firm, level base. Fill it to about one-third of its volume. Then, rotate the bottom layer 25 times. Read the air content off the dial. Each apparatus has a calibrated dial. Adjust the reading 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?
The Volumetric Method, ASTM C173, actively measures the air content of freshly mixed concrete. It offers both a physical test and an eLearning course.
What is a roll meter?
A roll meter accurately measures the air content in concrete mixes, offering reliable results for any mix, especially lightweight aggregate concrete.
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