What is the Air permeability test for concrete?
Air permeability testing of concrete structures evaluates the surface concrete's resistance to air and, by extension, fluid penetration.
This test serves as a critical indicator of the concrete's durability, directly impacting its long-term performance and susceptibility to environmental degradation.
High air permeability suggests a higher potential for structural deterioration.
How does Air permeability testing work?
Air permeability testing of concrete structures involves applying air pressure (positive or negative) to the concrete's surface and monitoring the rate of air pressure change within the measurement cell.
Devices are usually composed of an inner and an outer vacuum cell and work by applying vacuum pressure in one chamber and recording the pressure change in another (Figure 2).
This method assesses the concrete's porosity and its resistance to air flow, providing insights into the material's durability, quality, and potential for protecting reinforcement against corrosion and other environmental effects.
What is Air permeability testing used for?
Deterioration process | Defects | Control of repairs |
Reinforcement corrosion | Variation in quality of concrete | Concrete in-situ quality control (durability indicators) |
How do I carry out Air permeability testing?
There are limited standards documents concerning the air permeability testing of concrete structures. The Swiss Federal Highway Administration however issued recommendations in a document titled “Recommendations for the quality control of concrete with air permeability measurements” that have become the principal guidance document. A simple procedure based on this would be:
Ensure the concrete surface is clean and free of loose particles.
Mark the test area to ensure consistent testing locations.
Assemble the air permeability testing device according to the manufacturer's instructions and ensure the device is calibrated and ready for use.
Measure and record environmental conditions (temperature, humidity) as they can affect test results.
Determine the moisture condition of the concrete surface, ensuring it's within acceptable limits for testing.
Securely attach the testing device to the concrete surface. For methods like the Torrent, this involves creating a vacuum seal on the surface. For tests requiring a drilled hole carefully drill the hole as per the specifications, ensuring minimal impact on the concrete integrity.
Initiate the test sequence, typically involving the creation of a differential pressure across the concrete surface and measuring the rate of air flow or pressure change over time, then monitor and record the pressure changeover time.
Carefully remove the testing device from the concrete surface, if a hole was drilled, seal it according to best practice guidelines to prevent future ingress of water or contaminants.
Analyse the recorded data to calculate the air permeability coefficient or other relevant metrics.
Compare the results against established benchmarks or standards to assess the concrete's quality and durability and compile the findings into a report, including all relevant data, environmental conditions, and any deviations from standard procedures.
Provide recommendations or conclusions based on the test results.
What equipment and expertise are required for Air permeability testing?
A variety of testing equipment and methodologies have been developed, each based on a range of principles designed to measure the permeability of concrete. Notable examples include the AutoClam from Amphora NDT, Figg and Torrent Air Permeability Testers with each employing distinct approaches to evaluate the cover concrete's ability to resist the ingress of harmful substances.
Figg type models such as the Poroscope Plus require a 5.5 mm-diameter hole to be drilled into the concrete, the device then creates a vacuum pressure within it and a manometer tracks pressure changes from air permeating through the concrete structure. These small blemishes may mean this device in unsuitable for architectural concrete, concrete in aggressive exposure conditions or for ongoing monitoring of elements over time.
The AutoClam device works in a similar manner by applying controlled vacuum pressure and measuring the rate of air pressure decay. The AutoClam however does this on the surface of the concrete with four screws holding it in place. Designed for versatility across various concrete types and conditions, the AutoClam is user-friendly, requiring no specialized expertise for operation, thus ensuring reliable, consistent results in evaluating concrete's resistance to water and air ingress.
Torrent Air Permeability Testers like those from Proceq use a two-chamber vacuum cell mechanism to measure air permeability (Figure 4). Initially, a vacuum is created within these chambers sealed against the concrete surface, the system then isolates the inner chamber to monitor the pressure increase caused by air flow through the concrete into this chamber.
The rate of this pressure rise is directly related to the concrete's air permeability, allowing for the calculation of the permeability coefficient. This system does not require any drilling or alterations to the concrete surface leaving no sign the test has been carried out.
What are the advantages of Air permeability testing?
Allows for a detailed assessment of the concrete's surface condition, providing a metric for evaluating the concrete's potential durability and susceptibility to environmental degradation.
By identifying areas of higher permeability, it enables targeted maintenance, potentially extending the structure's service life and avoiding costly repairs.
Enables comparisons across different sections of a structure or between different structures, based on established benchmarks.
Identifies potential issues early, reducing long-term repair costs.
Acts as a benchmark for concrete quality, ensuring consistency across batches and suppliers.
Provides insights into concrete's resistance to all forms of ingress such as chlorides, sulphates and carbonation, freeze-thaw cycles and chemical attacks, critical in harsh environments.
Strong correlation between this test and chloride ingress test but through a much simpler test at much lower cost.
What are the disadvantages Air permeability testing?
Requires specific surface conditions, making it challenging to test weathered or treated surfaces accurately.
The concrete's internal humidity can affect readings, necessitating additional moisture content assessments.
Different equipment models may yield varying results, complicating comparisons.
Results require expert interpretation to inform meaningful action, potentially limiting utility for non-specialist.
Primarily assesses surface permeability, which may not represent the entire structure's condition.
Results can be affected by surface conditions and moisture.
Concrete surface may need to be dried for 48 hours reducing speed of results or suitable corrections made to results based on electrical resistivity tested moisture levels.
How accurate is Air permeability testing?
The accuracy of air permeability testing in concrete varies with the device used, influenced by factors such as calibration, environmental conditions, and the concrete's surface state.
While specific accuracy figures for methods like Torrent, Figg, or AutoClam are not directly provided, these methods have their unique approaches affecting precision.
What are the limits of Air permeability testing?
Air permeability testing of concrete structures offers insights into durability but comes with limitations. Variability in concrete composition can lead to inconsistent results, and such testing does not delve into deeper structural issues, often missing signs of significant deterioration or internal flaws.
Accurate data requires fully cured concrete, with environmental conditions like humidity and temperature affecting outcomes. Moreover, equipment calibration and operator skill significantly influence reliability.
The method is less effective on very moist surfaces, where securing an airtight seal for the instrument poses challenges, underscoring the need for a multifaceted approach to concrete assessment.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Inspector and specialist
Service disruption: No
Preliminary works: Yes
Time consumption Medium (one day)
Cost Medium
Access to element 1 face
References and further information