The performance-engineered-mixtures (PEM) approach to concrete design is increasing traction around the country and one beloved benefit is the greater pavement durability at lower cost! To justify the cost of PEM testing, pavement owners and contractors alike need to know why a given test is important, what it tells us, how it is run, and how to interpret its output. The Concrete Pavement Technology Center (CP Tech Center) recently published a series of one-page flyers on 4 tests that each address these aspects:
› Why do we need this test?
› What does the test tell us?
› How does the test work?
› What [equipment] do I need?
› What do the numbers mean?
The 4 TEST FLYERS:
VIBRATING KELLY BALL (VKelly) TEST: One of the six critical concrete mixture properties defined under the PEM program is workability. For slipform pavements, this is defined by the need for the mixture to be fluid when in the paver and able to stand up when the machine moves on.
With increasingly complex mixtures and placement processes, the need is increasing to measure how a mixture responds to vibration. The Vibrating Kelly Ball (VKelly) test meets that need—a test primarily intended for the mixture proportioning and approval stage of a project when selecting aggregate systems and the cementitious contents of a mixture. Developing a workable mixture during this stage results in several improvements that can lead to savings:
• Reduced cementitious content
• Reduced finishing effort
• Improved ride
• Improved durability
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Mixtures with similar slumps may respond very differently when a vibrator is applied to a mixture. The VKelly test directly measures how fluid a mixture becomes when it is vibrated. KELLY BALL TEST FLYER: https://intrans.iastate.edu/app/uploads/2020/08/PEM_VKelly_test_sheet.pdf
BOX TEST: The Box Test also addresses workability and meets the need to measure how a mixture responds to vibration. The Box Test is primarily intended for the mixture proportioning and approval stage of a project when selecting aggregate systems and the cementitious contents of a mixture. Developing a workable mix during this stage results in several improvements that can lead to savings:
• Reduced cementitious content
• Reduced finishing effort
• Improved ride
• Improved durability
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Mixtures with similar slumps may respond very differently when a vibrator is used during placement. The Box Test indicates how well a mixture will be consolidated with a given amount of energy and if it is prone to edge slump. BOX TEST FLYER: https://intrans.iastate.edu/app/uploads/2020/08/PEM_Box_Test_sheet.pdf
SUPER AIR METER (SAM) TEST: It is well understood that freeze–thaw durability of concrete is dependent on the size, distribution, and volume of air bubbles entrained in the concrete through the use of air-entraining admixtures (AEAs).
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Historically, measurement of the distribution of air voids in fresh concrete has been impossible, forcing specifications to rely on measurement of total air volume. This approach was reasonable when all AEAs were based on a single chemical. However, with an increasing range of products available, the correlation between air volume and bubble spacing is no longer precise. The SAM was developed to address this shortcoming.
Conducting the test during prequalification reassures agencies that the proposed mixture has the potential to be freeze-thaw durable. Testing at the point of delivery confirms that the mixture in the truck complies with the specification.
Reducing the amount of nondurable concrete in place will lead to savings in repairs and maintenance for agency owners.
SUPER AIR METER (SAM) TEST FLYER: https://intrans.iastate.edu/app/uploads/2020/08/PEM_test_SAM_sheet.pdf
RESISTIVITY TEST: Experience has shown that most premature failures in concrete pavements are due to durability-related factors and that historical approaches to specifications based on strength have proven to be insufficient.
All durability-related distresses in concrete involve the movement of moisture (transport); therefore, a fundamental part of extending pavement life is to reduce the permeability of the concrete matrix.
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The ability to specify and deliver concrete with low permeability significantly reduces the cost of ownership over time. The resistivity test has been shown to be faster, less expensive, and more reliable than approaches used in the past.
The resistivity test provides a nondestructive means to assess whether a given mixture has low permeability as an indicator that the concrete has the potential to survive exposure to the environment…
RESISTIVITY TEST FLYER: https://intrans.iastate.edu/app/uploads/2020/08/PEM_test_resistivity_sheet.pdf
These 4 FLYERS supplement other more detailed information on the CP Tech Center PEM resources webpage that includes:
• How-to VIDEOS
• Data calculation TEMPLATES, and
• Demonstration project REPORTS
For the FLYERS, please click on the links under each headline, or the headline itself.
For the CP Tech Center resources webpage, please go to: https://cptechcenter.org/performance-engineered-mixtures-pem/