The Super Air Meter (SAM) is a modified version of the ASTM C231 standard test method for measuring the air content of freshly mixed concrete by the pressure method. It is designed to measure the air-void spacing and air content of plastic concrete quickly, taking approximately 10 minutes. Note that void spacing is a better indicator of freeze-thaw durability than total air content, but it can be challenging to determine, especially in fresh concrete until the SAM.
By accurately measuring the actual air-void spacing in fresh concrete, the SAM allows for adjustments to be made before the concrete hardens, ensuring freeze-thaw durability. This capability enables practitioners to lower air content requirements in many mixtures, leading to greater strength development in hardened slabs and structures, as well as avoiding quality control issues associated with high air content. On the other hand, the SAM has also revealed that certain admixture combinations and construction practices may require higher air contents than typically specified to achieve the desired air-void spacing.
The primary modification of the SAM compared to the standard ASTM C231 device is the application of two sequential pressure steps to the concrete at 14.5, 30, and 45 psi to obtain a deformation figure. The difference between the first and second pressure steps yields the SAM number, which increases with the average spacing between air voids. Excessive spacing indicated by a higher SAM number alerts users to the concrete's susceptibility to freeze-thaw deterioration.
Research conducted at Oklahoma State University and the Federal Highway Administration Turner-Fairbank Highway Research Center has shown that a SAM number of 0.20 correctly determines over 90 percent of the time whether the spacing between air voids meets the ACI Committee 201 Durability of Concrete guidelines. This benchmark was established based on the investigation of more than 300 lab and field mixtures. Several state departments of transportation, have deployed the SAM in field concrete work, and its ease of use and accuracy have expanded its user base to agencies in 20 states and Canada.
The durability indicators obtained from SAM measurements are also being compared to the performance of hardened specimens using ASTM C666, the standard test method for the resistance of concrete to rapid freezing and thawing. An AASHTO Full Standard referencing the SAM has been approved and the SAM preforms AASHTO T395
For more information on the SAM, you can visit the website www.superairmeter.com.
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