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ASTM C457 Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete, Method B Point Count.Lab ID 56

Use
The test is a quantitative method that measures the air-void content and other air-void system parameters in hardened concrete. The parameters determined by this procedure are most often related to the susceptibility of the concrete to freezing and thawing damage. Thus, this method can be used to evaluate the potential for damage due to cyclic freezing and thawing of the concrete. The test results can also be used to explain the reason why such damage has occurred in concrete. Additionally, this test method can be used for concrete product and mixture development requiring resistance of the concrete against freezing and thawing damage. Results can also be applied to other situations in which the air content of concrete is in question.

Instructions
A 3 to 4- inch diameter core, about 4 to 6 inches long is typically needed to process a sufficient test area in accordance with the test method, depending on the top size of the aggregate. The CTLGroup contacts can assist with questions about sample size and number of samples. If scaling and suspected freeze-thaw distress is the issue, or if delamination is the suspected problem, the samples need to contain the finished top surface. When assessing strength problems it is helpful to comparatively analyze acceptable and low strength samples.

Results Produced
Numerical values for percent total air, spacing factor, specific surface, number of voids per inch, paste-air ratio, and percent paste are reported.

Time for Results
Results are usually available within a week, depending on the number of samples.

Alternate Tests
ASTM C 856 petrographic examination can only estimate total air content.

Related Tests
ASTM C457, Method A Linear Traverse generates the same results and includes air-void size (chord length) distribution. ASTM C856, petrographic examination of concrete.

Test Designation
C457 Air-Void, Method B - Mod. Pt. Ct.

Sample Type
hardened concrete, mortar, other portland-cement-based materials