What is it about?
Polymeric microspheres have proven to be an effective alternative that avoids the significant sensitivity of entrained air to concrete production and placement processes. The parameters of the microsphere system that can be obtained from microscopical examination of hardened concrete relate to the freezing-and-thawing durability of concrete as in the case of air-void system parameters. This publication develops and explains the relationships between microscopically determined parameters of microsphere system in hardened concrete and the actual parameters that are known from the size distribution of the microspheres dosed into the concrete.
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Why is it important?
It turns out that the findings of this paper explain an issue that has been unresolved regarding comparison between microscopically determined air content of hardened concrete and the air content measured in plastic concrete with a pressure air meter. The issue is that microscopically determined air content typically tends to be higher than the air content of the plastic concrete. The analysis described in the paper about polymeric microspheres in concrete also explains this typical discrepancy between air content of hardened concrete and that of the plastic concrete. In this regard, the paper sheds light on the results obtained from ASTM C457/C457M test method and would be highly valuable in interpretation of such results.
Perspectives
The motivation for this study came about when I observed that the microsphere content of hardened concrete measured through microscopical examination was consistently higher than the actual microsphere dosage used in the plastic concrete. I then realized that such a discrepancy is also observed between measurements of air content of plastic concrete obtained with a pressure meter and those obtained by microscopical examination of hardened air-entrained concrete. No viable explanation has ever been offered for this discrepancy in air content between the two methods. I, therefore, decided to study the issue from the fundamental standpoint of geometry and probability, which are involved when a single random section is cut through a sample of hardened concrete. The results of the study confirm the well-known fact that dealing with problems from first principles always sheds light on perplexing observations.
Emmanuel Attiogbe
Read the Original
This page is a summary of: Predicting the Magnitude of Microsphere Parameters Obtained from Microscopical Examination of Hardened Concrete, Journal of Testing and Evaluation, March 2023, ASTM International,
DOI: 10.1520/jte20220469.
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