Publication: “Comparison of Fresh Concrete Air Content Test Methods & Analysis of Hardened Air Content in Wisconsin Pavements”

Recently published, the technical report titled “Comparison of Fresh Concrete Air Content Test Methods & Analysis of Hardened Air Content in Wisconsin Pavements” by Le Pham and Steven Cramer, Ph.D., P.E., University of Wisconsin-Madison Department of Civil and Environmental Engineering, funded through the Wisconsin Highway Research Program by the Wisconsin Department of Transportation (WisDOT) and the Federal Highway Administration (FHWA), is a report on research that consisted of two phases:

PHASE 1 was a field study on the air void systems in Wisconsin pavements, and the second was a laboratory study to find the root causes of the problem identified in the field study. The first phase gathered sufficient measurements to verify the occurrence of disparities in air content measurements that had been anecdotally reported over the past few years. The research involved visiting twelve paving projects across Wisconsin in the construction season of 2014 to conduct field tests on fresh concrete and to gather samples for hardened air void analysis. Later drilled cores were taken from the pavement at approximately the same location as the samples. The results show that the pressure meter and ASTM C457 measurements of concrete cylinders were in reasonable agreement. The differences between air content measurements by the two methods were within ± 2 percentage points. In pavements where synthetic air entraining agents (AEAs) were used, the C457 air contents of sampled cylinders were in many cases significantly lower (up to about 5 air content percentage points) than that of drilled cores taken at approximately the same location. In pavements where neutralized vinsol resin (NVR) was used, air contents in the cylinders were similar or slightly greater than those in the cores.

PHASE 2 of the research was aimed at finding the root cause of the air content discrepancy observed in concrete made using synthetic AEAs. A laboratory program at multiple scales including concrete air void analysis, the foam drainage test, and fundamental tests for micro-properties of individual bubble shells was conducted. The results showed that the air bubbles in concrete entrained with synthetic AEAs were less robust than those with NVR and thus less able to survive during concrete sampling procedures for pressure air content.