Comparison of Fresh Concrete Air Content Methods & Analysis of Hardened Air Content in Wisconsin Pavements

Quarterly Reports Other Documents Final Report
March 2014

Primary Investigator

Steven M. Cramer
Professor and Director of Structures and Materials Testing Laboratory
University of Wisconsin-Madison
cramer@engr.wisc.edu

Abstract

The formation of air bubbles in concrete and their stability during transportation, placement, and finishing is a complex topic that has been studied repeatedly over several decades, yet the design prescriptions resulting from this research remain general. Models and methods for determining the air entrainment dosage to achieve a given level of entrainment in some cases remain vexingly inaccurate without calibration on the site [5]. In addition to the basic mechanics of bubble formation and stability, the properties of specific air entraining admixtures and interactions with other chemical additives within the alkaline environment of concrete dramatically affect their ability to stabilize air bubbles. Aggregate microfines may also disrupt the air void system although in our research we have been unable to prove this. There is further uncertainty as to when and where to measure air content in concrete pavement and to what extent the air void structure evolves in the concrete after the measurement is made. The literature on the action of air entraining agents is vast and the amphipathic nature of surfactant air entraining agents is well documented and taught in our college classrooms. Many detailed and current reviews of air void formation and protection mechanisms exist in the literature.

Objectives

Wisconsin Department of Transportation (WisDOT) and others have noted disparities between measured air entrainment as measured by the ASTM C231B pressure meter method and by ASTM C457 analysis of hardened concrete specimens. This proposal seeks to identify the source of this disparity and determine whether existing techniques for measuring fresh air content continue to be suitable for contemporary air entraining admixtures.

Tasks

  1. Literature review
  2. Design of sampling and testing matrix
  3. Field and laboratory testing
  4. Data analysis
  5. Reporting

Project Information

  • Duration: 24 months
  • Dates: October 17, 2013–October 16, 2015
  • Budget: $99,998
  • Student Involvement: One graduate student and one undergraduate
  • Modal Orientation: Highway
  • Project ID: CFIRE 08-06
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