Aggregate Freezing-Thawing Performance Using the Iowa Pore Index

Project status


Start date: 08/01/15
End date: 10/31/16


Principal investigators:

Co-principal investigators:

About the research

In cold climates, the use of non-durable aggregate leads to premature pavement deterioration due to damage caused by freezing-thawing cycles. Differentiating durable and non-durable aggregates is a crucial yet challenging task. The frost durability of coarse aggregate has been reported to be related to its pore structure; however, existing test methods to identify pore structure are often not cost-effective. There is a need for a quick, reliable, and cost-effective aggregate test whose results correlate well with aggregate freezing-thawing performance.

The Iowa pore index test has been used by the Iowa Department of Transportation (DOT) for three decades as a supplemental decision making tool. This study investigated the relationship between the Iowa pore index and the freezing-thawing performance of aggregates as measured by three other test methods: Canadian Standards Association (CSA) A23.2-24A, Test Method for the Resistance of Unconfined Coarse Aggregate to Freezing and Thawing; ASTM C88, Standard Test Method for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate; and an unconfined freezing-thawing test using conditioning according to ASTM C666, Standard Test Method for Resistance  of  Concrete to Rapid Freezing and Thawing.

The following results were observed:

  • The aggregates with a non-carbonate origin outperformed the carbonate aggregates in all three tests.
  • The Iowa pore index was found to correlate fairly well to the aggregate performance measured by the unconfined freezing-thawing test using ASTM C666 conditioning and the CSA A23.2-24A test. The correlation of the Iowa pore index to the ASTM C88 test was poor.
  • The aggregates with high volumes of micropores performed poorly compared to the aggregates with low volumes of micropores. The correlation between the volume of micropores in an aggregate and the freezing-thawing performance was fairly strong.


Report: Aggregate Freezing-Thawing Performance Using the Iowa Pore Index (902.69 kb pdf) November 2016



  • Iowa State University
  • Midwest Transportation Center