Particle Size and Specimen Preparation Effects on the Iowa Pore Index

The Iowa Pore Index (IPI) test has been useful in prediction of freezing-and-thawing damage susceptibility of aggregate used in concrete pavements. However, the index is based on larger top size gradations that have been used in the past. This study was performed to identify size corrections that would allow aggregate gradations of smaller nominal maximum sizes, other than the standard 1/2 to 3/4 in. (12.5 to 19 mm) fraction, to be used in the index test method. In addition to the size corrections, several modifications to the method were developed to reduce variability in the test, and material re-testability was shown to be feasible. A new method of additional data collection from the IPI test was developed that allows for the measurement of water that is retained in and expelled from the aggregate after depressurization. These data have shown to have a better correlation with freezing-and-thawing testing data than IPI.