National Concrete Pavement Technology Center

Institute for Transportation (InTrans) Faculty Affiliate Jeramy Ashlock has spent more than a decade studying aggregates in Iowa and providing guidance to maintain or improve the state’s granular road network.

His most recent research project brought together those years of experience and knowledge-building to help local agencies select the best-performing coarse aggregate materials.

The research project, sponsored by the Iowa Highway Research Board (IHRB), used materials collected from two previous IHRB efforts that included constructing granular road test sections and also new Clean and Class A coarse aggregate samples from nine quarries across the state to conduct laboratory tests on the materials.

“Through a clearer understanding of the deterioration mechanisms of carbonate coarse aggregates, critical material properties can be identified that will better guide the decision-making process used by county engineers and geologists to plan the construction and maintenance of granular-surfaced roads and shoulders,” Ashlock said.

Ashlock, who is also an Iowa State University Department of Civil, Construction, and Environmental Engineering professor and James M. Hoover Chair in Geotechnical Engineering, said county engineers and others can select the material types that produced the least breakage in quarry samples and field test sections as evaluated in the research.

The materials were evaluated through gyratory compaction tests, particle size distribution tests, petrophysical testing, petrographic inspection, and image analysis.

From those tests, a few of the findings include the following:

• From the quarry sample analysis, the Class A materials from the Pedersen, Crescent, and Moore Quarries produced the lowest total breakage values during gyratory compaction testing.
• From the test sections in Performance-Based Evaluation of Cost-Effective Aggregate Options for Granular Roadways, Oneota Formation Dolomite (OFD) Class A aggregates had the lowest breakage.
• From the test sections in Low-Cost Rural Surface Alternatives Phase III, the Optimized Gradation with Clay Slurry sections had the best overall performance.
• In general, the less durable rock types, such as those with higher clay contents or greater porosities, experienced a greater reduction in abundance over time.

“Ultimately, the results of this research can help decision-makers act in the best interest of taxpayers by minimizing the life-cycle costs of constructing and maintaining granular-surfaced roads while providing a safe and reliable transportation network for rural communities and producers,” Ashlock said.

For further findings and additional details about the coarse aggregates used in the research project, visit the InTrans project page.