Institute for Transportation

About the research

The previous IHRB project, TR-685: Feasibility of Granular Road and Shoulder Recycling, involved construction and testing of several granular road and shoulder test sections in which existing surface materials were recycled and blended with virgin materials. One of the most useful outcomes of the TR-685 Phase I project is the Gradation Optimization tool, a spreadsheet that allows engineers to determine the optimum mixture of existing granular surface materials with up to three virgin quarry materials (along with a selected thickness of subgrade for plasticity if desired).

This project will be a Phase II follow-on to TR-685, with a project goal of expanding the accuracy of the Gradation Optimization tool by more extensive testing of a wider range of material types and material blends. The representative surfacing aggregates will be collected from quarries across Iowa. The material types will include crushed river gravel, higher strength limestone, and various others typically used for granular surfaces in different regions of Iowa.