Program for Sustainable Pavement Engineering and Research

About the research

Over 71,000 miles (i.e., over 75%) of county roads in Iowa are granular (unpaved) roads. Iowa granular roads carry low daily traffic volumes (i.e., 10 to 200 vehicles/trucks per day) yet frequently support heavy vehicle (e.g., farm equipment) movements. According to a recent estimate, Iowa’s county road departments spend over $145 million annually on maintenance costs, which predominantly includes over $35 million for blading and over $110 million for resurfacing. In addition, a wide range in granular material quality, supply, and price available in different regions of the state results in significant differences in the level-of-service. Therefore, Iowa county engineers have a specific set of criteria based on their own experiences when designing and managing granular roads. Considering the lack of granular road structural design standards to meet Iowa county engineers’ requirements for current granular road management practices, significant research is needed to develop a comprehensive but practical structural design tool for cost-effective design and construction of local granular road systems in Iowa.

The primary objective of this study is to meet such research needs. This will be achieved through the execution of five concurrent research studies: (1) surveys/interviews, forensic investigations, and laboratory tests to identify the best practices for Iowa granular roads around the state; (2) construction, instrumentation, and performance monitoring of field demonstration sites; (3) development of deterioration prediction models subjected to Iowa granular roadways; (4) cost-effectiveness analysis; and (5) development of a structural design tool and additional guidance documents. The outcomes of this research will substantially improve overall performance, save on maintenance and operation costs, and enhance the safety and mobility of Iowa granular roads by addressing key performance indicators (e.g., drainage, cross-slope, aggregate loss, and freeze/thaw susceptibility) through the granular road design procedure.