In the early 1980s, the Michigan Department of Transportation (MDOT) reconstructed several interstate highways using recycled concrete aggregate (RCA). Although most of the RCA pavements performed acceptably, MDOT observed that some of the pavements deteriorated more rapidly than they should have. MDOT needed to know what caused these pavement failures and solutions to prevent their reoccurrence. Thus, research was conducted to diagnose the problem and to determine how mix designs can be modified to enhance RCA performance.


Because some of the pavement sections that were replaced had experienced problems with D-cracking, they were crushed to a small top size of about 3/4 inch to reduce the recycled aggregate's susceptibility to freeze-thaw cycles. Although that decision was based on sound engineering principles, it may have adversely affected the aggregate-interlock load-transfer capacity of the RCA pavements. In effect, the strategy for solving the D-cracking problem may have backfired, contributing to an accelerated pavement maintenance schedule and a shortened service life.


In the research study, which was conducted at Michigan State University, 35 slabs were tested. The study analyzed the impact of load transfer on the rate of crack deterioration for the various pavement materials and designs. The broadest conclusion reached by the test study was that natural aggregates (gravels and limestones) generally outperform manufactured aggregates (recycled concrete and slag) when all other factors are the same.