Case Studies: Overly Protected

By: Roads & Bridges

Many highway agencies are finding that rubblization of the deteriorated concrete and overlaying with HMA is the fastest, most cost-effective rehabilitation method. Providing pavement drainage is critical to the success of rubblized pavements. Edge drains are installed or replaced prior to fracturing the concrete. Any existing asphalt overlay or patches are removed. The concrete is fractured and rolled to achieve an interlocked, unbound base layer. The typical production rate when rubblizing is up to one lane mile per day per machine. Then the HMA overlay is applied.

The overlay thickness is determined in accordance with normal structural design procedures. The broken concrete is typically assigned a layer coefficient value of 0.20. The value can range from 0.14 to 0.30.

Alabama hosted a workshop on their experience with rubblization in December 2005. The site on I-65 near Montgomery was originally constructed in 1968 as a 9-in.-thick jointed plain concrete pavement built over 6 in. of cement-treated subbase. The original traffic volume was 3,550 vehicles per day with 14% trucks. By 2004, the traffic had grown to 29,120 vehicles per day.

After rubblization, the contractor placed an HMA overlay with a thickness of about 10.5 in., including an open-graded friction course wearing surface.