Research by the The National Concrete Pavement Technology (CP Tech) Center, in partnership with the Iowa Concrete Paving Association (ICPA), Iowa DOT,  and the Institute for Transportation (InTrans) at Iowa State University, reveals concrete overlays have generally outperformed performance expectations in the state, as well as some long standing roadbuilding standards. 

Overall, 89% of all concrete overlays in the state had a pavement condition index (PCI) of 60 or greater (good to excellent).(1)   Data also showed the majority of concrete overlays were on track to reach good PCI (60 or better) and adequate ride quality rating, based on International Roughness Index readings of 170 in./mi or better during the first 35 years of service life.

The majority of concrete overlays in Iowa have service life trends exceeding the expectations listed in the National Cooperative Highway Research Program Synthesis of Highway Practice 204.(2)

The researchers pursued the research in response to the existence of few comprehensive studies that evaluate long-term performance of concrete overlays.  Iowa roadways were selected because of the long history of concrete overlay construction in Iowa, coupled with wealth of performance data(3) presented an excellent opportunity for a comprehensive, long-term performance study of concrete overlays.  In fact, data collection on all paved secondary roads began in 2002, and since 2013, data has been collected on every paved public roadway in Iowa, according to the research. 

For the study, researchers analyzed concrete overlay performance using the PCI from the Iowa Pavement Management Program, as well as IRI data. In all, data came from 384 concrete overlays on 1,493 miles of roadway and encompassing 14 years of data collection.  “Although data collection has only occurred for 14 years, some of the overlays in this data set were built as early as 1977,” explained Dan King,  EIT,  Regional Services Manager for the ICPA.  “As such, we have performance data for a good number of overlays that are as much as 30 to 40 years old.”

Four overlay types were studied: unbonded and bonded concrete overlays on concrete and on asphalt (UBCOC, BCOC, UBCOA, and BCOA, respectively). Concrete overlays on composite pavements were included in the BCOA and UBCOA categories.  The researchers also reported unbonded concrete on asphalt (UBCOA) overlays have performed better than the three other overlay types.

The results of this study are beneficial to the Iowa DOT and local agencies, according to the researchers, who note, “The results provide definite evidence on a large scale that concrete overlays are a successful preservation technique that can provide extended service lives to roadways in need of rehabilitation.”

Please follow these links for the complete field data report and the tech transfer summary.

(1) Iowa DOT  pavement condition data includes IRI readings, as well as data on transverse cracking, longitudinal cracking, D-cracking, spalled joints, and faulting. 
(2) McGhee, K. H. 1994. NCHRP Synthesis of Highway Practice 204: Portland Cement Concrete Resurfacing. National Cooperative Highway Research Program, Washington, DC., as cited in the field report and T2 report.
(3) The Institute for Transportation (InTrans) at Iowa State University manages pavement condition data as part of the Iowa Pavement Management Program.