Allen, Harvey S.

This study was undertaken to find economical methods to reduce reflectance cracking of bituminous overlays placed on Portland Cement Concrete. The four methods studied were pavement cracking, open graded bituminous base course, aggregate interlayer, and increased thickness of the bituminous overlay. Pavement cracking was found to be an effective and economical method of reducing reflectance cracking. The aggregate interlayer and added bituminous thickness were found to reduce reflectance cracking to some degree but the added cost may exceed this benefit. The open graded bituminous base course was not an effective method of reducing reflective cracking on this project.

The need for new rehabilitation designs is very important as the funding for both maintenance and construction projects becomes increasingly difficult to obtain. The design thickness of a bituminous overlay on a PCC pavement has often been a matter of the past experience of individual engineers who have to make these recommendations. This special study was undertaken to gather data on three different thicknesses of bituminous overlays on cracked PCC pavement. This study will also provide additional data on the effects of cracking PCC pavement. It is anticipated that data from this study will provide the Design Engineer with information that will be helpful in selecting the thickness of bituminous overlay and specifications for pavement cracking. This study will continue for a minimum period of 5 years.

This report evaluates the effect of cracking, breaking, or shattering PCC pavements before overlay as a means of reducing the amount and severity of reflected cracking. This investigation was expanded from Special Study No. 375, "Evaluation of Variable Thickness of Bituminous Overlay on Cracked PCC Pavement." A report on this study was issued in 1981.

Deflection tests have been used in the past by some districts to provide information on the spring thaw period although there has not been a uniform procedure established for statewide use. The committee decided to have additional deflection data collected and analyzed to determine how these tests could be used to establish criteria for the setting or removal of spring load limits. The type of questions that had to be answered were: 1. Can deflection tests be used to determine when the posting period should start? 2. Can deflection be used to determine when the posting will end? 3. Are deflection tests necessary on all posted highways during the spring thaw period? 4. Should testing be done daily, weekly or bi-monthly? 5. What analysis can be done with deflection data that may lead to the establishment of spring posting period criterion? 6. How many test sections would be needed and where should they be located?

This study was initiated to study methods, procedures and/or materials that may reduce premature pavement failures of asphaltic concrete overlays on PCC pavement caused by excessive reflective cracking. Methods included in this study were reducing the existing PCC pavement panel size by saw cutting, full coverage fabrics, strip fabrics and Rubber-Asphalt Interlayer as a Stress Absorbing Membrane Interlayer (SAMI). No material or method was found that would totally eliminate reflective cracking, Reducing the existing PCC pavement panel size and the use of the Rubber-Asphalt Interlayer were the two procedures that provided the best results.

The purpose of this study is to evaluate a rubber modified plant-mixed bituminous surface mixture. This mixture was produced using the patented process called "Plus Ride™" "Plus Ride™" is advertised as having unique de-icing properties, is durable and has the ability to reduce reflective and thermal cracking. This study is part of the FHWA Demonstration Project No. 3 "Asphalt Additives", and financed jointly by the U.S. Department of Transportation, Federal Highway Administration, and the Minnesota Department of Transportation. The authors wish to acknowledge the contribution of Districts 3 and 9 Construction and Materials personnel, and the Office of Materials Engineering for laboratory work and recommendations; Roger Olson, Research Operations Engineer; and Jerry Teig, Research Assistant. The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented. The contents do not necessarily reflect the official views or policy of Mn/ DOT or the Federal Highway Administration. This report does not constitute a standard specification or regulation.