Blanchette, Andrea

This is the second revision of this handbook which was originally published in 1998. This update to the handbook, although still titled Minnesota Seal Coat Handbook, has changed all references of Seal Coat to Chip Seal, better aligning it with other state Departments of Transportation (DOTs), Federal Highway Administration (FHWA), and industry. Minnesota Department of Transportation (MnDOT) specifications will eventually be updated to reflect this change. As preventive maintenance and preservation of bituminous pavements continues to evolve, this version of the handbook has been expanded to include a brief discussion on spray applied bituminous surface seals and additional similar types of thin bituminous pavement surface treatments which are often referred to as BSTs.

This is the second revision of this handbook which was originally written in 1996. This update to the handbook, although still titled Minnesota Seal Coat Handbook, has changed all references of Seal Coat to Chip Seal, better aligning it with other state Department of Transportation’s (DOT‘s), Federal Highway Administration (FHWA), and industry. Minnesota Department of Transportation (MnDOT) specifications will eventually be updated to reflect this change. As preventive maintenance and preservation of bituminous pavements continues to evolve, this version of the handbook has been expanded to include a brief discussion on spray applied bituminous surface seals and additional similar types of thin bituminous pavement surface treatments which are often referred to as BSTs. Although information on the BSTs discussed above have been brought into this handbook, the intent is still the same, to provide guidance in the design and construction of high-quality chip seal surface treatments for bituminous pavements. Applying this treatment to the right pavement at the right time while paying attention to the quality of materials used and workmanship will result in better performing, longer lasting bituminous pavements. This revision of the handbook was sponsored by the MnDOT Pavement Section with assistance from WSB Consulting Engineers and input from a Technical Advisory Panel made up of MnDOT, City and County Engineers.

Spray on rejuvenators, designed to penetrate into the asphalt pavement to a certain depth, can be applied to hot mix asphalt (HMA) pavement surfaces, serving as a cost-effective method intended to reverse the effects of aging. Rejuvenators strengthen the HMA material at the surface to resist the detrimental effects of exposure to sun, water, and air. To achieve optimal performance, it is recommended that rejuvenators be applied to roadways in good condition as a preventive maintenance treatment. There are two major types of spray applied rejuvenators: petroleum-based and bio-based. The purpose of this project is to guide the research need statement for an upcoming research project on test sections investigating type of rejuvenating products, laboratory and performance testing, allowable or acceptable friction values, and pavement marking reflectivity. This synthesis includes a summary of experiences from various agencies and industries on the use of spray on rejuvenators. A literature review was performed and includes but is not limited to the type of rejuvenators used, application rate, type of testing conducted to evaluate the effectiveness of a spray on rejuvenator, and specifications.

Non-structural overlays such as ultra-thin bonded wearing course (UTBWC), chip seals, and micro-surfacing are commonly applied as a preventive maintenance method to extend the service life of a pavement. They are generally placed over flexible substrates, which include flexible pavements that have received bituminous interventions on bituminous upper layer (BOB), flexible pavements that have received bituminous interventions on concrete layer (BOC), and flexible pavements that have not received any intervention since constructed on aggregate base (BAB). These treatments have been widely applied, thus driving the need to conduct an analysis to determine the service life enhancements of these overlays using Weibull analysis. There are various factors that affect the expected service life of these preventive maintenance techniques such as the condition of the substrates and the maintenance window. The remaining service life (RSL) – service life enhancement since intervention – for all treatments from two agencies (Minnesota Department of Transportation (MnDOT) and North Dakota Department of Transportation (NDDOT)) appear to be relatively close to each other, except for the BOC substrates overlaid with micro-surfacing. All treatments have a pattern of wear-out failures, which are an indication that the treatments are effective in providing life extensions because the cause of failures is not random. Some of the interventions are second or third and these collectively synergistically improve service life of the substrate, for which further investigations are recommended. Additional data from other state members and an update on these existing data (MnDOT and NDDOT) in five years would enhance the performance curves and improve the accuracy of estimated remaining service life.

In recent years, the asphalt industry has seen an increase in using reclaimed asphalt pavements (RAP) and recycled asphalt shingles (RAS) in new asphalt concrete pavements. Rejuvenating additives are incorporated into asphalt mixes to neutralize the effects of using higher percentages of RAP and RAS in new asphalt concrete pavements. The implementation of incorporating rejuvenating agents in high-RAP or RAS asphalt mixes has led to the evaluation of their capability to restore the properties of aged binder to a condition that is similar to virgin asphalt binders. There are two major types of rejuvenators used: petroleum-based rejuvenators and bio-based rejuvenators. The purpose of this project is to compile a synthesis of current practices being used by the states and industries in the area of mix rejuvenators. This synthesis provides the state of practice in the National Road Research Alliance (NRRA) member states and will be used as guidance for the NRRA's Asphalt Mix Rejuvenator Field Section research that was in the contracting stage as of March 2020. This synthesis includes a summary of experiences from various agencies and industries on the use of asphalt mix rejuvenators. A literature review was performed and includes but is not limited to the type of rejuvenators used, dosage rate, method of blending the rejuvenators with the RAP and/or RAS, percentage of RAP and/or RAS used, and type of testing conducted to evaluate the effectiveness of a rejuvenator.

Bonded concrete overlay of asphalt (BCOA) pavements, also known as whitetopping, can help enhance the structural capacity and rideability of existing asphalt pavement. In this report, the generic term "BCOA" is used to describe all overlays that are between 3-inches and 7-inches thick and placed on an asphalt layer a minimum of 3-inches thick. BCOA is typically designed for a 20-year design life. Rehab should be considered when the distresses in a BCOA are causing ride quality issues or the panels have deteriorating cracks. Agencies have generally utilized concrete pavement restoration (CPR) techniques used for standard concrete pavements on grade to repair such overlays. However, these techniques may or may not be the appropriate repairs to address similar distresses in BCOA pavements. Over the past decade, the popularity of BCOA pavements has grown in many states and many of these projects are now reaching an age where rehab is needed. This has prompted the National Road Research Alliance (NRRA) to compile a synthesis of current practices of repairs being used on BCOA projects by the contributing state agencies. The most common type of repair of a BCOA pavement is to conduct a full-depth removal and replacement of the concrete panels when the area of distresses is localized. The main supporting factor is the BCOA pavement has such a thin overlay that it is more cost effective to perform this type of rehabilitation method as compared to the others.