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This study evaluates the use of seal coating as a method to protect bituminous pavements from oxidation, water infiltration, and raveling. The Minnesota Department of Transportation (Mn/DOT) applied seal coating to a roadway segment of Trunk Highway 21 in August 1998. The report outlines optimal requirements for the application of seal coat. Cost comparisons of the test sections are also presented. Mn/DOT will continue to examine the test strip for performance and provide regular updates until the strip's condition requires reconstruction or overlay.

This project introduced the use of micro surfacing as a pavement preventive maintenance surface treatment and tested different methods of using micro surfacing to correct or prevent defects in existing pavements. Micro surfacing mixtures include polymer-modified emulsified asphalt cement, a well-graded 100% crushed mineral aggregate, and mineral filler, such as portland cement or hydrated lime, with water and control additives added to control the speed of breaking and workability. Micro surfacing remains semi-liquid during mixing and placing phases and then cures chemically for a very durable asphalt surface treatment. Application and testing revealed that the fast-moving micro surfacing process minimizes the amount of down time for traffic; does an excellent job of reestablishing cross sections; fills ruts; improves ride quality; increases friction numbers; and provides an excellent background for pavement markings. It does not seal reflective cracks, has generated some concerns about increased traffic noise, and does not work favorably for smoothing humps in pavement. Overall, project selection played a key factor in the overall success of micro surfacing. A very thin surface treatment, microsurfacing cannot be expected to fix structural problems in existing pavements. One should avoid using micro surfacing on roadways that are still rutting and repair potholes before placement of micro surfacing.

The Minnesota Department of Transportation (Mn/DOT) has concluded a research study on the proper techniques involved in seal coating. A key part of the research project involved performing seal coat designs using the procedure developed by Norman McLeod. In addition, research personnel were present on many seal coat construction projects assisting the inspector and contractor. The primary purpose of this handbook, revised in 2006, is to provide a solid background in seal coat materials, equipment, design and construction for the field inspector. Divided into two main sections, this updated handbook provides direction for designers and field personnel. Thomas J. Wood handled this revision. The original work was prepared by David W. Janisch and Frank S. Gaillard. NOTE: A revised version of Minnesota Seal Coat Handbook was published in December 2022 (report 2022-22).

This report presents a summary of pavement preservation activities and recommended uses, expected longevity, and expected pavement life extension. It also includes some basic information intended to be used by those less familiar with pavement preservation, pavement management, life cycle cost analysis, cost estimating, contracting methods and others to help inform and educate in this important aspect of pavement engineering. Tools and techniques are presented to assist local agency engineers in evaluating costs, benefits, timing, longevity, and the decision-making process for developing an effective pavement preservation program on an individual pavement segment or over an entire network. The report includes examples using real pavement engineering data from several cities and counties in Minnesota to demonstrate topics such as activity timing and the benefits of a preventive maintenance plan rather than a reactive one. A set of guidelines was developed as part of the associated project intended to serve as reference material and as a training program.

Recycled Asphalt Shingles (RAS) include both manufacture waste scrap shingles (MWSS) and post-consumer tearoff scrap shingles (TOSS). It is estimated that Minnesota generates more than 200,000 tons of shingle waste each year. Recently, a portion of this waste has been incorporated into hot-mixed asphalt (HMA) pavement mixtures. The current technology limits the amount of RAS in HMA to no more than 5 percent by weight. This leaves a lot of underutilized shingle waste material throughout the state. This has prompted MnDOT to investigate other potential uses RAS. One potential use is to improve the performance of gravel surfacing and reduce dust by replacing common additives such as calcium chlorides with RAS. This is especially relevant as gravel sources in Minnesota have been depleted and/or have declined in quality, which has affected the performance of gravel surfacing. These poorer quality fines can increase the amount of dust generated and increase the difficulty of keeping the roadway smooth. Some agencies have used dust control additives to help the performance of these lower quality gravels. Successful implementation has the potential of removing valuable RAS materials from the waste stream to supplement the use of more expensive virgin materials and improve the performance of local roads.

The higher costs of hot-mix asphalt pavement are causing more agencies to choose pavement preservation techniques to maintain their pavements. Some agencies have experienced stripping of the asphalt surface under chip seals, this distress appears to occur mostly in urban areas on curb and gutter streets. The main objective of the study was to determine what causes the stripping and to develop test methods to determine if the street will strip prior to placement of the chip seal. Both field and lab methods were used. Research focused on determining air voids, permeability, and density of the samples. Once these were determined, correlations were developed to determine the conclusions.

The growth in recreational trails owned by the State, Cities, Counties, and Park systems over the last 20 plus years has exploded. Most if not all efforts related to recreational trails over these years has been focused on construction of new trails. There have been little organized efforts in trail preservation and or preventive maintenance (PM) methods to extend the usable life of the trails. The agencies that have a PM programs for their recreational trails rely on treatments that started out as highway or street treatments that may have been modified for use on the trails. The goals of this research project where to study existing treatments, how effective they are, promote new methods, and promote regular scheduled PPT for preserving trail systems.

Highway agencies have constructed expansive networks of pavements that are vital to the economic prosperity and vitality of the nation. These networks are currently deteriorating at such a rate that most agencies cannot afford to reconstruct them in a timely manner. Consequently, many agencies have employed low-cost preventive maintenance (PM) techniques such as crack and surface treatments in an attempt to slow the deterioration rates of the pavements, thus extending the service life and delaying the time until reconstruction. This study sought to address whether or not recent advances in bituminous mixtures and binder selection through SuperPave necessitated a re-examination of current PM practices. In other words should SuperPave pavements be managed differently, compared to other mixture types in the network. The first project task sought to analyze the effectiveness of PM treatments by using historical pavement management data to develop pavement decay curves with time. The results of the analysis indicated a life extension; however due to data limitations, a life cycle cost analysis (LCCA) as well as a specific life extension value were not conclusively determined. The second project task assembled a pavement owner's manual to provide general guidance on applying PM treatments throughout a pavement's life. The recommendations of applying PM are based primarily on the pavement's age and general surface characteristics. The recommendations of task 2 are based upon experienced engineering judgment, empirical evidence and a literature review; consequently they must be tempered to the local conditions, environment and materials.

Many governments and agencies responsible for the maintenance of local street systems have been applying low cost preventive maintenance (PM) treatments to their pavement network to extend pavement service life and reduce costs. Chip seals have become a popular PM treatment for these local streets; however cul-de-sacs have historically been less receptive to the treatments due in part to their geometry. This has caused many agencies to stop chip sealing their cul-de-sacs which not only creates a non-uniform appearance, but leaves the pavement more vulnerable to environmental induced damage. As an alternative to chip seals, fog seals can be considered as a PM treatment for cul-de-sacs.

The growth in recreational trails owned by the State, Cities, Counties, and Park systems over the last 20 plus years has exploded. Most if not all efforts related to recreational trails over these years has been focused on construction of new trails. There have been little organized efforts in trail preservation and or preventive maintenance (PM) methods to extend the usable life of the trails. The agencies that have a PM programs for their recreational trails rely on treatments that started out as highway or street treatments that may have been modified for use on the trails. The goals of this research project where to study existing treatments, how effective they are, promote new methods, and promote regular scheduled PPT for preserving trail systems.

Preventive maintenance is defined by AASHTO as “a planned strategy of cost-effective treatments to an existing roadway system that preserves the system, retards future deterioration, and maintains, or improves the functional condition (without adding additional structural capacity)”. Thus a treatment used as a stop-gap measure to hold together a distressed pavement would not be considered a cost effective PM treatment. The AASHTO definition encourages a paradigm shift away from a reactive mindset that responds to distresses in the pavement, toward a proactive one that seeks to prevent, or reduce the occurrence of distresses by selecting the right road and using the best methods at the proper time.

This review was part of ongoing research to determine how Bituminous over Concrete (BOC) pavement cracks, and how to reduce or eliminate cracking of the Hot Mix Asphalt (HMA) overlay

This brief describes the research that became Report 2013-08, "Stripping of Hot-Mix Asphalt Pavements under Chip Seals."

Rumble strips are a cost effective safety treatment for rural pavements, however they allow water to pool and increase the surface area of the pavement exposed to the elements. This research sought to address the maintenance effects of rumble strips on HMA pavements and what effect, if any, these have on the service life of the pavement. A survey was conducted which found that most respondents either noted the presence of distresses in rumble strips, or were concerned that the rumble strips were the direct cause of distresses. Next this study recommended several treatment options for pavements with rumble strips. Many of these recommendations are anecdotal and based on engineering judgment, which underscores the need for additional research. The recommended preventive maintenance treatment is to use construction funds to apply a cationic rapid set polymer modified diluted (CRS-2pd) fog seal over the entire shoulder, including the rumble strips. This will ensure an initially sealed surface and provide the maximum benefit in terms of service life extension. Crack sealing, although not an integral part of preventive maintenance for rumble strips should be applied to the adjacent cracks to slow the growth of cracks into ground in rumble strips.

The flexible slurry system is a mixture of emulsified asphalt, high quality crushed aggregate, and water. Depending upon the design, flexible slurry can be used in place of a blade leveling course prior to bituminous overlay or as a wear course. Flexible slurry is constructed using a micro surfacing machine, but is less brittle than a usual micro surface mixture. Historically Minnesota has used one type of emulsified asphalt (PG 64-22); but recent experimentation with binder grades shows that enhanced rutting and cracking performance is possible. Low speed traffic can aid in the curing and consolidation of flexible slurries.

The longitudinal construction joints on this segment of roadway, Interstate 494 from Mile Post 2.143 to Mile Post 7.461 in both directions a three to four lane divided urban freeway, had deteriorated to the point that they were a possible safety issue, especially for motorcyclist. The Metro District maintenance forces had tried different methods of patching the longitudinal joint failure. The methods tried are either very expensive or leave poor driving surface. The decision was made to try using the Micro Surfacing technology to see if this would fill the joints and leave a smooth durable driving surface. The intent of the project was to repair the right fog line and the two skip lines that where exhibiting failures.

On November 13, 2008, I reviewed the section of Interstate 35 southbound just north of junction with Interstate 90. The reason for reviewing this section is the following excerpted from report “Field Observations of the Coring of I-35 Between Mile Post 18 and 16 Southbound” Jerry Geib and Thomas Wood September 27, 2005. (Appendix A) This review is on going research to determine how Bituminous over Concrete (BOC) pavements crack, and how to reduce or eliminate cracking of the Hot Mix Asphalt (HMA) overlay.

To demonstrate and test the concept of stabilized full depth reclamation as pavement base material, Full Depth Reclamation (FDR) with asphalt emulsion re-uses the existing asphalt mixture and adds stabilized additive to further increase material stiffness. This method was applied on three (3) cells located on the MnROAD mainline (Cells 2, 3 and 4).

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.

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.

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.

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.

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.