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Sealing the edge joints on concrete pavements with bituminous shoulders reduces the volume of water entering the pavement system by as much as 85 percent. Longitudinal edge joint sealing should be considered as a pavement preventive maintenance treatment.

This report summarizes lessons learned about the field performance of local roads containing Recycled Asphalt Pavement (RAP) and associated field and laboratory work with asphalt activation as well as the design and performance testing of high-RAP bituminous mixtures. Transverse cracking performance of Minnesota county highways averaging 20-26% RAP was improved when PG 52-34 binder was selected over PG 58-28 or other binder grades. Testing of the activation of RAP asphalt binder in plant and laboratory settings showed that coarse aggregates from plant mixing achieved a more uniform coating and were subjected to less abrasion than those from laboratory mixing. Low temperature testing of laboratory mixture designs containing up to 55% RAP, and new-to-total asphalt cement ratios as low as 43%, found that indirect tensile test (IDT) creep stiffness increased along with RAP content. IDT critical temperature results showed that the addition of RAP significantly increased the critical temperature, predicting less crack resistance. Semi-circular bend fracture testing showed that the addition of RAP lowered the fracture energy and increased the fracture toughness of the mixtures, and the highest RAP contents had the most reduced fracture performance.

This study evaluated the performance and cost of commonly used dust palliatives using a mobile air sampling technique. Treatments of calcium chloride, magnesium chloride, and organic polymer-plus-binder were evaluated at standard application rates during the first year and at variable rates during the second year. The treatments were applied to a variety of subject roads that were located throughout Minnesota. Average daily traffic levels varied from 25 to 700 vehicles per day. The overall data trend showed that treatments reduced dust levels and measurements showed that aggregate surface moisture content was the best predictor of dust control efficiency. Positive relationships were measured between dust control efficiency and other variables in the study, generally reinforcing the concept that higher application rates may be more successful on gravels containing greater amounts of material passing the #200 sieve. A negative relationship was measured between dust control efficiency and sand equivalency, showing that treatments on gravels containing more sand material were less effective. In addition to dust control, study participants observed a secondary benefit of surface stabilization, which lasted for a period of time. Treated sections that developed surface stabilization were able to reduce maintenance activities to intersection areas only.

Foamed asphalt was discovered in Iowa by Csanyi in 1956, and has become a useful road rehabilitation tool when used in conjunction with cold in-place recycle (CIR) and full-depth reclamation (FDR) processes. The advance of pavement recycling and foaming technology has made foamed asphalt a common rehabilitation technique in many parts of the world including Europe, Asia, Africa, Canada, and parts of the United States. Iowa has used the technique extensively and has developed specifications for the construction of foamed asphalt FDR and CIR stabilized roadways. The intention of this research project, Investigation 873, is to develop FDR and CIR foamed asphalt specifications and report data and information that will assist engineers in Minnesota with successfully implementing foamed asphalt recycling techniques. There are already several foamed asphalt CIR projects in Minnesota that have been completed on low volume roads. The roadways were rehabilitated in Fillmore and Olmsted Counties from 2004 to 2008, and are performing quite well to date. The Minnesota Department of Transportation (Mn/DOT) has taken Falling Weight Deflectometer (FWD) and core data from these projects in order to examine the in-situ properties of the stabilized pavement layer, as well as the material properties of the foamed asphalt itself. The FWD data analysis reveals that the recycled pavement layer develops a relatively uniform strength despite the high variability inherent in most low-volume roads. Core data indicates that the foamed asphalt forms a cohesive matrix when mixed with the fines from the reclaimed material, which does not disintegrate when cored. Overall PG grade of the recycled layer changed significantly from the original mix in some cases, but not in others. The cause of this is unknown, however, differences in the procedures used and materials present at the different projects may help explain this. It is recommended that FWD, ground penetrating radar (GPR), and core analysis be performed before and after foamed asphalt projects to more accurately define these differences.

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.

This study included a survey of practicing local engineers, field performance observations of new bituminous and bituminous overlay construction, and laboratory testing. The most common binder performance grades were identified along with the most common percentage of recycled asphalt in bituminous mixtures. Local engineers regarded cracking, rutting, and construction as the most important issues when using recycled asphalt pavement. Roughly one-third of Minnesota agencies exclude RAP from wear course mixture. Analysis of dynamic modulus curves from field cores showed that full-depth specimens were more useful for relating field and laboratory performance than were the wear or non-wear course specimens. Analysis showed stronger relationships existed to low temperature performance grade and to the percentage of new asphalt binder in the mixture than to the percentage of RAP in the mixture. Field performance related well to mixture master curves in the middle portion of the test frequency range. Recommendations include using low-temperature grades of PG-34, including RAP in the wear course, and using material control to achieve good performance. Other consideration are specifying the source material origin, screening and separating by particle size (fractionated RAP), or specifying RAP asphalt content.

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.

This research looked at the perceived causes and winter maintenance strategies of tenting through a survey sent to municipal, county, and state engineers in Minnesota, before conducting field research based on the theory that deicing chemicals, sands, and crack sealing all influence pavement tenting. The research found that crack sealing can reduce the roughness and height of tented cracks.

A 5-year study of newly constructed pavements showed that a reduction in in situ air voids occurred both within and between wheelpaths for highways with an average daily traffic (ADT) load of less than 10,000 vehicles. Regardless of the level of voids immediately after construction, mixtures in the upper 65 mm (2.5 in.) within the wheelpath indicated a reduction in voids by 3 to 5 percent (e.g., from 10 to 6 percent voids), and by between 2 to 4 percent between the wheelpaths. Because only limited densification occurred below this depth for lower–traffic-volume facilities, reducing the mix design level of air voids from 4 percent to 2 percent for the lower lifts was suggested so that lower initial voids could be obtained during construction. An evaluation of older pavements indicated that moisture damage to the lower pavement layers was typical; thus, a change in mix design procedures might also help improve durability by increasing the film thickness. Pavements with high traffic volumes (>50,000 ADT) consistently indicated an increase in voids over time in the upper lift [40 mm (1.5 in.)], little change in the middle 65 mm (2.5 in.), and a decrease in the bottom 65 mm (2.5 in.). The hypothesis suggested to explain these findings was that a loss of material in the upper lifts was occurring, most probably due to moisture damage as the upper, more permeable wear course, commonly used in Minnesota, allowed water trapping at the wear and binder course (i.e., less permeable) interface. A further investigation of in situ void changes on an interstate indicated that for a pavement constructed with the same fine gradation in all lifts, traffic compacted the mixtures in a manner similar to that in low-volume roads. When the initial in situ voids increased from around 7 percent to nearly 10 percent, the influence of traffic on the densification was substantially increased. Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1575, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1575-01.

This investigation was included in the research program of the Minnesota Local Road Research Board as a project of special interest to County and Municipal Engineers in addition to Engineers of the Minnesota Department of Highways. The purpose of this study was to develop criteria for determining the need for seal coating bituminous surfaces. This investigation basically consisted of a review of current local practices made during the initial stages of the project, followed by field evaluations of a number of seal coat projects from the 1966 and 1967 seal program.