Thin bonded concrete overlays of existing asphalt pavements (BCOA), also known as “whitetoppings”, are becoming increasingly popular as an economical way to extend the life of an in-place pavement. While there had been several procedures developed in the past to structurally design this pavement rehabilitation option, the need for a more rational mechanistic-empirical based procedure still existed. Recognizing this gap in knowledge, the Minnesota Department of Transportation began in 1993 to construct various BCOA test sections designed to develop data for a comprehensive new design procedure for BCOA. By 2007, many other states in the U.S. were also interested in improved design procedures for BCOA. So in 2008, a 5-year long pooled fund research project was initiated and funded by 6 states, including Minnesota, Missouri, Mississippi, New York, Pennsylvania and Texas. By the completion of the project, the states of Iowa, Kansas, North Carolina and South Dakota had also joined the project.
The Minnesota Department of Transportation (MnDOT) is currently conducting a research project aimed at reducing longitudinal joint (L JT) deterioration in hot mixed asphalt (HMA) pavements through improved construction techniques, preventive maintenance practices, and repair treatments. Constructing durable HMA pavements, with adequate (L JT) performance, has been well documented and extensively researched, however preventive maintenance and repair treatments specific for (L JT) have received little attention in the literature.
The research work plan seeks to address the deterioration through improved construction, targeted preventive maintenance, and repair methods.
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
Bonded concrete overlays over existing asphalt pavements, also known as “whitetopping,” are becoming an increasingly popular rehabilitation solution for many agencies. As with any rehabilitation technique, it is important to understand and incorporate cost effective features that will insure long lasting performance. Since the long term performance of thin whitetopping is reliant on a strong bond to the underlying asphalt, it is important to protect that bond for as long as possible. The primary way to reduce bond degradation is by keeping water away from the surface of the underlying asphalt. This is typically done by filling or sealing the contraction and panel edge joints with liquid (“hot-pour”) asphalt sealant. Due to the thin slab designs typically used for whitetoppings, panel sizes need to be smaller, thereby resulting in many more joints than in typical concrete pavements. With today’s restricted budgets, owners and engineers must consider whether the sealing or filling of joints in whitetopping provides an economic benefit.
In Minnesota the transition from winter to spring is normally accompanied by the formation of potholes and other distresses as streets and highways weaken and adjust to warmer conditions. At times the extent of this seasonal deterioration can be so vast that maintenance crews are required to give full-time attention to the problem. Patching often continues, or is repeated, as the seasons pass from spring to fall.
During winter and early spring agencies often use “cold mix” asphalt for patching, and eventually return to “hot mix” as soon as bituminous plants can be activated. The
effectiveness of these standard materials depends largely on the level of effort that patching crews can devote to site preparation and material placement.
In the spring of 2011, the cities of Bloomington and Minnetonka, Minnesota collaborated on a field investigation of the installation and field performance, of two “mastic” patching materials along with standard patches that were applied at the same time. The investigation was funded by the OPERA program and normal maintenance budgets. Mn/DOT Road Research assisted in documenting the installation and conducting autumn performance evaluations.
The two primary types of crack sealing methods commonly used in Minnesota include: ROUT AND SEAL and CLEAN AND SEAL. The ROUT AND SEAL method is preferred on transverse cracks less than ¾” wide. The clean and seal method is recommended for longitudinal cracks, or if the cracks are too numerous or too large for the route and seal method. Crack Sealing is intended to prevent moisture from entering the base and subgrade, which can weaken the pavement’s subsurface structural layer and contribute to pavement deterioration. Sealing the pavement cracks and preventing the intrusion of moisture can be expected to extend the pavements’ service life and slow the rate of deterioration.
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.
Shoulders are critical roadway components. They provide repose for vehicles to stop during an emergency and a recovery area when vehicles depart the driving lane. Granular shoulder installation is inexpensive and therefore is a commonly found roadway section. However, they often result in a condition called shoulder drop-off.
Shoulder drop‐offs become dangerous when errant drivers unexpectedly swerve off the paved roadway, which is sometimes inches from the drive lane, and attempt to quickly redirect their vehicle onto the road. The vertical edge created by the paved roadway prevents the vehicle from easily returning to the roadway. The driver is forced to over steer to
compensate for the drop‐off and can lose control of the vehicle.
Maintaining shoulders generally consists of replacing the lost aggregate material, regrading, and compacting. This is a temporary solution and needs to be repeated frequently. The money saved initially by constructing aggregate shoulders is often surpassed by on‐going maintenance costs.
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.
Mn/DOT demonstrated a porous pavement vacuuming process using equipment owned and operated by Reliakor, a Minnesota based Company at MnROAD on November 4, 2009. Pervious concrete test cells 85 and 89 and porous asphalt cells 86 and 88 were vacuumed. Representatives from Mn/DOT Metro District, Mn/DOT Research, Mn/DOT Tech Support, Mn/DOT Maintenance Research, the City of Minneapolis, DNR, and Reliakor Services Inc were in attendance.
The test cells were approximately one year old at the time of the demonstration and were in good condition. The pervious concrete test cells had no surface raveling or joint distress and very few fine cracks. The porous asphalt test cells had isolated areas of surface raveling and light rutting. The voids in the pervious concrete and porous asphalt test cells appeared to be clean and free of debris. It is important to note that the brush on the vacuum was not used. The brush could pack debris further into the voids and increase clogging in the pervious/porous pavements.
