The development of small bumps in the surface of hot-mix asphalt overlays has been a problem for state and local highway agencies for many years. Sometimes these bumps are small and are not large enough to be felt by drivers. Under many conditions, however, they can be large enough to cause ride-related problems at normal operating speeds. Under this project, a survey was conducted of local and state engineers in Minnesota responsible for highway construction and maintenance to compile corrective actions that they have used avoid these bumps and to mitigate their effects if they occur. Instrumentation sites were incorporated into this project to determine the magnitudes and profiles of temperature in the existing asphalt layer when a new layer of hot asphalt is placed on top of it. The instrumentation sites were also used to gain further information on the common practices of highway construction personnel in reducing the probability of bumps, and mitigation efforts if bumps occur. This report describes the survey, site visits, construction instrumentation, laboratory studies, and evaluation conducted by the project team. It also presents a draft booklet compiling the common practices for avoiding and mitigating bumps gathered throughout the project.
The purpose of this document is to report on the performance and various distresses on the MnROAD Mainline HMA sections. Other than simple observations and conclusions, this report will not delve into the causations of the distresses. It is expected that future reports will do so. One observation though is clear; unlike some other test tracks and accelerated test facilities, MnROAD, now eight years old, in a harsh environment, shows that performance is governed as much by the interaction of environment, traffic and material properties as by the interaction of traffic and structural design. It is clear that any proper pavement design must integrate not only structural design but also material properties appropriate to the environment, for all elements of the pavement are under attack, not only by traffic but also the environment, and the environment coupled with traffic.
More Minnesota projects across the state are using Superpave pavements for their roadways. Now into its seventh year of Superpave, Minnesota is seeing a decrease in the cost per ton of Superpave mixes and in the construction problems seen with earlier Superpave projects. The amount of Superpave placed in Minnesota has more than doubled in five years, going from 807,000 tons in 1998 to over 1,718,000 tons in 2002. As the mix design becomes more common, the average cost per ton has decreased over 14% in the same time frame, from $30.58 to $26.34 per ton in 2002.
In the summer of 2003, Minnesota’s Department of Transportation (Mn/DOT) conducted a series of preventative maintenance activities to the hot mix asphalt (HMA) test cells at its MnROAD test facility. The activities took place on MnROAD’s mainline test road, which consists of 3 miles (4.8 km) of two lane, westbound Interstate Highway 94 with an average daily traffic (ADT) level of 25,000.
Open to traffic in 1994, the fourteen HMA test cells were in need of maintenance to address rutting, top-down cracking, and cupped transverse cracks. Each cell is 500 feet (150 m) long and is designed as a 5-year or 10-year pavement with a variety of mixtures and bases.
Mn/DOT applied a series of maintenance activities either alone or in combination for re-sealing sealed transverse cracks, leveling out cupped transverse cracks and filling rutted wheelpaths. Two control cells, one 5-year and one 10-year, were left alone to compare the restored cells against. The goal was to restore the ride quality of the mainline cells, measured by International Roughness Index (IRI).
The ride quality improved 48% four months after the application of the maintenance work. Early results showed leveling of the cupped transverse cracks prior to applying a thin maintenance surface (TMS) provides better ride quality results, as does a double application of the TMS compared to a single application. The results gathered are early in the life of the treatments and they will change in time.
On September 15 and 16, 2003, TH-60 had transverse cracks leveled with Deery’s Level-N-Go mastic and Crafco PolyPatch – Fine Mix Type 3 material. For study purposes, the full-width transverse cracks were filled with both materials. One material was placed in the eastbound lane and the other material was placed in the westbound lane of the same transverse crack. See Appendix # 1 for the layout of each material. The portion of TH-60 that received the mastics began at milepost 125, just west of Elysian, and proceeded west.
Highway Improvements, Inc., of South Dakota, performed the work. The original intent of the study was to place approximately 4,700 pounds of both materials in as many cracks as possible. The final amount of material was less than the 4,700 pounds. Highway Improvements stopped work at the point of traffic control, which was provided by Mn/DOT District 7 personnel.
The intent of this study is to determine the mastic’s effectiveness in leveling cupped transverse cracks for improved ride. Other factors that will be monitored include the durability of the material, how soon cracks appear in the material, the maintenance of these cracks should they appear, the cost of the material, the productivity rate of applying the material, and the material’s ability to accept a future HMA overlay.
Mn/DOT hopes to partner with Minnesota State University (MSU) at Mankato and Dr. Jim Wilde in a study to determine acceptability of mastic materials with HMA overlays. This work will be similar in nature to LRRB 802 currently underway between MSU & Mn/DOT where crack sealants and HMA overlays are being studied.
The goal of LRRB 770 is to develop a list of acceptable sealant types and methods of resealing previously sealed cracks or joints. Local road authorities have used crack sealing as a method to reduce water infiltration in hot mix asphalt (HMA) pavements for many years. The original rubberized crack and joint sealants work well for 3 to 7 years, then they begin to fail. There is no accepted method of how to reseal these cracks and joints after they begin to fail. Working with the assumption that reducing water infiltration in HMA pavements extend the life of these pavements, it is imperative that an acceptable method of resealing these cracks and joints be determined.
There was a significant change in the condition of the sealant since the 2003 review, with many of the cracks observed now showing signs of sidewall adhesion failure. The two primary reasons for the failures are thought to be traffic and weather. Because the sealant was applied over a previously sealed crack or joint, it basically has no shape factor to it.
Instead, it is typically a thin band of sealant spread over the crack and therefore susceptible to traffic wear and tear. That may explain some of the failures seen, but one would expect the failures to be more common in the wheelpaths of the cracks or joints, and this was not the case.
The failures seen tended to be across the entire crack or joint, and weather related stresses might be the reason. The winter of ’03 – ’04 was colder than the previous winter, when an extended cold spell in January 2004 had 3 straight days with temperatures never reaching 0°F (-18°C) and bottoming out at -22°F (-30°C) on consecutive nights. There was also a stretch from late January to early February where 15 out of 19 nights had below 0°F (-18°C) temperatures. With the thin band of sealant placed over the cracks or joints, these temperature extremes could be the primary reason so many adhesion failures were seen
The purpose of this report is to document the reconstruction process and to provide background information about the historical performance and subsequent deterioration of Cell 26 that lead up to the reconstruction. Cell 26 extends from Station 170 + 75 to Station 174 + 65 on the LVR. The cell, one of eleven LVR HMA test cells, was originally designed to be a 6? full depth hot mix asphalt cell. The HMA had a Marshall Hammer design of 50 blows and uses an AC 120/150 penetration grade asphalt binder. Laboratory testing has shown that the 120/150 asphalt binder used at MnROAD has a Performance Grade (PG) of 58-28.
More Minnesota projects across the state are using Superpave pavements for their roadways. Now into its seventh year of Superpave, Minnesota is seeing a decrease in the cost per ton of Superpave mixes and in the construction problems seen with earlier Superpave projects.
In a partnership formed with the Minnesota Department of Natural Resources (DNR), the Local Road Research Board (LRRB) investigation 819, the Minnesota Department of Transportation (Mn/DOT), and other partners, MnROAD test cell 31 was reconstructed with a hot mix asphalt (HMA) that contained 80% (by volume) Mesabi Select Hard Rock aggregate. It marked the first asphalt mix of its kind that utilized Mesabi Select Hard Rock aggregate as both the coarse and fine aggregates of the asphalt mix in the twin cities area. The purpose of this test cell is to demonstrate to the industry that Mesabi Select Hard Rock can be used to produce a HMA mixture meeting Mn/DOT specifications. It also demonstrates that the mixture can be placed like other HMA mixtures, and through instrumentation installed at the MnROAD site, its performance can be documented and quantified.
