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In the spring of 2000 cell 26, a 6" full depth hot mix asphalt (HMA) over clay loam subgrade, at the Minnesota Road Research Project (MnROAD) began to debond at the centerline cold joint. Dynamic Cone Penetrometer (DCP) testing on the subgrade was found to be consistent throughout the section and not any weaker then would be expected. A change in traffic pattern from the MnROAD semi tractor/trailer over the centerline cold joint and incomplete compaction of the asphalt surface layers contributed to the failure. The continued deterioration of the asphalt lead to the reconstruction. The 6" HMA was reclaimed and compacted in place. A 2" oil gravel was placed as the surface in August 2000. The oil gravel began to show sign of shoving immediately after 38 laps of the MnROAD truck. By the spring of 2001 the pavement had deteriorated to such a degree that it had to be regarded to provide a drivable surface. Two trenches were subsequently excavated in which unbound samples were collected for laboratory testing. Results of the testing indicate that the stresses induced in the reclaimed base by the MnROAD truck exceeded the shear strength of the material. The purpose of this report is to document the forensic investigation and to record observations and conclusions as to the historical performance and subsequent deterioration of cell 26.

This paper is a review of the forensic investigations completed on the original14 hot-mix asphalt (HMA) mainline test cells at the Minnesota Road Research Project (Mn/ROAD) during the summers of 1998 and 2001. These forensics were generated to take an in-depth look at the rutting that has taken place to the mainline test cells. Rutting is one of the primary distresses seen at MnROAD and describing how rutting is affecting the pavement structure will help validate models being developed to design better pavements and predict pavement performance. The forensic investigations themselves have consisted of full forensic trenches of all the pavement layers with complete laboratory testing. Between 1990 and 1994 the Minnesota Department of Transportation constructed the Minnesota Road Research Project (Mn/ROAD). The Mn/ROAD site is located 40 miles northwest of Minneapolis/St. Paul and is an extensive pavement research facility consisting of two separate roadway segments containing 50 500-foot long distinct test cells. The 3 ½-mile Mainline Test Roadway (Mainline) is part of westbound interstate 94 and contains 31 test cells and carries an average of 20,000 vehicles daily. Parallel and adjacent to the Mainline is a Low Volume Roadway that is a 2 ½-mile-closed loop that contains the remaining 19 test cells. Traffic on the LVR is restricted to a Mn/ROAD operated 18 wheel, 5-axle, tractor/trailer with two different loading configurations of 102kips and 80kips.

This paper’s purpose is to provide an update on the pavement condition of MnROAD’s three low volume road (LVR) Superpave test cells constructed in 1999 with different asphalt binders, see table below. These cells were built to field validate the current low temperature performance grading (PG) system currently being used at Mn/DOT and many other agencies around the world. The paper will document the mix designs, laboratory testing, forensics, environmental conditions, and the resulting distresses observed include rutting, transverse cracking, fatigue cracking and how they are affecting pavement performance and ride.

In 1999 the Minnesota Department of Transportation (Mn/DOT) joined the California, Texas, and Washington State Departments of Transportation in forming a research partnership. The partnership was named the State Pavement Technology Consortium (SPTC). The consortium was formed to share information on pavement practices including design, rehabilitation, decision-making, and research. Specific to research the consortium is concerned with how pavement orientated studies are identified, conducted, funded, and implemented. The main objective of this paper was to gather infrared temperature and density data on a number of Minnesota Hot Mix Asphalt (HMA) paving projects in the 2000 construction season to investigate the effects, if any, temperature segregation has on the paving process and the resulting pavement compaction. The second objective was to collect specific information related to the construction such as the type of mix, the equipment used in the construction process, and environmental conditions and the effects they may have on the paving process and the resulting pavement compaction. One of the main problems facing the asphalt paving industry is hot mix asphalt segregation. Segregation is generally put into two categories, one is aggregate segregation and the other is temperature segregation. In aggregate segregation there is a concentration of either coarse or fine material in some areas of the paved mat. These areas are often characterized by different surface textures from the surrounding material and can usually be seen by the naked eye. Temperature segregation is the isolated pockets of different temperatures created in the paving process. These areas may or may not produce irregularities in the mat that can be seen. Stroup-Gardiner and Brown (1) have come up with a more thorough definition of segregation: "Segregation is the lack of homogeneity in the hot mix asphalt constituents of the in-place mat of such a magnitude that there is a reasonable expectation of accelerated pavement distress(es)." Previous research from the Washington Department of Transportation (WSDOT), NCAT and others has suggested that there is a correlation between material segregation and temperature differentials created in the paving process. Temperature differentials greater than 25‘F can cause areas of cooler material not to be compacted to the same densities as the surrounding warmer material. These areas can exhibit poor structural and textural characteristics, poor performance and durability, and can have shorter life expectancy and higher maintenance costs. The identification of these temperature differentials is captured with the use of a thermal imaging infrared camera. All objects no matter their temperature emit radiation. Measuring this radiation emitted allows you to determine the temperature of any and all points in the viewing spectrum of the camera. The temperature segregation will show up as different colors representing areas of different temperature. After a maximum predetermined temperature differential has been exceeded additional testing and inspection can be preformed to determine the level of distress that may or may not be present.

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.

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.

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.