Testing

Under the auspices of the Long Term Pavement Performance (LTPP) program eight SPS-5 overlay sections were constructed in Manitoba in 1989 and Minnesota in 1990. In addition to a control section the variables included mix design (virgin or recycled materials), overlay thickness (50 or 125 mm), and type of surface preparation (minimum or extensive). Over the past 15 years these sites have been monitored to evaluate and compare the pavement performance. The pre-rehabilitation condition record of the Manitoba test site was that it was rough with fatigue and block cracking evident. The predominant distress of the pre-rehabilitation condition of the Minnesota site was recorded as severe depressed transverse cracks. As much of the original amount of cracking has reflected through the applied bituminous overlays, none of the design options have outperformed the others in preventing or reducing the severity of reflective cracking. This paper concludes that the SPS-5 study has demonstrated that given pavements in the original condition of these two test sites, the use of the more expensive options of milling, thicker overlays, and virgin bituminous material have not resulted in significant pavement performance gains. Thus the lowest cost design alternatives (minimal surface preparation, thin overlay, and RAP in HMA mixture) would be chosen as the most cost-effective overlay design options.

MnDOT and Aggregate Ready Mix Industries of Minnesota constructed a 6 “ thick 60 ft X16 ft pervious concrete pavement on a 12” thick, Coarse Aggregate CA-50 Base at MnROAD in September 2005. Prior to this a pervious granular layer, and pavement instrumentation were placed. This driveway was made up of sections representing 3 different mix designs placed 6 inches thick with one joint grooved into the pervious concrete while it was still in a plastic condition and a second joint that was constructed as a temporary header during the placement operation. To facilitate sampling without compromising the pervious matrix, replicate test pads of two mix designs were constructed on the east side of the Driveway. For destructive testing, cores will be taken from these pads periodically. This project will help answer the following questions. • What is the Permeability change over a winter? • Does sanding and salting affect the permeability? • Does the surface ever get ice when the other surrounding surfaces do not? Bituminous and concrete pads are next to the Pervious Driveway. • Can the Pervious Concrete withstand the environmental effects of a winter under sanding and salting conditions? • What is the number of freeze thaw cycles monitored in the Pervious Concrete? This study is expected to produce valuable research results after the first 2 winters. The report also discusses yield, and workability as well as hydraulic modeling issues germane to pervious concrete.

In 1993, the Minnesota Department of Transportation (Mn/DOT) commissioned the University of Minnesota Department of Civil Engineering to develop, construct and evaluate a laboratory-based test facility for rapidly applying repeated heavy vehicle loads (simulated) to pavement test structures. The purpose of this facility was to efficiently and accurately evaluate the long-term performance potential of new and experimental highway pavement designs and materials. This facility was dubbed “Minnesota Accelerated Loading Facility” or “Minne-ALF.”

Expansion and maintenance of roadway infrastructure creates a demand for high quality paving aggregates. Taconite industry rock and tailings are a potential source of virgin paving aggregates. Currently there is limited information available for implementing these products in construction design specifications. Preliminary information of product performance within current design constraints is valuable to both state design engineers and to future pooled-fund studies. This information can identify the potential for using these products in surface courses or possibly for use in rich-bottom leveling layers. This study examined the viability of utilizing these products in the Minnesota Department of Transportation (Mn/DOT) Superpave bituminous mixture design specifications. As part of the study 40 laboratory specimens were produced from 11 asphalt mixtures and then evaluated for asphalt content, air voids, and aggregate gradation. This report summarizes the results of the laboratory mixture evaluation.

“D”-cracking and other forms of aggregate-related freeze-thaw damage have often been associated with concrete pavements in Minnesota. The best approach for preventing these types of distress is to avoid using aggregate sources that are known to be susceptible to freeze-thaw damage in concrete applications. The most widely accepted methods of evaluating aggregate freeze-thaw durability involve the preparation and freeze-thaw testing of concrete beams that contain the aggregate in question. These tests are generally time-consuming, sometimes requiring months to complete, and often require the use of expensive equipment and/or highly skilled operators. Furthermore, the variable nature of many aggregate sources necessitates frequent testing to ensure the adequate freeze-thaw resistance of material being produced at any given point in time. A more rapid test of aggregate freeze-thaw durability was developed under the Strategic Highway Research Program in 1994. This test, called the Washington Hydraulic Fracture test (WHFT), was relatively inexpensive and allowed a single laboratory technician to assess the freeze-thaw durability of several samples of aggregate in as few as seven working days. Broader evaluations of the WHFT revealed several deficiencies, however.

Mineralogical analyses were performed on the Mesabi Select aggregate taken from a stockpile (-1 inch size) at MnROAD comprised of crushed material obtained from the top 25 feet of the 'Lower Cherty' member, or LC-8 bed (LC-6 bed in NRRI study), of the United Taconite mine near Eveleth. The material was utilized in asphalt (cell 32) and concrete pavement (cell 54) constructed at MnROAD's low volume loop.

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.

Top-down cracking is becoming more prevalent at MnROAD. Longitudinal cracks have developed in the wheelpaths of several cells. In the year 2000 a total of 20 cores were taken from four mainline cells. It was determined at that time that the cracking initiated at the pavement surface and that the cracks stopped at the first layer interface. In August 2005 13 more cores were taken from four mainline cells. The main goal was to further investigate the top-down cracking and its progression over time. A few cores were taken along transverse cracks to observe the deterioration present. This paper summarizes the results of this cracking investigation.

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.

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