Watson, Mark J.

MnDOT is currently implementing in-place recycling techniques as a maintenance and rehabilitation strategy for bituminous pavement structures. The techniques being employed include: Full Depth Reclamation (FDR), Bituminous Stabilized Full Depth Reclamation (SFDR), and Cold In-Place (Partial Depth) Recycling (CIR). In-place recycling of bituminous pavements has been used in Minnesota for more than ten years at the local level, longer in other parts of the country and the world. MnDOT has constructed 10 state projects since 2010 using a variety of processes and stabilizing additives.

Full Depth Reclamation (FDR) is the process of pulverizing a roadway’s flexible pavement section and a portion of its underlying base, and crushing and blending the recovered material to create a uniform base material.

The Minnesota Department of Transportation (Mn/DOT) is currently conducting a research project aimed at reducing longitudinal joint (Ljt) deterioration in hot mixed asphalt (HMA) pavements through improved construction techniques, preventive maintenance practices, and repair treatments. Constructing durable HMA pavements, with adequate Ljt performance, has been well documented and extensively researched, however preventive maintenance and repair treatments specific for Ljt have received little attention in the literature. It is commonly accepted that adequate density is critically important in achieving a durable HMA pavement. Insufficient density, or high air voids, usually results from the difficulty of compacting an unconfined pavement edge, and the localized area of low density creates a density gradient. Pavements with lower densities can have more interconnected air voids, leaving them more susceptible to moisture and environmental deterioration resulting in distresses such as weathering and raveling.

In 2008, Mn/DOT initiated a five year study that examines the performance of two thin unbonded concrete overlay projects: Cell 5 of the MnROAD Phase II (SP 8680‐157) and a section of TH 53 near Duluth, Mn (SP 6916‐99). These pavement test locations provide a unique opportunity for researchers to include additional environmental and traffic factors in validating performance results. It is anticipated that the results from these studies will improve the understanding of the behavior of this complicated composite system, which will lead to the development of better distress and life prediction models and ultimately contribute to more sustainable pavement designs.

This report presents results of the research that examined various asphalt pavement surfaces in the MnROAD facility. It covers the fundamentals of surface profilometry, describes the construction of the textures and elucidates the performance trends of the various surface parameters. The variables examined include friction, measured with the lock wheel skid truck, smoothness, measured with the light weight profiler, mean profile depth measured by the circular track meter, sound absorption measured by the acoustic impedance tube and Tire- Pavement-Interaction-Noise measured by the on board sound intensity device. Traffic difference was found to be a significant variable in the friction trend of the asphalt surfaces when the low-volume road inside lane of the cells were compared to the corresponding outside lane and when the mainline driving and passing lanes were compared. Based on the Wilcoxon Rank sum, Wilcoxon Sign Rank, and the T-test, traffic levels affected skid resistance. Additionally, the frictional-time series appeared to follow the half-life equation typical of disintegrating materials. A similar test on tire-pavement-noise difference found traffic to be insignificant within the five years of monitored performance of the same test tracks. This study found that certain surface characteristics change with time regardless of traffic while others change with time and traffic. As the study found friction to be related to traffic, periodic measurements of friction can be performed when practicable, otherwise the half-life model developed in this study may be a rough predictor. In the deduced model, friction degradation appeared to be a function of the initial friction number and traffic-induced decay factor. In the low-volume road, there was hardly any evidence of effect of traffic on friction from a comparison of the traffic and environmental lanes. However, at higher traffic levels, (mainline driving versus passing lanes) traffic appeared to affect noise and friction. The study also proposes a temperature-based correction algorithm for Tire-Pavement-Interaction-Noise. From distress mapping, IRI, and permeability measurements, there were no noticeable trends within the five years of study. Additionally, this research performed advanced data analysis, identified significant variables and accentuated intrinsic relationships between them. Additionally, the "on board sound intensity" (OBSI)-Temperature correlation exhibited a negative polynomial relationship indicating the higher importance of temperature to OBSI relationship in asphalt than published characteristics of concrete pavements. It ascertained that texture mean profile depth was not as significant as texture skewness in predicting surface properties. Smoothness measurements indicated that most asphalt surfaces are not associated with laser-induced anomalous IRI reading errors. The major properties affecting ride in most asphalt surfaces were evidently extraneous to the surface texture features..

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.

The report describes the construction and design of composite pavements as a viable design strategy to use an asphalt concrete (AC) wearing course as the insulating material and a Portland cement concrete (PCC) structural layer as the load-carrying material. These pavements are intended for areas with heavy trucks and problem soils to increase the service life and minimize maintenance. The project focused specifically on thermally insulated concrete pavements (TICPs) (that is, composite thin AC overlays of new or structurally sound existing PCC pavements) and developed design and construction guidelines for TICPs. Specific research objectives include determining behavior of the layers of the TICP system, understanding life-cycle costs and the feasibility of TICPs, and incorporating the results into design and construction guidelines. Both construction and design guidelines are considered in light of the construction and performance of TICP test sections at the Minnesota Road Research project (MnROAD).

This report summarizes lessons learned about the field and laboratory performance of the Recycled Asphalt Pavement (RAP) and Fractionated Recycled Asphalt Pavement (FRAP) test cells at the Minnesota Road Research Project (MnROAD) between 2008 and 2012. The project scope included: developing specifications for FRAP, construction of FRAP and RAP test cells at MnROAD, field performance evaluations, and laboratory testing of binders and mixtures. The project that monitored 11 test cells.

In the summer of 2008, after roughly fourteen years of service many of the pavement test cells at the Minnesota Road Research project (MnROAD) required rehabilitation or reconstruction. This massive construction effort was also known as "Phase II" (SP 8680-157). Among the cells that were rehabilitated was Cell 5, which is located on the mainline or interstate 94 section of the research facility. Cell 5 received a thin (4 to 5") unbonded concrete overlay. This cell was heavily instrumented with electronic sensors designed to collect environmental and load response data. In addition the pavement in this cell will be thoroughly evaluated and rigorously tested at various times during the year. The thin design, and consequently shorter life, of this overlay should produce valuable data over the life of the sensors. This report describes the physical characteristics of the new thin unbonded concrete overlay test cell 5 (sub-cells 105-405). Included in the report are the construction plans (including sensor layouts), quantities and bid prices, as well as the special provisions. The report also summarizes the results from the initial material tests, various surface characteristics measurements and other initial test results.

Unbonded concrete overlays are generally used to rehabilitate pavements by restoring lost ride and structural capacity. Historically, their design has been conservative (thick) due to the lack of a rational design method. In the summer of 2008, TH 53 near Duluth, MN, was rehabilitated with a thin (5-inch thick) unbonded concrete overlay. The Minnesota Department of Transportation (Mn/DOT) included the TH 53 overlay as part of a research project on thin unbonded concrete overlays. Falling weight deflectometer (FWD) measurements were taken both before and after construction. A short section of the project was instrumented with electronic sensors designed to collect environmental and load response data. The TH 53 test section is currently undergoing thorough evaluations and rigorous testing in accordance with the research project work plan. This report presents the initial baseline testing results, which include: distress survey and mapping, ride quality measurements, and structural testing. A visual distress survey, conducted in April 2009, revealed that approximately 40 transverse cracks have formed in the overlay over the nearly nine mile project length. FWD measurements indicate that the new pavement is providing good structural support.