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Current Research Projects - Phase Two
The MnROAD Phase Two Research initiative is a combination of multi-state pooled fund projects, initiatives led by public and private partners, and MnDOT projects. These projects address a range of issues for the effective design, construction and maintenance of pavement systems.
In addition to pooled fund and partner projects, MnROAD will be conducting projects directed at solving local problems, for MnDOT and for the local agencies, through research sponsored by the Local Road Research Board.
Brief project descriptions, objectives and links to more information:
Use of Taconite aggregates in pavement applications (NRRI, Partner Project)
Investigation of Low Temperature Cracking in Asphalt Pavements - Phase Two (Pooled Fund Project)
HMA Surface Characteristics related to Ride, Texture, Friction, Noise, Durability (Pooled Fund Project)
MnROAD Field Investigation of Polyphosphoric Acid Modified Asphal (Ergon Inc, ICL Performance Products, Innophos, MTE, FHWA)
Recycled Asphalt Pavements (MnDOT Project)
Warm Mix Asphalt (MnDOT Project)
Design and Construction Guidelines for Thermally Insulated Concrete Pavements (Pooled Fund Project)
Composite Pavement Systems (SHRP 2 Project)
PCC Surface Characteristics - Rehabilitation (Pooled Fund Project)
60 Year Design Concrete Pavement - Performance Model Development (MnDOT Project)
PCC Surface Characteristics - Construction (MnDOT Project)
Concrete Overlays (Whitetopping/Unbonded Overlays)
Performance of Thin Unbonded Concrete Overlays on High Volume Roads (MnDOT, American Concrete Pavement Association and Portland Cement Association Project)
Full Depth Reclamation
Full Depth Reclamation Study (SEM Material, Partner Project)
Low Volume Roads
The Effects of Implements of Husbandry "Farm Equipment" on Pavement Performance (MnROAD Study, Pooled Fund Project)
Pervious Concrete Mix Design for Wearing Course Applications (CTRE, Partner Project)
Permeable (HMA) Pavement Performance in Cold Regions (LRRB, MnDOT project)
Pervious Concrete Pavement Study (LRRB, MnDOT project)
Recycled Unbound Pavement Materials (Pooled Fund Project)
Recycled Asphalt Pavements (MnDOT Project)
Field Investigation of Highway Base Material Stabilized With High Carbon Fly Ash (Bloom Consulting, Partner Project)
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. The main goal of this coordinated research effort is to determine if taconite aggregates can be practically used in pavement construction projects. The issues involve both engineering/ material properties and economics/logistics of transportation. Several questions that need to be answered include:
- Can taconite aggregates be used (either exclusively or in combination with other aggregates) in the production of “typical” HMA and PCC mixtures?
- What engineering properties (texture, friction, strength, etc.) of the aggregates can be used to our advantage to build premium pavements? Possibilities include SMA, NovaChip, microsurfacing, or quiet pavements.
- What are the differences (size, shape, texture, mineralogy, etc.) between each taconite aggregate source? All taconite aggregates are not the same.
- What is the quality of the bond between taconite aggregates and asphalt binder (HMA) or paste (PCC)? Dallas Little’s work on surface energy may be applicable here.
- Should payment schedules be adjusted because of the increased Gsb of the taconite?
Investigation of Low Temperature Cracking in Asphalt Pavements - Phase Two
Low temperature cracking is the most prevalent distress found in asphalt pavements built in cold weather climates. As the temperature drops the restrained pavement tries to shrink. The tensile stresses build up to a critical point at which a crack is formed. The current Superpave specification attempts to address this issue by specifying a limiting low temperature for the asphalt binder. The specification does a reasonable job predicting performance of conventional asphalt cements, but this does not hold true for polymer-modified asphalt binders that are manufactured to reach very cold temperature grades needed in cold climates. Currently the low temperature specification considers only the asphalt binder. Specifications must be developed for the asphalt mixture as well. It is very important to understand the mechanism of crack initiation and propagation. Thermal cracks can be initiated by traffic loading or cycles of temperature changes and then propagated by a large drop in temperature. In addition, the significant effects of aging and moisture on crack formation and propagation are not fully understood and need investigation.
A comprehensive research effort is in progress by a team led by Dr. Mihai Marasteanu at the University of Minnesota. This project is a unique partnership between MnDOT and four universities: University of Minnesota, Michigan Technological University, University of Illinois at Urbana-Champagne, and University of Wisconsin at Madison. The goal of the current project is to evaluate different laboratory procedures, material properties, and pavement features in order to develop an optimal system for selecting low temperature crack resistant materials. There is a critical need to validate the findings of this experimental work with field data. To this end, two sections will be constructed at MnROAD. MnROAD provides a unique combination of instrumentation, regular performance monitoring, controlled traffic applications, researcher expertise, and a safe work environment that makes it an ideal location for this study. More
More and more attention has been paid recently to hot mix asphalt pavement surface characteristics. In addition to structural capacity and durability, it is now desirable to design pavements to meet noise, texture, friction, and ride requirements. Noise (both interior and roadside) is at the forefront of the minds of both pavement designers and the traveling public. Many studies are currently underway around the United States and in Europe to address noise and these other issues.
The traditional way to reduce noise for nearby residents and businesses has been to build noise walls. Besides being large and undesirable to look at, noise walls can also be quite expensive. Innovative pavement surfaces have recently been developed as an alternative to building noise walls. The type of wearing course plays a major role in determining the surface characteristics of a pavement. Several options that can provide lower noise levels than conventional dense-graded pavements include stone matrix asphalt (SMA), open graded friction course (OGFC), porous HMA, 4.75-mm Superpave mixes, and NovaChip. In general pavements with smaller maximum aggregate size, open gradation, and negative macrotexture produce less noise.
SMA and OGFC pavements have been used extensively in the southern United States with great success. However, far fewer states in cold climates have used these open-textured mixes. As a result little is know about the performance of open-textured mixes in cold climates. There is a fear that over the harsh winter the pavement will disintegrate due to sand and salt operations, freeze-thaw action, snow plowing operations, and the like. There is a need to conduct a controlled experiment in a northern state like Minnesota to determine the durability and performance of a pavement built for certain surface characteristics. MnROAD offers an experimental site where the risk can be taken to construct and monitor open-texture mixes in a cold environment.
This research project will progress on two tracks:
- Construct two new HMA pavements using SMA, 4.75-mm Superpave mix, etc. specifically for the purpose of reducing the noise while maintaining other important surface characteristics.
- Monitor all of the new test cells built at MnROAD for their noise, texture, friction, and ride characteristics.
One of the major tasks in any transportation agency pavement management system is to select the appropriate alternative for rehabilitation and maintenance. There is a need to understand how preventive maintenance improves the performance of the existing pavements, to develop new techniques, and to determine the optimal timing for the application of these treatments.
Perhaps the main reason to apply a preventive maintenance treatment to an HMA pavement is to reduce the aging of the asphalt binder and therefore maintain a higher level of pavement performance. Some research has documented the aging of asphalt through traffic loadings. However, the mechanisms that cause environmental aging are not well understood. This research aims to better understand the mechanisms behind aging and therefore apply the right surface treatment at the right time.
This research requires a mixture of fundamental analyses based on laboratory experiments and field investigations. The timing of the surface treatment is related to the aging and distresses that develop in asphalt pavements over time. Ideally, a surface treatment should be applied at the proper time to provide a balance between maximum life and minimum cost. The progression of the asphalt pavement surface condition is mostly related to the aging characteristics of the asphalt binder and to the evolution of the mechanical properties of the binder with aging. An ongoing project at the University of Minnesota is investigating some of the issues related to the application of surface treatments, including environmental (climatic) modeling and mixture and binder testing to determine when preventive maintenance activities should be done.
The goal of this study is to determine the proper timing of preventive maintenance treatments in order to optimize life cycle costs and pavement performance. This pooled fund study will perform preventive maintenance research on Phase Two test sections at MnROAD. More
Polyphosphoric acid has been used for some thirty years to stiffen asphalt for paving applications. More recently it has been used to stiffen asphalts that may be marginal on the Superpave RTFOT test. This has been particularly so in the case of polymer modified binders. It was found more cost effective to add a small amount of acid, which could readily be dispersed in the binder rather than mill in additional quantities of more expensive polymer. It was then found that by adding polyphosphoric acid the amount of polymer could be reduced thereby saving cost for the contractor. The Federal Highway Administration, Office of Infrastructure, is completing a laboratory project to address the risks and benefits associated with the use of polyphosphoric acid as an asphalt modifier. To clearly identify which grades can and cannot be used and the pitfalls associated with the use of polyphosphoric acid with antistrip compounds, such as amines and lime as well as asphalt binders from differing sources. The MnROAD study will build upon the findings of this study and conduct a field trial to assess the performance of PPA mixes over a 5 year period. This study will be a joint venture between MnDOT (overall project management and administration), Ergon Inc, ICL Performance Products, and Innophos, Inc.( funding support, advice and guidance on the proper inclusion of PPA into the asphalt mixtures), Federal Highway Administration (asphalt binder/mixture performance testing and financial support for MnROAD operations), and Mathy Construction (asphalt binder supply and evaluation of stripping susceptibility).
The goal of this project is to investigate the field performance of asphalt mixtures modified with polyphosphoric acid (PPA) and compare them to similar mixtures using traditional modification techniques. Traditionally the addition of polymers (SBS, SBR, Elvaloy, etc.) have been used to enhance the properties of asphalt binders. Specifically, polymers have improved the pavement performance at high temperatures (i.e., rutting) without adversely affecting the low temperature properties (i.e., low temperature cracking). The use of PPA is seen as a lower-cost alternative to polymers in order to achieve the same increased performance. Several laboratory experiments have successfully demonstrated the effectiveness of PPA modification. What is needed now is a field validation study, which will be undertaken with this project. Development of a solid experimental plan will be part of forthcoming work agreements between the parties. Related previous or ongoing studies Federal Highway Administration, Mathy Construction, Western Research Institute, and other organizations have recently performed research on several aspects of acid modification of asphalt binders. The MnROAD study is seen as field validation of the findings from those studies. Construction of five MnROAD Low Volume Road test cells to study the performance of asphalt mixtures modified with polyphosphoric acid was completed in 2007. The cells include the following binder materials:
- PPA + SBS polymer
- SBS polymer
- PPA + Elvaloy polymer
- Degree of composite action (bond) of PCC and HMA layers
- Thermal blanket effect of the HMA layer on the PCC layer
- Development of cracking in the PCC layer
- Development of reflective cracking and rutting in the HMA layer
- Degree of reduction in roughness
- Criteria for applicability of TICP for existing rigid pavements
The main objective of the proposed research is to develop design and construction guidelines for thermally insulated concrete pavements (TICP), i.e. composite thin HMA overlays of new or structurally sound existing PCC pavements. A secondary objective is to develop recommendations for feasibility analysis of newly constructed TICP or thin overlays of the existing concrete pavements. These objectives would be accomplished by collecting field performance data and evaluating the influence of design, material properties, and construction on the performance of TICP. More
MnROAD will conduct a five-year project to specifically study the performance of RAP under controlled testing conditions. Several asphalt concrete test sections will be built at the Minnesota Road Research Facility. The sections will have similar structural designs and contain 30 percent RAP but vary by binder grade and fractionated RAP content. Although RAP is a widely used component in asphalt concrete perceptions about best practices tend to vary between agencies. Current national trends promote the use of high-RAP asphalt concrete. The incorporation of fractionated RAP at the asphalt mix plant can potentially improve the quality of existing designs and also to enable higher percentages of RAP to be used in mixtures. The Minnesota Department of Transportation specifies the maximum amount of RAP allowed in a mix based on pavement layer and traffic level. Binder grade also affects the maximum allowed RAP percentage. MnDOT wishes to determine if the present limits on RAP are justified. This pooled fund study will include laboratory, construction, and field monitoring components, and it is intended that the RAP research will be performed on newly built test sections at MnROAD.
Thermally insulated concrete pavements consist of a concrete pavement structure (jointed or continuously reinforced) covered by an asphalt layer during construction (before opening to traffic) or soon after construction to address ride quality or surface characteristic issues. The reverse process of constructing concrete over an asphalt pavement is called whitetopping, and it will be considered in other projects outside of this study. Thin asphalt overlays encompass many of the same ideas as TICPs, and they will also be considered in this pooled fund study.
TICPs combine the structural longevity of PCC pavements with the serviceability of HMA pavements. One of the perceived benefits of TICPs is the simplification of the PCC design and construction through a thinner PCC layer, simplified finishing, and simplified joint formation techniques.
There is a need for effective design and construction guidelines for TICPs. These guidelines should be based on a better understanding of the effects of design, materials, and construction parameters on the performance of the TICPs. The research proposed in this pooled fund study aims to develop such guidelines for mechanistic design and construction. The study will require extensive field performance data as validation of the design process.
Several TICP sections will be constructed at MnROAD and their performance will be compared with the performance of adjacent concrete and asphalt pavements. The following issues will be addressed:
Composite Pavement Systems
This project will investigate the design and construction of new composite pavement systems. The research will focus on two promising applications of composite pavement systems: (1) an asphalt layer(s) over a PCC layer and (2) a PCC surface over a PCC layer. This project will determine the behavior and identify critical material and performance parameters, develop and validate mechanistic-empirical performance models and design procedures consistent with the Mechanistic-Empirical Pavement Design Guide (MEPDG), and recommend specifications, construction techniques and quality management procedures. Several Cells will be constructed at MnROAD in 2009 as part of this project. More
People desire smooth, quiet, and safe pavements. To encourage smooth pavements, we need to quantify the effects of other important pavement performance parameters on ride. These parameters include texture, noise, and friction. An understanding of the interaction of texture and ride is still very rudimentary. In 2002 the MnDOT Concrete Engineering Unit and the Concrete Pavers Association of Minnesota created a test section on TH 212 at Bird Island to study the effects of texture and joints in pavement smoothness. The results showed that profile index was affected by texture and joints. However, data is so far insufficient to define a global correlation between texture values and their effect on ride, and the results obtained for the effects of joints on ride were not conclusive because of unanticipated construction issues.
One option is for rehabilitating Portland cement concrete pavements without the need to restore structural capacity is to diamond grind the surface. This process removes much of the pavement roughness and restores texture and friction. Many variables play into the grinding operation, such as blade spacing, depth of cut, kerf configuration, etc. There is a need for a standardized specification for diamond grinding. These parameters affect and govern the preponderant frequencies that cause noise when such frequencies are not randomized. Power spectrum density analysis of results obtained in the Bird Island Test section as well as profilometer-generated roughness showed that diamond grinding did improve the ride. The resulting texture and noise were not measured until 2005 when the FHWA PSC study team measured the site. Minor changes in the geometry of diamond grinding equipment tremendously affect the friction and noise performance, but the optimum geometry is still unknown.
This research item is in harmony with the CPTP track 4 of the CPTP road map. This track seeks better understanding of concrete pavement surface characteristics and provides tools for engineers to help meet pre-determined requirements for ride quality, quietness, safety against hydroplaning and splash/spray, and durability.
Research findings will enable Mn/DOT to specify friction, ride, and texture ranges of values that will optimize quietness, ride, texture and friction in program delivery. It will reduce the incidence of uncomfortable ride, hydroplaning, and obnoxious whines. The average road user benefits from the results of this study.
Due to increased traffic congestion and reduced highway construction budgets, emphasis is now being placed on designing and constructing longer life pavements. For concrete pavements, the new goal for urban high volume highways in Minnesota is toward a 60-year design life. Using the current MnDOT design guide for concrete pavement design (based on 1986 AASHTO Design Guide), MnDOT is now constructing what is believed to be 60-year design concrete pavements. However, during the design process, both the traffic prediction and service life of the concrete pavement is being extrapolated far beyond the available charts in the current design method. This research will strive to improve MnDOT’s concrete pavement design method by measuring and characterizing the actual stresses and strains experienced by the 60-year design pavements currently being built in Minnesota.
Concrete Pavement Optimization – Determining the Lower Threshold of Slab Thickness for High Volume Roads
The thicknesses of today’s concrete pavements in Minnesota are a result of many years of empirical research and design. Due to uncertainty with traffic predictions and material performance, these designs tend to be conservative, resulting in very few concrete pavements failing due to fatigue cracking. Many of the designs are actually based on extrapolation of original AASHO Road Test data, which was based on a limited set of traffic loadings, subgrade type, and environmental exposure (2 years). Work has been done recently to evaluate and calibrate the new mechanistic empirical pavement design guide (MEPDG), but datasets have been limited to thicker pavements. To improve the calibration of new mechanistic-empirical concrete pavement design methods, data is needed to fully develop the distress and life prediction models of thinner, more optimized and economical pavements.
The primary objective of this research study is to develop better distress and life prediction models for more optimized (thinner) concrete pavements. Secondary objectives include understanding the behavior of these pavements with regards to maturity, slab warp and curl, thermal expansion, and repair techniques. These objectives will be accomplished through extensive testing of materials during construction, as well as the application of interstate traffic, conducting extensive seasonal load response testing, and monitoring the field performance of an instrumented variable thickness concrete pavement test cell. New MnROAD concrete test cells will be built with slab thicknesses of 5, 5.5, 6 and 6.5 inches. All other design variables will be fixed, except for dowel bar types in the 5-inch thick subsection. For that subsection, flat rectangular dowel bars will be installed into three of the twelve transverse joints, and monitored for load transfer performance.
People desire smooth, quiet, and safe pavements. To encourage smooth pavements, we need to quantify the effects of other important pavement performance parameters on ride. These parameters include texture, noise, and friction. Since Minnesota’s introduction of the astro-drag we have seen the need to consistently evaluate the pavement finishing technique. So far this technique appears to be an optimization of these 4 parameters but more data and research is required for a conclusive decision. An understanding of the interaction of texture and ride is still very rudimentary. This project will evaluate the above parameters on several test sections constructed at MnROAD, and also evaluate the performance over time.
This is a pooled fund project
The primary purpose of this project is to create a unified national design guide for thin and ultrathin concrete overlays of existing asphalt pavements. This consists of the following distinct objectives:
1. Study and understand the field performance history of TCOAP and UTCOAP as demonstrated by various research test sections. These include current (and future) test sections at the MnROAD facility, accelerated loading facility test sections (FHWA), and other test sections installed and monitored by various local, national and international agencies.
2. Develop a design guide for concrete overlays of existing asphalt pavements utilizing existing validated performance models, as well as new analytical models derived to address design aspects not currently considered in existing methods. The design guide will be based on mechanistic-empirical principles, including the effects of various concrete overlay and existing asphalt materials, panel thickness and geometry, joint opening and stiffness, traffic loads, and climates under which they must perform.
3. Create a user-friendly design guide software program and user¿s manual. The program format should be such that it could become a module in the future national Mechanistic-Empirical Pavement Design Guide (MEPDG) for highway pavements. More
Performance of Thin Unbonded Concrete Overlays on High Volume Roads
One method of restoring and increasing the structural capacity of a concrete pavement is by the application of an unbonded concrete overlay. The design of unbonded concrete overlays has become quite conservative recently (thick PCC surface layer), and therefore higher in cost than perhaps necessary for good performance. The objective of this experiment is to test the performance of thinner unbonded concrete overlays (4 to 5 inch thick) subject to interstate traffic and Minnesota’s extreme climate. Another challenge being examined is the placement of concrete overlays with perpendicular (to traffic direction) transverse joints over pavements with skewed joints, because of the perceived tendency for the skewed joints to forcibly reflect upwards. Also, a select number of the existing skewed transverse joints will be artificially weakened to mimic an older, more distressed, concrete pavement that would typically receive this type of overlay. The innovative used of wick drains (to drain the porous separator layer) will also be examined.
Geocomposite Capillary Barrier Drain (GCBD) for Limiting Moisture Changes in Pavements: Product Application
The problems associated with excessive moisture in pavement bases and subgrades are numerous and well known. Conventional drainage may not be wholly effective in reducing water-related problems (e.g., Christopher and McGuffey, 1997; Hall and Correa, 2003). Conventional drainage is designed for saturated conditions, however, most water movement near the surface occurs under unsaturated (or partially saturated) conditions. Recent studies suggest that conventional drainage systems can only be understood if unsaturated flow principles are considered (Birgisson and Roberson, 2000; Stormont and Zhou, 2004).
The performance of GCBD systems has been evaluated in the laboratory and in a limited field test (in the Muddy Roads project sponsored by the Vermont Agency of Transportation). The next step in GCBD development is to document its drainage performance in a field scale pavement section and to obtain related mechanical performance indicators. Field scale testing includes conditions that are more realistic for the eventual deployment of the GCBD technology, including pavement cracks and variability in base course properties. Field scale testing should include a side-by-side comparison with a control section. In this way, the benefits of the GCBD can be clearly demonstrated.
This project is geared toward implementing GCBD technology. A key objective of the project is to select the most effective transport layer for use in a prototype GCBD. A second objective of the project is incorporation of the prototype GCBD into a full-scale test section at the Minnesota Road Research Facility (MnROAD), a comprehensive pavement test track facility. In addition to demonstrating construction using the GCBD, measurements of GCBD test section performance, side-by-side with a control section will quantify its benefits. The final objective is development of design tools to aid in the design of the GCBD for specific climate, geometry, and soils. More
Full-depth reclamation is a technique where the full flexible pavement section and a predetermined portion of the underlying materials are uniformly crushed, pulverized, or blended, resulting in a stabilized base course. Pavements that have experienced base failure are considered ideal candidates for FDR. Further stabilization may be obtained through the use of available additives. These additives include cement, fly ash, lime, foamed asphalt and asphalt emulsions. A new surface course is placed on the recompacted base. Depending upon the amount of RAP, the properties and amount of the base, the type and condition of the base and subbase, and the amount and type of additive, the stiffness and strength of the reclaimed base varies, as does the performance of the new pavement system.
Several research projects have done laboratory evaluations of the mechanistic properties of reclaimed materials, and some field studies of individual projects have been performed. This project will compare the characteristics and performance of three reclamations using asphalt emulsion stabilization: 90% RAP-10% Aggregate base, 50% RAP-50% Aggregate base, and 75% RAP-25% Aggregate base.
Three MnROAD test cells will be constructed to evaluate the properties and performance of 3 variations of full depth reclamations using asphalt emulsion stabilization. The results will be used to develop the best-cost design procedures to achieve the strength and flexibility needed for a pavement.
The Effects of Implements of Husbandry "Farm Equipment" on Pavement Performance (MnROAD Study)
Over the past few decades, there have been significant changes in both farm size and farm equipment. Combined with a regulatory emphasis that has encouraged farmers to store manure as a liquid and apply it in a short time frame, the farm equipment industry has responded by producing larger and larger manure hauling and application equipment. The shift to larger and heavier equipment has occurred at a faster rate than both pavement design technology and the state regulatory approach to larger farm equipment. Innovations such as steer able axles, flotation tires, and tire design changes are not reflected in state DOT regulations. In the minds of some manure applicators and farmers, this has forced the adoption of equipment and practices that, while complying with the letter of the law, actually create more pavement damage.
The Iowa Department of Transportation conducted a study in 1999 to address pavement damage caused by heavy farm equipment. Based on the results from this study Iowa passed legislation that was found acceptable to both the DOT and industry. South Dakota also performed a similar study in 2001. In their study field test sections were constructed and instrumented to measure pavement responses such as strain, pressure, and deflection caused by some agricultural equipment. Theoretical modeling was also conducted to investigate pavement damage. The study resulted in recommendations on changing regulations concerning certain types of farm equipment.
In 2001 the Minnesota Department of Transportation conducted a scoping study on the impact of agricultural equipment (animal husbandry vehicles, grain carts, etc.) on Minnesota's low volume roads. The main purpose of the study was to determine if agricultural equipment caused excess pavement damage in Minnesota. The study reviewed several county roads that were claimed to have been destroyed by farm equipment. However, the study found that other heavy vehicles, such as trucks hauling gravel or rock from quarries, might also have contributed to the damage on the roads. This study concluded, "it is difficult to link specific pavement damage to agriculture equipment and quantitatively estimate the reduction in pavement life with current available information." One of the recommendations from the study was to conduct a field study at the MnROAD test facility to specifically address pavement damage due to agricultural equipment.
The regional aspect of this project is a major selling point. Many states in the Upper Midwest have the same concerns about heavy farm equipment, and the pooled fund study framework allows for these states to pool their resources and research some common issues. As noted earlier in this proposal, farm equipment is constantly changing weights, configurations, tire pressures, etc. This project will study the current version of a number of vehicles. Finally, it is envisioned that MnROAD could become a national center for testing overweight vehicles from farming and a number of other industries. The proposed new test sections will be used for other types of equipment long after this project is complete. The basic framework for this research might be of interest to other industries such as tire manufacturers, logging trucks, mining vehicles, forage harvesting equipment, and other heavy farm equipment.
The objectives of this study are to determine the pavement response under various types of agricultural equipment (including the impacts of different tires and additional axles) and to compare this response to that under a typical 5-axle semi tractor-trailer. This will be accomplished by constructing new instrumented test sections at MnROAD and/or to retrofit instrumentation into the existing test sections. The final scope and work plan for the study will be developed by the participating agencies.
Portland cement pervious concrete has great potential to reduce roadway noise, improve splash and spray, and improve friction as a surface wearing course. A pervious concrete mix design for a surface wearing course must meet the criteria of adequate strength and durability under site-specific loading and environmental conditions. To date, two key issues that have impeded the use of pervious concrete in the United States are that compressive strengths of pervious concrete have been lower than necessary for required applications and the freeze-thaw durability of pervious concrete has been suspect.
The objectives of the integrated research study include finding optimal pervious concrete mix designs for wearing course sections in pavement applications. Information needed for the wearing course sections must address the issues of noise and skid resistance, assuming adequate strength and durability are developed. The constructability issues are also very critical. It is of paramount importance for the research to determine techniques for construction that utilizes existing pavement equipment. At present the construction of pervious concrete sections is quite labor intensive. The use of pervious concrete as a wearing course entails construction of a concrete overlay in rehabilitation efforts. In new construction two-lift construction is a possibility.
Traditional asphalt pavement roadways generate storm water runoff, requiring secondary treatment systems such as detention ponds. Porous asphalt roadways combine access needs with effective storm water treatment. This technology will also improve safety by reducing water spray and ice formation, reducing deicing needs, and minimizing the need for additional land dedicated to storm water management. Porous asphalt pavement is an emerging technology in pavement design especially because of the potential benefits of treating runoff through the pavement rather than through a storm water system. Recently, the Capitol Region Watershed District began requiring a higher level of water quality and quantity control, such as reducing 1 inch of rainfall runoff on any project disturbing over 1 acre of land. This type of pavement may offer an effective means of managing storm water runoff with the potential to reduce or eliminate the need for a water detention basin. However, prior research on porous asphalt in the seasonally diverse Midwest climate is lacking.
The objectives of this research are to evaluate the durability, hydrologic characteristics, and environmental effects of porous asphalt pavement when used on a low volume roadway in a cold climate. Appropriate construction and maintenance procedures will also be documented. The research will include the following: 1. Construct a fully instrumented test section on the MnROAD Low Volume Road. 2. Monitor pavement performance on a regular basis in terms of low temperature cracking, rutting, and ride. 3. Document the maintenance procedures and results, in terms of when to vacuum and sweep roads based on stormwater monitoring data. 4. Monitor the volume of stormwater runoff for comparison to a standard asphalt roadway. 5. Test for water quality, such as solids, pH, Chloride, Phosphorus, Nitrogen, heavy metals.
The reduction of pervious surfaces has been an issue of concern with the construction of bound pavement surfacing. Some Cities in the Metro area have been forced to improvise methods of minimizing storm water intrusion from developments that are in proximity to wetlands or some trout streams. Run-off from impervious surfaces has been known to distort the thermal balance of streams when extreme temperatures precede heavy rains. In solving this problem some communities have made various attempts to encourage some infiltration by constructing pervious concrete on porous bases. While their understanding of the performance of pervious concrete in Northern climates is still rudimentary, MnDOT in collaboration with the Aggregate Ready Mix Association of Minnesota provides leadership in this technology. The partnership resulted in the construction of a pervious concrete pavement in a parking lot in MnROAD in 2005. Ordinarily stormwater run-off necessitates expensive design and construction of storm water structures that include detention or infiltration ponds. Intuitively, there is a huge saving in cost if the paved surface is pervious and conducts the stormwater directly to the ground. The pervious concrete design provides this benefit. Normal concrete is impervious and may contain entrained air up to 7.5 % as in our high performance concrete. The entrained air is discontinuous in normal concrete; permeability is infinitesimal compared to the rate of flooding or ponding or run-off on the pavement surface. Pervious concrete is made up of gap-graded aggregate linked by cement paste, systematically placed to allow for contiguous voids or cavities that allow for free passage of water.
Due to the limitation of funds, the pervious concrete initiative of 2005 on a MnROAD parking lot was done on a small scale. The instrumentation is skeletal and detached from the omnibus MnROAD data collection system and the technology at that time was rudimentary. In order to adequately evaluate pervious concrete in this climate, we need a test section with a proper mix design and instrumentation on the MnROAD Low Volume Road. This will also provide an operations research advantage as the porosity and infiltration advantage can be monitored over time and standard measurable traffic loads and environmental effects can be measured. This study will provide validation of the mix design recommendations in the lab based on a previous Iowa study. It will also validate pervious concrete pavements as a tool for local communities to fulfil the environmental requirements of the Clean Water Act and as a pavement noise attenuation tool in the kit.
Recycled Unbound Pavement Materials
In the current global economy, the United States is in competition for non-renewable resources. In this country, and Minnesota in particular, aggregate materials are being depleted at a rapid pace. Environmental stewardship will continue to be more restrictive along with permitting criteria. It is becoming increasingly important to investigate the use of recycled materials in pavement construction.
Minnesota has had a long history of using recycled materials in pavement construction. Recycled materials have been used in all layers of the pavement, from the surface down to the unbound supporting layers. MnDOTs current Class 7 specification (Spec 3138) allows salvaged or recycled HMA, PCC, and glass to be used as part of the granular base materials. However, their material properties (strength, stiffness, unsaturated properties, etc.) are not well understood. Under the current design procedures, Class 7 materials are assigned the same empirical properties as a typical Class 5 (gravel) material. New mechanistic-empirical design procedures require more detailed material properties in order to accurately predict pavement performance. In addition, the use of crushed concrete in particular has raised some environmental concerns. These concerns have focused on the relatively high pH of the effluent produced by drainage systems that remove water from untreated recycled concrete aggregate foundation layers. Also of concern is the identification of some constituents (arsenic, chromium, aluminum, and vanadium) that are considered hazardous in drinking water.
The objective of this study is to monitor the performance of several test cells at the Minnesota Road Research Facility (MnROAD) constructed using recycled materials in the granular base layers, including blended with virgin materials and 100% recycled asphalt and concrete pavement materials. The material properties will be monitored during construction and throughout the pavement life in order to determine their effects on pavement performance. The properties will be used to verify mechanistic-empirical design inputs, especially their variation with changing seasons and moisture regimes. More
Field Investigation of Highway Base Material Stabilized With High Carbon Fly Ash (Bloom Consulting, DOE)
Fly ash is a byproduct produced from the combustion of coal. It is a material having cementitious properties, and is frequently used to enhance mixtures of Portland cement concrete. High Carbon Fly Ash has a carbon content that is out of range for use in the concrete industry. Laboratory testing has shown high carbon fly ash to be a viable stabilizing material. Field construction is necessary to validate the structural and environmental performance of high carbon fly ash stabilized bases. This work is a portion of Phase II of a fly ash stabilization project performed by Bloom Consultants, LLC and is sponsored by the U.S. Department of Energy. Phase II is titled Use of High Carbon Fly Ash to Stabilize Recycled Pavement as Base Course, and is funded by DOE for $750,000. Phase II has a two year time requirement and includes MnROAD test sections constructed in 2007.
The purpose of these test sections is to evaluate the physical and environmental properties of base materials stabilized with high carbon fly ash in comparison to recycled pavement materials and crushed stone. Testing will include aggregate characterization, construction, field testing, and long term monitoring of the test cells.
The Warm Mix Asphalt (WMA) study at MnROAD came about from the desire of MnDOT researchers to demonstrate the potential benefits of WMA to other MnDOT staff. By placing WMA at MnROAD, the results of the study will be disseminated to a wider audience of city and county engineers, consultants, contractors, and researchers throughout Minnesota and the entire country. The environmental, health, and construction-related benefits realized by WMA are well-documented, but we are most interested in its potential for better low temperature cracking performance. Thermal cracking is the predominant mode of distress of HMA pavements in Minnesota, and it is our hypothesis that the reduced level of oxidation at the mix plant will lead to better long-term pavement performance. We will also monitor other performance measures such as rutting, fatigue cracking, top down cracking, and ride.
The WMA was placed on six test cells on the MnROAD Mainline, which sees just under 1 million ESALs per year. The mix is a level 4 Superpave (3-10 million ESALs) with PG 58-34 binder and up to 20% RAP. In the 2008 construction Contract, we specified that Warm Mix Asphalt must be paved, but we left it up to the contractor to decide the particular process they wanted to use. In this case, Hardrives chose the Evotherm 3G product because of its ease of use. This product is a chemical-based additive that does not use any water but still promotes coating at lower temperatures. Mathy Construction mixed the WMA additive directly into the binder at the terminal, and they shipped the ready-made binder to Hardrives in a tanker, where it was hooked up directly to the drum for mixing.