Siekmeier, John A.

Throughout its decade of operation, MnROAD has become a major resource in the pavement community for test track expertise, pavement data, and pavement research. However, one overlooked benefit of MnROAD’s first phase of operation is the effort of MnROAD engineers to introduce, develop, and encourage the use of new technologies and techniques for pavement engineers. While the list of new products tested and/or developed at MnROAD is extensive, this brief will focus on three products and the influence of those products outside of MnROAD: the Dynamic Cone Penetrometer, used to estimate the strength of subgrades; Ground Penetrating Radar, used in pavements to assess, among other things, layer thicknesses and subsurface conditions; and Continuous Compaction Control, which involves continuously measuring soil compaction and adjusting the needed force to compact the soil. These three highlights emphasize the ability of MnROAD to: 1. serve as a test facility for pavement and pavement foundation experiments, 2. develop new technologies and procedures for pavement engineering, 3. contribute in a significant manner to pavement engineering both at a local and national level. It is hoped that this brief exposes the reader not only to a few past accomplishments of MnROAD in new technologies but will give a better idea of the promise and ability of MnROAD in the development and adoption of these technologies.

The purpose of this report is to provide details on the 2006 reconstruction of Cells 27 and 28 on MnROAD’s Low Volume Road. There were three significant aspects of research behind the test cell reconstruction: field validation of a Geocomposite Capillary Barrier Drain (GCBD) for limiting moisture changes in pavements, Intelligent Compaction (IC) research performed on the unbound base and subgrade layers, and accelerated testing of PG 52-34 binder to support a Local Road Research Board (LRRB) project. This report documents the previous pavement condition, pavement structural and mix designs, instrumentation plan, field construction activities, material sampling, and laboratory test results. Significant effort in communication and coordination between research and construction personnel led to a successful construction project.

This innovation update relates to Report 2009-12, "Using the Dynamic Cone Penetrometer and Light Weight Deflectometer for Construction Quality Assurance," published in February of 2009.

A performance specification has been developed for geogrid reinforced aggregate base; which utilizes the dynamic cone penetrometer (DCP) and light weight deflectometer (LWD) to test the aggregate base reinforced with geogrid. These quality assurance devices; in particular the DCP; are very familiar to construction inspection staff in Minnesota; and therefore this performance specification is expected to be readily implemented. In summary; the construction quality assurance test locations are selected to accurately represent the constructed aggregate base layer and the DCP or LWD is placed at the appropriately prepared test location. For both the DCP and LWD; the weight is raised and released to deliver a predetermined number of drops that result in a measured penetration (DCP-MV) or plate displacement (LWD-MV); which is then compared to a predetermined target value (DCP-TV or LWD-TV).

The National Road Research Alliance (NRRA); a multi-state pooled-fund program; exists to provide strategic implementation of pavement engineering solutions through cooperative research. NRRA is led by an Executive Committee of state DOT partners; and supported by numerous agency and industry partner representatives. Members provide expertise to NRRA; from the selection of research topics; to communication; and implementation. NRRA consists of five project teams: Flexible; Rigid; Geotechnical; Preventive Maintenance; and Technology Transfer. The 2017 construction season at MnROAD saw construction of 35 new and unique pavement test sections. The sections; designed to address NRRA high-priority research topics; were conceived and planned by NRRA project teams. This report details development; design; and construction of each research project and the test sections supporting them. Individual study details are left to future reports generated by the individual research contracts and their respective teams.

The pavement design package created by Itasca extends the capabilities of PFC3D to support triaxial testing of a synthetic unsaturated aggregate base containing geogrid. The geogrid provides lateral restraint to the aggregate base as a result of interlocking and friction between the geogrid and the aggregate particles. The macroscopic system properties are affected by the microstructural system properties. Therefore, the modeled system was used to study and quantify the effect of microstructural properties on the macroscopic properties, which include the stress-strain curves produced during triaxial tests at different confinements. The microstructural properties of the aggregate base include: particle size, particle type (density, Youngs modulus, and Poissons ratio of each particle; and friction between particles), aggregate base moisture content (suction and gap), and initial aggregate base porosity. The microstructural properties of the geogrid include: geometry (aperture and rib dimensions), Youngs modulus, bond stiffness, and grid-grain interface behavior. The pavement design package provides a mechanistically defensible model for aggregate-geogrid interaction, which was used to improve pavement design by estimating geogrid gain factors for typical geogrid-reinforced aggregate roadways. It is anticipated that a simplified geogrid gain factor adjustment will be trialed during pavement design for projects where geogrid is being considered. As expected, this study concludes that geogrid provides benefit and that this benefit varies during the year. Therefore, it is recommended that the seasonal effects be included during implementation. This would allow the fatigue and rutting to be more accurately estimated over the expected pavement design life.

In September 2011 MnDOT constructed two cells in the MnROAD Mainline in continuation of the study of unbonded overlay (Cell 5) and to facilitate studies on a drainable base (Cell 6) with a longitudinal tined texture. Additionally, roller-compacted concrete shoulders were constructed in these cells to replace the preexisting asphalt shoulders. Finally, repairs were done to a thin concrete overlay of existing asphalt pavement installed in 2004 (Cell 63). This report discusses the construction procedure, instrumentation and the initial monitoring from these test cells.

Specification target values for granular materials and fine grained soils are proposed. For granular material, the grading number and field moisture content are used to select the dynamic cone penetrometer (DCP) and light weight deflectometer (LWD) target values. A sieve analysis is used to determine the grading number and an oven dry test to determine the field moisture content. For compacted fine grained soil, the plastic limit and field moisture content are used to determine the target values. The plastic limit is used to classify the soil and to estimate the optimum moisture content for compaction. This report also provides further standardization of the LWD and DCP testing procedures and recommends three seating drops to ensure greater uniformity during testing. The DCP and LWD estimate the strength and modulus of compacted materials. More specifically, they measure the penetration and deflection. When measuring penetration and deflection, the moisture content remains a critical quality control parameter for all compaction operations. Therefore, the moisture content needs to be measured, or estimated confidently, at each location. The LWD and DCP are performance related construction quality assurance tests that are expected to: increase compaction uniformity, lower life cycle pavement costs, increase inspector presence at the construction site, improve documentation, and increase inspector safety and productivity.

Advances in technology have produced a new generation of in situ soil testing devices. Implementation of quality assurance procedures that make use of these devices would improve test precision, increase inspector efficiency and safety, and allow for the direct verification of values used in mechanistic design procedures. During this study, the dynamic cone penetrometer (DCP) and light weight deflectometer (LWD) were used on laboratory prepared specimens. It was found that the Mn/DOT DCP specification accurately assessed compaction quality, although there were some suggestions for improvement. This study reached the following conclusions and recommendations. The DCP penetration should continue until the cone passes through the subbase lift of interest. The DCP seating requirement serves little purpose for a subbase lift that will be covered by subsequent lifts. The acceptable range of moisture contents during DCP testing of granular subbase should be capped at 10%. A sufficient amount of data exists to create an LWD trial specification for granular subbase. A mass of 10 kg, drop height of 50 cm, and plate diameter of 20 cm are recommended. It is also recommended that the LWD specification include three seating drops followed by three data drops at each new height.

Many northern states allow an increase in the gross vehicle weight (GVW) for certain vehicles during the winter to more efficiently use the increased load carrying capacity of frozen pavement structures. The increased load limits and dates are usually set according to legislation, which may not account for seasonal differences in the depth of frost. This report documents the effects of increasing the winter load limits for a pilot study in Minnesota and suggests a possible method for placing and removing increased winter load limits. A pilot study was conducted in which the northern sugar beet haulers were allowed to increase the winter weight of the 6-axle tractor-trailer combination vehicles from 391 kN (88,000 lbs.) to 416 kN (93,500 lbs.). This load limit was chosen to match North Dakota since this was the final destination. The sugar beet haulers were allowed to increase the GVW when the frost level reached 150 mm (6 in.) into the subgrade layer and end when 150 mm of the base layer thawed. Frost and thaw depths in the pavement structures were monitored with Watermark and thermocouple sensors. It was found that there was a significant increase in the structural carrying capacity of the frozen pavement as measured by decreased deflections during falling weight deflectometer testing. A similar trend was seen in the strain data from the Mn/ROAD site. The condition surveys conducted showed no visible signs of increased surface distress due to the increased loads, however the results from this study are limited because the transporter was only able to participate in the study for three weeks. Several recommendations related to improving seasonal load limit implementation are suggested and subsequent activities during the 2000-2003 period are described.