With the construction of four new test cells in 2008, the Minnesota Department of Transportation (Mn/DOT) now has six unique pervious pavement test sections at the MnROAD test facility. Recorded temperatures in the pervious pavements and subgrades were compared to impervious Portland Cement Concrete (PCC) test sections over the same time interval. It was found that the subgrade in pervious PCC and Hot Mix Asphalt (HMA) was up to 4 °C warmer in the winter than impervious PCC pavements. The frost depth in an impervious PCC pavement was found to be 45.7 cm deeper than in a pervious PCC pavement of similar thickness. One pervious pavement test cell experienced 60% less freezing cycles over a three year interval than impervious PCC pavements of similar thickness. The air trapped in the pavement voids was suspected to be the main reason for the reduced number of freeze-thaw cycles by creating an insulating effect. In another pervious pavement, entrapped air within the base material may also insulate the pavement from the subgrade.
From the beginning, MnROAD was imagined by its planners as a cold-regions research facility for pavements. In its first decade of operation, MnROAD was the site of numerous experiments whose main aim was to observe the effects of a Minnesota winter (or more than one winter) on the pavement system, from the materials in the surface course to the soils in subgrade. In holding to its goals as a cold-regions research facility, MnROAD engineers developed an extensive knowledge of pavement construction, design, and maintenance in cold-regions climates. In many areas, MnROAD engineers were pioneers in their particular cold-regions study: for instance, MnROAD engineers were some of the first in the United States to closely observe low-temperature cracking in pavements. Furthermore, MnROAD has gathered a significant amount of environmental data and data related to cold-regions phenomena such as low-temperature cracking. This brief details some of the MnROAD products dealing with MnROAD’s experience in cold-regions pavements.
The Minnesota Department of Transportation (Mn/DOT) built the Minnesota Road Research Project MnROAD between 1990-1993. The 2.5-mile low volume road and the 3.5-mile mainline consists of a 2-lane roadway that originally contained gravel, hot mix asphalt, and concrete test cells designed for both low volume roads and interstate traffic. The mainline interstate cells are trafficked by public interstate traffic and the low volume road has a Mn/DOT 5-axle tractor-semi-trailer to simulated conditions of rural roads in two load configurations, resulting in the same equivalent axle loads or ESALS. MnROAD is located in a wet freeze zone that has affected both its base and subgrade materials with seasonal frost movements. This movement has slowly deteriorated each test cells ride over time. MnROAD has monitored the frost movements using frost pins and has measured the ride (international ride index – IRI) using high-speed profilers over for the life of the project. This paper investigates the loss of ride from both environmental and traffic loadings and how they have combined to cause the deterioration of ride over the last 10 years at MnROAD. The findings suggest that our current process to develop a mechanistic empirical design is currently missing the fact that seasonal differential frost movements play an important role in pavement performance in northern climates and need to be taken into account.
This technical note describes how to assemble and install the frost resistivity gages used to collect data for the report "Resistivity Probes, Installation and Readout Techniques."
Resistivity gages discussed in this manual rely on the measurement of electrical resistance between conductors mounted along a cylindrical probe (see Figure 1) to determine where the soil is frozen and where it is thawed. This determination is based on the wide difference between the volume resistivity of frozen soil (from 500,000 up to several million ohms) and thawed soil (20,000 to 50,000 ohms normally). Frost penetration is determined by making sequential resistance measurements between adjacent pairs of electrodes down the resistivity probe and documenting at what depth the resistance goes from a high to a low value. It is not even necessary to actually read the resistance since a readout circuit may be used in which voltage measurements for each probe section may be ratioed to a fixed one megohm resistor located in the output circuit. This arrangement will work just as well as the actual resistance measurement since it is the shape of the curve that contains the frost depth information, not the absolute value of the measurements. Figure 1 is a sample resistivity installation. Typical curves are shown in Figure 2. For comparison, two curves of temperature vs depth are also shown, one at mid-winter conditions and one during spring thaw. The resistivity gage measurements were made by reading the resistance (or voltage drop) between solid copper rings spaced evenly on a buried PVC rod using an alternating current (ac) voltage source.
Deflection tests have been used in the past by some districts to provide information on the spring thaw period although there has not been a uniform procedure established for statewide use. The committee decided to have additional deflection data collected and analyzed to determine how these tests could be used to establish criteria for the setting or removal of spring load limits.
The type of questions that had to be answered were:
1. Can deflection tests be used to determine when the posting period should start?
2. Can deflection be used to determine when the posting will end?
3. Are deflection tests necessary on all posted highways during the spring thaw period?
4. Should testing be done daily, weekly or bi-monthly?
5. What analysis can be done with deflection data that may lead to the establishment of spring posting period criterion?
6. How many test sections would be needed and where should they be located?
A field program of strain and deflection measurements was conducted by the Construction Technology Laboratories for the Minnesota Department of Transportation. The objective of the measurement program was to evaluate the effect of frozen support, tied concrete shoulder, and tridem-axle loading on concrete pavement performance. Results of the investigation are reported separately for each of the three topics. Results of the tied concrete shoulder and tridem-axle loading studies are given in References 1 and 2, respectively.
Minnesota's current concrete pavement design procedure does not consider climatic effects. When the base, subbase, and subgrade are frozen, pavement strains and deflections due to load are smaller. Therefore, traffic induced damage during winter months is greatly reduced. Since concrete pavement design procedures consider repeated application of traffic loading and fatigue damage. It should be possible to take advantage of the frozen support conditions in the design of concrete pavements.
A three-month research project was conducted on the frost heaving patterns of a culvert. Problems are typically encountered when such a culvert is placed under a road in a frost-susceptible soil. Major differential frost heaving is produced and has a negative effect on the structure of the road itself while creating a rough ride and reducing safety for road users. This project analyzes the performance over the winter period of several potential remedial designs. The goal is to find a design that will minimize the differential frost heave for the broadest possible conditions in terms of frost-susceptibility and of freezing pattern.
The proprietary product Verglimit claims to decrease the amount of materials and man-hours needed for snow and ice control while maintaining adequate safety levels. Verglimit
consists of calcium chloride flakes encapsulated in linseed oil which are blended into the plant-mixed bituminous wearing surface. The manufacturer claims that exposed CaCl will
attract moisture and form a solution which prohibits adhesion of snow and ice to the pavement.
A Verglimit test section was constructed on U.S. Route 8 near Taylors Falls, MN. The applied mix appeared to be tender and some compactions difficulties were experienced. Manufacturer's recommendations were closely followed and no other unexpected difficulties occurred.
Evaluation of the test section consisted of deicing observations as well as other pavement performance characterizations. Portions of the Verglimit overlay experienced shoving and
were milled and replaced. Significant deicing benefits were not observed. No future Verglimit sections are planned.
