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This report culminates one of the first projects undertaken for study in the Local Road Research Program. The primary purpose of this project when it was initiated was to develop correlation between the plate bearing test and the Benkelman beam test. Such a correlation, or other acceptable procedure for using the Benkelman beam, would provide a practical and relatively economical means for our local highway engineers to obtain a measure of the strength (load carrying capacity) of flexible pavements.

The method presently used for flexible pavement design in Minnesota utilizes either average daily traffic (ADT) or heavy commercial average daily traffic (HCADT), along with a designation of 5-ton, 7-ton or 9-ton spring axle loads to categorize traffic. The AASHO soil system is used to classify the subgrade soil in order to vary the required base thickness from sections designated for an A-6 soil. The relative strengths of the layers in the pavement section are indicated by granular equivalent factors. The procedures and levels of thickness required have been established based on experience and performance evaluation on Minnesota Highway pavements for the past 30 years.

The 1969 Legislature of the State of Minnesota under Minnesota Statutes, Chapter 169.72, directed the Commissioner of Highways to conduct an in-depth study on the safety and pavement-wear effects of studded tires. This, the final report of that study, summarizes the research efforts and the results. The report is prepared for the specific use of the 1971 Legislature. The Commissioner of Highways is indebted to the many organizations that cooperated in providing information: The American Oil Company for conducting the pavement-wear tests; Kennametal Corporation for furnishing and installing studs in test tires; Cornell Aeronautical Laboratories for the accident study and analyses; the Minnesota Highway Patrol and other offices of the Department of Public Safety for accident reporting and survey coordination; and the many city police departments for supplementing accident reports with data required for the study. Participating cities were Brooklyn Center, Duluth, Edina, Grand Rapids, Mankato, Minneapolis, , Richfield, Rochester, Roseville, St. Cloud and St. Paul. Special thanks are due those states that contributed funds for defraying part of the project costs: Illinois, Iowa, Michigan, New York, North Dakota, Pennsylvania, Utah and Wisconsin. The content, findings, and conclusions expressed or implied in this report are those of the Minnesota Department of Highways. They do not necessarily represent the views of the organizations providing data for the report or the cooperating states.

Transverse joints were sawed in a deep-strength (12") flexible pavement, which is over a granular subgrade, prior to the opening of the roadway to traffic. This research project was located on the two southbound lanes of Interstate 35 near Stacy. Each of the three test sections is approximately 500 feet long. Joints were sawed at 40, 60 and 100-foot intervals for a total of 30 joints. Two 700-foot control sections, where no joints were sawed, were left between the sawed sections for comparison purposes. After 4-1/2 years or 5 winters of service almost complete crack arresting was accomplished in the test sections where joints were sawed at 40 and 60-foot intervals. A few cracks had formed in the test section where joints were sawed at 100-foot intervals. In contrast, numerous cracks had developed in the control sections.

A number of flexible pavement sections were constructed using limestone aggregate as the base material. As controls for comparison, identical sections were built using gravel base material. Evaluation was based primarily on Benkelman beam deflections. The results indicate that there is not any significant difference in the granular equivalency of the two aggregate types

Six methods of floating roadway widening sections over a peat swamp were designed and constructed on a two-lane roadway in 1976. The project location was on T.H. 53 between International Falls and Ray. Peat depths ranged from 8 to 15 feet. The investigation to date has shown that widenings can be floated on peat when fill height and loading rates are controlled. Performance of the sections will be monitored for a period of at least three years.

This research investigation, conducted by the Physical Research Unit of the Minnesota Department of Transportation, began in 1971 to learn more about the behavior of Full-Depth Asphalt pavements. The investigation has 26 test sections, each 1200 feet (365.8m) long, of a variety of thicknesses, on a variety of soils. The thicknesses range from approximately five inches (12.7 cm) to 17.5 inches (44.5 cm) and soil types include AASHO soil classification A-2-4's. A-3's. A-4's. A-6's and A-7-6's. These soils include a stabilometer R value range of 5 to 75. The major portions of the research work on this investigation consisted of Benkelman Beam measurements on the zest sections at 50 foot (15.2 m) intervals, taken weekly throughout rh2 spring, bi-weekly throughout the summer and monthly into the fall. The temperature of the upper 1.5 inches (3.8 cm) of the mat was measured each time the Benkelman Beam deflections were taken. These data were then used to determine the effect the temperature and the season had on the deflections and also created a set of correction factors to apply to the measured deflections to adjust the deflections to an 80‘F (26.70C) peak season deflection. The peak season 80‘F (26.7C) mat temperature deflection was then taken to be the standard deflection for each of he test sections. These standard deflections were then compared to the deflections of aggregate base pavements and a relationship was developed between the Full-Depth thickness and the granular equivalency of an equivalent deflection aggregate base pavement. That relationship was then used to develop a Full-Depth bituminous pavement design chart which is the deflection equivalent of the flexible pavement design chart currently in use by Mn/DOT. The serviceability of the Full-Depth has also been monitored in terms of pavement roughness, rut depth and surface condition. The serviceability of the rest sections have nor changed enough to adequately estimate the performance of the test sections at the rime of this report.

Field and laboratory pavements were instrumented and load tested to evaluate the effect of lane widening, concrete shoulders, and slab thickness on measured strains and deflections. Eight slabs were tested in the field and two in the laboratory. Pavement slabs were 8- 9-, or 10-in. thick. Other major design variables included the width of lane widening, presence or absence of dowels, presence or absence of a concrete shoulder, joint spacing, and the type of shoulder joint construction. Generally, there was good agreement between measured strains and deflections and values calculated using Westergaard's theoretical equations. Concrete shoulders were effective in reducing the magnitude of measured strains and deflections. A chart is presented to show the reduction in thickness of the outer lane of the mainline pavement that may be permitted with a tied concrete shoulder.

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.

The Minnesota Department of Transportation (Mn/DOT) investigated a polymer concrete (PC) patching material in cooperation with the Brookhaven National Laboratories (BNL) and the Federal Highway Administration (FHWA). This material has been previously tested by other states throughout the country. The material is claimed to be a rapid curing, durable material for patching potholes and deteriorated cracks in Portland cement concrete pavements and bridge decks. Previous field tests of PC materials have been small in scope and size. The problems associated with the material were the tendency of the monomer to drain from the system, the development of shrinkage cracks in the polymerized material, and the need for a knowledge of chemistry to mix the monomer system. The BNL material is supposed to correct these drawbacks. Mn/DOT made a laboratory study of the PC material by producing a control mix of portland cement, low-slump concrete to evaluate how PC material compares to the low-slump concrete with respect to: - freeze thaw durability, - compressive strength, - tensile splitting strength; and - chloride permeability. Shear bond strength tests of the PC material are being conducted by the BNL. Field evaluation of the PC material has proven to be inconclusive. Patches failed in both the concrete pavement and the bridge deck. The bridge deck patches had to be removed completely. These failures are not due to the PC material itself.