The purpose of this investigation is to evaluate the practicality and accuracy of using nuclear devices for determining moisture and density of materials used in highway subgrades and base courses and the density of bituminous paving courses. In Minnesota the sand cone method of density determination is presently used for control of embankments and granular base materials, In the last two years the burner dry moisture content has been supplemented with the "quickie" moisture method using the carbide pressure meter. It was felt that the nuclear method showed enough promise to make a study on it to compare the performance of devices using this method to that of the presently used methods in terms of accuracy and of time requirements in obtaining the results.
During the summer of 1965, a test road was constructed in southeastern Minnesota. The subgrade of this road is a silty soil typical of the area and similar to soils which have been extensively studied in the University of Minnesota laboratories. The test road is 8000 feet in length and contains eight 1000-foot test sections,, Two of the sections are for control and were not stabilized while the other six were stabilized with 6% or 9% of RT-6 or with 9% of MC-2. In all cases, the upper six inches of the subgrade was stabilized and then covered with three or five inches of base and two inches of surfacing.
A comprehensive sampling program was carried out to permit more detailed analysis of the test road performance. This began with sampling of the unstabilized subgrade for determination of soil properties. These samples indicated soil variations which must be considered in future evaluation. As the subgrade was stabilized, stabilometer specimens were molded in the field and tested after appropriate curing and conditioning treatments. Other specimens were stabilized in the laboratory at comparable moisture and bitumen contents. The results of these sampling and testing programs are used to compare the various test sections. These comparisons show tendencies but final conclusions must be withheld until they are substantiated through service.
The final evaluation of the test road will require additional testing over a period of years. This evaluation will have to consider effects of traffic, frost action, soil moisture, etc. Provisions have been made for the Materials and Research Division of the Minnesota Department of Highways to make field measurements and observations at periodic intervals for this purpose. A final report after this more extensive investigation should prove of great value in future stabilization projects.
Since the initiation of Investigation No. 603 in the summer of I960, Materials and Research personnel have been conducting plate bearing and Benkelman beam tests on County Roads and Municipal Streets located throughout the state. County and Municipal Engineers have indicated their enthusiasm for this project through the numerous letters received each year submitting roads for testing. The plate bearing spring axle load data, the condition survey results, and the boring information have provided them with information related to the performance of their typical flexible pavement design and some guide lines for use in placing spring axle load restrictions.
In addition to providing performances arid load restriction data, the study was initiated to determine the relationship of the time tested plate bearing test and the more economic Benkelman beam test. This relationship has been established and a means of computing an estimated spring axle load capacity using Benkelman beam deflection data is presented in this report. However, there are certain limitations that must be considered before this method can be used with any degree of confidence. The 1964 field tests will be used to evaluate this method as well as the other relationships presented in this report.
During 1969, 1970 and 1971 density data were obtained on bituminous wearing courses that were being constructed on several Minnesota trunk highways. Data were collected and analyzed from randomly selected locations on five bituminous surfacing projects. A statistical analysis was also performed on results from eleven other bituminous projects and on laboratory test results. Variation was determined from these data by computing the mean and standard deviation to reveal existing variability in acceptable construction of bituminous wearing courses. The results were used to evaluate present specifications and to develop a new acceptance sampling plan. The plan is based on statistical concepts that will define the degree of acceptable variation upon which decisions can be made with an established degree of confidence. Proposed statistical specifications are presented.
During 1969, 1970 and 1971 density data were obtained on bituminous wearing courses that were being constructed on several Minnesota trunk highways. Data were collected and analyzed from randomly selected locations on five bituminous surfacing projects. A statistical analysis was also performed on results from eleven other bituminous projects and on laboratory test results. Variation was determined from these data by computing the mean and standard deviation to reveal existing variability in acceptable construction of bituminous wearing courses. The results were used to evaluate present specifications and to develop a new acceptance sampling plan. The plan is based on statistical concepts that will define the degree of acceptable variation upon which decisions can be made with an established degree of confidence. Proposed statistical specifications are presented.
During the fall of 1969 transverse cracks were sealed in a 13-mile section of bituminous pavement. Five hot-poured rubber asphalt sealers, three tack coat materials for priming the crack sidewall, a bond breaker and 40 different application procedures were used. Test sections were established to evaluate the materials and procedures. Field surveys were conducted to determine the amount of footage failed. Reference pins were also installed to measure crack movement. The field results were used to evaluate the materials and procedures incorporated in the study program.
This report describes the traffic phase of the comprehensive study, Investigation Number 183, Application of AASHO Road Test Results to Design of Flexible Pavements in Minnesota. It refines and utilizes the procedures outlined in the 1970 Investigation 183 Interim Report, Use of Traffic Data for Calculating Equivalent 18,000 lb. Single Axle Loads.
Data used in this report were collected at 41 Test Sections in 1964 and at 48 Test Sections in the 1969-1971 period.
This investigation is being conducted as part of the Highway Planning and Research Program financed jointly with Federal-Aid Funds provided through the United States Department of Transportation, Federal Highway Administration together with State Funds.
The overall purpose of Investigation 183 is to use the findings and concepts of the AASHO Road Test to study the design of flexible pavements for actual highway conditions and traffic in Minnesota. At the Road Test, relationships between load and pavement thickness were established for one set of materials and for controlled traffic. In this investigation an attempt is being made to expand these relationships to other embankment materials and mixed traffic in Minnesota. For a comprehensive review of the Road Test and its results see Highway
Research Board Special Reports 6 IA-G( 1).
To accomplish this purpose 50 test sections have been set up throughout the State of Minnesota. The location and thicknesses of the layers of each test section are listed in Part I of Reference 2. The 1963 and 1964 Annual Reports (2), (3) for Investigation 183 review all of the field, laboratory, and analysis work done through those years. This work included the preliminary establishment of the field test sections, the sampling and testing of the materials in the test sections, and setting up routine test programs which will evaluate the performance and overall strength of the test sections. This report does not contain complete listings of all the routine data which have been obtained from each test section but will refer to the previous reports for such information. Some new data will be presented and previous data will be shown where they are significant to a concept being considered. The report will cover the topics which have been worked on since the 1964 annual report and which have been deemed to be of importance in discussions with personnel of the Minnesota Highway Department.
This report contains the results of experiments performed to discover the suitability of the concrete retarder Plasitment for Minnesota Department of Highways construction projects.
The objective of this investigation was to evaluate the use of a reduced structure thickness for the passing lane, (left lane) on four lane roadways. The design lane, right lane, on these roadways is estimated to carry between 81 and 97 percent of the total one way traffic load. In this report ASAL, Accumulated Standard Axle Load, will be used to replace the term Sigma N18. Present practice is to construct both right and left lanes to the same thicknesses. This results in an overdesign of the left lane.
