On highway construction projects it is necessary to determine moisture contents of soils and aggregates in connection with earthwork, subbase, base, concrete, and bituminous construction. This determination by the present conventional methods is time consuming, and there has been increasing criticism by contractors that tests of this type are causing delays in the progress of their work. Consequently more rapid methods have been sought for making reliable moisture control tests particularly on base materials and embankment soils.
The purpose of this investigation was to determine the accuracy and time saving possibilities of the Calcium Carbide Gas Pressure (CCGP) Moisture Tester when used as a field testing device in comparison with conventional field methods for moisture content determination. This report presents the results of extensive field tests with the instrument. A previous study (Investigation No. 122) had established that moisture contents can be accurately determined with this device under the ideal working conditions of the laboratory.
Moisture testers were placed on 14 field projects selected so that the widest possible range of soil types could be tested. Some base and subbase materials were also tested.
A revised method for designing flexible pavements in Minnesota has been proposed for use. It has been developed based on the performance of 49 in-service test sections throughout -the state. This method is developed in the Annual Report for Investigation 183 in June, 1969.
Investigation 183 began in April, 1963, with preliminary selection, of flexible pavements in each Construction District of the Minnesota Highway Department. Projects were selected where it was thought that well-defined
design occurred and a good traffic history could be obtained. With the aid of the district soils engineers, the areas were checked for uniformity and forty-one test sections were laid out. In 1964 an additional nine test sections were set up, bringing the total to fifty.
During the summers of 1963 and 1964 three phases of field work were completed on each test section, These were: (1) fractional plate load testing with in-place moisture and density determination of each layer and with samples of materials taken from each layer for laboratory testing, (2) determination of Benkelman beam deflections, rut depth, and cracking for each section, and (3) determination of the roughness index for each section. A second set of beam deflection tests has been run during the fall periods. Item (1) was conducted only once on each test section, i. e. on the original 41 sections in 1963 and on the nine new sections in 1964. Items (2) and (3) were conducted on all test sections in both 1963 and 1964. It is planned to run deflection and condition tests on each of the test sections on a periodic basis about once a year. The roughometer index is used along with the rut depth and cracking to determine a Present Serviceability Index as shown in Part V of this report. The trend of the PSI with traffic will define the performance of the test section.
The purpose of Investigation 183 is to translate the findings of the AASHO Road Test to Minnesota conditions, and in general to actual highway conditions. At the Road Test, relationships between load and pavement thickness were established for one set of materials and for controlled traffic. In this investigation relationships for other embankment materials and normal highway traffic as found in Minnesota will be developed, starting with the basic relationships obtained from the Road Test
In parts of Minnesota, the supply of good quality gravel is quite limited. For this reason, attempts have been made to improve the poorer quality gravel which is available thus making it, suitable for use as base material on highway projects. The purpose of this investigation was to evaluate the results of treating a typical poor quality aggregate with the following additives: portland cement, asphalt emulsion and hydrated lime.
The project was constructed on a trunk highway with a relatively low traffic volume near Mapleton in Southern Minnesota in 1960. The design called for 22 test, sections, most of which were 1000 feet in length. These sections included seven with soil-cement or cement modified base, three with cement modified base using a delayed compaction procedure, two with lime treated base and seven with asphalt emulsion treated base. Two sections with untreated aggregate base and one with four inches of Class 5 base and six inches of Class 4 subbase were included as control sections. This report covers the design and construction of the project and results of tests and observations made during construction and the five-year period which followed.
The results of this investigation to date indicate that the stabilometer may be a very useful tool in the evaluation of Minnesota soils and aggregates. However, the method of applying the results of the test to the design of flexible pavements still has to be established. This remaining problem is undoubtedly the most difficult and will be the third phase of Investigation No. 176
This investigation was begun in 1951 for the purpose of evaluating selected bituminous-surfaced highways by means of the plate bearing test. It was continued through 1952, 1953 and 1954' without significant change in procedure or purpose.
In 1955 this program was interrupted by other research work and has no-t been resumed as a controlled investigation. However, nearly every year there were requests for plate bearing test data on a number of trunk highways for various purposes, and this information has been assembled in supplementary reports to Investigation No. 161. The purpose of this supplement is to report the miscellaneous plate bearing test data accumulated during 1958 and 1959.
This investigation is conducted every year for the purpose of securing information as to the compressive strength and thickness of concrete pavements as constructed under present methods, and to ascertain these factors as they pertain to specification requirements.
The following data are obtained for each core drilled: project number, station and location with respect to center line at which each core was drilled, date concrete was placed, date drilled, date core was tested, the height, strengths, and diameter of each core. In the summary of results some of the data is omitted and some is indicated in a different form. The date placed is omitted and the age when drilled and the age when tested is used in place of the drilling and testing dates. The height of the core as shown in the report is the height prior to capping.
The location from which the core was taken is measured in the field and the data submitted with the cores for use in the report. Side cores were generally taken two feet from the outer edge of the pavement, and the center cores were taken two to six feet from the center line.
Concrete pavements, particularly In the northern states, are subjected to stresses from climatic changes which not. only affect the load carrying capacity of the slab, but also the life expectancy or the durability of the structure. It was for the purpose of securing additional data to use in computing total stresses under load, and to determine durability that this investigation was started. Measurements have been taken over a twelve-month period. The method of taking measurements, and a summary of the data obtained are shown graphically.
A series of laboratory tests were made by compacting 18 different soils at a variety of density and moisture conditions in boxes. Density determinations were made with the nuclear apparatus and with the sand cone and by calculation from the volume of the box. Comparisons of the sand cone and nuclear results to the box-volume results gave root mean squared errors (RMSE) which indicated their probable errors. Accuracy of the sand cone and the direct transmission device was about the same, and slightly better than the backscatter device. Improvements on the calibration curves furnished by the equipment supplier were made with the box tests.
The field tests on soils permitted the comparison of a large number of nuclear tests by both direct transmission and backscatter taken in a limited area on several projects with sand cone results. The direct transmission results checked the sand cone densities much better than the backscatter results. The nuclear densities were calculated both from. the laboratory box-volume correlation curves and also from a correlation with the field sand cone densities. Root mean squared errors are used to depict the comparisons.
Comparison of moisture contents measured with the backscatter device to oven dry values as well as other methods and the effect of these determinations on calculated dry densities are presented.
Nuclear density measurements of bituminous pavements check displacement densities made on cores quite closely. The time requirements for various types of density tests and notes on the maintenance of the equipment are briefly discussed.
The summary and conclusions list the probable errors in the nuclear methods using the box-volume or sand cone results as standards, and also list the recommended equations for determining densities from count ratios. The direct transmission device gives better results than the backscatter, especially in the field tests. The manner in which the equipment could be used for additional measurements is indicated.
