A Mechanistic Explanation of The Physical Properties of Undisturbed Loess, February, 1968

The relation between the properties and the water content of an undisturbed loess were investigated to provide insight into the mechanical behavior of the natural soil. Hand-carved samples from a single deposit, at their natural water contents, and at water contents modified in the laboratory to provide a range from 870 to 3270, were subjected to unconsolidated-undrained triaxial compression tests, consolidation tests, and initial negative pore water pressure tests. In addition, the clay-size fraction was separated from the remainder of the loess for a separate series of tests to establish its properties. The natural water content of the deposit in the field was measured at regular intervals for one year to provide an example of the range in properties that would be encountered. at this site. The test results are presented and their interpretation leads to conclusions regarding the volumetric relations that exist as the water content varies. The significance of the water content in relation to the properties of the natural soil is explored and the concept of a critical water content for loess is introduced.

Camping in Iowa, 1968

This directory is intended to assist the general camping public and contains listings of both public and private facilities known to exist as a result of survey questionnaires.

Evaluation of Limestone Filler in Gravel Mixtures "Asphaltic Concrete", R-228, 1968

This study was designed to provide background information on asphaltic concrete mixtures peculiar to northwest Iowa. This background is necessary to provide the basis for future specifications. There were several projects let in 1967 involving l", 3/4" and 3/8" mixes of Type "B'' asphaltic concrete which specified in part, II Not less than 40% of the material passing the No. 200 sieve shall be pulverized limestone or mineral filler, but in no case shall the per cent of pulverized limestone or mineral filler passing the No. 200 sieve be less than 2%. No credit will be allowed for limestone in gravel - II Northwest Iowa has no suitable limestone or mineral filler locally available. As a result, this material has to be imported, raising the cost of the mix approximately twenty-five cents per ton. The purpose of this study, therefore, was designed to compare some original job mix samples with alternate mixes from the same local material, but without the addition of pulverized limestone or mineral filler. Since the filler from the crushed gravel does not have the same crushing characteristics or sieve analysis as the pulverized limestone or mineral filler, they could not be compared on an equal percentage basis. Therefore, the alternate mixes were made to conform to the following proposed specification, "No less than 40% of the material passing No. 200 sieve shall be pulverized limestone or mineral filler or a 100% crushed gravel, but in no case shall the per cent of pulverized limestone or mineral filler or a 100% crushed gravel passing the No. 200 sieve be less than 2%."

Field Testing of Asphaltic Concrete Mixes, HR-101 and R-183, 1968

The amount of asphalt cement in asphaltic concrete has a definite effect on its durability under adverse conditions. The expansion of the transportation system to more and heavier loads has also made the percentage of asphalt cement in a mix more critical. The laboratory mixer does not duplicate the mixing effect of the large pugmills; therefore, it is impossible to be completely sure of the asphalt cement needed for each mix. This percentage quite often must be varied in the field. With a central testing laboratory and the high production of mixing plants today, a large amount of asphaltic concrete is produced before a sample can be tested to determine if the asphalt content is correct. If the asphalt content lowers the durability or stability of a mix, more maintenance will be required in the future. The purpose of this project is to determine the value of a mobile laboratory in the field, the feasibility of providing adequate, early testing in the field, and correlation with the central laboratory. The major purpose was to determine as soon as possible the best percentage of asphalt.