Factors Influencing Stability of Granular Base Course Mixes, Progress Report, HR-99, 1965

The problems of laboratory compaction procedures, the effect of gradation and mineralogy on shearing strength, and effect of stabilizing agents on shearing strength of granular base course mixes are discussed. For the materials tested, a suitable laboratory compaction procedure was developed which involves the use of a vibratory table to prepare triaxial test specimens. A computer program has been developed to facilitate the analysis of the test data of the effect of gradation and mineralogy on shearing strength of soils. The effects of the following materials have been selected for evaluation as stabilizing agents’ portland cement, sodium and calcium chloride, lime organic cationic waterproofer, and asphaltic materials.

Factors Influencing Stability of Granular Base Course Mixes, Progress Report, HR-99, 1964 (April)

The problems of laboratory compaction procedures, the effect of gradation and mineralogy on shearing strength, and effect of stabilizing agents on shearing strength of granular base course mixes are discussed. For the materials tested, a suitable laboratory compaction procedure was developed which involves the use of a vibratory table to prepare triaxial test specimens. A computer program has been developed to facilitate the analysis of the test data of the effect of gradation and mineralogy on shearing strength of soils. The effects of the following materials have been selected for evaluation as stabilizing agents’ portland cement, sodium and calcium chloride, lime organic cationic waterproofer, and asphaltic materials.

Factors Influencing Stability of Granular Base Course Mixes, Progress Report, HR-99, 1964 (November)

The problems of laboratory compaction procedures, the effect of gradation and mineralogy on shearing strength, and effect of stabilizing agents on shearing strength of granular base course mixes are discussed. For the materials tested, a suitable laboratory compaction procedure was developed which involves the use of a vibratory table to prepare triaxial test specimens. A computer program has been developed to facilitate the analysis of the test data of the effect of gradation and mineralogy on shearing strength of soils. The effects of the following materials have been selected for evaluation as stabilizing agents’ portland cement, sodium and calcium chloride, lime organic cationic waterproofer, and asphaltic materials.

A Study to Correlate Soil Consistency Limits with Soil Moisture Tensions, HR-27, 1965

The liquid and plastic limits of a soil are consistency limits that were arbitrarily chosen by Albert Atterberg in 1911. Their determination is by strictly empirical testing procedures. Except for the development of a liquid limit device and subsequent minor refinements the method has remained basically unchanged for over a half century. The empirical determination of an arbitrary limit would seem to be contrary to the very foundations of scientific procedures. However, the tests are relatively simple and the results are generally acceptable and valuable in almost every conceivable use of soil from an engineering standpoint. Such a great volume of information has been collected and compiled by application of these limits to cohesive soils, that it would be impractical and virtually impossible to replace the tests with a more rational testing method. Nevertheless, many believe that the present method is too time consuming and inconsistent. Research was initiated to investigate the development of a rapid and consistent method by relating the limits to soil moisture tension values determined by porous plate and pressure membrane apparatus. With the moisture tension method, hundreds of samples may be run at one time, operator variability is minimal, results are consistent, and a high degree of correlation to present liquid limit tests is possible.

Effect of CA-Montmorillonite Expansion on X-Ray Diffraction Intensities, Progress Report, HR-111, 1966

The most abundant clay mineral group in Iowa soils is montmorillonite, most commonly calcium-saturated (Hanway et al, 1960). The calcium montmorillonite-water system was therefore selected for detailed X-ray study. Montmorillonite is unusual among minerals in that it has an expanding lattice in the c direction. That is, upon wetting with water, the individual silicate layers separate to allow entry of water, and the mineral expands. Characteristics of this expansion are readily studied by means of X-ray diffraction: the X-ray diffraction angle gives the average layer-to-layer "d001" spacing for any given moisture condition; the sharpness of the diffraction peak is a measure of uniformity of the d001 spacing; and the intensity of the peak relates to uniformity of the d001 spacing and in addition to the electron density distribution within the repeating elements. The latter is embodied in the "structure factor".

Soil Erosion Control for Secondary Roads, HR-155

Research project HR-155 was initiated to study soil erosion problems along the secondary road system in Iowa and to find a substitute for straw for the control of soil erosion during the period of seed establishment. Accordingly, six field research sites were established to test the ability of commercial soil conditioners to control soil erosion. The six field research sites were selected on the basis of terrain and type of soil material exposed on the cut-slope areas.

An Evaluation of Cover Aggregate Stripping Characteristics, Progress Report, HR-182, 1977

The increasing use of seal coats for surface restoration and the concurrent increase in failures of such treatments prompted the current research. Field observations indicated that certain aggregate types seemed to be more susceptible to failure, including stripping and disintegration. The research was thus designed to try to identify those aggregate types which would perform satisfactorily under normal conditions.

Study of Type 'A' Asphaltic Concrete Surface Mix Design, R-232, 1968

In some asphaltic concrete mixes asphalt absorption in field mixes is difficult to predict by the routine mix design tests presently being used. Latent or slow absorption in hot mixes is hard to compensate for in field control due to aggregate gradations being near maximum density. If critical asphalt need could be changed by increasing voids in the mineral aggregate so that more freedom could be exercised in compensating for the absorption, this may aid in design. The voids in the mineral aggregate can be related to composite gradation of total aggregate in a mixture, i.e. if a composite gradation of aggregate is finer than that of maximum density curve, the V.M.A. will be greater than that of a mix of maximum density. The typical gradation of Iowa Type 'A' mixes is finer than a gradation which is near the centerline of the specification at sieves larger than the No. 30 and coarser at the lower sieve sizes. The mixes of the typical gradation will have higher V.M.A. than those of the near centerline mixes. By studying properties of the mixes of the typical gradation and comparing them with those of the mixes of maximum density, it may aid in the modification and simplification of our present testing methods and specification requirements while still maintaining control of quality of the mix by controlling voids, stability, gradation and asphalt content.

Evaluation of Changes in Productivity Resulting from Removal of Soil for Highway Construction, HR-186, 1981

Borrow areas are created where soil is removed to provide needed fill material for highway and other construction projects. Where these areas are located beyond the highway right-of-way, they must be restored and returned to useful purposes. In Iowa, borrow areas are often developed on agricultural lands and therefore, it is necessary to return them to agricultural uses whenever possible. This research project was established to evaluate the changes in row crop productivity where borrow is removed for highway construction. Secondly, several reclamation techniques were selected to be applied to borrow area research sites and the response of crops to each treatment will be evaluated. All borrow area research sites were selected in 1977 from Iowa Department of Transportation construction plans. The Audubon and Buchanan County sites were completed in the fall of 1977 and May 1978, respectively. Both were used for research in 1978, 1979, and 1980. The two remaining sites in Hamilton and Lee Counties were completed in the fall of 1978 and research was conducted at these sites in 1979, 1980, and 1981. In this report, the 1981 results from the Hamilton and Lee County borrow sites will be presented. Secondly, a summary of the three years of research from each borrow area will be presented along with specific and general conclusions from the research project.

The Economic Potential of the Spergen Formation in Seven Southeastern Iowa Counties, HR-189, 1978

The middle Mississippian (Meramec Series) units include the Spergen Formation, the St. Louis Limestone and the Ste. Genevieve Formation which outcrop sporadically within a curvilinear subcrop band trending through southeastern and central Iowa. Studies of these units as they occur in Iowa have been cursory in the past, especially with regard to the lowermost occurring Meramecan unit, the Spergen Formation. The Spergen Formation, as it occurs in southeastern Iowa is being considered as a desirable concrete aggregate source. At present, the depth of occurrence, thickness variations and geographic extent are very poorly known and the nature of lithologic variation in Iowa is obscure. Due to a paucity of information of its thickness, extent and nature of rapid lateral facies variations, the full economic potential of the unit has not been realized in some areas of southeastern Iowa. This is especially disheartening in view of the decline of acceptable concrete aggregate source materials in southeastern Iowa. This report is an attempt to synthesize subsurface and surface data in order to present a more coherent picture of the depth, thickness and lithologic variations of the Spergen Formation. Recommendations have been made for the exploration of specific areas within the field area for future development of surface quarrying and subsurface mining operations where thickness, lithology and depth characteristics deem consideration. Due to the lack of adequate data points in some quadrants of the field area, some of the recommendations are drawn on rather tenuous grounds, but a concerted effort has been made to be conservative in these judgements.

Evaluation of Fly Ash in Bridge Deck Concrete, MLR-84-2, 1985

Fly ash was used in this evaluation study to replace 15% of the cement in Class D-57 structural concrete containing ASTM C494 Type B, retarding admixtures. Two Class "C" ashes and one Class "F" ash from Iowa approved sources were examined in each mix. When Class "C" ashes were used, they were substituted on the basis of 1.0 pound for each pound of cement removed. When Class "F" ash was used, it was substituted on the basis of 1.25 pounds of ash for each pound of cement removed. Compressive strengths of the retarded mixes, with and without fly ash, were determined at 7, 28 and 56 days of age. In most cases, with few exceptions, the mixes containing the fly ash exhibited higher strengths than the same concrete mix without the fly ash. The exceptions were the 7, 28, and 56 days of the mixes containing Class F ash. The freeze/thaw durability of the concrete studied was not affected by the presence of fly ash. The data obtained suggested that the present Class D-57 structural concrete mix with retarding admixtures can be modified to allow the substitution of 15% of the cement with an approved fly ash when Class III coarse aggregates are used. Setting times of the concretes were not materially changed due to the incorporation of fly ash.

Frictional Properties of Asphalt Concrete Pavements in Iowa, MLR-87-5, 1987

Friction testing of pavements has been a continuing effort by the Iowa Department of Transportation since 1969. This report details results of tests of asphaltic concrete pavements on the primary and interstate road systems. Both sprinkle treated and non-sprinkle treated pavements placed between 1975 - 1985 are included. A total of 1785 miles representing 216 separate paving projects were examined. The effect of fog sealing sprinkle treated pavements was studied by testing friction levels before and after the application of the fog seals. Conclusions of the report are: 1. Current aggregate selection criteria for a.c. pavement surface courses provides adequate friction levels through 10 years and should remain effective through a 15 year design life. 2. Sprinkle treatment of pavements has, for the most part, provided macrotexture in the pavement surface as evidenced by smooth tire testing. 3. Fog sealing sprinkle treated pavements does not significantly alter the friction properties.

Pilot Construction Project for Granular Shoulder Stabilization, TR-634, 2013

Granular shoulders need to be maintained on a regular basis because edge ruts and potholes develop, posing a safety hazard to motorists. The successful mitigation of edge-rut issues for granular shoulders would increase safety and reduce the number of procedures currently required to maintain granular shoulders in Iowa. In addition, better performance of granular shoulders reduces the urgency to pave granular shoulders. Delaying or permanently avoiding paving shoulders where possible allows more flexibility in making investments in the road network. To stabilize shoulders and reduce the number of maintenance cycles necessary per season, one possible stabilizing agent—acidulated soybean oil soapstock—was investigated in this research. A pilot testing project was conducted for selected problematic shoulders in northern and northeastern Iowa. Soapstock was applied on granular shoulders and monitored during application and pre- and post-application. Application techniques were documented and the percentage of application success was calculated for each treated shoulder section. As a result of this research, it was concluded that soybean oil soapstock can be an effective stabilizer for granular shoulders under certain conditions. The researchers also developed draft specifications that could possibly be used to engage a contractor to perform the work using a maintenance-type construction contract. The documented application techniques from this project could be used as guidance for those who want to apply soapstock for stabilizing granular shoulders but might not be familiar with this technique.

Evaluation of Gap-Graded Asphalt Concrete Mixtures, Vol. 1. Physical Properties (Part I: Mechanical Properties), HR-157, Volume 1, 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper-combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100(d/D)^n is not justified. It is recommended that the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Evaluation of Gap-Graded Asphalt Concrete Mixtures Vol. 3. Appendix, HR-157, Volume 3 (Part 3), 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100 (d/D)n is not justified. It is recommended that. the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.