Evaluation of Recycled Rubber in Asphalt Concrete, HR-330, 1996

The purpose of this research was to evaluate the performance and the use of asphalt rubber binders and recycled rubber granules in asphalt pavement in the state of Iowa. This five year research project was initiated in June 1991 and it was incorporated into Muscatine County Construction Project US 61 from Muscatine to Blue Grass over an existing 10 in. (25.4 cm) by 24 ft (7.3 m) jointed rigid concrete pavement constructed in 1957. The research site consisted of four experimental sections (one section containing rubber chip, one section containing reacted asphalt rubber in both binder and surface, and two sections containing reacted asphalt rubber in surface) and four control sections. This report contains findings of the University of Northern Iowa research team covering selected responsibilities of the research project "Determination of the aging and changing of the conventional asphalt binder and asphalt-rubber binder". Based on the laboratory test, the inclusion of recycled crumb rubber into asphalt affects the ductility of modified binder at various temperatures.

The Effects of Crushed Particles in Asphalt Mixtures, HR-311 and MLR-88-16, 1990

One of the most serious impediments to the continued successful use of hot-mix asphalt (HMA) pavements is rutting. The Iowa Department of Transportation has required 85% crushed particles and 75-blow Marshall mix design in an effort to prevent rutting on Interstate roadways. Relationships between the percent of crushed particles and resistance to rutting in pavement through the use of various laboratory test procedures must be developed. HMA mixtures were made with 0, 30, 60, 85, and 100% crushed gravel, crushed limestone, and crushed quartzite combined with uncrushed sand and gravel. These aggregate combinations were used with 4, 5, and 6% asphalt cement (ac). Laboratory tests included Marshall stability, resilient modulus, indirect tensile, and creep. A creep resistance factor (CRF) was developed to provide a single numeric value for creep test results. The CRF values relate well to the amount of crushed particles and the perceived resistance to rutting. The indirect tensile test is highly dependent on the ac with a small effect from the percent of crushed particles. The Marshall stability from 75-blow compaction relates well to the percent of crushed particles. The resilient modulus in some cases is highly affected by grade of ac.

Refinement of Rapid PCC Coarse Aggregate Testing Program, HR-1071, 1999

The characterization and categorization of coarse aggregates for use in portland cement concrete (PCC) pavements is a highly refined process at the Iowa Department of Transportation. Over the past 10 to 15 years, much effort has been directed at pursuing direct testing schemes to supplement or replace existing physical testing schemes. Direct testing refers to the process of directly measuring the chemical and mineralogical properties of an aggregate and then attempting to correlate those measured properties to historical performance information (i.e., field service record). This is in contrast to indirect measurement techniques, which generally attempt to extrapolate the performance of laboratory test specimens to expected field performance. The purpose of this research project was to investigate and refine the use of direct testing methods, such as X-ray analysis techniques and thermal analysis techniques, to categorize carbonate aggregates for use in portland cement concrete. The results of this study indicated that the general testing methods that are currently used to obtain data for estimating service life tend to be very reliable and have good to excellent repeatability. Several changes in the current techniques were recommended to enhance the long-term reliability of the carbonate database. These changes can be summarized as follows: (a) Limits that are more stringent need to be set on the maximum particle size in the samples subjected to testing. This should help to improve the reliability of all three of the test methods studied during this project. (b) X-ray diffraction testing needs to be refined to incorporate the use of an internal standard. This will help to minimize the influence of sample positioning errors and it will also allow for the calculation of the concentration of the various minerals present in the samples. (c) Thermal analysis data needs to be corrected for moisture content and clay content prior to calculating the carbonate content of the sample.

Pipe Rehabilitation with Polyethylene Pipe Liners, HR-370, Construction Report, 1995

Corroded, deteriorated, misaligned, and distorted drainage pipes can cause a serious threat to a roadway. Normal practice is to remove and replace the damaged drainage structure. An alternative method of rehabilitating these structures is to slip line them with a polyethylene liner. Twelve drainage structures were slip lined with polyethylene liners during 1994 in Iowa. Two types of liners installed were "Culvert Renew" and "Snap-Tite". It was found that the liners could be easily installed by most highway, county, and city maintenance departments. The liners restore the flow and increase the service life of the original drainage structure. The liners were found to be cost competitive with the removal and replacement of the existing drainage structure. Slip lining has the largest economic benefit when the roadway is paved, the culvert is under a deep fill, or traffic volumes are high. The annular space between the original pipe and the liner was filled with flowable mortar. Care should be taken to properly brace and grout the annular space between the liner and the culvert.

X-Ray Diffraction Studies of Soils and Soil Stabilizers, HR-106, 1965

The two goals of this project stated in the Proposal were: (1) study lime diffusion in clayey soils, and (2) find the role of MgO in soil-dolomitic lime stabilization. Because of the practice significance of these goals we temporarily overstaffed this project, giving somewhat a "crash" program. As a result, proposed work was finished up early (as were the funds), and more important, some of the findings were early enough and of sufficient merit to put into field trials in the Fall of 1964. The work now being completed and the funds all being expended, this Final Report is therefore submitted before the anticipated project termination date.

Performance of Various Thicknesses of P.C. Concrete Secondary Pavement, HR-9, 1979

In 1951 Greene County and the Iowa Highway Research Board paved County Road E-33 from Iowa Highway No. 17 (now Iowa 4) to Farlin with various thicknesses [ranging from 4.5 in. (11.4 cm) to 6 in. (15.2 cm)] of portland cement concrete pavement. The project, designated HR-9, was divided into ten research sections. This formed pavement was placed on the existing grade. Eight of the sections were non-reinforced except for centerline tie bars and no contraction joints were used. Mesh reinforcing and contraction joints spaced at 29 ft 7 in. (9.02 m) intervals were used in two 4.5-in. (11.4-cm) thick sections. The concrete in one of the sections was air entrained. Signs denoting the design and limits of the research sections were placed along the roadway. The pavement has performed well over its 28-year life, carrying a light volume of traffic safely while requiring no major maintenance. The 4.5-in. (11.4-cm) thick mesh-reinforced pavement with contraction joints has exhibited the best overall performance.

Investigation of the Loss of Prestress in Prestressed Concrete Beams due to Steam Curing, HR-62, 1961

Mass production of prestressed concrete beams is facilitated by the accelerated curing of the concrete. The ·method most commonly used for this purpose is steam curing at atmospheric pressure. This requires concrete temperatures as high as 150°F. during the curing period. Prestressing facilities in Iowa are located out of doors. This means that during the winter season the forms are set and the steel cables are stressed at temperatures as low as 0°F. The thermal expansion of the prestressing cables should result in a reduction of the stress which was placed in them at the lower temperature. If the stress is reduced in the cables, then the amount of prestress ultimately transferred to the concrete may be less than the amount for which the beam was designed. Research project HR-62 was undertaken to measure and explain the difference between the initial stress placed in the cables and the actual stress which is eventually transferred to the concrete. The project was assigned to the Materials Department Laboratory under the general supervision of the Testing Engineer, Mr. James W. Johnson. A small stress bed complete with steam curing facilities was set up in the laboratory, and prestressed concrete beams were fabricated under closely controlled conditions. Measurements were made to determine the initial stress in the steel and the final stress in the concrete. The results of these tests indicate that there is a general loss of prestressing force in excess of that caused by elastic shortening of the concrete. The exact amount of the loss and the identification of the factors involved could not be determined from this limited investigation.

Fatigue and Residual Stress Investigation of Composite Prestressed Steel Beams, HR-74, 1963

Two composite, prestressed, steel beams, fabricated by slightly different methods, were fatigue tested to destruction. Stresses and deflections were measured at regular intervals, and the behavior of each beam as failure progressed was recorded. Residual stresses were then evaluated by testing segments of each beam. An attempt was made to assess the effects of the residual stresses on fatigue strength.

Comparison of Various Commercial Hydrated Limes for Reducing Soil Plasticity, HR-82 and HR-106, 1964

Atterberg limits tests were performed on mixtures of gumbotil soil and the various chief chemical compounds found in hydrated limes. The results were then checked with commercial hydrated limes of varying chemical compositions. Results indicate that among the major constituents of hydrated limes Ca(OH)2 is most effective in reducing soil plasticity. MgO shows a moderate effect, but Mg(OH)2 and CaCO3 show practically no effect. There is, however, practically no difference between different types or between the same type of commercial hydrated limes for the reduction of soil plasticity. The choice of lime for soil-lime stabilization should, therefore, be dictated by the relative price and pozzolanic strength characteristics of the lime.

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.

Evaluation of Experimental Data Obtained from Lightweight Aggregate Bridge Girders, HR-104, 1968

The use of lightweight aggregates in prestressed concrete is becoming more of a reality as our design criteria become more demanding. Bridge girders of greater lengths have been restricted from travel on many of our highways because the weight of the combined girders and transporting vehicle is excessive making hauls of any distance prohibitive. This, along with new safety recommendations, prompted the State of Iowa to investigate the use of lightweight aggregate bridge girders. A series of three projects was started to investigate the possibility of using lightweight aggregate in prestressed concrete. The object of this project is to study the effect which lightweight aggregate concrete has on the camber of bridge girders when used in a field situation.

Field Observation of Five Lightweight Aggregate Pretensioned Prestressed Bridge Beams, HR-104, 1969

The use of lightweight aggregates in pretensioned prestressed concrete beams is becoming more advantageous as our design criteria dictate longer span concrete bridges. Bridge beams of greater lengths have been restricted from travel on many of our highways because the weight of the combined beams and transporting vehicle was excessive, making hauls of any distance prohibitive. This, along with the fact that new safety requirements necessitate the use of longer spans in grade separation structures over major highways, prompted the State of Iowa to investigate the use of lightweight aggregate bridge beams. The objective of this project is the collection of field deflection measurements for five pretensioned prestressed lightweight aggregate concrete bridge beams fabricated by conventional plant processes; also the comparison of the actual cambers and deflections of the beams with that predicted from the design assumptions.

Clay Mineralogy of a Gumbotil, HR-106, 1964

Investigation of the clay minerals in a gumbotil associated with the Mahaska soil series in Keokuk County, Iowa, indicates that the principal clay mineral is a dioctahedral calcium montmorillonite. Other clay minerals present in this gumbotil are kaolinite and mica, although they are in much smaller percentages. The investigation also pointed out difficulties involved in analyzing this type of soil by standard X-ray procedures and the complications introduced in the analysis of soil samples with high iron content utilizing standard accepted diffraction techniques.

Modification of Ca-Montmorillonite by Low-Temperature Heat Treatment, HR-106, 1964

Objectives of this investigation were to measure the effects of moderate heat treatments (below the dehydroxylation temperature) on physical and chemical properties of a calcium-montmorillonite clay. Previous workers have noted the reduction in cation exchange capacity and swelling property after heating in the range 200 to 400°C, and have suggested several possible explanations, such as hysteresis effect, increased inter-layer attractions due to removal of inter-layer water, or changes in the disposition of inter-layer or layer surface ions. The liquid limits of Ca-montmorillonite were steadily decreased with increased temperature of treatment, levelling at about 450°C. The plastic limit decreased slightly up to 350°C, above which samples could no longer be rolled into threads. The gradual change is in contrast with sudden major changes noted for weight loss (maximum rates of change at l00°C and 500°C), glycol retention surface area (520°C), and d001 diffraction peak intensity (17.7 A spacing) and breadth after glycolation (530°C). Other properties showing more gradual reductions with heat treatment were amount of exchangeable calcium (without water soaking), cation exchange capacity by NH4AC method, and d001 intensity (21 A spacing) after storing at 100% r.h. one month and re-wetting with water. Previous water soaking allowed much greater release of fixed Ca++ up to 450°C. Similar results were obtained with cation exchange capacities when samples were treated with N CaCl2 solution. The 21.0 A peak intensity curve showed close similarity to the liquid limit and plastic index curves in the low temperature range, and an explanation is suggested.

Compositional and Mechanical Properties of Carbonate Rocks, HR-110, 1967

The research project, HR-110, was begun in the fall of 1964 to further investigate the compositional and mechanical properties of some of the carbonate rocks used as aggregate in portland cement concrete. Samples were taken only from those portions of the quarries that are used as aggregate in portland cement concrete by the Iowa State Highway Commission except where designated by commission personnel for purposes of evaluation of potential aggregate sources. Where practical, the samples were taken from each bed recognized by the Highway Commission geologists, and in most instances, the thicker beds were sampled at the top, middle, and bottom to detect any lithologic changes that escaped megascopic observation.