University of Iowa School of Library and Information Science newsletter. 1994-1995, no. 36.

Newsletter from the University of Iowa School of Library and Information Science.

Iowa's Recreation Trails, 1994

Includes maps and lists with contact information of Iowa's recreation trails including ones for canoeing, hiking, snowmobiling, equestrian, atv, cross county skiing and bicycling.

Field Demonstration of Foamed Asphalt Muscatine County, HR-257, 1988

The foamed asphalt concept has been around since the 1950's. Rising oil prices have created a renewed interest in this process. The purpose of this project was to construct an asphalt base using the foamed asphalt process and to evaluate its performance. A 4.2 mile length of Muscatine County road A-91 was selected for the research project. Asphalt contents of 4.5% and 5.5%, moisture contents of 70% and 90% of optimum, and fog, single chip, and double chip seal coats were used in various combinations to lay 9 test sections of 4-inch foamed asphalt base. After five years of service and evaluation, several conclusions can be made concerning the performance of the foamed asphalt bases: (1) the foamed asphalt process can work as shown by the excellent performance of Sections 2 and 3; (2) foamed asphalt base requires a well compacted subgrade and a road profile suitable for good drainage of water--test section failures were mostly due to a poor subgrade and subsurface moisture; and (3) when the base is placed in two or more lifts, extreme care must be exercised to insure adequate bonding is achieved between lifts. Any future research with foamed asphalt should include various asphalt depths in order to determine a thickness/strength relationship for foamed asphalt.

Construction and Evaluation of Submerged Vanes for Stream Control, HR-274, 1988

The objective of this study was to determine the practicality and effectiveness of using submerged vanes ("Iowa Vanes") to control bank erosion in a bend of East Nishnabotna River, Iowa. The vane system was constructed during the summer of 1985. It functions by eliminating, or reducing, the centrifugally induced helical motion of the flow in the bend, which is the root cause of bank undermining. The system was monitored over a 2-year period, from September 1985 to October 1987. Two surveys were conducted in the spring of 1986 in which data were taken of depths and velocities throughout the bend and of water-surface slope. The movement of the bank was determined from aerial photos and from repeated measurements of the vane-to-bank distance. The bankfull scour depths and velocities along the bank have been reduced significantly; and the movement of the bank has been stopped or considerably reduced. The improvements were obtained without changing the energy slope of the channel. Areas of design improvements were identified.

An Investigation of Emulsion Stabilized Limestone Screenings, HR-309, 1994

A significant amount of waste limestone screenings is produced during aggregate production. This waste material cannot be used in highway construction because it does not meet current highway specifications. The purpose of this research was to determine if a waste limestone screenings/emulsion mix could be used to construct a base capable of supporting local traffic. A 1.27 mile (2.04 km) section of roadway in Linn County was selected for this research. The road was divided into seven sections. Six of the sections were used to test 4 in. (100 mm) and 6 in. (150 mm) compacted base thicknesses containing 2.5%, 3.5%, and 4.5% residual asphalt contents. The seventh section was a control section containing untreated waste limestone screenings. This research on emulsion stabilized limestone screenings supports the following conclusions: (1) A low maintenance roadway can be produced using a seal coat surface on 6 in. (150 mm) of stabilized limestone screenings with 4.5% asphalt cement; (2) A 6 in. (150 mm) emulsion stabilized base with less than 3.5% asphalt cement does not produce a satisfactory low cost maintenance roadway; (3) A 4 in. (100 mm) emulsion stabilized base does not produce a satisfactory low cost maintenance roadway; and (4) A 2 in. (50 mm) asphalt concrete surface would be necessary on many roads to provide a low maintenance roadway using emulsion stabilized limestone screenings.

Field Measurement of Bridges for Long-term Structural Movement, HR-295, 1988

This report describes the field application of the tilt sensing method for monitoring movement of the Black Hawk and Karl King Bridges. The study objectives were: to design a data acquisition system for tilt sensing equipment utilizing a telephone telemetry system; to monitor possible movement of the main span pier, Pier No. 2, on the Black Hawk Bridge in Lansing and the possible long-term movement of Pier No. 4 on the Karl King Bridge in Fort Dodge; and to assess the feasibility, reliability, and accuracy of the instrumentation system used in this study.

The Role of Magnesium in Concrete Deterioration, HR-355, 1994

Concretes with service lives of less than 15 years and those with lives greater than 40 years were studied with petrographic microscope, scanning electron microscope, and electron microprobe to determine why these two groups of concrete exhibit such different degrees of durability under highway conditions. Coarse aggregate used in both types of concrete were from dolomite rock, but investigation revealed that dolomite aggregate in the two groups of concretes were much different in several respects. The poorly-performing aggregate is fine-grained, has numerous euhedral and subhedral dolomite rhombohedra, and has relatively high porosity. Aggregate from durable concrete is coarse-grained, with tightly interlocked crystal fabric, anhedral dolomite boundaries, and low porosity. Aggregate in short service life concrete was found to have undergone pervasive chemical reactions with the cement which produced reaction rims on the boundaries of coarse aggregate particles and in the cement region adjacent to aggregate boundaries. Textural and porosity differences are believed to be chiefly responsible for different service lives of the two groups of concrete. The basic reaction that has occurred in the short service life concretes between coarse aggregate and cement is an alkali-dolomite reaction. In the reaction dolomite from the aggregate reacts with hydroxide ions from the cement to free magnesium ions and carbonate ions, and the magnesium ions precipitate as brucite, Mg(OH)2. Simultaneously with this reaction, a second reaction occurs in which product carbonate ions react with portlandite from the cement to form calcite and hydroxide ions. Crystal growth pressures of newly formed brucite and calcite together with other processes, e.g. hydration state changes of magnesium chloride hydrates, lead to expansion of the concretes with resultant rapid deterioration. According to this model, magnesium from any source, either from reacting dolomite or from magnesium road deicers, has a major role in highway concrete deterioration. Consequently, magnesium deicers should be used with caution, and long-term testing of the effects of magnesium deicers on highway concrete should be implemented to determine their effects on durability.

Field Evaluation of Class A Subbase Using Fly Ash, MLR-87-3, 1988

This project consisted of slipforming a 4-inch thick econocrete subbase on a 6-mile section of US 63. The project location extends south from one mile south of Denver, Iowa to Black Hawk County Road C-66 and consisted of the reconstruction and new construction of a divided four-lane facility. The econocrete was placed 27.3 feet wide in a single pass. Fly ash was used in this field study to replace 30, 45 and 60 percent of the portland cement in three portland cement econocrete base paving mixes. The three mixes contained 300, 350 and 400 pounds of cementitious material per cubic yard. Two Class "C" ashes from Iowa approved sources were used. The ash was substituted on the basis of one pound of ash for each pound of cement removed. The work was done October 6-29, 1987 and May 25-June 9, 1988. The twelve subbase mixes were placed in sections 2500 to 3000 feet in length on both the north and southbound roadways. Compressive strengths of all mixes were determined at 3 and 28 days of age. Flexural strengths of all mixes were determined at 7 and 14 days. In all cases strengths were adequate. The freeze/thaw durability of the econocrete mixes used was reduced by increased fly ash levels but remained above acceptable limits. The test results demonstrate the feasibility of producing econocrete with satisfactory properties even using fly ash at substitution rates up to 45 percent.

Development of a Rational Characterization Method for Iowa Fly Ash, HR-286, 1988

This research project was conducted in an attempt to determine the cause of paste strength variability in Iowa fly ashes and to develop test methods to more adequately reflect fly ash physical and chemical characteristics. An extensive three year sampling and testing program was developed and initiated which incorporated fly ash from several Iowa power plants. Power plant design and operating data were collected. The variability was directly linked to power plant maintenance schedules and to sodium carbonate coal pretreatment. Fly ash physical and chemical properties can change drastically immediately before and after a maintenance outage. The concentrations of sulfate bearing minerals in the fly ash increases sharply during shutdown. Chemical, mineralogical, and physical testing indicated that the sodium, sulfate bearing minerals, lime and tricalcium aluminate contents of the fly ashes play important roles in the development of hydration reaction products in fly ash pastes. The weak pastes always contained ettringite as the major reaction product. The strong pastes contained straetlingite and monosulfoaluminate as the major reaction products along with minor amounts of ettringite. Recommendations for testing procedure changes and suggested interim test methods are presented.

Impacts on Safety of Left-Turn Treatment at High Speed Signalized Intersections, HR-347, 1994

Left-turning traffic is a major source of conflicts at intersections. Though an average of only 10% to 15% of all approach traffic turns left, these vehicles are involved in approximately 45% of all accidents. This report presents the results of research conducted to develop models which estimate approach accident rates at high speed signalized intersections. The objective of the research was to quantify the relationship between traffic and intersection characteristics, and accident potential of different left turn treatments. Geometric, turning movement counts, and traffic signal phasing data were collected at 100 intersections in Iowa using a questionnaire sent to municipalities. Not all questionnaires resulted in complete data and ultimately complete data were derived for 63 intersections providing a database of 248 approaches. Accident data for the same approaches were obtained from the Iowa Department of Transportation Accident Location and Analysis System (ALAS). Regression models were developed for two different dependent variables: 1) the ratio of the number of left turn accidents per approach to million left turning vehicles per approach, and 2) the ratio of accidents per approach to million traffic movements per approach. A number of regression models were developed for both dependent variables. One model using each dependent variable was developed for intersections with low, medium, and high left turning traffic volumes. As expected, the research indicates that protected left turn phasing has a lower accident potential than protected/permitted or permitted phasing. Left turn lanes and multiple lane approaches are beneficial for reducing accident rates, while raised medians increase the likelihood of accidents. Signals that are part of a signal system tend to have lower accident rates than isolated signals. The resulting regression models may be used to determine the likely impact of various left turn treatments on intersection accident rates. When designing an intersection approach, a traffic engineer may use the models to estimate the accident rate reduction as a result of improved lane configurations and left turn treatments. The safety benefits may then be compared to any costs associated with operational effects to the intersection (i.e., increased delay) to determine the benefits and costs of making intersection safety improvements.

Alternative Flexible Overlays, HR-229, 1988

The objective of this project was to determine if any of several cutback and emulsified asphalt plant mixed and road mixed overlays had the ability to resist thermal cracking at low temperatures without inducing shoving and/or ruttinq at high temperatures. A 2.6 mile section of Osceola County road A-34 and a 7.0 mile section of A-46 were divided into 14 test sections of various lengths. After six years, results show an MC-3000 asphalt cutback cold mix can reduce the amount of reflective cracking when compared to an AC-5 hot mix. This can be done without inducing high temperature related problems. Cold road mixing can be effective in reducing cracking on low volume roads. However, more experience is required if the full benefits of road mixing are to be realized.

Evaluation of Preformed Neoprene Joint Seals, HR-318, 1994

Most pavement contraction joint seals in Iowa, in general, have been performing in less than a satisfactory manner. The effective life of the seals, in maintaining a watertight joint, has been only from two to five years. In search of improvements, research was proposed to evaluate preformed neoprene joint seals. The performance of those seals was to be compared mainly with the hot poured rubberized asphalt sealants and cold applied silicone sealants or other sealants commonly used at the time this research began. Joint designs and methods of sawing were also investigated. All evaluations were done in new portland cement concrete (PCC) pavements. Three projects were initially selected and each included a research section of joint sealing. Some additional sites were later added for evaluation. Several joint sealants were evaluated at each research site. The various sites included high, medium and low levels of traffic. Evaluations were done over a five-year period. Neoprene joint seals provided better performance than hot or cold field formed joints.

Air Formed Arch Culvert Construction - Washington County, HR-313, 1994

Iowa's secondary roads contain nearly 15,000 bridges which are less than 40 ft (12.2 m) in length. Many of these bridges were built several decades ago and need to be replaced. Box culvert construction has proven to be an adequate bridge replacement technique. Recently a new bridge replacement alternative, called the Air-O-Form method, has emerged which has several potential advantages over box culvert construction. This new technique uses inflated balloons as the interior form in the construction of an arch culvert. Concrete was then shotcreted onto the balloon form. The objective of research project HR-313 was to construct an air formed arch culvert to determine the applicability of the Air-O-Form technique as a county bridge replacement alternative. The project had the following results: The Air-O-Form method can be used to construct a structurally sound arch culvert; and the method must become more economical if it is to compete with box culverts. Continued monitoring should be conducted in order to evaluate the long-term performance of the Air-O-Form method.

Development of a Conductometric Test for Frost Resistance of Concrete, HR-272, 1988

Research is described that was aimed at developing a test method which can be reasonably and rapidly performed in the laboratory and in the field to predict, with a high degree of certainty, the behavior of concrete subjected to the action of alternate freezing and thawing. The conductometric evaluation of concrete durability was explored with 3 different test methods: conductometric evaluation of the resistance of concrete to rapid freezing and thawing; conductomtric evaluation of the resistance of concrete to natural freezing and thawing, and conductometric evaluation of the pore size distribution of concrete and its correlation to concrete durability. The study showed that conductance could be used as a viable method for determining the durability of portland cement concrete. This would also allow the continuous monitoring of concrete durability without the removal twice per week from the freeze/thaw chamber. Recommendations for the continued development of these test methods are also included.

Thermogravimetric Analysis of Carbonate Aggregate, HR-336, 1994

Research has shown that one of the major contributing factors in early joint deterioration of portland cement concrete (PCC) pavement is the quality of the coarse aggregate. Conventional physical and freeze/thaw tests are slow and not satisfactory in evaluating aggregate quality. In the last ten years the Iowa DOT has been evaluating X-ray analysis and other new technologies to predict aggregate durability in PCC pavement. The objective of this research is to evaluate thermogravimetric analysis (TGA) of carbonate aggregate. The TGA testing has been conducted with a TA 2950 Thermogravimetric Analyzer. The equipment is controlled by an IBM compatible computer. A "TA Hi-RES" (trademark) software package allows for rapid testing while retaining high resolution. The carbon dioxide is driven off the dolomite fraction between 705 deg C and 745 deg C and off the calcite fraction between 905 deg C and 940 deg C. The graphical plot of the temperature and weight loss using the same sample size and test procedure demonstrates that the test is very accurate and repeatable. A substantial number of both dolomites and limestones (calcites) have been subjected to TGA testing. The slopes of the weight loss plot prior to the dolomite and calcite transitions does correlate with field performance. The noncarbonate fraction, which correlates to the acid insolubles, can be determined by TGA for most calcites and some dolomites. TGA has provided information that can be used to help predict the quality of carbonate aggregate.