Design Manual for Strengthening Single-Span Composite Bridges by Post-Tensioning Part 3, HR-238, 1985

The authors have post-tensioned and monitored two Iowa bridges and have field tested the post-tensioning of a composite bridge in Florida. In order to provide the practical post-tensioning distribution factors given in this manual, the authors developed a finite element model of a composite bridge and checked the model against a one-half scale laboratory bridge and two actual composite bridges, one of which had a 45 deg skew. Following a brief discussion of this background research, this manual explains the use of elastic, composite beam and bridge section properties, the distribution fractions for symmetrically post-tensioned exterior beams, and a method for computing the strength of a post-tensioned beam. Also included is a design example for a typical, 51.25-ft (15.62-m) span, four-beam composite bridge. Moments for Iowa Department of Transportation rating trucks, H 20 and HS 20 trucks, have been tabulated for design convenience and are included in the appendix.

Reducing the Problem of Transverse Cracking, HR-232, 1985

The Iowa Department of Transportation (DOT) is continually improving the pavement management program and striving to reduce maintenance needs. Through a 1979 pavement management study, the Iowa DOT became a participant in a five state Federal Highway Administration (FHWA) study of "Transverse Cracking of Asphalt Pavements". There were numerous conclusions and recommendations but no agreement as to the major factors contributing to transverse cracking or methods of preventing or reducing the occurrence of transverse cracking. The project did focus attention on the problem and generated ideas for research. This project is one of two state funded research projects that were a direct result of the FHWA project. Iowa DOT personnel had been monitoring temperature susceptibility of asphalt cements by the Norman McLeod Modified Penetration Index. Even though there are many variables from one asphalt mix to another, the trend seemed to indicate that the frequency of transverse cracking was highly dependent on the temperature susceptibility. Research project HR-217 "Reducing the Adverse Effects of Transverse Cracking" was initiated to verify the concept. A final report has been published after a four-year evaluation. The crack frequency with the high temperature susceptible asphalt cement was substantially greater than for the low temperature susceptible asphalt cement. An increased asphalt cement content in the asphalt treated base also reduced the crack frequency. This research on prevention of transverse cracking with fabric supports the following conclusions: 1. Engineering fabric does not prevent transverse cracking of asphalt cement concrete. 2. Engineering fabric may retard the occurrence of transverse cracking. 3. Engineering fabric does not contribute significantly to the structural capability of an asphalt concrete pavement.

Field Demonstration and Laboratory Evaluation of Foamed Asphalts - Muscatine County, HR-233, 1985

In view of the energy, environmental, and economic advantages of the foamed asphalt process using local aggregates in cold mixes and the promising results from Research Project HR-212, a 4.2-mile section of county road in Muscatine County was built with foamed asphalt and local aggregates during August-September 1983. Extensive laboratory evaluation was carried out on five plant mixes representing foamed mixes used in the nine test sections, a laboratory prepared foamed mix, and a laboratory prepared hot mix similar to Plant Mix 1. The foamed mixes were compacted, cured under 15 curing conditions and tested for bulk specific gravity, Marshall stability at 77° F and at 140° F, cured moisture content, resilient modulus and effects of moisture damage due to freeze-thaw cycles, water soaking, and vacuum saturation. In addition, four sets of 83 core samples were taken at 1 to 15 months and tested for moisture content, specific gravity, Marshall stability, and resilient modulus. In summary, the test road has performed satisfactorily for almost two years. The few early construction problems encountered were to be expected for experimental projects dealing with new materials and technologies. Overall results to date are encouraging and foamed asphalt mixes have proved to have the potential as a viable base material in areas where marginal aggregates are available. It is hoped and expected that performance evaluation of the test sections will be continued and that more foamed asphalt trial projects will be constructed and monitored so that experiences and findings from this project can be verified and mix design criteria can be gradually established. For future foamed asphalt projects it is recommended that anti-stripping additives, such as hydrated lime, be added in view of the potential moisture susceptibility of foamed mixes observed in the laboratory evaluation.

A Sufficiency Rating System for Secondary Roads in Iowa, HR-264, Volume II, 1985

The goal of this study is to develop a usable sufficiency rating system for secondary roads. There are several assumptions that have been made at the outset. These are: 1. County engineers currently use at least a limited set of decision criteria to make decisions regarding project priorities. 2. Some degree of consensus exists among the county engineers in terms of which are the most important criteria and that there is some agreement on their relative importance. Accordingly, a questionnaire was developed which could be used as a survey tool. The results of the survey were used to develop a final list of weighted rating elements which were used as part of the proposed sufficiency rating system. State and local jurisdictions from other states were also surveyed to determine the status of the use of sufficiency rating systems for secondary roads outside of Iowa and to gather some applicable data.

Engineering Study for the Evaluation of Public Road Administration and Maintenance Alternatives, HR-265, 1985

Iowa's public road system of 112,000 miles is one of the largest and the best in the nation. It represents a considerable financial investment of taxpayer revenues over the years. And, it requires a sustained investment to preserve an economical level of transport service into the future. In 1982, a Governor's Blue Ribbon Transportation Task Force evaluated the effectiveness of Iowa's entire transportation system. Four important Task Force recommendations dealt with public road administrative issues in Iowa. These issues were related to: (1) Design criteria and levels of maintenance; (2) Consistency in the use of standards among jurisdictions; (3) Consolidation of maintenance operations at one jurisdiction level; and (4) Jurisdicational authority for roads; The issues formed the background for Research Project HR-265.

Data Acquisition and Computer Plotting of Delamtect Data, HR-269, 1985

The overall system is designed to permit automatic collection of delamination field data for bridge decks. In addition to measuring and recording the data in the field, the system provides for transferring the recorded data to a personal computer for processing and plotting. This permits rapid turnaround from data collection to a finished plot of the results in a fraction of the time previously required for manual analysis of the analog data captured on a strip chart recorder. In normal operation the Delamtect provides an analog voltage for each of two channels which is proportional to the extent of any delamination. These voltages are recorded on a strip chart for later visual analysis. An event marker voltage, produced by a momentary push button on the handle, is also provided by the Delamtect and recorded on a third channel of the analog recorder.

Asphalt Emulsions for Highway Construction, HR-216, 1985

A 5.8 mile section of Dubuque County (Iowa) Road D-53 was selected for this project, the objective of which were to: 1. identify a cost effective asphalt emulsion bound macadam typical cross section; 2. determine the effectiveness of engineering fabric placed under macadam roadbeds; and 3. evalaute the use of emulsions in surface seal coats. A number of conclusions were reached: 1. The minus #200 sieve material for the macadam stone should be held to a minimum. For the emulsion used on this project, the minus #200 material had less than 4 percent to achieve satisfactory coating of the macadam stone. 2. The placement of the emulsion treated macadam required no additional equipment or time than the plain macadam placement. 3. Emulsion treating the macadam stone for the shoulder base appears unnecessary. 4. The emulsion treated macadam base beneath an asphaltic concrete wearing surface yielded a higher structural rating than the plain macadam beneath a comparable ashaltic concrete surface. 5. The performance of the fabric between the subgrade and the macadam base to prevent soil intrusion into the base could not be determined by the non-destructive testing conducted. 6. When no choke stone is used over the macadam base, allowance for ac mix overrun should be made. 7. Use of an emulsion instead of a cutback asphalt saved money and energy. However, the poor performance of the seal coat negated any real savings.

Iowa Transportation Laws, HR-234, 1985

Research project HR-234 was sponsored by the Iowa Highway Research Board and the Iowa Department of Transportation. In the preparation of this compilation of highway and street laws of Iowa, an attempt has been made to include those sections of the Code to which reference is frequently required by the Department of Transportation, counties, cities and towns in their conduct of highway and street administration, construction and maintenance. Because of the broad scope of highway and street work and the many interrelated provisions of Iowa law, and in the interests of keeping this volume in a convenient and usable size, some Code provisions which have some bearing on the principal subject were of necessity omitted. The volume has been compiled in loose leaf form with the expectation that periodic updates will keep the reader informed regarding changes in the law and/or new laws. A general index is provided at the end of the text of this volume. Each major topic is divided into relevant subtopics and are accompanied by appropriate Code sections. This publication is offered with the hope and belief that it will prove to be of value and assistance to those concerned with the problems of establishing, maintaining and administering a highway and street system. The reader is cautioned to consult legal counsel on all matters beyond the scope of this text.

Addendum to Perception and Interpretation of Advance Warning Signs on County Roads, HR-256, 1985

This contract extension was granted to analyze data obtained in the original contract period at a level of detail not called for in the original contract nor permitted by the time constraints of the original contract schedule. These further analyses focused on two primary questions: I. What sources of variation can be isolated within the overall pattern of driver recognition errors reported previously for the 16 signs tested in Project HR-256? 2. Were there systematic relations among data on the placement of signs in a simulated signing exercise and data on the respondents' ability to detect the presence of a sign in a visual field or their ability to recognize quickly and correctly a sign shown them or the speed with which these same persons can respond to a sign for a driver decision?

Engineering Study for the Evaluation of Public Road Administration and Maintenance Alternatives, Executive Summary for HR-265, 1985

Iowa's public road system of 112,000 miles is one of the largest and the best in the nation. It represents a considerable financial investment of taxpayer revenues over the years. And, it requires a sustained investment to preserve an economical level of transport service into the future. In 1982, a Governor's Blue Ribbon Transportation Task Force evaluated the effectiveness of Iowa's entire transportation system. Four important Task Force recommendations dealt with public road administrative issues in Iowa. These issues were related to: 1. design criteria and levels of maintenance 2. consistency in the use of standards among jurisdictions 3. consolidation of maintenance operations at one jurisdictional level and 4. jurisdictional authority for roads. The issues formed the background for Research Project HR-265.

Asphalt Cement Containing AC-13, HR-522, Construction Report, 1985

Stopping and turning maneuvers on high traffic volume asphalt cement concrete surfaced roads and streets often causes distortion of the pavement. Distortion may show up as excessive rutting in the wheel path, shoving of the pavement and/or rippling of the surface. Often times repeated corrective work such as cold milling or heater planing is required in these areas to maintain the pavement surface in a reasonable condition. In recent years polymer additives have been developed for asphalt cement concrete paving mixes that show promise in improving the inplace stability of the pavements. AC-13 (Styrelf 13) available from Bitucote Products Company, St. Louis, Missouri is an asphalt cement that has been modified by an additive to exhibit characteristics of very high stability in asphalt mixes.

Evaluation of Control Structures for Stabilizing Degrading Stream Channels in Western Iowa, Phases II and III, HR-208A, 1985

Since the turn of the century, tributaries to the Missouri River in western Iowa have entrenched their channels to as much as six times their original depth. This channel degradation is accompanied by widening as the channel side slopes become unstable and landslides occur. The deepening and widening of these streams have endangered about 25% of the highway bridges in 13 counties [Lohnes et al. 1980]. Grade stabilization structures have been recommended as the most effective remedial measure for stream degradation [Brice et al., 1978]. In western Iowa, within the last seven years, reinforced concrete grade stabilization structures have cost between $300,000 and $1,200,000. Recognizing that the high cost of these structures may be prohibitive in many situations, the Iowa Department of Transportation (Iowa DOT) sponsored a study at Iowa State University (ISU) to find low-cost alternative structures. This was Phase I of the stream degradation study. Analytical and laboratory work led to the conclusion that alternative construction materials such as gabions and soil-cement might result in more economical structures [Lohnes et al. 1980]. The ISU study also recommended that six experimental structures be built and their performance evaluated. Phase II involved the design of the demonstration structures, and Phase III included monitoring and evaluating their performance.

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.

Technology News, March, 1985

Technology News is a newsletter produced by the Iowa Department of Transportation to provide information to the transportation specialist in Iowa's cities and counties. Technology News is one of CTRE's primary avenues for exchanging transportation-related information with local agencies. The bimonthly newsletter gives an up-to-date look to the up-to-date information our 2,500+ readers have grown to expect.

Technology News, May, 1985

Technology News is a newsletter produced by the Iowa Department of Transportation to provide information to the transportation specialist in Iowa's cities and counties. Technology News is one of CTRE's primary avenues for exchanging transportation-related information with local agencies. The bimonthly newsletter gives an up-to-date look to the up-to-date information our 2,500+ readers have grown to expect.