Relating Creep Testing to Rutting of Asphalt Concrete Mixes, HR-311, Part 2, 1991

The Iowa Department of Transportation began creep and resilient modulus testing of asphalt concrete mixtures in 1989. Part 1 of this research reported in January 1990 was a laboratory study of hot mix asphalt (HMA) mixtures made with O, 30, 60, 85 and 100% crushed gravel, crushed limestone and crushed quartzite combined with uncrushed sand and gravel. Creep test results from Marshall specimens related well to the percent of crushed particles and the perceived resistance to rutting. The objective of this research, part 2, was to determine if there was a meaningful correlation between pavement rut depth and the resilient modulus or the creep resistance factor. Four and six inch diameter cores were drilled from rutted primary and interstate pavements and interstate pavements with design changes intended to resist rutting. The top 2 1/2 inches of each core, most of which was surface course, was used for creep and resilient modulus testing. There is a good correlation between the resilient modulus of four and six inch diameter cores. Creep resistance factors of four and six inch diameter cores also correlated well. There is a poor correlation between resilient modulus and the creep resistance factor. The rut depth per million 18,000 pound equivalent single axle loadings (ESAL) for these pavements did not correlate well with either the resilient modulus or the creep resistance factor.

Self Instructional Math, HR-324, 1995

The Self Instructional Math course book is designed to provide a basic math knowledge for those involved in the planning, design, and construction of highways. It was developed in a manner to allow the student to take the course with minimal supervision and at times that the work schedule allows. The first version of the course was developed in the early 1970's and due to its popularity was revised in the early 1990's to reflect changes in the highway construction math needs. The anticipated move to metric (System International) measurements by the highway industry has necessitated the need to change the math course problem values to metric units. The course includes the latest in Iowa DOT policy information relative to the selection and use of metric values for highway design, and construction. Each unit of the book contains instructional information, section quizzes and a comprehensive examination. All problem values are expressed in metric rather than dual (english and SI) units. The appendix contains useful conversion factors to assist the reader in making the change to metric.

Design Methodology for Corrugated Metal Pipe Tiedowns, HR-362, Phase II, 1995

This investigation is the final phase of a three part study whose overall objectives were to determine if a restraining force is required to prevent inlet uplift failures in corrugated metal pipe (CMP) installations, and to develop a procedure for calculating the required force when restraint is required. In the initial phase of the study (HR-306), the extent of the uplift problem in Iowa was determined and the forces acting on a CMP were quantified. In the second phase of the study (HR- 332), laboratory and field tests were conducted. Laboratory tests measured the longitudinal stiffness ofCMP and a full scale field test on a 3.05 m (10 ft) diameter CMP with 0.612 m (2 ft) of cover determined the soil-structure interaction in response to uplift forces. Reported herein are the tasks that were completed in the final phase of the study. In this phase, a buried 2.44 m (8 ft) CMP was tested with and without end-restraint and with various configurations of soil at the inlet end of the pipe. A total of four different soil configurations were tested; in all tests the soil cover was constant at 0.61 m (2 ft). Data from these tests were used to verify the finite element analysis model (FEA) that was developed in this phase of the research. Both experiments and analyses indicate that the primary soil contribution to uplift resistance occurs in the foreslope and that depth of soil cover does not affect the required tiedown force. Using the FEA, design charts were developed with which engineers can determine for a given situation if restraint force is required to prevent an uplift failure. If an engineer determines restraint is needed, the design charts provide the magnitude of the required force. The design charts are applicable to six gages of CMP for four flow conditions and two types of soil.

Epoxy and Thermoplastic Pavement Markings on US 30 in Carroll County, HR-545, 1995

A one mile section each of thermoplastic and epoxy pavement marking materials were placed on new ACC pavement near Carroll, IA on Highway 30. The markings were evaluated for four years to see if they were suitable materials for durable pavement markings. The epoxy markings were inadvertently repainted after two years. They were performing well up to that time with little plow damage and good retroreflectivity. The thermoplastic dash lines suffered heavy snow plow damage after the first year and were repainted after the third winter. The thermoplastic edge lines performed fairly well for four years.

Elgard Cathodic Protection System, HR-553, 1995

Following is the Operations Manual for the Pennsylvania Ave Bridge over I-235 located in Des Moines, Iowa, which was installed from July 1992 to October 1992. The project uses ELGARD™ 210 Anode Mesh and is divided into 3 zones. Periodic data collection and/or inspection of the cathodic protection system is required to insure proper operation and a long life. This Operation Manual contains a schedule, operation procedures, operation log forms, a rectifier panel drawing, and pertinent reference matenal. Operation procedures and operating records are contained in the body of the manual, while blank operation forms, as built drawings, and pertinent reference material are contained in the appendices.

Evaluation of Visibeads in Epoxy markings on I-235, HR-554, 1995

In recent years, the nighttime wet pavement retroreflectivity of pavement markings has become an important issue. In a effort to continue research in this area, the Iowa Department of Transportation evaluated the effectiveness of Visibeads in the Des Moines metropolitan area. Visibeads are three to four times larger in diameter then conventional glass beads. This larger size provides for better retroreflectivity under nighttime wet pavement conditions. The areas chosen for evaluation do not have roadway lighting, therefore, making them a good choice for Visibeads. Although the DOT has tested Visibeads in the past with moderate success, it is believed that using Visibeads with longer life markings such as epoxy will improve their performance.

Evaluation of Snowplowable Raised Pavement Markers, HR-558, 1995

In 1992, the Iowa DOT installed 6200 snowplowable Raised Pavement Markers (RPM) in six areas around the state. They were evaluated at six-month intervals until the replacement of the reflective lenses in 1995. During this time, the RPM performed well. The Iowa Department of Transportation uses de-icers and sand during the winter to control snow and ice on the pavement. The sand and the chemicals reduced the reflectivity of the reflectors. With minimum or no maintenance the visibility of the RPM is low. Although the RPM appear to present a problem during snow plowing, they are an excellent device for lane delineation at night in adverse weather.

Minimum Retroreflectivity of Traffic Signs and Pavement Markings, HR-562, 1995

This final report contains two separate reports which describe the retroreflectivity levels of various traffic signs and pavement markings on the Iowa primary road system. The data was collected in the fall/winter of 1994 and given to the Federal Highway Administration in March of 1995. This information is currently being combined with similar information from other jurisdictions across the country for the purpose of determining the impact of mandated minimum retroreflectivity levels. The FHWA will be releasing their report sometime in 1996. In October 1992, Congress mandated (Public Law 102-388) the Secretary of Transportation to revise the Manual of Uniform Traffic Control Devices to include a minimum level of retroreflectivity for pavement markings and traffic signs which shall apply to all roads open to public travel. In 1994, the FHWA initiated research studies to determine the retroreflectivity levels which currently exist for signs and markings in an attempt to develop standards which are reasonable to implement. The Iowa Department of Transportation participated in both of the studies and the final reports are included. After compilation and analysis of the collected retroreflectivity data, the FHWA will propose the new MUTCD standards through the federal rule making process. It is estimated that the actual MUTCD change will occur sometime in late 1997 or early 1998.

Chemistry in Catalonia 1990-1995

The seven-year period studied here differs very little from the sixyear period described in the previous Report (1990-1995). Sustained growth was observed in almost all the indicators used to evaluate the resources invested and the scientific results obtained

Chemistry in Catalonia 1990-1995

The seven-year period studied here differs very little from the sixyear period described in the previous Report (1990-1995). Sustained growth was observed in almost all the indicators used to evaluate the resources invested and the scientific results obtained

Correlation of the Road Rater and the Dynatest Falling Weight Deflectometer, MLR-91-04, 1991

The Falling Weight Deflectometer (FWD) has become the "standard" for deflection testing of pavements. Iowa has used a Road Rater since 1976 to obtain deflection information. A correlation between the Road Rater and the FWD was needed if Iowa was going to continue with the Road Rater. Comparative deflection testing was done using a Road Rater Model 400 and a Pynatest 8000 FWD on 26 pavement sections. The SHRP contractor, Braun Intertec Pavement, Inc., provided the FWD testing. The r^2 for the linear correlations ranged from 0.90 to 0.99 for the different pavement types and sensor locations.

Strength Development of Concrete Based on Maturity and Pulse Velocity, MLR-95-03, 1995

The effect of curing temperature, in the range of 4.4 to 22.8 degrees C (40 to 73 degrees F), on strength development was studied based on the maturity and pulse velocity measurements in this report. The strength-maturity relationships for various mixes using a Type I cement and using a Type IP cement, respectively, were experimentally developed. The similar curves for early age strength development of both the patching concrete, using a Type I cement with the addition of calcium chloride, and the fast track concrete, using a Type III cement and fly ash, have also been proposed. For the temperature ranges studied, the strength development of concrete can be determined using a pulse velocity measurement, but only for early ages up to 24 hours. These obtained relationships can be used to determine when a pavement can be opened to traffic. The amount of fly ash substitution, up to 30%, did not have a significant influence on the strength-maturity relationship.

“All we want in Laos is peace, not war": Intervención de Estados Unidos en Laos, 1954-1961

La guerra de Laos es probablemente uno de los episodios de la Guerra Fría más desconocidos e ignorados por la historiografía a pesar de las terribles consecuencias que tuvo. El hecho de que frecuentemente se considere como un conflicto periférico y ligado a la Guerra de Vietnam no contribuye tampoco a mejorar esta imagen.