Embankment Quality, TR-401, Phase I, 1998

Phase I was initiated as a result of internal Iowa Department of Transportation (Iowa DOT) studies that raised concerns about the quality of embankments being constructed. Some large embankments have recently developed slope stability problems. In addition, pavement roughness has been noted shortly after roads were opened to traffic. This raised the question as to whether the current Iowa DOT embankment construction specifications are adequate. The primary objective of Phase I was to evaluate the quality of embankments being constructed under the current Iowa DOT specifications. The project was initiated in May 1997 with a tour of several embankment projects being constructed around the state. At each of these projects the resident construction engineer, field inspector, and contractor were interviewed with respect to their opinion of the current specifications. From construction observations and discussion during these visits it became obvious that there were problems with the current embankment construction specifications. Six embankment projects were selected for in-depth analysis and to represent the full range of soil types being used across the state. The results of Phase I field and laboratory construction testing and observations and post construction testing are presented in this report. Overall evaluation of the results of Phase I indicate that Iowa is not consistently obtaining a quality embankment constructed under the current Iowa DOT specifications. Based on these results, recommendations are made for Phase II to evaluate alternative specifications and develop rapid field methods for compaction control and soil identification.

A Laboratory Evaluation of Asphaltic Concrete Containing Asphadur, MLR-78-2, 1978

This report describes a laboratory evaluation of three asphaltic concrete, plant produced mixtures containing Asphadur. The mixtures represent a type A asphaltic concrete and two type B asphaltic concretes. The type A and one of the type B mixtures were used in pavements and will be evaluated later for durability and serviceability. The second type B mixture was made only for laboratory testing. In each instance, control batches of the same mixtures but without Asphadur were made for comparison. Type A is a high type asphaltic concrete, requires a minimum of 65 percent crushed particles and is generally used for higher traffic volume roads. Type B is used for intermediate or lower traffic volumes and requires a minimum of 30 percent crushed particles.

Iowa Pore Index Test, MLR-80-2, 1980

The objective of the investigation was the development of a test that would readily identify the potential of an aggregate to cause D-cracking because of its susceptivity to critical saturation. A Press-Ur-Meter was modified by replacing the air chamber with a one-inch diameter plastic tube calibrated in milli-. It was concluded that the pore index was sufficiently reliable to determine the D-cracking potential of limestone aggregates in all but a few cases where marginal results were obtained. Consistently poor or good results were always in agreement with established service records or concrete durability testing. In those instances where marginal results are obtained, the results of concrete durability testing should be considered when making the final determination of the D-cracking susceptibility of the aggregate in question. The following applications for the pore index test have been recommended for consideration: concrete durability testing be discontinued in the evaluation process of new aggregate sources with pore index results between 0-20 (Class 2 durability) and over 35 (Class 1) durability; composite aggregates with intermediate pore index results of 20-35 be tested on each stone type to facilitate the possible removal of low durability stone from the production process; and additional investigation should be made to evaluate the possibility of using the test to monitor and upgrade the acceptance of aggregate from sources associated with D-cracking.

Underseal Evaluation Project: Poweshiek County I-80 Near Milepost 189.5, Eastbound Roadway, MLR-85-10, 1985

The purpose of this project was to determine the optimal hole pattern needed for undersealing work, and also to determine if it is feasible to underseal a roadway with existing longitudinal subdrains without plugging the subdrain system. At the test site the hole pattern had little effect on the grout distribution. It was found that the hole pattern, to be effective, must locate existing voids and that holes must extend at least 2 in. (5 cm) below the underside of the pavement. It appeared that pavements can be undersealed without significant damage to the existing subdrains, but special care is needed to assure that excess grout is not injected into the drainage system. Recommendations are made concerning the hole pattern, grout efflux time, and procedures for minimizing the risk of plugging the subdrains with grout.

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.

Laboratory Evaluation of Asphalt-Rubber in Asphalt Paving Mixture, MLR-89-15, 1990

Interest in the use of ground rubber from used tires as a hot asphalt mix binder has been increasing due to the magnitude of the disposal problem posed by the annual addition of millions of waste tires to the refuse stream. This study evaluates, through laboratory means, the performance of asphalt-rubber as a hot mix binder as compared to conventional asphalt. The results indicate that asphalt-rubber outperforms its base asphalt in mixes of identical gradation and comparable void content on tests that are heavily dependent on binder characteristics (resilient modulus and indirect tension). An appreciable increase in rut resistance due to the use of asphalt-rubber is not indicated.

Load Ratings for Standard Bridges, HR-239 Phase IV, 2008

In this report, sixteen secondary and primary bridge standards for two types of bridges are rated for AASHTO HS20-44 vehicle configuration utilizing Load Factor methodology. The ratings apply only to those bridges which: (1) are built according to the applicable bridge standard plans, (2) have no structural deterioration or damage, and (3) have no added wearing surface in excess of one-half inch integral wearing surface.

Development of a New Process for Determining Design Year Traffic Demands, TR-528, 2007

Researchers should continuously ask how to improve the models we rely on to make financial decisions in terms of the planning, design, construction, and maintenance of roadways. This project presents an alternative tool that will supplement local decision making but maintain a full appreciation of the complexity and sophistication of today’s regional model and local traffic impact study methodologies. This alternative method is tailored to the desires of local agencies, which requested a better, faster, and easier way to evaluate land uses and their impact on future traffic demands at the sub-area or project corridor levels. A particular emphasis was placed on scenario planning for currently undeveloped areas. The scenario planning tool was developed using actual land use and roadway information for the communities of Johnston and West Des Moines, Iowa. Both communities used the output from this process to make regular decisions regarding infrastructure investment, design, and land use planning. The City of Johnston case study included forecasting future traffic for the western portion of the city within a 2,600-acre area, which included 42 intersections. The City of West Des Moines case study included forecasting future traffic for the city’s western growth area covering over 30,000 acres and 331 intersections. Both studies included forecasting a.m. and p.m. peak-hour traffic volumes based upon a variety of different land use scenarios. The tool developed took goegraphic information system (GIS)-based parcel and roadway information, converted the data into a graphical spreadsheet tool, allowed the user to conduct trip generation, distribution, and assignment, and then to automatically convert the data into a Synchro roadway network which allows for capacity analysis and visualization. The operational delay outputs were converted back into a GIS thematic format for contrast and further scenario planning. This project has laid the groundwork for improving both planning and civil transportation decision making at the sub-regional, super-project level.

Feasibility of Cooperative Development of Wetland Mitigation Projects, TR-526, 2006

The Iowa Department of Transportation (Iowa DOT) currently performs wetland mitigation on a project-by-project basis. At the same time, other agencies like the Iowa Department of Natural Resources and Natural Resource Conservation Service are performing wetland restoration projects, and counties and cities may be mitigating wetland losses as well. This project examined the feasibility of developing cooperative wetland mitigation projects in order to utilize state and local resources more efficiently to benefit both Iowa and local communities. The project accomplished the following objectives: (1) Identified and characterized cooperative wetland mitigation programs nationwide; (2) Developed a needs assessment through a survey of state, county, and large city agencies in Iowa to describe wetland mitigation programs and determine challenges with mitigation and program improvements, including long-term risks associated with maintenance and monitoring programs; (3) Surveyed state, county, and city agencies and organizations to identify resources available for developing cooperative mitigation projects and procedures; (4) Developed a conceptual framework for cooperative wetland mitigation.

Evaluation of Asphalt Mix Permeability, MLR-90-2, 1992

Efforts to eliminate rutting on the Interstate system have resulted in 3/4 in. aggregate mixes, with 75 blow Marshall, 85% crushed aggregate mix designs. On a few of these projects paved in 1988-1989, water has appeared on the surfaces. Some conclusions have been reached by visual on-sight investigations that the water is coming from surface water, rain and melting snow gaining entry into the surface asphalt mixture, then coming back out in selected areas. Cores were taken from several Interstate projects and tested for permeability to investigate the surface water theory that supposedly happens with only the 3/4 in. mixtures. All cores were of asphalt overlays over portland cement concrete, except for the Clarke County project which is full depth AC. The testing consisted of densities, permeabilities, voids by high pressure airmeter (HPAM), extraction, gradations, AC content, and film thicknesses. Resilient modulus, indirect tensile and retained strengths after freeze/thaw were also done. All of the test results are about as expected. Permeabilities, the main reason for testing, ranged from 0.00 to 2.67 ft per day and averages less than 1/2 ft per day if the following two tests are disregarded. One test on each binder course came out to 15.24 ft/day, and a surface course at 13.78 ft/day but these are not out of supposedly problem projects.

Characteristics of Iowa Fine Aggregate, MLR-92-6, 1996

The objective of this research was to evaluate the quality (angularity, mortar strengths and alkali-silica reactivity) of fine aggregate for Iowa portland cement concrete (PCC) pavements. Sands were obtained from 30 sources representative of fine aggregate across Iowa. The gradation, fineness modulus and mortar strengths were determined for all sands. Angularity was evaluated using a new National Aggregate Association (NAA) flow test. The NAA uncompacted void values are significantly affected by the percent of crushed particles and are a good measure of fine aggregate angularity. The alkali-silica reactivity of Iowa sands was measured by the ASTM P214 test. By P214 many Iowa sands were identified as being reactive while only two were innocuous. More research is needed on P214 because pavement performance history has shown very little alkali-silica reactivity deterioration of pavement. Six of the sands tested by P214 were evaluated using the Canadian Prism Test. None were identified as being reactive by the Canadian Prism Test.

Correlation of the IJK Roadmeter to the International Roughness Index, MLR-91-5, 1992

The Iowa Department of Transportation has been determining a present serviceability index (PSI) on the primary highway system since 1968. A CHLOE profilometer has been used as the standard for calibrating the Roadmeters that do the system survey. The current Roadmeter, an IJK Iowa DOT developed unit, is not considered an acceptable Roadmeter for determining the FHWA required International Roughness Index (IRI). Iowa purchased a commercial version of the South Dakota type profile (SD Unit) to obtain IRI. This study was undertaken to correlate the IRI to the IJK Roadmeter and retire the Roadmeter. One hundred forty-seven pavement management sections (IPMS) were tested in June and July 1991 with both units. Correlation coefficients and standard error of estimates were: r' Std. Error PCC pavements 0.81 0.15 Composite pavements 0.71 0.18 ACC pavements 0.77 0.17 The correlation equations developed from this work will allow use of the IRI to predict the IJK Roadmeter response with sufficient accuracy. Trend analysis should also not be affected.

PC Concrete Texturing, R-246, 1975

Skid resistance is a major concern of the safety engineer since wet pavement conditions are present for approximately 18% of the total accidents in Iowa according to studies by the Traffic and Safety Department. Many of these accidents may be influenced by the low skid resistant quality of the pavement. The size, shape, type, and arrangement of the concrete's particles interrelate with each other in a complex manner to give us frictional resistance. The purpose of this investigation was to determine which method of texturing provides the best skid resistance properties on portland cement concrete pavement.

Iowa Department of Transportation Major Items - Preliminary Quantity Report, March 18, 2014; With Addendums

Weekly letting report.

Using Scanning Lasers for Real-Time Pavement Thickness Measurement, TR-538, 2006

Due to limited budgets and reduced inspection staff, state departments of transportation (DOTs) are in need of innovative approaches for providing more efficient quality assurance on concrete paving projects. The goal of this research was to investigate and test new methods that can determine pavement thickness in real time. Three methods were evaluated: laser scanning, ultrasonic sensors, and eddy current sensors. Laser scanning, which scans the surface of the base prior to paving and then scans the surface after paving, can determine the thickness at any point. Also, scanning lasers provide thorough data coverage that can be used to calculate thickness variance accurately and identify any areas where the thickness is below tolerance. Ultrasonic and eddy current sensors also have the potential to measure thickness nondestructively at discrete points and may result in an easier method of obtaining thickness. There appear to be two viable approaches for measuring concrete pavement thickness during the paving operation: laser scanning and eddy current sensors. Laser scanning has proved to be a reliable technique in terms of its ability to provide virtual core thickness with low variability. Research is still required to develop a prototype system that integrates point cloud data from two scanners. Eddy current sensors have also proved to be a suitable alternative, and are probably closer to field implementation than the laser scanning approach. As a next step for this research project, it is suggested that a pavement thickness measuring device using eddy current sensors be created, which would involve both a handheld and paver-mounted version of the device.