Behavior of Asphalts in the Production of Asphaltic Concrete, HR-107, 1965

Project 540-S of the Iowa Engineering Experiment Station (Project HR-107, Iowa Highway Research Board) was started in June, 1964. During the year ten 2-gallon samples of asphalt cement and ten 100-lb samples of asphaltic concrete were studied by the personnel of the Bituminous Research Laboratory, Iowa State University. The samples were from tanks and mixers of asphalt plants at various Iowa State Highway Commission paving jobs. The laboratory's research was in two phases: 1. To ascertain if properties of asphalt cement changed during mixing operations. 2. To determine whether one or more of the several tests of asphalt cements were enough to indicate behavior of the heated asphalt cements. If the reliability of one or more tests could be proved, the behavior of asphalts would be more simply and rapidly predicted.

Macadam Base Shoulders, HR-181, 1977

Highway safety and pavement performance can be directly influenced by the type of shoulders that are constructed. Shoulder design alternatives have always been rather limited. Moreover, the use of some of the alternatives has always been restricted by funding limitations. This research project seeks to explore the use of modified macadam base construction for shoulders. This type of shoulder design could offer the designer another option when paved or stabilized shoulders are being considered. Macadam base construction has in the past been shown to be quite strong and freedraining. Two macadam base shoulder designs were developed and constructed for this research project. A new roadway embankment and P.C.C. pavement were constructed on a section of US 6 east of Adel in Dallas County. The macadam base shoulders were constructed adjacent to the pavement as part of the project. The north shoulder was finished with a choke stone course and bituminous surface treatment and the south shoulder was finished with a two (2) inch layer of Type B Class II asphalt concrete. The initial results are considered satisfactory. Follow-up performance evaluation and load bearing tests are planned.

Glasgrid Fabric to Control Reflective Cracking, HR-535, 1990

The major problem with durability of asphalt cement concrete (ACC) overlays to rehabilitate jointed portland cement concrete (PCC) pavement comes from reflective cracking. The objective of this research was to evaluate the effectiveness of Glasgrid in regard to preventing reflection cracking. Glasgrid is a glass fiber mesh with 1/2 inch by 1 inch openings (Figure 1). Each strand is composed of many small glass fibers. After the grid is formed, it is coated with a polymer modified asphalt cement. In 1986, four experimental Glasgrid test sections were incorporated into Polk County project IR-35-2(191)67--12-77 on Interstate 35 from IA 5 to the west 1-80 interchange on the west edge of Des Moines, Single and double layers of Glasgrid were placed over transverse cracks and joints of the existing PCC pavement. The Glasgrid was placed on the PCC pavement for one section and between lifts of the ACC resurfacing on the other three sections. The four Glasgrid sections were compared to two sections without Glasgrid for four years. The sections were reviewed annually to determine how many cracks or joints had reflected through the resurfacing. Glasgrid placed on the PCC pavement was more effective at preventing reflection cracking than Glasgrid between lifts of AC resurfacing. In general, Glasgrid yielded a small reduction or retardation in the amount of reflection cracking, but not sufficient to justify additional expense for the use of Glasgrid.

Iowa Ultra Thin Whitetopping at Two Years of Age, HR-559, 1996

An 11.6 km research project was constructed in 1994 on a portion of Iowa Highway 21 in Iowa County, from U.S. 6 to Iowa Highway 212. This research is intended to evaluate the effect of four primary variables on long term performances of the PCC concrete overlay, commonly called whitetopping. The variables are thickness (50 mm, 100 mm, 150 mm, and 200 mm), joint spacing (0.6 m squares, 1.2 m squares, 1.8 m squares, and 4.6 m spacing), fiber use (concrete with and without polypropolene fibers) and surface preparation (patch only, scarifying the surface, and cold-in-place recycling). After two years, only two sections exhibit a small amount of debonding and distress cracking. Both sections are 50 mm thick. Within each of these two sections, only 2% of the area is affected. Two other 50 mm thick sections have a small number of cracks but no debonding has been found. No adverse effects of these cracks are evident. Three asphalt overlay sections were also constructed. In each asphalt section, transverse cracks have recently been found. At two years of age, the research sections are performing very well. An insignificant number of cracks and no distressed areas have been found in any research sections thicker than 50 mm.

Crack Sealing Utilizing a Heat Lance, HR-2058, 1997

Four Iowa DOT asphalt concrete pavement crack sealing projects were selected to evaluate the benefits of heat lance crack preparation. Two, one-half mile sections, both with and without heat lance preparation, were constructed in Story, Monroe, Clinton and Wayne Counties in 1991 and 1992. They were visually evaluated annually from 1992 through 1996. The heat lance preparation did not yield improved seal performance or extended longevity. There was no perceivable difference between crack sealing with and without heat lance preparation.

Portland Cement Concrete Utilizing Recycled Pavement, MLR-77-3, 1977

Two objectives were involved in this recycling project: To determine if the asphalt concrete surfacing from an existing roadway could be removed, the existing portland cement concrete pavement broken, removed, crushed to 1-1/2 inch minus, proportioned through a conventional central mix proportioning plant with the addition of concrete sand, and placed with a conventional slipform paver; and to determine if a two course, composite pavement, each course of different mix proportions, could be placed monolithically with conventional slipform equipment after being proportioned and mixed in a conventional central mix plant. The project was completed with no major problem. The objectives were satisfactorily met. The project was a success to the degree that the Iowa D.O.T. is proceeding with at least two projects for the 1977 construction season that will utilize the old pavement as appregate for the new pavement.

Gradation Analysis of Cold Feed and Extracted Bituminuous Mix Samples, MLR-88-2, 1988

Since 1987, the Iowa Department of Transportation has based control of hot asphalt concrete mixes on cold feed gradations. This report presents results of comparisons between cold feed gradations and gradations of aggregate from the same material after it has been processed through the plant and laydown machine. Results are categorized based on mix type, plant type, and method of dust control, in an effort to quantify and identify the factors contributing to those changes. Results of the report are: 1. From the 390 sample comparisons made, aggregate degradation due to asphalt plant processing was demonstrated by an average increase of +0.7% passing the #200 sieve and an average increase in surface area of +1.8 sq. ft. per pound of aggregate. 2. Categories with Type A Mix or Recycling as a sorting criteria generally produced greater degradation than categories containing Type B Mixes and/or plants with scrubbers. 3. None of the averages calculated for the categories should be considered unacceptably high, however, it is information that should be considered when making mix changes in the field, selecting asphalt contents for borderline mix designs, or when evaluating potential mix gradation specification or design criteria changes.

A Study on the Use of Fabric to Retard Reflective Cracking Over Widened Joints, MLR-88-4, 1992

Reflective cracking of asphalt resurfacing has been a concern for a long time. Years ago wire mesh was used to control widening cracks. More recently it has been fabrics or fiberglass. In 1986, part of the proposed fabric was deleted from projects in different parts of Iowa with various histories and designs. These projects were monitored in 1988, 1989, 1990 and 1992 with only the thin (3 inch) overlays on newly widened pavements showing a significantly greater percentage of cracks in the areas where the fabric was deleted.

ProScan Automated Profilogram Reduction System, MLR-94-7, 1994

Kansas State University, with funding from the Kansas Department of Transportation (KDOT), has developed a computerized reduction system for profilograms produced by mechanical profilographs. The commercial version of the system (ProScan (trademark)) is marketed by Devore Systems, Inc. The system consists of an IBM Compatible PC 486SX33 computer or better, Epson LQ-570 printer, a Logitech Scanman 32 hand scanner system, a paper transport unit, and the ProScan software. The Scanner is not adaptable to IBM computers with the micro channel architecture. The Iowa DOT Transportation Centers could realize the following advantages by using ProScan: (1) Save about 5 to 8 staff hours of reduction and reporting time per Transportation Center per week for a Materials Technician 3 or 4 (the time savings would come during the busiest part of the season); (2) Reduce errors in reduction, transfer, and typing of profile values; (3) Increase the accuracy of the monitor results; and (4) Allow rapid evaluation of contractor traces when tolerance limits between monitor and certified results are exceeded.

Determination of the Optimum Base Characteristics for Pavements, TR-482, 2004

In recent years, it has become apparent that the design and maintenance of pavement drainage extends the service life of pavements. Most pavement structures now incorporate subsurface layers. Part of the function of these subsurface layers is to drain away excess water, which can be extremely deleterious to the life of the pavement. To assure the effectiveness of such drainage layers after they have been spread and compacted, simple, rapid, in-situ permeability and stability testing and end-result specification are needed. This report includes conclusions and recommendations related to four main study objectives: (1) Determine the optimal range for in-place stability and in-place permeability based on Iowa aggregate sources; (2) Evaluate the feasibility of an air permeameter for determining the permeability of open and well-graded drainage layers in situ; (3) Develop reliable end-result quality control/quality assurance specifications for stability and permeability; and (4) Refine aggregate placement and construction methods to optimize uniformity.

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field Distress Survey, TR-502, 2007

Cold in-place recycling (CIR) has become an attractive method for rehabilitating asphalt roads that have good subgrade support and are suffering distress related to non-structural aging and cracking of the pavement layer. Although CIR is widely used, its use could be expanded if its performance were more predictable. Transportation officials have observed roads that were recycled under similar circumstances perform very differently for no clear reason. Moreover, a rational mix design has not yet been developed, design assumptions regarding the structural support of the CIR layer remain empirical and conservative, and there is no clear understanding of the cause-effect relationships between the choices made during the design/construction process and the resulting performance. The objective of this project is to investigate these relationships, especially concerning the age of the recycled pavement, cumulative traffic volume, support conditions, aged engineering properties of the CIR materials, and road performance. Twenty-four CIR asphalt roads constructed in Iowa from 1986 to 2004 were studied: 18 were selected from a sample of roads studied in a previous research project (HR-392), and 6 were selected from newer CIR projects constructed after 1999. This report summarizes the results of a comprehensive program of field distress surveys, field testing, and laboratory testing for these CIR asphalt roads. The results of this research can help identify changes that should be made with regard to design, material selection, and construction in order to lengthen the time between rehabilitation cycles and improve the performance and cost-effectiveness of future recycled roads.

Correlation of Locally-Based Performance of Asphalts with their Physicochemical Parameters, Task 1 Report, HR-298, 1988

This is the first report of 6 tasks to be performed in an effort to establish locally-based quality and performance criteria for asphalts, and ultimately to develop performance-related specifications based on simple physicochemical methods. Three of the most promising chemical methods (high performance liquid chromatography (HPLC), thermal analysis, and X-ray diffraction were selected to analyze 4 different types of samples. The results will indicate the fundamental asphalt property variables that directly affect the field performance in Iowa. The details of the materials and procedures employed are described, and the results of the tests are presented.

Reducing the Adverse Effects of Transverse Cracking, Construction Report, HR-217, 1981

The objective of this research project was to identify a method of reducing the adverse effect of transverse cracking and to improve the performance of asphalt pavement. The research involved three variations from the contractor's planned operation. Briefly, they were: (1) use of another asphalt cement; (2) saw and seal transverse joints; and (3) increased asphalt cement content. The following conclusions were reached: (1) an improved sealant or sealing procedure is needed if transverse joints are to be used in asphalt pavements; (2) the penetration-viscosity number (PVN) is an effective measure of the temperature susceptibility of asphalt cements; (3) the use of a high temperature susceptible asphalt cement produced severe transverse cracking; (4) the use of asphalt cements with low temperature susceptibility will reduce the frequency of transverse cracking; and (5) an increased asphalt cement content in the asphalt treated base will reduce the frequency of transverse cracking.

Ultrathin Portland Cement Concrete Overlay Extended Evaluation, Construction Report, TR-432, 2000

In recent years, ultra-thin whitetopping (UTW) has evolved as a viable rehabilitation technique for deteriorated asphalt cement concrete (ACC) pavement. Numerous UTW projects have been constructed and tested, enabling researchers to identify key elements contributing to their successful performance. These elements include foundation support, interface bonding condition, portland cement concrete (PCC) overlay thickness, synthetic fiber reinforcement usage, joint spacing, and joint sealing. The interface bonding condition is the most important of these elements. It enables the pavement to act as a composite structure, thus reducing tensile stresses and allowing an ultra-thin PCC overlay to perform as intended. The Iowa Department of Transportation (Iowa DOT) UTW project (HR-559) initiated UTW in Iowa. The project is located on Iowa Highway 21 between Iowa Highway 212 and U.S. Highway 6 in Iowa County, near Belle Plaine, Iowa. The objective of this research was to investigate the interface bonding condition between an ultra-thin PCC overlay and an ACC base over time, considering the previously mentioned variables. This research lasted for five years, at which time it was extended an additional five years. The new phase of the project was initiated by removing cracked panels existing in the 2-inch thick PCC sections and replacing them with three inches of PCC. The project extension (TR 432) will provide an increased understanding of slab bonding conditions over a longer period, as well as knowledge regarding the behavior of the newly rehabilitated areas. In order to accomplish the goals of the project extension, Falling Weight Deflectometer (FWD) testing will continue to be conducted. Laboratory testing, field strain gage implementation, and coring will no longer be conducted. This report documents the planning and construction of the rehabilitation of HR 559 and the beginning of TR 432 during August of 1999.

Design and Operation of the Traffic Simulator, HR-100, 1967

Heavy traffic volumes frequently cause distress in asphalt pavements which were designed under accepted design methods and criteria. The distress appears in the form of rutting in the wheel tracks and rippling or shoving in areas where traffic accelerates or decelerates. Apparently accepted stability test methods alone do not always assure the desired service performance of asphaltic pavements under heavy traffic. The Bituminous Research Laboratory, Engineering Research Institute of Iowa State University undertook the development of a laboratory device by which the resistance of an asphalt paving mix to displacement under traffic might be evaluated, and also be used as a supplemental test to determine adequacy of design of the mix by stability procedures.