Ralumac Latex Modified Asphalt, HR-2041, 1994

Some asphalt roadways tend to develop wheelpath ruts over time when exposed to heavy traffic. As the rutting increases in depth, the travel comfort and levels of safety decrease. A variety of remedies involving major or minor operations can be applied to eliminate ruts and renew the roadway surface. One of the simple remedies, called Ralumac microsurfacing, involves only a longitudinal band over the rut. For better coverage, ruts are filled initially and followed by a complete thin surface wearing cover over the roadway.

Asphalt Rubber Cement Concrete Webster County, HR-555, Construction Report, 1993

Discarded tires have become a major disposal problem in the U.S. Different techniques of recycling these discarded tires have been tried. The state of Iowa is currently evaluating the use of discarded tires ground into crumb rubber and blending it with asphalt to make asphalt rubber cement (ARC}. This was the sixth project this process has been used in. This project is located on US 169 from the east junction of IA 175 west and north to US 20. Only the binder course was placed this year with the surface course to be let at a later date. There are four test sections, two sections with conventional mixtures and two with ARC mixtures.

Asphalt Resurfacing Structural Research, HR-556, Construction Report, 1995

Discarded tires present major disposal and environmental problems. One method of recycling tires is to use finely ground rubber from tires in asphalt cement concrete (ACC). This process has been researched in Iowa since 1991. There are currently eight projects being researched. This project involved using crumb rubber modifier (CRM) in ACC using a dry process. This project is located on US 63 in Howard County. It involved 17 test sections. There were five test sections using 20 lb of CRM per ton, four test sections using 10 lb of CRM per ton and eight test sections using a conventional mix. Not only were different mixes used, but the overlay was also placed in various thicknesses ranging from 2 in. to 8 in. (5 cm to 20 cm). The project was completed in August 1994. The project construction went well with only minor problems. This report contains information about procedures and tests that were completed and those that will be completed. Evaluation on the project will continue for five years.

Evaluation of Recycled Rubber in Asphalt Concrete, HR-330, 1996

The purpose of this research was to evaluate the performance and the use of asphalt rubber binders and recycled rubber granules in asphalt pavement in the state of Iowa. This five year research project was initiated in June 1991 and it was incorporated into Muscatine County Construction Project US 61 from Muscatine to Blue Grass over an existing 10 in. (25.4 cm) by 24 ft (7.3 m) jointed rigid concrete pavement constructed in 1957. The research site consisted of four experimental sections (one section containing rubber chip, one section containing reacted asphalt rubber in both binder and surface, and two sections containing reacted asphalt rubber in surface) and four control sections. This report contains findings of the University of Northern Iowa research team covering selected responsibilities of the research project "Determination of the aging and changing of the conventional asphalt binder and asphalt-rubber binder". Based on the laboratory test, the inclusion of recycled crumb rubber into asphalt affects the ductility of modified binder at various temperatures.

The Effects of Crushed Particles in Asphalt Mixtures, HR-311 and MLR-88-16, 1990

One of the most serious impediments to the continued successful use of hot-mix asphalt (HMA) pavements is rutting. The Iowa Department of Transportation has required 85% crushed particles and 75-blow Marshall mix design in an effort to prevent rutting on Interstate roadways. Relationships between the percent of crushed particles and resistance to rutting in pavement through the use of various laboratory test procedures must be developed. HMA mixtures were made with 0, 30, 60, 85, and 100% crushed gravel, crushed limestone, and crushed quartzite combined with uncrushed sand and gravel. These aggregate combinations were used with 4, 5, and 6% asphalt cement (ac). Laboratory tests included Marshall stability, resilient modulus, indirect tensile, and creep. A creep resistance factor (CRF) was developed to provide a single numeric value for creep test results. The CRF values relate well to the amount of crushed particles and the perceived resistance to rutting. The indirect tensile test is highly dependent on the ac with a small effect from the percent of crushed particles. The Marshall stability from 75-blow compaction relates well to the percent of crushed particles. The resilient modulus in some cases is highly affected by grade of ac.

Evaluation of Air Pollution Control Devices for Asphalt Pavement Recycling Operations, HR-188, Progress Report, 1977

This report discusses the asphalt pavement recycling project designated Project HR-188 in Kossuth County, Iowa. Specific objectives were: (a) to determine the effectiveness of drum mixing plant modifications designed to control air pollution within limits specified by the Iowa Department of Environmental Quality; (b) to assess the impact of varying the proportions of recycled and virgin aggregates, (c) to assess the impact of varying the production rate of the plant, and (d) to assess the impact of varying the mixing temperature. The discussion includes information on the proposed use of research funds, project location and description, the project planning conference, plan development, bid letting, asphalt plant configuration, actual plant operation, why this method is successful, probable process limitations, pollution results, recycled pavement test results, and the cost of virgin vs. recycled asphalt pavements.

Dust Control Using an Asphalt Emulsion, HR-196, 1977

In an effort to control fugitive dust on a gravel surfaced roadway in Boone County, a cationic asphalt emulsion was blended with warm water and applied with an asphalt distributor. The test included various application procedures. After visual observations, it was concluded that this procedure utilizing a dilute asphalt emulsion was not an effective method of dust control.

Sprinkle Treatment of Asphalt Surfaces, HR-199, 1984

Methods of improving highway safety are of major concern to everyone who is involved in the planning, development and construction of improvements of our vast highway network. Other major concerns are the conservation of our rapidly disappearing sources of energy and quality building materials. This research is devoted to further exploration of a process which will: 1. help preserve higher quality aggregates; and, 2. improve the frictional characteristics and surface texture of asphalt pavement surfaces. Sprinkle treatment of asphalt concrete pavement surfaces with a non-polishing aggregate, a procedure which was developed in Europe, is one method which has shown promise in accomplishing the above listed objectives. This research seeks to explore the feasibility and cost effectiveness of using standard asphalt mixtures of local, less expensive aggregates for surface courses followed by a surface sprinkle treatment of a hard, durable, non-polishing layer of precoated chips to produce a durable, non-skid pavement surface for safe highway travel. Three standard mixture types are being evaluated for aggregate retention characteristics and six sprinkle aggregates are being evaluated for durability, polishing and friction characteristics. In addition, measurements of the surface texture by the silicone putty method are being made. Another feature of this research is the evaluation of a rubberized asphalt material called Overflex MS as a crack filler. It has been reported that the material could be beneficial in reducing reflective cracking. The project was begun in July of 1978 and was completed in August. A review made in the spring of 1979 indicates very satisfactory performance. It was determined from slide photos taken after construction and again in the spring that aggregate retention was very good. However, many cracks had reflected indicating that the Overflex MS had not been effective. Follow up friction test results and texture analysis were also very good. The results of these tests are shown in Appendix A.

Improved Asphalt Surfaces and Asphalt Resurfacing Performance through Crack Maintenance, HR-213, 1987

In 1980, a Vanguard High Pressure Water Blaster capable of providing 10 gallons of water per minute at 2000 psi was purchased to evaluate water blasting as a crack cleaning method prior to crack filling on asphalt concrete pavements. Afer some iniital trials demonstrated its effectiveness of removing dirt, debris and vegetation, it was included in joint and crack maintenance research on Iowa 7 in Webster County. The objective of the research was to evaluate six crack preparation methods and seven "sealant" materials. The cleaning and sealing was performed in the spring of 1983. Visual evaluations of the performance were made in the fall of 1983 and spring of 1985. Compressed air and/or high pressure water did not adequately prepare cracks less than 3/8 inch wide. Routing or sawing was necessary to provide a sealant reservoir. The water blaster was more effective than compressed air in removing dirt, debris and vegetation but this did not yield significant improvement in sealant adhesion or longevity. Periodic crack filling is necessary on ACC surfaces throughout the remaining life of the pavement.

Asphalt Emulsion Bound Macadam in Dubuque County, Iowa, HR-216, Construction Report, 1981

This construction report describes a project investigating macadam base construction of roads. The objectives of this project were to: 1. identify a cost effective asphalt emulsion bound macadam typical cross section; 2. obtain useful data comparing seven typical cross sections; 3. determine the effectiveness of engineering fabric placed under macadam roadbeds; and 4. evaluate the use of emulsions in surface seal coats.

Evaluation of Recycled Rubber in Asphalt Concrete - Plymouth County, HR-330A, 1992

The Iowa Department of Transportation is evaluating the use of ground recycled crumb rubber from discarded tires in asphalt rubber cement. There were four projects completed during 1991 and another one constructed in 1992. This project is located on IA 140 north of Kingsley in Plymouth County. The project contains one section with reacted asphalt rubber cement (ARC) used in both binder and surface courses, one with reacted ARC used in the surface course and a conventional binder course, and a conventional mix control section. The reacted rubber binder course was placed on October 17, 1991 and the reacted rubber surface course was placed on October 17, 18, and 19. Inclement weather caused a slight delay in placing or constructing the surface. There was a minor problem with shoving and cracking of the binder course. The construction went well otherwise. Information included in this report consists of test results, construction reports, and cost comparisons.

Evaluation of Recycled Rubber in Asphalt Concrete - Dubuque County, HR-330C, 1992

The Iowa Department of Transportation is evaluating the use of discarded tires in asphalt rubber cement. There have been five projects completed in Iowa. This project is located on US 151 north of Cascade to US 61 in Dubuque. One section consists of an asphalt rubber cement surface and a conventional binder and two sections contain both asphalt rubber cement surface and binder. The control section of conventional asphalt was completed this spring. Information included in this report consists of test results, construction reports, and cost comparisons.

Evaluation of Recycled Rubber in Asphalt Concrete - Black Hawk County, HR-330D, 1992

The disposal of discarded tires has become a major problem. Different methods of recycling have been researched. Currently, Iowa is researching the use of ground recycled crumb rubber from discarded tires in asphalt rubber cement. Six projects have been completed in Iowa using asphalt rubber cement. This project is located on IA 947 (University Avenue) in Cedar Falls/Waterloo. The project contains one section with asphalt rubber cement used in both the binder and surface courses and one section using asphalt rubber cement in the surface course with a conventional binder. There are two control sections where conventional asphalt pavement was placed.

Field Evaluation of Engineering Fabrics for Asphalt Concrete Resurfacing - Audubon County, HR-360, Construction Report, 1994

An asphalt concrete (ACC) overlay is most often the rehabilitative effort used to maintain the serviceability of either an ACC or PCC pavement. The major problem in durability of this ACC overlay comes from reflective cracking. These cracks usually open, allowing water to enter the unsealed crack and strip the ACC in the overlay. The stripping of the ACC allows accelerated deterioration at the crack. Two engineering fabrics were evaluated in this project in order to determine their effectiveness in reducing reflective cracking. These two materials are: PavePrep, Contech Construction Products, Inc., and Pro-Guard, Phillips Fiber Corporation. A 4.2 km (2.6 mi) roadway in Audubon County was selected for the research project. The roadway was divided into eight test sections. Four of the test sections are conventional resurfacing. The other four sections are split between the two engineering fabrics (two Pro-Guard and two PavePrep). A 75 mm (3 in.) thick overlay was placed over the entire project.

Polymerized Asphalt Cement, HR-533, 1989

In 1986, a 0.34 mile experimental section of polymerized asphalt cement (PAC30) concrete was placed in the westbound driving lane of Interstate 80 in western Iowa. It was used in a 2" asphalt concrete inlay using 20% recycled asphalt pavement. The virgin aggregate included 41% crushed gravel, 25% crushed quartzite and 14% natural sand. The evaluation of the project was severely limited when a 1987 reconstruction project extended into the experimental section leaving only 395 feet. Rut depths under a 4-foot gage were taken for a period of two years. No significant rutting occurred in the experimental polymerized section. The frequency of transverse cracking in the polymerized AC section was the same as that of the comparative AC-20 section. The asphalt paving mixture made with polymerized AC cost 120% of the cost of the conventional mix.