Sprinkle Treatments for Asphalt Concrete, HR-507, 1986

In recent years, the Iowa Department of Transportation has put greater emphasis on improving highway safety. This effort has been relatively successful with a reduction in traffic-related fatalities to levels experienced prior to 1950. The nationwide speed limit of 55 mph was probably the greatest contributor to the decline in traffic fatalities, but there have been many other efforts that have also contributed to this decline. The Iowa DOT has been testing all paved roadways periodically for friction coefficient since 1969. New techniques have been used to obtain a greater depth of surface texture on paved roadways. Transverse tined grooving has been used on portland cement concrete to provide increased texture depth.

Asphalt Stabilization (Asphadur)/Reduction of Reflection Cracks (Monsanto Bidim Synthetic Fabric), HR-511, 1979

ASPHALT STABILIZATION (ASPHADUR): Asphadur (now called 3M Additive 5990) was incorporated into asphaltic concrete on a lane delineation, AC resurfacing, project in Council Bluffs. The experimental feature was included in the eastbound lanes of Interstate 480, beginning at the bridge over the Missouri River and ending at the bridge over North 41st Street. The project was constructed in October 1979. The objective of the project was to investigate the manufacturer's claims of improved strength, stability and durability of an asphalt mix. REDUCTION OF REFLECTION CRACKS (MONSANTO BIDIM SYNTHETIC FABRIC): A lane delineation project was constructed in the eastbound lanes of Interstate 480 in Council Bluffs. A synthetic fabric, Monsanto Bidim C-28, was placed between the portland cement concrete and two inches of Type A asphaltic concrete resurfacing containing Asphadur. The experimental feature began at the bridge over the Missouri River and ended at the bridge over North 41st Street. The project was constructed in October 1979. The objective of this experimental project was to determine the effectiveness of the fabric in reducing reflective cracking in an asphaltic concrete overlay.

Thin Bonded Overlay Evaluation, HR-559, Final Report, 2001

In 1994 the Iowa Department of Transportation constructed a 7.2-mile Portland Cement Concrete overlay project in Iowa County on Iowa Highway 21. The research work was conducted in cooperation with the Department of Civil Engineering and the Federal Highway Administration under the Iowa Highway Research Board project HR-559. The project was constructed to evaluate the performance of an ultrathin concrete overlay during a 5-year period. The experiment included variables of base surface preparation, overlay depth, joint spacing, fiber reinforcement, and the sealed or non-sealed joints. The project was instrumented to measure overlay/base interface temperatures and strains. Visual distress surveys and deflection testing were also used to monitor performance. Coring and direct shear testing was accomplished 3 times during the research period. Results of the testing and monitoring are identified in the report. The experiment was very successful and the results provide an insight into construction and design needs to be considered in tailoring a portland cement concrete overlay to a performance need. The results also indicate a method to monitor bond with nondestructive methods.

The First 5 Years, April 2000 - March 2005, 2005

This report discusses the accomplishments of the Center for Portland Cement Concrete Pavement Technology (PCC Center) at Iowa State University, which was founded in April 2000. The report discusses the advisory groups that guide the Center, and describes the facilities included in the Center. The two Center facilities are the PCC Pavement and Materials Research Laboratory and the Mobile Concrete Research Lab. The report details the combined test capability of the Center's two labs, and describes the research undertaken at the Center. Also included in the publication are long-term planning efforts and technology transfer studies.

Recycling of Asphalt Concrete From I-80 in Cass County, HR-1011, 1978

Approximately 40,000 tons of deteriorated asphalt concrete has been removed from Interstate 80 in Cass County and stockpiled. Laboratory tests indicate that this material has considerable value when upgraded with new aggregate and asphalt cement. This report documents the procedures used and results obtained on an experimental recycling project. It was demonstrated that present drum mixing-recycling equipment and procedures can be used to utilize this material with satisfactory results. Laboratory analyses of material components and mixtures were performed; these analyses indicate mixture can be produced that is uniform, stable, and very closely resembles mixture produced with all virgin material. A 1700 foot long test section was constructed on US 169 in Kossuth County wherein salvaged asphalt concrete from I-80 in Cass County was utilized. The salvaged mix was blended with virgin aggregate and recycled through a modified drum mixing plant, the reprocessed mixture was satisfactorily placed 1 1/2 inches thick as a resurfacing course on an old PCC pavement. An inspection of the test section was made in December of 1978 to evaluate the performance after one full year of service. There was no evidence of rutting or shoving from traffic. The surface does, however, have a very dry and somewhat ravelled appearance. This can be related to a low asphalt content in the mix and some temperature control problems which were difficult to get fully corrected on such a short project and with a short supply of readily available materials.

The Use of Fly Ash in Highway Construction, HR-1031, 1990

In 1982 the Iowa DOT allowed a successful bidder the option of submitting materials and proportions using fly ash to produce a portland cement concrete (PCC) paving mixture to meet a specified compressive strength. The contractor, Irving F. Jensen, received approval for the use of a concrete mixture utilizing 500 lbs. of portland cement and 88 lbs. of fly ash as a replacement of 88 lbs. of portland cement. The PCC mixture was utilized on the Muscatine County US 61 relocation bypass paved as project F-61-4(32)--20-70. A Class "C" fly ash obtained from the Chillicothe electric generating plant approximately 100 miles away was used in the project. This use of fly ash in lieu of portland cement resulted in a cost savings of $64,500 and an energy savings of approximately 16 billion BTU. The compressive strength of this PCC mixture option was very comparable to concrete mixtures produced without the use of fly ash. The pavement has been performing very well. The substitution of fly ash for 15% of the cement has been allowed as a contractor's option since 1984. Due to the cost savings, it has been used in almost all Iowa PCC paving since that time.

Establishing Load Transfer in Existing Jointed Concrete Pavements, HR-1041, 1985

In this paper are described the results of a research project that had the objective of developing construction procedures for restoring load transfer in existing jointed concrete pavements and of evaluating the effectiveness of the restoration methods. A total of 28 test sections with various load transfer devices were placed. The devices include split pipe, figure eight, vee, double vee, and dowel bars. Patching materials used on the project included three types of fast-setting grouts, three brands of polymer concrete, and plain portland cement concrete. The number and spacing of the devices and dowel bars were also variables in the project. Dowel bars and double vee devices were used on the major portion of the project. Performance evaluations were based on deflection tests conducted with a 20,000-lb axle load. Horizontal joint movement measurements and visual observations were also made. The short-term performance data indicate good results with the dowel bar installations regardless of patching materials. The sections with split pipe, figure eight, and vee devices failed in bond during the first winter cycle. The results with the double vee sections indicate the importance of the patching material to the success or failure of the load transfer system: some sections are performing well and other sections are performing poorly with double vee devices. Horizontal joint movement measurements indicate that neither the dowel bars nor the double vee devices are restricting joint movement.

Design, Fabrication, and Operation of the Pavement Crack Monitor Gauge, HR-1054, 1990

A mechanical gauge was developed to monitor the movement of crack or joint openings in portland cement concrete structures, in general, and portland cement concrete pavements in particular. Designed to be inexpensive and simple to operate, this gauge is capable of recording maximum, minimum, and instantaneous crack or joint openings. Specific recommendations were made for recording minimum and maximum pavement temperature over the monitoring period. The report was written as a set of guidelines for design, fabrication, installation, and operation of the gauge as well as the temperature measuring device.

Development of In Situ Detection Methods for Materials-Related Distress (MRD) in Concrete Pavements: Phase 2, HR-1081, 2005

This project utilized information from ground penetrating radar (GPR) and visual inspection via the pavement profile scanner (PPS) in proof-of-concept trials. GPR tests were carried out on a variety of portland cement concrete pavements and laboratory concrete specimens. Results indicated that the higher frequency GPR antennas were capable of detecting subsurface distress in two of the three pavement sites investigated. However, the GPR systems failed to detect distress in one pavement site that exhibited extensive cracking. Laboratory experiments indicated that moisture conditions in the cracked pavement probably explain the failure. Accurate surveys need to account for moisture in the pavement slab. Importantly, however, once the pavement site exhibits severe surface cracking, there is little need for GPR, which is primarily used to detect distress that is not observed visually. Two visual inspections were also conducted for this study by personnel from Mandli Communications, Inc., and the Iowa Department of Transportation (DOT). The surveys were conducted using an Iowa DOT video log van that Mandli had fitted with additional equipment. The first survey was an extended demonstration of the PPS system. The second survey utilized the PPS with a downward imaging system that provided high-resolution pavement images. Experimental difficulties occurred during both studies; however, enough information was extracted to consider both surveys successful in identifying pavement surface distress. The results obtained from both GPR testing and visual inspections were helpful in identifying sites that exhibited materials-related distress, and both were considered to have passed the proof-of-concept trials. However, neither method can currently diagnose materials-related distress. Both techniques only detected the symptoms of materials-related distress; the actual diagnosis still relied on coring and subsequent petrographic examination. Both technologies are currently in rapid development, and the limitations may be overcome as the technologies advance and mature.

Thin Asphalt Concrete Pavement on Crushed Rock Base, HR-2075, 2001

The road paving cost continues to increase and the backlog of projects waiting for funding is growing. Finding a more cost-effective way to use the available money to pave roads will result in more miles of road being paved with the same amount of money. This project is in Cass County on G35 between US 71 and Norway-Center. It consists of a thin layer of asphalt over a base designed to achieve stability while having some permeability. This project was paved in 1996. An asphalt cement concrete pavement was chosen for the project based on cost, convenience, and historic portland cement concrete problems in Cass County. The new pavement gives quicker access time to farms and residences.

Longitudinal Joint Forming in PCC Pavements, MLR-00-05, Construction Report, 2003

In conventional construction practices, a longitudinal joint is sawed in a PCC (Portland Cement Concrete) pavement to control concrete shrinkage cracking between two lanes of traffic. Sawing a joint in hardened concrete is an expensive and time consuming operation. The longitudinal joint is not a working joint (in comparison to a transverse joint) as it is typically tied with a tie bar at 30 inch spacing. The open joint reservoir, left by the saw blade, typically is filled or sealed with a durable crack sealant to keep incompressibles and water from getting into the joint reservoir. An experimental joint forming knife has been developed. It is installed under the paving machine to form the longitudinal joint in the wet concrete as a part of the paving process. Through this research method, forming a very narrow longitudinal joint during the paving process, two conventional paving operations can be eliminated. Joint forming eliminates the need of the joint sawing operation in the hard concrete, and as the joint that is formed does not leave a wide-open reservoir, but only a hairline crack, it does not need the joint filling or sealing operation. Therefore, the two conventional longitudinal joint sawing and sealing operations are both being eliminated by this innovation. A laboratory scale prototype joint forming knife was built and tested, initially forming joints in small concrete beams. The results were positive so the method was proposed for field testing. Initial field tests were done in the construction season of 2001, limited to one paving contractor. A number of modifications were made to the knife throughout the field tests. About 3000 feet of longitudinal joint was formed in 2001. Additional testing was done in the 2002 construction season, working with the same contractor. About 150,000 feet of longitudinal joint was formed in 2002. Evaluations of the formed joints were done to determine longitudinal joint hairline crack development rate and appearance. Additional tests will be done in the next construction season to improve or perfect the longitudinal joint forming technique.

Evaluation of Lightweight Profilers for Construction Smoothness Evaluation, MLR-02-02, 2004

High-speed non-contact laser profilers have become the standard testing equipment for pavement management ride quality testing. The same technology used in the high-speed profilers is now being used in lightweight profilers for construction smoothness testing. The lightweight profilers have many advantages over the California 25-ft profilograph. Despite the many advantages of the lightweight profilers, there is resistance from the contracting industry toward eliminating the 25-ft profilograph for construction ride testing. One way to reduce or overcome the resistance is to evaluate and demonstrate the advantages/disadvantages of the lightweight profiler in actual field use in Iowa. The objective of the study was to purchase a lightweight profiler and to evaluate its suitability for construction smoothness quality verification and quality acceptance on Iowa projects. A lightweight profiler, an Ames Engineering, Inc. LISA single laser unit, was received in February 2003 for the study. Based on the work done during the 2003 construction season, the following conclusions can be made: (1) For hot mix asphalt surfaces, the LISA correlated well with the contractors' profilographs; (2) LISA results are significantly affected by longitudinal tining on portland cement concrete pavements, requiring a laser system upgrade to give accurate results; (3) A significant timesaving was realized by using the LISA; (4) Increasing visibility and reducing time in the construction zone improved safety; (5) One person with limited lifting capabilities could set up and operate the LISA; and (6) With the current Iowa Department of Transportation specification, the LISA cannot totally replace the profilograph, since bridges and short segments with no adjoining pavement would still require a profilograph.

Air Content and Permeability of PCC Pavements: 1909 to 2006, MLR-05-02, 2007

Portland cement concrete pavements have given excellent service history for Iowa. Many of these pavements placed during the 1920’s and 1930’s are still in service today. Many factors go in to achieve a long term durable concrete pavement. Probably the most important is the durability of the aggregate. Until the 1930’s, pit run gravel was the most predominant aggregate used. Many of these gravels provided long term performance and their durability is dependent upon the carbonate fraction of the gravel. Later, limestone (calcium carbonate) and dolomite (calcium, magnesium carbonate) sources were mined across Iowa. The durability of these carbonate aggregates is largely dependent upon the pore system which can cause freeze thaw problems known as D-cracking, which was a problem with some sources during the 1960’s. Also, some of these carbonate aggregates are also susceptible to deterioration from deicing salts. Geologists have identified the major components that affect the durability of these carbonate aggregates and sources are tested to ensure long term performance in Portland cement concrete. Air entrainment was originally put in concrete to improve scaling resistance. It is well known that air entrainment is required to provide freeze thaw protection in concrete pavements today. In Iowa, air entrainment was not introduced in concrete pavements until 1952. This research investigates properties that made older concrete pavements durable without air entrainment.

Evaluation of Metakaolin for HPC Deck Overlays, MLR-11-01, 2011

The use of High Performance Concrete (HPC) in Iowa has consisted of achieving slightly higher compressive strengths with an emphasis on reduced permeability. Concrete with reduced permeability has increased durability by slowing moisture and chloride ingress. Achieving reduced permeability has typically been accomplished with combinations of slag and Class C fly ash, or the use of blended cements such as locally available Type IS(20), IS(25) and Type IP(25) in conjunction with Class C fly ash. Fly ash has been used in the majority of concrete placed in Iowa since 1984 and slag has been available in Iowa since 1995. During the economic downturn in 2008, one of the cement plants that produced a Type IS(25) cement was forced to shut down, which reduced the availability of blended cements, typically used on HPC deck overlays. Recently, a source of high reactivity metakaolin has been made available. Metakaolin is produced by heating a pure kaolinite clay to 650 to 700 °C in a rotary kiln (calcining). Metakaolin is a white pozzolan that is used to produce concrete with increased strengths, reduced permeability, reduced efflorescence, and resistance to alkali silica reactivity. The W.R. Grace MK-100 metakaolin will likely be available in dissolvable bags between 25 and 50 pounds. Thus, the mix designs were based on the anticipated bag size range for field use. This research evaluated metakaolin mixes with and without Class C fly ash. Results indicated a seven percent replacement with metakaolin produced concrete with increased strengths and low permeability. When used with Class C fly ash, permeability is reduced to very low rating. Metakaolin may be used to enhance hardened concrete properties for use in high performance concrete (HPC).

Special Report on Alkali-Aggregate Reactivity in Iowa, MLR-80-03, 1980

The purpose of this investigation was to obtain information relative to the alkali-silica reaction in Iowa aggregates. Of particular concern were those aggregates in southwestern Iowa thought to be potentially alkali reactive. Further, should those aggregates have proven to be alkali-reactive, at what cement alkali content could these aggregates be considered to be deleteriously reactive? If the aggregates were proven to be reactive, what types of effects might show up in a structure in which an alkali-silica reaction has occurred? Also, what environmental conditions would cause the reaction? Finally, based on the information obtained from the investigation, would it be possible to raise the cement alkali content specifications? Would the Iowa DOT eliminate the alkali content limits altogether except for cement used with reactive aggregate in the same manner as AASHTO or ASTM? Also, would there be any other side effects that might occur as the result of using high alkali-cement?