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.

Investigation of Two Bridge Alternatives for Low Volume Roads Volume 2 of 2 Concept 2: Beam In Slab Bridge, HR-382, 1997

Recent reports have indicated that 23.5% of the nation's highway bridges are structurally deficient and 17.7% are functionally obsolete. A significant number of these bridges are on the Iowa secondary road system where over 86% of the rural bridge management responsibilities are assigned to the counties. Some of the bridges can be strengthened or otherwise rehabilitated, but many more are in need of immediate replacement. In a recent investigation (HR-365 "Evaluation of Bridge Replacement Alternatives for the County Bridge System") several types of replacement bridges that are currently being used on low volume roads were identified. It was also determined that a large number of counties (69%) have the ability and are interested in utilizing their own forces to design and construct short span bridges. After reviewing the results from HR-365, the research team developed one "new" bridge replacement concept and a modification of a replacement system currently being used. Both of these bridge replacement alternatives were investigated in this study, the results of which are presented in two volumes. This volume (Volume 2) presents the results of Concept 2 - Modification of the Beam-in-Slab Bridge. Concept 1 - Steel Beam Precast Units is presented in Volume 1. Concept 2 involves various laboratory tests of the Beam-in-Slab bridge (BISB) currently being used by Benton County and several other Iowa counties. In this investigation, the behavior and strength of the BISB were determined; a new method of obtaining composite action between the steel beams and concrete was also tested. Since the Concept 2 bridge is primarily intended for use on low-volume roads, the system can be constructed with new or used beams. In the experimental part of the investigation, there were three types of laboratory tests: push-out tests, service and ultimate load tests of models of the BISB, and composite beam tests utilizing the newly developed shear connection. In addition to the laboratory tests, there was a field test in which an existing BISB was service load tested. An equation was developed for predicting the strength of the shear connection investigated; in addition, a finite element model for analyzing the BISB was also developed. Push-out tests were completed to determine the strength of the recently developed shear connector. A total of 36 specimens were tested, with variables such as hole diameter, hole spacing, presence of reinforcement, etc. being investigated. In the model tests of the BISB, two and four beam specimens [L=9,140 mm (30 ft)] were service load tested for behavior and load distribution data. Upon completion of these tests, both specimens were loaded to failure. In the composite beam tests, four beams, one with standard shear studs and three using the shear connection developed, were tested. Upon completion of the service load tests, all four beams were loaded to failure. The strength and behavior of the beams with the new shear connection were found to be essentially the same as that of the specimen with standard shear studs.

Image Analysis for Evaluating Air Void Parameters of Concrete, HR-396, 1998

This research project investigated the use of image analysis to measure the air void parameters of concrete specimens produced under standard laboratory conditions. The results obtained from the image analysis technique were compared to results obtained from plastic air content tests, Danish air meter tests (also referred to as Air Void Analyzer tests), high-pressure air content tests on hardened concrete, and linear traverse tests (as per ASTM C-457). Hardened concrete specimens were sent to three different laboratories for the linear traverse tests. The samples that were circulated to the three labs consisted of specimens that needed different levels of surface preparation. The first set consisted of approximately 18 specimens that had been sectioned from a 4 in. by 4 in. by 18 in. (10 cm by 10 cm by 46 cm) beam using a saw equipped with a diamond blade. These specimens were subjected to the normal sample preparation techniques that were commonly employed by the three different labs (each lab practiced slightly different specimen preparation techniques). The second set of samples consisted of eight specimens that had been ground and polished at a single laboratory. The companion labs were only supposed to retouch the sample surfaces if they exhibited major flaws. In general, the study indicated that the image analysis test results for entrained air content exhibited good to strong correlation to the average values determined via the linear traverse technique. Specimens ground and polished in a single laboratory and then circulated to the other participating laboratories for the air content determinations exhibited the strongest correlation between the image analysis and linear traverse techniques (coefficient of determination, r-squared = 0.96, for n=8). Specimens ground and polished at each of the individual laboratories exhibited considerably more scatter (coefficient of determination, r-squared = 0.78, for n=16). The image analysis technique tended to produce low estimates of the specific surface of the voids when compared to the results from the linear traverse method. This caused the image analysis spacing factor calculations to produce larger values than those obtained from the linear traverse tests. The image analysis spacing factors were still successful at distinguishing between the frost-prone test specimens and the other (more durable) test specimens that were studied in this research project.

Recycled Portland Cement Concrete Pavement in Iowa, HR-506, 1984

In recent years, there has been an increased interest in conservation of our resources, preservation of our environment and maintaining our ecology. Recycling of materials is a procedure that will immediately contribute to all of these desirable end results. Our economy is built on private enterprise and profit incentive and in the past, with abundant inexpensive resources, there was little incentive to recycle. Shortages of materials and energy (once considered abundant) along with regulations to protect the environment have emphasized the need for recycling. These environmental conditions coupled with the loss of purchase power by inflation has generated more interest in recycling in the transportation field. The Iowa Department of Transportation (Iowa DOT) is interested in recycling portland cement concrete (pcc) pavement to: 1. Provide aggregate where high quality aggregate is no longer economically available. 2. Eliminate the need for locations to waste the large amount of pavement rubble. 3. Conserve the present aggregate sources. 4. Reduce the need for disrupting land for quarrying purposes. 5. Save fuel and energy by reducing aggregate transportation.

Thin Bonded Portland Cement Concrete Overlay, HR-520, 1990

A four and one-half inch thick, bonded portland cement concrete (PCC) overlay and integral widening were used to rehabilitate a 4.5 mile section of Iowa route 141 from US 169 to Iowa 210 in Dallas County. There was a substantial amount of cracking in the old 20 feet wide PCC pavement. Most of the widening, which was tied to the original slab by dowel bars, was placed as a four feet wide section on one side. Coring has shown that the overlay is well bonded and testing with the Delamtect has shown less than 1% debonding. Midpanel transverse cracks in the old pavement have reflected through the overlay (as expected). Some new transverse cracking has occurred. This cracking has not caused any significant problems. In general, the overlay is performing quite well.

Evaluation of an International Barrier Corporation Barrier, HR-532, 1990

In 1986, the Iowa DOT installed 700 feet of International Barrier Corporation (IBC) barrier between the 1-235 eastbound off ramp and the adjacent eastbound loop on ramp at 8th Street in West Des Moines. It is a 3 foot 6 inch high sand-filled galvanized sheet metal barrier. The bid price on this project was $130 per lineal foot. It was evaluated annually for four years. During this time, there have been no severe accidents where vehicles hit the barrier. There are scrapes and dents indicating minor accidents. The barrier has performed very well and required no maintenance. Due to its initial cost, the IBC barrier is not as cost-effective as portland cement concrete barrier rails.

Fast Track Portland Cement Concrete Pavement, HR-538, 1997

In 1987, 1.5 km (0.935 mi.) of Spruce Hill Drive in Bettendorf, Iowa was reconstructed. It is an arteriel street with commercial usage on both termini with single family residential dwellings along most of the project. A portland cement concrete (PCC) pavement design was selected, but a 14 day curing period would have been an undue hardship on the residents and commercial businesses. An Iowa DOT Class F fast track concrete was used so the roadway could be used in 7 to 10 days. The Class F concrete with fly ash was relatively sticky and exhibited early stiffening problems and substantial difficulty in obtaining the target entrained air content of 6.5%. These problems were never completely resolved on the project. Annual visual field reviews were conducted through 1996. In November 1991, severe premature distress was identified on the westbound two lanes of the full width replacement. The most deteriorated section in a sag vertical, 152 m (500 ft.) of the westbound roadway, was replaced in 1996. Premature distress has been identified on a dozen other conventional PCC Iowa pavements constructed between 1983 and 1989, so the deterioration may not be related to the fact that it was fast track pavement.

Production of Asphalt Rubber Concrete by the Dry Process, HR-1062, 1994

Disposal of used tires has been a problem throughout the United States. The 1991 Intermodal Surface Transportation Efficiency Act (ISTEA) requires the use of recycled rubber in asphalt concrete starting in FY94. A moratorium has delayed this requirement until FY95. The Iowa DOT has researched six projects using crumb rubber modifier in asphalt concrete using the wet process. This process involves using a blender-reactor to blend the asphalt cement and crumb rubber. Using the wet process the asphalt cement has to reach a hotter temperature, than is normally required, for reaction to occur. The wet process is also much more expensive than conventional asphalt. This research deals with using a dry process to incorporate crumb rubber into the asphalt concrete mix. The project was constructed by Western Engineering of Harlan, Iowa, on IA 37 between Earling, Iowa and US 59. It was completed in September 1993. Western Engineering used a double drum mixer to produce the crumb rubber modified asphalt concrete by the dry process. The production and construction went well with minor difficulty and the dry process is a less expensive procedure for producing crumb rubber modified asphalt concrete.

A Statistical Analysis of Iowa Premature Concrete Pavement Deterioration, Supplementary Study, HR-1063, 1997

This supplementary project has been undertaken as an effort to continue work previously completed in the Pooled Fund Study of Premature Concrete Pavement Deterioration. As such, it shares the objective of "Identifying the variables that are present in those pavements exhibiting premature deterioration," by collecting additional data and performing statistical analysis of those data. The approach and philosophy of this work are identical to that followed in the above project, and the Pooled Fund Study Final Report provides a detailed description of this process. This project has involved the collection of data for additional sites in the state of Iowa. These sites have then been added to sites collected in the original study, and statistical analysis has been performed on the entire set. It is hoped that this will have two major effects. First, using data from only one state allows for the analysis of a larger set of independent variables with a greater degree of commonality than was possible in the multi-state study, since the data are not limited by state to state differences in data collection and retention. Second, more data on additional sites will increase the degrees of freedom in the model and hopefully add confidence to the results.

Pooled Fund Study of Premature Concrete Pavement Deterioration, HR-1063, Supplementary Study, 1997

Recently, a number of roads have begun to exhibit the onset of deterioration at relatively early ages. Since this deterioration appears to be the result of materials issues, data concerning raw materials, design, and paving conditions have been collected and analyzed for correlation between independent variables and deterioration. This analysis shows that there is a positive and statistically significant correlation between deterioration and the following variables: alkali and sulfate content of the cementitious materials, impermeable base course, paving temperature, and the presence of fly ash. This study also concludes that there is a significant need for improvement in data collection and maintenance by many organizations responsible for the production of concrete.

A Different Perspective for Investigation of PCC Pavement Deterioration, HR-2074, 1995

Portland Cement Concrete (PCC) pavement has served the State of Iowa well for many years. The oldest Iowa pavement was placed in LeMars in 1904. Beginning in 1931, many miles of PCC pavement were built to "get out of the mud". Many of these early pavements provided good performance without deterioration for more than 50 years. In the late 1950s, Iowa was faced with severe PCC pavement deterioration called D cracking. Research identified the cause of this deterioration as crushed limestone containing a bad pore system. Selective quarrying and ledge control has alleviated this problem. In 1990, cracking deterioration was identified on a three-year-old pavement on US 20 in central Iowa. The coarse aggregate was a crushed limestone with an excellent history of performance in PCC pavement. Examination of cores showed very few cracks through the coarse aggregate particles. The cracks were predominately confined to the matrix. The deterioration was identified as alkali-silica reactivity (ASR) by a consultant. To investigate the cause of the deterioration, the Iowa DOT and Iowa State University jointly purchased a high resolution, low vacuum Hitachi Scanning Electron Microscope (SEM) with an energy dispersion detector. Subsequent evaluation identified no concentration of silica gel (silicon-Si), but did identify substantial amounts of sulfur-S and aluminum-AL (assumed to be ettringite) in the air voids. Some of these voids have cracks radiating from them leading us to conclude that the ettringite filled voids were a center of pressure causing the crack. The ettringite in the voids, after being subjected to sodium chloride (NaCl), initially swells and then dissolves. This low vacuum SEM research of PCC pavement deterioration supports the following conclusions: (1) A low vacuum SEM and an energy dispersion detector are very important for proper evaluation of PCC pavement deterioration; (2) There are instances today where PCC pavement deterioration is mistakenly identified as ASR; (3) Ettringite initially expands when subjected to NaCl; and the ettringite filled voids are a center-of-pressure that cracks the PCC; and (4) The deterioration of some current premature PCC pavement distress locations is caused by factors related to the formation of excessive ettringite.

Thin Asphalt Concrete Pavement on Crushed Rock Base - Cass County, Construction Report, HR-2075, 1997

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.

Asbestos Fibers in Type B Asphaltic Concrete Surface Course, MLR-67-1, 1968

The Standard Specifications for this project included requirements for placing two 500 foot test sections of Type B asphaltic concrete with 1-1/2 per cent asbestos fibres (mix size 3/8 inch, lift thickness 3/4 inch) as part of the regular construction of the surface course. These requirements were designed to provide asbestos modified mixtures for laboratory analysis and road performance evaluation. This report provides the preliminary results and analysis of test data obtained from tests on the mixtures placed on the roadway. Previous research by G. S. Zuelke (1) and J. H. Kestzman et al (2) indicated that asphaltic concrete mixtures modified with asbestos fibres improved stability, decreased permeability, and allowed the use of higher bitumen contents. This study indicated that the addition of asbestos fibres would permit the use of higher bitumen contents, theoretically improving durability, without adverse results. An indication was also obtained to the effect that asbestos mixtures were more difficult to compact in the field.

An Evaluation of Concrete Bridge Deck Surfacing in Iowa (with corrections), MLR-75-1, 1975

Iowa has been using low slump concrete for repair and surfacing of deteriorated bridge decks on a routine basis since the mid 1960'2. More than 150 bridges have been resurfaced by this method with good results. A study was initiated in 1973 to evaluate 15 bridges resurfaced with low slump concrete, and one bridge resurfaced with latex modified concrete. The evaluation includes an assessment of concrete physical properties, chloride penetration rates, concrete consolidation, and riding qualities of the finished bridge deck. Results indicate that the overall properties of these two types of concrete are quite similar and have resulted in a contractor option concerning which system shall be used on bridge deck repair/resurfacing projects.

An Evaluation of the Roto-Mill Profiler on Concrete Pavements in Iowa, MLR-76-1, 1976

A new machine, the ROTO-MILL Profiler, became available in early 1976. This machine, manufactured by CMI Corporation of Oklahoma City, Oklahoma provides pavement surface Scarification at a much higher production rate than was previously possible. Iowa had the opportunity to observe and evaluate this machine on two separate sections of primary portland cement concrete pavement in October, 1976. The marked improvement in the profile index and the skid resistance indicates this machine may be considered a viable method for improving rideability and skid resistance of a roadway that is otherwise reasonably sound.