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.

Recycled Asphalt Pavement Kossuth County Iowa, HR-176, 1982

In 1975, Kossuth County had 492 miles of asphalt pavements, sixty percent of which were between l5 and 20 years old. Many of these roadways were in need of rehabilitation. Normally, asphaltic resurfacing would be the procedure for correcting the pavement deterioration. There are areas within the state of Iowa which do not have Class I aggregate readily available for asphalt cement concrete paving. Kossuth County is one of those areas. The problem is typified by this project. Limestone aggregate to be incorporated into the asphalt resurfacing had to be hauled 53 miles from the quarry to the plant site. The cost of hauling good quality aggregate coupled with the increasing cost of asphalt cement encouraged Kossuth County to investigate the possibility of asphaltic pavement recycling. Another problem, possibly unique to Kossuth County, was the way the original roadways had been constructed. A good clay soil was present under 3 to 4 feet of poorer soil. In order to obtain this good clay soil for subbase construction, the roadway ditches were excavated 1 to 3 feet into the clay soil layer. The resultant roadway tops were several feet above the surrounding farm land and generally less than 26 feet wide. To bring the existing roadway up to current minimum design width, there were two choices: One was to widen the roadway by truck hauling soil and constructing new 4 to 6 foot shoulders. The cost of widening by this method averaged $36,000 per mile in 1975. The other choice was to remove the old pavement and widen the roadway by lowering the grade line. The desire to provide wider paved roadways gave Kossuth County the additional incentive needed to proceed with a pavement recycling project.

Behavior of Carbonate Rocks as Concrete Aggregates, HR-15, 1962

The problem of determining the suitability of carbonate rocks as concrete aggregates is extremely complex and calls for more new data than has been available or obtainable from usual methods. Since 1955 the approach which has served as a primary basis for the project has been to gather as much new information as possible to apply to the problem. New information obtained by new and different techniques provides better understanding. This approach was decided on since, in all prior studies, a standard petrographic and petrologic approach correlated in many instances with standard engineering tests did not provide the answer in Iowa or elsewhere. One can theorize that concrete fails (excluding external causes such as traffic, foundation failure, etc.) because of stresses of internal origin. The stresses can be of a physical nature, such as frost action, or result from chemical activity such as the alkali aggregate reaction. If, as service records show, the aggregate is considered the cause of distress in concrete, it will without doubt be the manner in which an aggregate can create or contribute to stress of internal origin by physical or chemical means. Therefore the main emphasis was placed on studying physical and chemical properties of aggregates as well as the behavior of carbonate rocks in concrete environments. Although standard geologic and engineering methods were also utilized, the approach adopted required considerable effort in devising new techniques and methods. This report is intended to be a detailed summary of the research performed. Whenever possible, the work accomplished will be summarized and all pertinent data will be included. For further details, reference to the various theses and publications transmitted with this report or at previous times will be made wherever possible.

Absorptive Aggregates in Asphalt Paving Mixtures, HR-142, 1971

In this study, the asphalt absorption of six Iowa limestones were investigated. It was found that the most important factors that determined the nature, amount, and rate of asphalt absorption are porosity and pore-size distribution of the aggregate, viscosity of the asphalt, and time. Methods needed to determine the realistic maximum and minimum asphalt absorption by aggregates are recommended. Simple methods of asphalt absorption were developed. Since the most important factor that determines the accuracy of asphalt absorption is the bulk specific gravity of aggregates and since the current ASTM method is not adequate in this respect, several new methods were developed. Preliminary treatment studies for the purpose of upgrading absorptive aggregates were conducted using close to 40 chemicals. The improvements of some of these treatments on the mixture properties were demonstrated.

Treating Iowa's Marginal Aggregates and Soils by Foamix Process, HR-212, 1980

Quality granular materials suitable for building all-weather roads are not uniformly distributed throughout the state of Iowa. For this reason the Iowa Highway Research Board has sponsored a number of research programs for the purpose of developing new and effective methods for making use of whatever materials are locally available. This need is ever more pressing today due to the decreasing availability of road funds and quality materials, and the increasing costs of energy and all types of binder materials. In the 1950s, Professor L. H. Csanyi of Iowa State University had demonstrated both in the laboratory and in the field, in Iowa and in a number of foreign countries, the effectiveness of preparing low cost mixes by stabilizing ungraded local aggregates such as gravel, sand and loess with asphalt cements using the foamed asphalt process. In this process controlled foam was produced by introducing saturated steam at about 40 psi into heated asphalt cement at about 25 psi through a specially designed and properly adjusted nozzle. The reduced viscosity and the increased volume and surface energy in the foamed asphalt allowed intimate coating and mixing of cold, wet aggregates or soils. Through the use of asphalt cements in a foamed state, materials normally considered unsuitable could be used in the preparation of mixes for stabilized bases and surfaces for low traffic road construction. By attaching the desired number of foam nozzles, the foamed asphalt can be used in conjunction with any type of mixing plant, either stationary or mobile, batch or continuous, central plant or in-place soil stabilization.

Recycled Asphalt Pavements - Kossuth County Iowa, HR-176, 1975

Kossuth County is located in North Central Iowa bordering on the State of Minnesota. It is the largest county in Iowa consisting of 28 congressional townships. The population of the county is 23,000 of which 11,000 people live in the rural area. There are 13 towns located in the county with the county seat, Algona, being the largest with a population of 6,100. Major industry of the area is grain farming with some beef and hog production. Naturally, where there is good grain farm land it follows that there is poor soil available for road construction and pavements. However, below the 3 to 4 feet of good farm land of Kossuth there is present a good grade of clay soil which does make an adequate base for surfacing when placed and compacted on top of the roadbed. As early as 1950, the then Kossuth County Engineer, H.M. Smith, embarked on a program of stage construction in building new grades and pavements. The goal of his program was primarily to conserve the county's rapidly dwindling supply of surfacing materials, and also, to realize the side effects of providing smooth and dustless roads for the public. Engineer Smith was fully aware of the poor soils that existed for road construction, but he also knew about the good clay that lay below the farm soil. Consequently, in his grading program he insisted that road ditches be dug deep enough to allow the good clay soil to be compacted on top of the roadbed. The presence of the compacted clay on top of the road resulted in a briding affect over the farm soil. The stage construction program satisfied the objectives of aggregate construction and dust control but did generate other problems which we are now trying to solve as economically as possible.

Use of Recycled Products FY2014

The report summarizes the purchasing activity for soy based inks and recycled content trash bags for the Iowa DOT.

Development of Quality Standards for Inclusion of High Recycled Asphalt Pavement Content in Asphalt Mixtures – Phase II, TR-658, 2015

To conserve natural resources and energy, the amount of recycled asphalt pavement has been steadily increasing in the construction of asphalt pavements. The objective of this study is to develop quality standards for inclusion of high RAP content. To determine if the higher percentage of RAP materials can be used on Iowa’s state highways, three test sections with target amounts of RAP materials of 30%, 35% and 40% by weight were constructed on Highway 6 in Iowa City. To meet Superpave mix design requirements for mixtures with high RAP contents, it was necessary to fractionate the RAP materials. Three test sections with actual RAP materials of 30.0%, 35.5% and 39.2% by weight were constructed and the average field densities from the cores were measured as 95.3%, 94.0%, and 94.3%, respectively. Field mixtures were compacted in the laboratory to evaluate moisture sensitivity using a Hamburg Wheel Tracking Device. After 20,000 passes, rut depths were less than 3mm for mixtures obtained from three test sections. The binder was extracted from the field mixtures from each test section and tested to identify the effects of RAP materials on the performance grade of the virgin binder. Based on Dynamic Shear Rheometer and Bending Beam Rheometer tests, the virgin binders (PG 64-28) from test sections with 30.0%, 35.5% and 39.2% RAP materials were stiffened to PG 76-22, PG 76-16, and PG 82-16, respectively. The Semi-Circular Bending (SCB) test was performed on laboratory compacted field mixtures with RAP amounts of 30.0%, 35.5% and 39.2% at two different temperatures of -18 and -30 °C. As the test temperature decreased, the fracture energy decreased and the stiffness increased. As the RAP amount increased, the stiffness increased and the fracture energy decreased. Finally, a condition survey of the test sections was conducted to evaluate their short-term pavement performance and the reflective transverse cracking did not increase as RAP amount was increased from 30.0% to 39.2%.

Chemical Reactions Involving Aggregates, HR-15, 1960

The discussion presented below concerns the section on "Unidentified Cement-Aggregate Reactions" in which mention is made of concrete deterioration related to argillaceous dolomitic limestone aggregates. A considerable amount of research has been conducted on carbonate aggregate-cement reactions as part of the general study on the suitability of carbonate rocks as concrete aggregate which inadvertently did not reach the authors in time to be incorporated in their paper. These reactions which occur in response to the alkaline environment of concrete are not typical alkali-aggregate reactions associated with siliceous aggregates such as opaline cherts, volcanic glasses and etc. The reactions are associated with certain carbonate aggregates whose service records indicate deleterious performance in concrete has occurred. It is my purpose to review briefly carbonate aggregate research conducted at Iowa State University and present some new data on the problem of carbonate aggregate-cement paste reactions.

Relationship of Carbonate Aggregates to Concrete Aging, HR-116, 1967

HR-116 is concerned with the relationship of carbonate aggregate to aging of highway concrete. The ultimate purpose of the research is to provide the Materials Department with better criteria for selection of carbonate aggregates for use in highway concrete. The research stems from the problem in Iowa which relates durability of highway concrete to use of certain aggregates. Service records of certain highways have shown that concrete deterioration is related to the source of coarse carbonate aggregate. Research on this problem in projects HR-15 and HR-86 helped define three broad areas of the problem in more detail: 1. The problem of evaluation of rocks which pass current specifications but have poor service records 2. The basic problem of how rocks contribute to distress in concrete 3. The problem of how concrete ages or weathers.

Evaluation of Recycled Rubber in Asphalt Cement Concrete - Field Testing, Final Report for HR-330, 330A, 330B, 330C, 330D, 2002

Roughly 242 million used tires are generated annually in the United States. Many of these tires end up being landfilled or stockpiled. The stockpiles are unsightly, unsanitary, and also collect water which creates the perfect breeding ground for mosquitoes, some of which carry disease. In an effort to reduce the number of used tire stockpiles the federal government mandated the use of recycled rubber in federally funded, state implemented department of transportation (DOT) projects. This mandate required the use of recycled rubber in 5% of the asphalt cement concrete (ACC) tonnage used in federally funded projects in 1994, increasing that amount by 5% each year until 20% was reached, and remaining at 20% thereafter. The mandate was removed as part of the appropriations process in 1994, after the projects in this research had been completed. This report covers five separate projects that were constructed by the Iowa Department Of Transportation (DOT) in 1991 and 1992. These projects had all had some form of rubber incorporated into their construction and were evaluated for 5 years. The conclusion of the study is that the pavements with tire rubber added performed essentially the same as conventional ACC pavement. An exception was the use of rubber chips in a surface lift. This performed better at crack control and worse with friction values than conventional ACC. The cost of the pavement with rubber additive was significantly higher. As a result, the benefits do not outweigh the costs of using this recycled rubber process in pavements in Iowa.

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.

A Laboratory Investigation of An Accelerated Polishing Method for Determining the Skid Resistance Potential of Aggregates, MLR-76-02 and R-264, 1976

An initial feasibility study indicated that the "Purdue Accelerated Polishing Method" gave repeatable results when testing the skid resistance of laboratory specimens. The results also showed a rough correlation with the field performance of the same aggregate sources. The research was then expanded to include all available asphalt aggregates. The results of the expanded study indicated that the method is not presently capable of developing and measuring the full skid potential of the various aggregate sources. Further research in the area of polishing times and/or pressures is needed.

A Review of the Frictional Classification of Iowa Aggregates, MLR-81-04, 1981

The Iowa D.O.T. has a classification system designed to rate coarse aggregates as to their skid resistant characteristics. Aggregates have been classified into five functional types, with a Type 1 being the most skid resistant. A complete description of the classification system can be found in the Office of Materials Instructional Memorandum T-203. Due to the variability of ledges within any given quarry the classification of individual ledges becomes necessary. The type of aggregate is then specified for each asphaltic concrete surface course. As various aggregates become used in a.c. paving, there is a continuing process of evaluating the frictional properties of the pavement surface. It is primarily through an effort of this sort that information on aggregate sources and individual ledges becomes more refined. This study is being conducted to provide that needed up-to-date information that can be used to monitor the aggregate classification system.

Evaluation of Asphalt Mixes Made from Reclaimed Concrete Aggregates, MLR-85-07, 1986

Three comparable hot mixed asphalt paving mixes were produced using two different aggregates produced from reclaimed portland cement concrete paving and one from a crushed limestone aggregate. These were subjected both dry and soaked to indirect tensile tests to determine the wet strength retention. One mix made from reclaimed concrete demonstrated a slightly better strength retention than the limestone mix and the other less. Satisfactory asphalt paving mixes can be produced from reclaimed concrete pavements but the increased asphalt demand (about 1%) negates part of the potential savings.