Performance of Randomly Oriented, Fiber-Reinforced Roadway Soils, HR-211, 1982

Several primary techniques have been developed through which soil aggregate road material properties may be improved. Such techniques basically involve a mechanism of creating a continuous matrix system of soil and/or aggregate particles, interlocked through the use of some additive such as portland cement, lime, or bituminous products. Details by which soils are stabilized vary greatly, but they are dependent on the type of stabilizing agent and nature of the soil, though the overall approach to stabilization has the common feature that improvement is achieved by some mechanism(s) forcing individual particles to adhere to one another. This process creates a more rigid material, most often capable of resisting the influx of water during freezing, loss of strength due to high moisture content and particle dispersion during thawing, and loss of strength due to migration of fines and/or water by capillarity and pumping. The study reported herein, took a new and relatively different approach to strengthening of soils, i.e., improvement of roadway soils and/or soil-aggregate materials by structural reinforcement with randomly oriented fibers. The purpose of the study was to conduct a laboratory and field investigation into the potential of improving (a) soil-aggregate surfaced and subgrade materials, including those that are frost-prone and/or highly moisture susceptible, and (b) localized base course materials, by uniting such materials through fibrous reinforcement. The envisioned objective of the project was the development of a simple construction technique(s) that could be (a) applied on a selective basis to specific areas having a history of poor performance, or (b) used for improvement of potential base materials prior to surfacing. Little background information on such purpose and objective was available. Though the envisioned process had similarities to fibrous reinforced concrete, and to fibrous reinforced resin composites, the process was devoid of a cementitious binder matrix and thus highly dependent on the cohesive and frictional interlocking processes of a soil and/or aggregate with the fibrous reinforcement; a condition not unlike the introduction of reinforcing bars into a concrete sand/aggregate mixture without benefit of portland cement. Thus the study was also directed to answering some fundamental questions: (1) would the technique work; (2) what type or types of fibers are effective; (3) are workable fibers commercially available; and (4) can such fibers be effectively incorporated with conventional construction equipment, and employed in practical field applications? The approach to obtaining answers to these questions, was guided by the philosophy that an understanding of basic fundamentals was essential to developing a body of engineering knowledge, that would serve as the basis for eventual development of design procedures with fibrous products for the applications previously noted.

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.

Engineering Fabric Repair Prior to Resurfacing - Roadglas - US 30, HR-525, 1992

In Iowa it is normal procedure to either use partial or full-depth patching to repair deteriorated areas of pavement prior to resurfacing. The Owens/Corning Corporation introduced a repair system to replace the patching process. Their Roadglas repair system was used in this research project on US 30 in Story County. It was installed in 1985 and has been observed annually since that time. There were some construction problems with slippage as the roller crossed the abundant Roadglas binder. It appears the Roadglas system has helped to control reflective cracking in the research areas. Since the time when this project was completed it has been reported that Owens/Corning has discontinued production of the Roadglas system.

Studies on Soil-Aggregate-Sodium Chloride Stabilized Roads in Franklin County, Iowa, HR-33

This investigation was conducted to study the performance characteristics of low cost roadway surfaces of soil-aggregate-sodium chloride mixtures. Many roads have been successfully stabilized with sodium chloride. However, little information is available on either the properties of the road materials or the effects of sodium chloride on the materials. The performance of some of the sodium chloride stabilized roads in Franklin County, Iowa, and the performance of some near-by nonchemically treated roads has been studied. The study of sodium chloride stabilized roads was restricted to the roads in which the binder soil used in construction came from the same source. The effects of sodium chloride on some of the engineering properties of the soil and soil-aggregate mixtures used were studied in the laboratory.

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.

Assessment of Asphalt Interlayer Designed on Jointed Concrete, InTrans Project 13-475, 2014

Reflective cracking in hot mix asphalt (HMA) overlays has been a common cause of poor pavement performance in Iowa for many years. Reflective cracks commonly occur in HMA overlays when deteriorated portland cement concrete is paved over with HMA. This results in HMA pavement surfaces with poor ride quality and increased transportation maintenance costs. To delay the formation of cracks in HMA overlays, the Iowa Department of Transportation (Iowa DOT) has begun to implement a crack-relief interlayer mix design specification. The crack-relief interlayer is an asphalt-rich, highly flexible HMA that can resist cracking in high strain loading conditions. In this project, the field performance of an HMA overlay using a one inch interlayer was compared to a conventional HMA overlay without an interlayer. Both test sections were constructed on US 169 in Adel, Iowa as part of an Iowa DOT overlay project. The laboratory performance of the interlayer mix design was assessed for resistance to cracking from repeated strains by using the four-point bending beam apparatus. An HMA using a highly polymer modified binder was designed and shown to meet the laboratory performance test criteria. The field performance of the overlay with the interlayer exceeded the performance of the conventional overlay that did not have the interlayer. After one winter season, 29 percent less reflective cracking was measured in the pavement section with the interlayer than the pavement section without the interlayer. The level of cracking severity was also reduced by using the interlayer in the overlay.

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%.

Asphalt Rubber Cement Concrete Webster County, HR-555, Final Report, 2003

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 has evaluated 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 using this process. The 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 during this research with the surface course to be let at a later date. There were four test sections, two sections with conventional mixtures and two with ARC mixtures. There were no significant differences in placement or performance between the two mix types. The cost of the ARC mixture was significantly higher.

Crushed Stone Granular Surfacing Materials, HR-2046 and MLR-90-07, 1990

This project included the following tasks: (1) Preparation of a questionnaire and survey of all 99 Iowa county engineers for input on current surfacing material practice; (2) County survey data analysis and selection of surfacing materials gradations to be used for test road construction; (3) Solicitation of county engineers and stone producers for project participation; (4) Field inspection and selection of the test road; (5) Construction of test road using varying material gradations from a single source; and (6) Field and laboratory testing and test road monitoring. The results of this research project indicate that crushed stone surfacing material graded on the fine side of Iowa Department of Transportation Class A surfacing specifications provides lower roughness and better rideability; better braking and handling characteristics; and less dust generation than the coarser gradations. It is believed that this material has sufficient fines available to act as a binder for the coarser material, which in turn promotes the formation of tight surface crust. This crust acts to provide a smooth riding surface, reduces dust generation, and improves vehicle braking and handling characteristics.

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field and Laboratory Testing, 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 describes the results of comprehensive field and laboratory testing for these CIR asphalt roads. The results indicate that the modulus of the CIR layer and the air voids of the CIR asphalt binder were the most important factors affecting CIR pavement performance for high-traffic roads. For low-traffic roads, the wet indirect tensile strength significantly affected pavement performance. The results of this research can help identify changes that should be made with regard to design, material selection, and construction in order to improve the performance and cost-effectiveness of future recycled roads.

Thin Maintenance Surfaces for Municipalities, TR-507, 2007

As streets age, officials must deal with rehabilitating and reconstructing these pavements to maintain a safe and comfortable ride. In light of nationwide budget shortfalls, cost-effective methods of extending pavement service life must be developed or the overall condition of street systems will continue to fall. Thin maintenance surfaces (TMSs) are a set of cost-effective preventive maintenance surfacing techniques that can be used to extend the life of bituminous pavement—pavement built with hot mix asphalt, hot mix asphalt overlays of portland cement concrete pavements, built-up seal coat (chip seal), stabilized materials, or a combination of these. While previous phases of TMS research have provided information about the uses of thin maintenance surfaces in rural settings, urban areas have different road maintenance challenges that should be considered separately. This research provides city street officials with suggestions for TMS techniques that street departments can easily test and include into their current programs. This research project facilitated the construction of TMS test sections in Cedar Rapids, Council Bluffs, and West Des Moines (all urban settings in Iowa). Test section sites and surfaces were selected to suit the needs of municipalities and were applied to roads with an array of various distresses and maintenance needs. Condition surveys of each test section were performed before construction, after construction, and after the first winter to record the amount and severity of existing distress and calculate the pavement condition index. Because conditions of the test sections varied greatly, determining which surface was most successful by comparing case studies was not feasible. However, some general conclusions can be made from this research. TMSs are suitable preventive maintenance techniques for a municipal street department’s program for preserving existing pavements. Careful attention should be paid to proper planning, quality control during construction, aggregate and binder selection, and aggregate embedment in order to support successful TMS application.

Investigation of Electromagnetic Gauges for Determination of In-Place Density of HMA Pavements, TR-576, 2009

This study evaluated the use of electromagnetic gauges to determine the adjusted densities of HMA pavements. Field measurements were taken with two electromagnetic gauges, the Pavement Quality Indicator (PQI) 301 and the Pavetracker Plus 2701B. Seven projects were included in the study with 3 to 5 consecutive paving days. For each day/lot 20 randomly selected locations were tested along with seven core locations. The analysis of PaveTracker and PQI density consisted of determining which factors are statistically significant, and core density residuals and a regression analysis of core as a function of PaveTracker and PQI readings. The following key conclusions can be stated: 1. Core density, traffic and binder content were all found to be significant for both electromagnetic gauges studied, 2. Core density residuals are normally distributed and centered at zero for both electromagnetic gauges, 3. For PaveTracker readings, statistically one third of the lots do not have an intercept that is zero and two thirds of the lots do not rule out a scaler correction factor of zero, 4. For PQI readings, statistically the 95% confidence interval rules out the intercept being zero for all seven projects and six of the seven projects do not rule out the scaler correction factor being zero, 5. The PQI 301 gauge should not be used for quality control or quality assurance, and 6. The Pavetracker 2701B gauge can be used for quality control but not quality assurance. This study has found that with the limited sample size, the adjusted density equations for both electromagnetic gauges were determined to be inadequate. The PaveTracker Plus 2701B was determined to be better than the PQI 301. The PaveTracker 2701B could still be applicable for quality assurance if the number of core locations per day is reduced and supplemented with additional PaveTracker 2701B readings. Further research should be done to determine the minimum number of core locations to calibrate the gauges each day/lot and the number of additional PaveTracker 2701B readings required.

Asphalt Binders for Thin Maintenance Surfaces, TR-435, 2003

Asphalt is used as a binder for thin maintenance surface (TMS) applications because of two key properties, it is waterproof and it adheres relatively well to the aggregate. Since asphalt is too stiff at room temperature to apply to the road surface, it is usually applied as either a cutback asphalt or an asphalt emulsion. The asphalt emulsions can be further divided into high float emulsions, cationic emulsions or polymer-modified binders, which are emulsions with polymers added to them. These types of binders are discussed further below.