Polymer Additive Ductilad D1002 in a Bituminous Seal Coat, HR-2035, 1994

Seal coat and chip seal treatments are commonly used as an economical treatment to provide a new surface to an old asphalt roadway. To be successful, the aggregate or chips must be held in place on the roadway by the asphalt binder over a long period of time. It is common, over time, that the binder becomes aged and brittle and loses its ability to be flexible and hold the aggregate in place. Modifiers have been introduced to extend the life and adhesion characteristics of asphaltic binders.

Asphalt Emulsions for Highway Construction (Emulsion Seal Coat), HR-1028, 1980

For the past several year Kossuth County has had a scheduled maintenance program of bituminous seal coating. This program has been used to maintain the 467 miles of asphaltic concrete surfaced roads in Kossuth County. Since most of the experience that Kossuth County had in seal coating was with cutback asphalt, it was decided to include the use of emulsified asphalt in Kossuth County's 1980 seal coat program. Federal Demonstration Project Funds were requested from the Federal Highway Administration to study the use of emulsified asphalt and funding was granted under Demonstration Project No. 55,:Asphalt Emulsions for Highway Construction." Items studied were design and construction procedure cost of alternate material, energy consumption and environmental considerations. A construction contract was awarded to Everds Brothers, Inc. of Algona, Iowa, on July 1, 1980. There were four bidders on the 54.5 miles of seal coating that was let. A map showing the location of the seal coating projects is shown in Appendix A, and a copy of the contract is shown in Appendix B. The contractor started the project on July 11, 1980 and completed the project on August 1, 1980. Construction inspection and follow-up inspections of the project were conducted by personnel of the Kossuth County Engineer's Office and testing of the materials, friction testing and road rater testing were conducted by the Material's Department of the Iowa Department of Transportation.

Development of Updated Specifications for Roadway Rehabilitation Techniques, May 2011

As our nation’s highway system continues to age, asphalt maintenance and rehabilitation techniques have become increasingly important. The deterioration of pavement over time is inevitable. Preventive maintenance is a strategy to extend the serviceable life of a pavement by applying cost-effective treatments that slow the deterioration of pavement and extend its usable life. Thin maintenance surfaces (TMSs) are preventive maintenance techniques that can effectively prolong the life of pavement when applied at an opportune time. Common TMSs include bituminous fog seal, bituminous seal coat, slurry seal, cold in-place recycling (CIR), and micro-surfacing. This research project investigated ways to improve Iowa Statewide Urban Design and Specifications (SUDAS) and Iowa Department of Transportation (DOT) documents regarding asphalt roadway maintenance and rehabilitation. Researchers led an effort to review and help ensure that the documents supporting proper selection, design, and construction for asphalt maintenance and rehabilitation techniques reflect the latest research findings on these processes: seal coating, slurry sealing, micro-surfacing, and fog sealing. Full results of this investigation are included in this report and its appendices. This report also presents a summary of the recommendations based on the study results.

Evaluation of 1977 Asphalt Concrete Sprinkle Treatments, December 1980

Iowa's first sprinkle treatment in 1974 was applied to a short section of old US 30 west of Ames. A roll type seal coat spreader was used to apply several types of sprinkle aggregates. The following year a spinner type tailgate spreader was used for sprinkle application of an Iowa 7 project in Webster County. Uniform spreading and tire marks were problems in these early projects. A special spinner spreader was built in 1976 and mounted on a truck specially equipped with smooth tires. This special unit was tested in early 1977 on a project that had been scheduled for 1976. Spinner type spreaders proved unacceptable due to non-uniformity of spreading.

An Investigation of Emulsion Stabilized Limestone Screenings, HR-309, 1994

A significant amount of waste limestone screenings is produced during aggregate production. This waste material cannot be used in highway construction because it does not meet current highway specifications. The purpose of this research was to determine if a waste limestone screenings/emulsion mix could be used to construct a base capable of supporting local traffic. A 1.27 mile (2.04 km) section of roadway in Linn County was selected for this research. The road was divided into seven sections. Six of the sections were used to test 4 in. (100 mm) and 6 in. (150 mm) compacted base thicknesses containing 2.5%, 3.5%, and 4.5% residual asphalt contents. The seventh section was a control section containing untreated waste limestone screenings. This research on emulsion stabilized limestone screenings supports the following conclusions: (1) A low maintenance roadway can be produced using a seal coat surface on 6 in. (150 mm) of stabilized limestone screenings with 4.5% asphalt cement; (2) A 6 in. (150 mm) emulsion stabilized base with less than 3.5% asphalt cement does not produce a satisfactory low cost maintenance roadway; (3) A 4 in. (100 mm) emulsion stabilized base does not produce a satisfactory low cost maintenance roadway; and (4) A 2 in. (50 mm) asphalt concrete surface would be necessary on many roads to provide a low maintenance roadway using emulsion stabilized limestone screenings.

Bond Enhancement Techniques for PCC Whitetopping, HR-341, 1996

This research was initiated in 1991 as a part of a whitetopping project to study the effectiveness of various techniques to enhance bond strength between a new portland cement concrete (PCC) overlay and an existing asphalt cement concrete (ACC) pavement surface. A 1,676 m (5,500 ft) section of county road R16 in Dallas County was divided into 12 test sections. The various techniques used to enhance bond were power brooming, power brooming with air blast, milling, cement and water grout, and emulsion tack coat. Also, two sections were planed to a uniform cross-section, two pavement thicknesses were placed, and two different concrete mix proportions were used. Bond strength was perceived to be the key to determining an appropriate design procedure for whitetopping. If adequate bond is achieved, a bonded PCC overlay technique can be used for design. Otherwise, an unbonded overlay procedure may be more appropriate. Conclusions are as follows: (1) Bond Strength Differences - Milling increased bond strength versus no milling. Tack coat showed increased bond strength versus no tack coat. Planing, Air Blast and Grouting did not provide noticeable improvements in bond strength; nor did different PCC types or thicknesses affect bond strength significantly. (2) Structure - Structural measurements correlated strongly with the wide variation in pavement thicknesses. They did not provide enough information to determine the strength of bonding or the level of support being provided by the ACC layer. Longitudinal cracking correlated with PCC thicknesses and with planing. (3) Bond Over Time - The bond between PCC and ACC layers is degrading over time in the outside wheel path in all of the sections except tack coat (section 12). The bond strength in the section with tack coat was lower than the others, but remained relatively steady.

Asphalt Emulsions for Highway Construction, HR-216, 1985

A 5.8 mile section of Dubuque County (Iowa) Road D-53 was selected for this project, the objective of which were to: 1. identify a cost effective asphalt emulsion bound macadam typical cross section; 2. determine the effectiveness of engineering fabric placed under macadam roadbeds; and 3. evalaute the use of emulsions in surface seal coats. A number of conclusions were reached: 1. The minus #200 sieve material for the macadam stone should be held to a minimum. For the emulsion used on this project, the minus #200 material had less than 4 percent to achieve satisfactory coating of the macadam stone. 2. The placement of the emulsion treated macadam required no additional equipment or time than the plain macadam placement. 3. Emulsion treating the macadam stone for the shoulder base appears unnecessary. 4. The emulsion treated macadam base beneath an asphaltic concrete wearing surface yielded a higher structural rating than the plain macadam beneath a comparable ashaltic concrete surface. 5. The performance of the fabric between the subgrade and the macadam base to prevent soil intrusion into the base could not be determined by the non-destructive testing conducted. 6. When no choke stone is used over the macadam base, allowance for ac mix overrun should be made. 7. Use of an emulsion instead of a cutback asphalt saved money and energy. However, the poor performance of the seal coat negated any real savings.

Thin Maintenance Surfaces - Phase II, TR-435, 2003

In recent years there has been renewed interest in using preventive maintenance techniques to extend pavement life and to ensure low life cycle costs for our road infrastructure network. Thin maintenance surfaces can be an important part of a preventive maintenance program for asphalt cement concrete roads. The Iowa Highway Research Board has sponsored Phase Two of this research project to demonstrate the use of thin maintenance surfaces in Iowa and to develop guidelines for thin maintenance surface uses that are specific to Iowa. This report documents the results of test section construction and monitoring started in Phase One and continued in Phase Two. The report provides a recommended seal coat design process based on the McLeod method and guidance on seal coat aggregates and binders. An update on the use of local aggregates for micro-surfacing in Iowa is included. Winter maintenance guidelines for thin maintenance surfaces are reported herein. Finally, Phase One's interim, qualitative thin maintenance surface guidelines are supplemented with Phase two's revised, quantitative guidelines. When thin maintenance surfaces are properly selected and applied, they can improve the pavement surface condition index and the skid resistance of pavements. For success to occur, several requirements must be met, including proper material selection, design, application rate, workmanship, and material compatibility, as well as favorable weather during application and curing. Specific guidance and recommendations for many types of thin maintenance surfaces and conditions are included in the report.

Evaluation of Cover Aggregate Stripping Characteristics, HR-182, 1979

The purpose of Research Project HR-182 was to identify those aggregate types which would perform satisfactorily as seal coat aggregates. Aggregates were chosen from across the State to represent the various types normally encountered and were used with two different types of binder bitumens. A water spray treatment was also included to simulate the effects of rainfall. The evaluation was based upon aggregate retention. Due to the influence of unexpected variables upon the field samples, the laboratory data are reliable for only the most general observations. Namely, that gravels as a group appear to be retained better than carbonates and rain-fall shortly after seal coat placement can affect aggregate retention. The subsequent field observations and analysis of skid resistance data permit the following conclusions: 1. Aggregate retention is influenced by lithologic type with the gravels, quartzite, haydite, dolomites, and medium grained limestones performing best. 2. Aggregate retention is not influenced by binder bitumen type. 3. Friction values of seal coats are influ-enced by aggregate retention and/or lithologic type. The following recommendations have been determined: The aggregate used for cover aggregate/seal coat projects should be Type 4 or better skid resistance as identified in Iowa DOT Materials Instructional Memorandum T-203. This will result in maximizing the possibility of good aggregate retention and skid resistance.

Investigation of Field Corrosion Performance and Bond/Development Length of Galvanized Reinforcing Steel, TR-666, 2014

In reinforced concrete systems, ensuring that a good bond between the concrete and the embedded reinforcing steel is critical to long-term structural performance. Without good bond between the two, the system simply cannot behave as intended. The bond strength of reinforcing bars is a complex interaction between localized deformations, chemical adhesion, and other factors. Coating of reinforcing bars, although sometimes debated, has been commonly found to be an effective way to delay the initiation of corrosion in reinforced concrete systems. For many years, the standard practice has been to coat reinforcing steel with an epoxy coating, which provides a barrier between the steel and the corrosive elements of water, air, and chloride ions. Recently, there has been an industry-led effort to use galvanizing to provide the protective barrier commonly provided by traditional epoxy coatings. However, as with any new structural product, questions exist regarding both the structural performance and corrosion resistance of the system. In the fall of 2013, Buchanan County, Iowa constructed a demonstration bridge in which the steel girders and all internal reinforcing steel were galvanized. The work completed in this project sought to understand the structural performance of galvanized reinforcing steel as compared to epoxy-coated steel and to initiate a long-term corrosion monitoring program. This work consisted of a series of controlled laboratory tests and the installation of a corrosion monitoring system that can be observed for years in the future. The results of this work indicate there is no appreciable difference between the bond strength of epoxy-coated reinforcing steel and galvanized reinforcing steel. Although some differences were observed, no notable difference in either peak load, slip, or failure mode could be identified. Additionally, a long-term monitoring system was installed in this Buchanan County bridge and, to date, no corrosion activity has been identified.

Portland Cement Concrete Curing Compound Performance Phase I and Phase II, MLR-02-03, 2003

Testing the efficiency of Portland Cement Concrete (PCC) curing compounds is currently done following Test Method Iowa 901-D, May 2002. Concrete test specimens are prepared from mortar materials and are wet cured 5 hours before the curing compound is applied. All brands of curing compound submitted to the Iowa Department of Transportation are laboratory tested for comparative performance under the same test conditions. These conditions are different than field PCC paving conditions. Phase I tests followed Test Method Iowa 901-D, but modified the application amounts of the curing compound. Test results showed that the application of two coats of one-half thickness each increased efficiency compared to one full thickness coat. Phase II tests also used the modified application amounts, used a concrete mix (instead of a mortar mix) and applied curing compound a few minutes after molding. Measurements of losses, during spraying of the curing compound, were noted and were found to be significant. Test results showed that application amounts, testing techniques, concrete specimen mix design and spray losses do influence the curing compound efficiency. The significance of the spray losses indicates that the conventional test method being used (Iowa 901 D) should be revised.

Penetration Characteristics of Asphalt in a Recycled Mixture, MLR-79-03, 1979

Samples of both recycled and nonrecycled asphaltic concrete were extracted in increments by the Abson Recovery Method and the penetration of the asphalt from each increment determined. The recycled projects were plantsite operations containing various amounts of virgin gravel. Cored samples were taken from the pavements on Kossuth County roads that were constructed as recycled projects in 1975, 1976, and 1977. Cored samples were also taken from a Kossuth County paving project done in 1975, that was not recycled. Comparison mix samples from 1978 construction projects in Marshall and Woodbury Counties of non - recycled projects are included. The test data from the penetrations of the recovered asphalt indicates that mixing of the old and new asphalt occurs very extensively in the hot recycling process. In laboratory controlled conditions it is difficult to coat aggregates with different penetration asphalts and prevent them from mixing.

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.

Hydro-Surface Preparation and Coating for Painted Structural Steel, TR-407, 1999

Cities and counties in Iowa have more than 8,890 steel bridges, most of which are painted with red lead paint. The Iowa Department of Transportation (Iowa DOT) maintains less than 35 bridges coated with red lead paint, including seven of the large border bridges over the Mississippi and Missouri Rivers. Because of the federal and state regulations for bridge painting, many governmental agencies have opted not to repaint, or otherwise maintain, lead paint coatings. Consequently, the paint condition on many of these bridges is poor, and some bridges are experiencing severe rusting of structural members. This research project was developed with two objectives: 1) to evaluate the effectiveness of preparing the structural steel surface of a bridge with high pressure water jetting instead of abrasive blasting and 2) to coat the structural steel surface with a moisture-cured polyurethane paint under different surface preparation conditions.

Bond Contribution to Whitetopping Performance on Low Volume Roads, Construction Report, HR-341, 1993

This research was initiated in 1991 as a part of a whitetopping project to study the effectiveness of various techniques to enhance bond strength between a new Portland cement concrete (PCC) overlay and an existing asphalt cement concrete (ACC) pavement surface. A 1,676 m (5,500 ft) section of county road R16 in Dallas County, Iowa was divided into 12 test sections. The various techniques used to enhance bond were power brooming, power brooming with air blast, milling, cement and water grout, and emulsion tack coat. As a part of these bonding techniques, two pavement thicknesses were placed; two different concrete proportions were used; and two sections were planed to a uniform cross-slope.