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.

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.

Reinforced Slope with Geogrids, HR-548, 1997

The objective of this research study is to evaluate the performance, maintenance requirements and cost effectiveness of constructing reinforced slope along a concrete bikeway overpass with a Geogrid system such as manufactured by Tensar Corporation or Reinforced Earth Company. This final report consists of two separate reports - construction and performance. An earlier design report and work plan was submitted to the Iowa DOT in 1989. From the Design Report, it was determined that the reinforced slope would be the most economical system for this particular bikeway project. Preliminary cost estimates for other design alternatives including concrete retaining walls, gabions and sheet pile walls ranged from $204/L.F. to $220/L.F. The actual final construction cost of the reinforced slope with GEDGRIDS was around $112/L.F. Although, since the reinforced slope system was not feasible next to the bridge overpass because of design constraints, a fair cost comparison should reflect costs of constructing a concrete retaining wall. Including the concrete retaining wall costs raises the per lineal foot cost to around $122/L.F. In addition to this initial construction cost effectiveness of the reinforced slope, there has been little or no maintenance needed for this reinforced slope. It was noted that some edge mowing or weed whacking could be done near the concrete bikeway slab to improve the visual quality of the slope, but no work has been assigned to city crews. It was added that this kind of weed whacking over such steep slope is more difficult and there could possibly be more potential for work related injury. The geogrid reinforced slope has performed really well once the vegetation took control and prevented soil washing across the bikeway slab. To that end, interim erosion control measures might need to be considered in future projects. Some construction observations were noted. First, there i s no specialized experience or equipment required for a contractor to successfully build a low-to-medium geogrid reinforced slope structure. Second, the adaptability of the reinforced earth structure enables the designer to best fit the shape of the structure to the environment and could enhance aesthetic quality. Finally, a reinforced slope can be built with relatively soft soils provided differential settlements between facing are limited to one or two percent.

Longitudinal Grinding and Transverse Grooving to Improve Frictional and Profile Properties, HR-1035, 1983

There are many miles of portland cement concrete pavement in Iowa that due to normal wear, and in some cases accelerated wear from studded tires, the surface has become polished resulting in less than desirable friction values. Retexturing the surface may be an economical way to re-establish desirable friction values. Retexturing by grinding with diamond blades and transverse grooving with diamond blades are two methods of rehabilitating p.c.c. surfaces. MU Inc. of Lebanan, Tennessee proposed to provide without charge to the Iowa Department of Transportation, one 1500 ft x 12 ft section each of three methods of texturing. They are longitudinal grinding, transverse grooving and longitudinal grinding followed by transverse grooving. A section of 1500 feet is needed to properly evaluate a texturing method. It was decided by Iowa DOT personnel that due to possible differential friction it would be undesirable to texture only one lane. The decision was made to do test sections of 1500 ft x 24 ft with the cost of the additional texturing paid by the Iowa DOT. Iowa also has areas where the p.c.c. pavement has faulted at the joints and cracks which results in poor riding quality. Methods of correcting the faulting are to underseal the pavement where needed and/or grinding the surface to eliminate the faulted areas. It was decided to include in this research project a section for profiling by grinding.

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.

Portland Cement Concrete Utilizing Recycled Pavement, MLR-77-3, 1977

Two objectives were involved in this recycling project: To determine if the asphalt concrete surfacing from an existing roadway could be removed, the existing portland cement concrete pavement broken, removed, crushed to 1-1/2 inch minus, proportioned through a conventional central mix proportioning plant with the addition of concrete sand, and placed with a conventional slipform paver; and to determine if a two course, composite pavement, each course of different mix proportions, could be placed monolithically with conventional slipform equipment after being proportioned and mixed in a conventional central mix plant. The project was completed with no major problem. The objectives were satisfactorily met. The project was a success to the degree that the Iowa D.O.T. is proceeding with at least two projects for the 1977 construction season that will utilize the old pavement as appregate for the new pavement.

Effect of Grooved Concrete on Curing Efficiency, MLR-83-4, 1983

The textured concrete surface on all PCC primary paving projects (and when specified on secondary projects) is required to be grooved in a specified manner. The laboratory test for determining the efficiency index of concrete curing compounds is made on slabs that are not grooved. This short investigation was undertaken to determine any changes in the curing efficiency index when using various rates of application of curing compound on grooved concrete. Currently a 95 percent curing efficiency index is specified at an application rate of 15 square yards per gallon. Can this efficiency be achieved, and if so at what application rate, on grooved concrete? Grooving the concrete greatly increases the surface area and also causes the liquid curing compound to run off the high spots and collect in the grooves.

Determination of Tension Crack Development in Plastic P.C. Concrete with Retarding Admixtures, MLR-86-12, 1987

Bridge deck cracking occasionally occurs during construction for any number of reasons. Improper design, concrete placement or deck curing can result in cracks. One contributing factor toward cracking may be dead load deflections induced during concrete placement. For both continuous and non-continuous bridges, specific placement sequences are required to minimize harmful deflections in previously placed sections. Set retarding admixtures are also used to keep previously placed concrete plastic until the pour is completed. The problem is--at what point does movement of the concrete cause permanent damage to the deck. The study evaluated the time to crack formation relationship for mixes with low and high dosages of set retarding admixtures currently approved for use in Iowa state and county projects.

Deicing Salt Corrosion with and without Inhibitors, MLR-87-8, 1989

Chloride ion penetration through concrete to reinforcing steel is causing the premature deterioration of numerous bridge decks in Iowa. The purpose of the research reported in this paper was to determine whether any of several additives or alternative deicing chemicals could inhibit corrosion of reinforcing steel. The deicers tested were calcium magnesium acetate (CMA), CMA plus NaCl (NaCl: sodium chloride), Quicksalt plus PCI, and CG-90, a polyphosphate solution being developed by Cargill. Two tests were established. First, steel coupons were placed in a 15% solution of a deicer and distilled water to determine which alternative deicer would cause the least amount of corrosion in solution. The coupons were weighed periodically to determine each coupon's weight loss from corrosion. The second test involved ponding a 15% solution of each material on reinforced concrete blocks. Weekly copper-copper sulfate electrical half-cell (CSE) potential readings were taken on each block to determine whether corrosive activity was occurring at the steel surface. When the ponding research was concluded, concrete samples were taken from one of the three blocks ponded with each deicer. The samples were used to determine the chloride ion content at the level of the steel. Results show that all the deicers were less corrosive than NaCl. Only pure CMA, however, significantly inhibited the corrosion of steel embedded in concrete.

Gradation Analysis of Cold Feed and Extracted Bituminuous Mix Samples, MLR-88-2, 1988

Since 1987, the Iowa Department of Transportation has based control of hot asphalt concrete mixes on cold feed gradations. This report presents results of comparisons between cold feed gradations and gradations of aggregate from the same material after it has been processed through the plant and laydown machine. Results are categorized based on mix type, plant type, and method of dust control, in an effort to quantify and identify the factors contributing to those changes. Results of the report are: 1. From the 390 sample comparisons made, aggregate degradation due to asphalt plant processing was demonstrated by an average increase of +0.7% passing the #200 sieve and an average increase in surface area of +1.8 sq. ft. per pound of aggregate. 2. Categories with Type A Mix or Recycling as a sorting criteria generally produced greater degradation than categories containing Type B Mixes and/or plants with scrubbers. 3. None of the averages calculated for the categories should be considered unacceptably high, however, it is information that should be considered when making mix changes in the field, selecting asphalt contents for borderline mix designs, or when evaluating potential mix gradation specification or design criteria changes.

A Study on the Use of Fabric to Retard Reflective Cracking Over Widened Joints, MLR-88-4, 1992

Reflective cracking of asphalt resurfacing has been a concern for a long time. Years ago wire mesh was used to control widening cracks. More recently it has been fabrics or fiberglass. In 1986, part of the proposed fabric was deleted from projects in different parts of Iowa with various histories and designs. These projects were monitored in 1988, 1989, 1990 and 1992 with only the thin (3 inch) overlays on newly widened pavements showing a significantly greater percentage of cracks in the areas where the fabric was deleted.

Vibration Study for Consolidation of Portland Cement Concrete, MLR-95-4, 1999

The Iowa Department of Transportation has noticed an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements can be observed in several sections of PCC highways across the state of Iowa. Also, excessive vibration is believed to be a factor in the premature deterioration of several pavements in Iowa. To address the problem of excessive vibration, a research project was conducted to document the vibratory practices of PCC slipform paving in Iowa and determine the effect of vibration on the air content of pavement. The primary factors studied were paver speed, vibrator frequency, and air content relative to the location of the vibrator. The study concluded that the Iowa Department of Transportation specification of 5000 and 8000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds observed on the three test paving projects. Excessive vibration was clearly identified on one project where a vibrator frequency was found to be 12,000 vpm. When the paver speed was reduced to half the normal speed, hard air contents indicated that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8000 vpm. Analysis of variance testing indicated many variables and interactions to be significant at a 95% confidence level; however, the variables and interactions that were found to be significant varied from project to project. This affirms the complexity of the process for consolidating PCC.

Vibration Study for Consolidation of Portland Cement Concrete, Preprint, MLR-95-4, 1997

The Iowa Department of Transportation has discovered an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements has been observed in several projects across the state. Overconsolidation is also believed to be a factor in acceleration of premature deterioration of at least two pavement projects in Iowa. To address the problem, a research project in 1995 documented the vibratory practices of PCC slipform paving in Iowa in order to determine the effect of vibration on consolidation and air content of pavement. Paver speed, vibrator frequency, and air content relative to the location of the vibrator were studied. The study concluded that the Iowa Department of Transportation specification of 5,000 to 8,000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds on the three projects that were examined. Excessive vibration was clearly identified on one project where a vibrator frequency of 12,000 vpm was discovered. When the paver speed was reduced to half the normal speed, hard air contents indicate that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8,000 vpm. The study also indicates that the radius of influence of the vibrators is smaller than has been claimed.