Performance of a Nongrouted Thin Bonded PCC Overlay, HR-291, 1992

The use of a thin bonded concrete overlay atop an older surface has been widely incorporated for pavement rehabilitation in Iowa since the early 70's. Two test sections were constructed in 1985 on county road T61 on the Monroe-Wapello County line without the use of grout as a bonding agent to determine if adequate bond could be achieved and structural capacity uncompromised. Both test sections have performed well with one section having higher bond strengths, lower roughness values, higher structural capacity, and less debonding at the joints than the other section. Overall, both ungrouted sections have performed well under substantial truck traffic with minimal surface distress. More attention should be given, however, to rectifying apparent debonding at the joints when no grout is used as a bonding agent.

Validation of Design Recommendations for Integral Abutment Piles, HR-292, 1989

Since integral abutment bridges decrease the initial and maintenance costs of bridges, they provide an attractive alternative for bridge designers. The objective of this project is to develop rational and experimentally verified design recommendations for these bridges. Field testing consisted of instrumenting two bridges in Iowa to monitor air and bridge temperatures, bridge displacements, and pile strains. Core samples were also collected to determine coefficients of thermal expansion for the two bridges. Design values for the coefficient of thermal expansion of concrete are recommended, as well as revised temperature ranges for the deck and girders of steel and concrete bridges. A girder extension model is developed to predict the longitudinal bridge displacements caused by changing bridge temperatures. Abutment rotations and passive soil pressures behind the abutment were neglected. The model is subdivided into segments that have uniform temperatures, coefficients of expansion, and moduli of elasticity. Weak axis pile strains were predicted using a fixed-head model. The pile is idealized as an equivalent cantilever with a length determined by the surrounding soil conditions and pile properties. Both the girder extension model and the fixed-head model are conservative for design purposes. A longitudinal frame model is developed to account for abutment rotations. The frame model better predicts both the longitudinal displacement and weak axis pile strains than do the simpler models. A lateral frame model is presented to predict the lateral motion of skewed bridges and the associated strong axis pile strains. Full passive soil pressure is assumed on the abutment face. Two alternatives for the pile design are presented. Alternative One is the more conservative and includes thermally induced stresses. Alternative Two neglects thermally induced stresses but allows for the partial formation of plastic hinges (inelastic redistribution of forces). Ductility criteria are presented for this alternative. Both alternatives are illustrated in a design example.

Experimental Project No. 621, Pavement Instrumentation, HR-293, 1992

This document contains a discussion of the reasons why the project did not succeed. A detailed discussion of the steps taken by the Iowa Department of Transportation to make the experiment work are contained in this document, along with recommendations for future projects.

Ammonium Phosphate/Fly Ash Road Base Construction, HR-294, 1993

The objective of this research project was to evaluate the construction and service performance of ammonium phosphate/fly ash (APFA) treated base courses of crushed fines and/or unprocessed sand. Specific test results related to construction of the test sections were included in the 1987 construction report by Iowa State University. The performance of the experimental sections is dealt with in this final report. This 1986 project demonstrated that in all cases the control sections utilizing a Type B base experienced dramatically less cracking in the surface than the APFA treated base sections. The cost per mix and subsequent surface maintenance costs for the APFA base sections, especially those having a substantial amount of limestone, were higher than the Type B base control sections. This type of construction may prove to be economical only when petroleum product costs escalate.

Laboratory Study of Slurry Seal Coats, HR-185, Revised, 1978

Extensive programmed laboratory tests involving some 400 asphalt emulsion slurry seals (AESS) were conducted. Thirteen aggregates including nine Iowa sources, a quartzite, a synthetic aggregate (Haydite), a limestone stone from Nebraska, and a Chat aggregate from Kansas were tested in combination with four emulsions and two mineral fillers, resulting in a total of 40 material combinations. A number of meetings were held with the Iowa DOT engineers and 12 state highway departments that have had successful slurry seal experiences and records, and several slurry seal contractors and material and equipment suppliers were contacted. Asphalt emulsion slurry seal development, uses, characteristics, tests, and design methods were thoroughly reviewed in conjunction with Iowa's experiences through these meetings and discussions and through a literature search (covering some 140 articles and 12 state highway department specifications). It was found that, while asphalt emulsion slurry seals (when properly designed and constructed) can economically improve the quality and extend the life of existing pavement surface, experiences with them had been mixed due to the many material, slurry, and construction variables that affect their design, construction, and performance. The report discusses those variables identified during the course of the project and makes recommendations concerning design procedures, design criteria, specifications and the means of evaluating them.

Reducing the Adverse Effects of Transverse Cracking, HR-217, 1984

This research was initiated to identify methods of reducing the occurrence of transverse cracking. Eight (four repetitive) research sections were established to study three variations in the asphalt concrete pavement. The first variation was the comparison of low- and high-temperature-susceptible asphalt cement (AC) from two different sources. The second variable was to saw and seal transverse joints at spacings varying from 40 to 100 ft. The third variable was to increase the AC content in the asphalt treated base by 1 percent. The research sections were constructed with relatively few problems. Crack and joint surveys have been conducted on all research sections at intervals of less than 1 year since construction. No cracking was identified after the first winter season. The sawed joints also remained sealed through the first winter. At an age of approximately 1 1/2 years there was substantial cracking of the high-temperature-susceptible AC sections and substantial failure of the sealant material in the sawed joints. After almost 4 years, the asphalt pavement constructed with the high-temperature-susceptible AC produced a crack interval of 35 ft, the low-temperature-susceptible AC yielded an interval of 170 ft, and the low-temperature-susceptible AC with an increased AC content yielded an interval of 528 ft. The Pen-Vis number is an effective measure of temperature susceptibility of asphalt cements. The frequency of transverse cracking is affected by the temperature susceptibility of the AC. An increased AC content also reduces the frequency of transverse cracking.

User's Manual for the County Road Evaluation Program - Volume I, HR-242, 1986

Provides instructions for using the computer program which was developed under the research project, "The Economics of Reducing the County Road System: Three Case Studies In Iowa". This program operates on an IBP personal computer with 300K storage. A fixed disk is required with at least 3 megabytes of storage. The computer must be equipped with DOS version 3.0; the programs are written in Fortran. The user's manual describes all data requirements including network preparation, trip information, cost for maintenance, reconstruction, etc. Program operation instructions are presented, as well as sample solution output and a listing of the computer programs.

Bridge Deck Delamination Study Infrared Inspection, HR-244, 1982

The Iowa Department of Transportation is responsible for maintaining approximately 3800 bridges throughout the State. Of these bridges approximately 3200 have concrete decks. The remaining bridges have been constructed or repaired with a Portland Cement (P. C.) concrete overlay. Surveys of the overlays have indicated a growing incidence of delaminations and surface distress. The need to replace or repair the overlay may be dictated by the amount of delamination in the deck. Additionally, the concrete bridges are periodically inspected and scheduled for the appropriate rehabilitation. Part of this analysis is an assessment of the amount of delamination present in the deck. The ability to accurately and economically identify delamination in overlays and bridge decks is necessary to cost-effectively evaluate and schedule bridge rehabilitation. There are two conventional methods currently being used to detect delaminations. One is ref erred to as a chain drag method. The other a electro-mechanical sounding method (delamtect). In the chain drag method, the concrete surface is struck using a heavy chain. The inspector then listens to the sound produced as the surface is struck. The delaminated areas produce a dull sound as compared to nondelaminated areas. This procedure has proved to be very time consuming, especially when a number of small areas of delamination are present. With the · electro-mechanical method, the judgement of the inspector has been eliminated. A· device with three basic components, a tapping device, a sonic receiver, and a system of signal interpretation has been developed. This· device is wheeled along the deck and the instrument receives and interprets the acoustic signals generated by the instrument which in turn are reflected through the concrete. A recently developed method of detecting delaminations is infrared thermography. This method of detection is based on the difference in surface temperature which exists between delaminated and nondelaminated concrete under certain atmospheric conditions. The temperature difference can reach 5°C on a very sunny day where dry pavement exists. If clouds are present, or the pavement is wet, then the temperature difference between the delaminated and nondelaminated concrete will not be as great and therefore more difficult to detect. Infrared thermography was used to detect delaminations in 17 concrete bridge decks, 2 P. C. concrete overlays, and 1 section of continuously reinforced concrete pavement (CRCP) in Iowa. Thermography was selected to assess the accuracy, dependability, and potential of the infrared thermographic technique.

Experimental Use of Calcium Magnesium Acetate, HR-253, 1983

The Iowa Department of Transportation Materials Laboratory personnel announced in early 1982 a process to produce a road deicer consisting of sand grains coated with calcium magnesium acetate (CMA). From that point forward the Iowa DOT began searching for a means of economically producing CMA to their concept. During 1983 and 1984 the first attempts devised for commercially producing CMA were attempted by the W.G. Block Company, Davenport, Iowa, under Iowa Highway Research Board Project HR-253. This first attempt at commercially producing CMA was accomplished by the use of concrete transit mixer equipment. Even though this procedure proved successful in the batch mixing of CMA, the need for higher production rates to reduce the cost per ton still existed. During the fall of 1984, Cedarapids Inc, Cedar Rapids, Iowa, proposed to Iowa DOT personnel the application of their technology to a continuous mixing concept for CMA. Arrangements were made for the continuous test mixing of 60 to 100 tons of CMA/sand deicer. This report covers the production effort, description and results of procedures outlined in Cedarapids Inc's proposal of September 19, 1984. The objectives of this research were: 1. To produce the CMA/sand deicer concept on a continuous mixing basis to Iowa DOT CMA concentration levels. 2. To evaluate the results of preheating the carrying vehicle (sand) prior to CMA ingredient introduction. 3. To analyze the feasibility of production equipment and procedures necessary for portable and/or stationary applications of continuous mixing concepts.

Bridge Deck Repair Using Epoxy Resin, HR-177, 1979

Research funds were approved for the purchase of equipment designed to proportion and inject epoxy resins into delaminated areas of bridge decks. Through investigation and refining of this process, it was anticipated that a maintenance procedure would be developed to delay spalling of bridge decks by "gluing down" delaminated areas before spalling occurred.

Evaluation of Fly Ash in Portland Cement Concrete Pavement in Monona County, Iowa, HR-200, 1980

The primary objectives of this research project were: 1. Determine and recommend solutions for problems relating to shipping, storing and batching of fly ash. 2. Establish a procedure for batching, mixing and placing uniform concrete with specified air content and consistency. 3. Demonstrate that concrete of comparable quality can be produced.

Evaluation of Calcium Magnesium Acetate Deicer in Scott County, HR-253, Progress Report, 1987

The field testing of the noncorrosive alternative deicing agent, calcium magnesium acetate is described. Seventy three tons were produced of one part CMA and three parts sand deicer which was field tested on I-280 from I-80 to the Mississippi River (7,000 ADT with 50% trucks). A comparative application was made with one part sand and one part sodium chloride. The study found that CMA deicer required a longer time for the pavement to reach normal conditions, and 20-25% more CMA deicer to provide the desired deicing. It was concluded that the CMA deicer was not as dependable as the sodium chloride deicing agent, and it was more difficult to clean up the equipment for spreading the CMA deicer.

Innovative Leak Test for Pavement Joint Seals, Progress Report, HR-318, 1993

Premature failure of concrete pavement contraction joint seals is an ongoing and costly problem for the Iowa Department of Transportation. Several joint seal test sections consisting of variations in sawing methods, joint cleaning techniques, sealant installation, and sealant types have been established over the past few years. Laboratory analysis and field inspections were done as a part of the tests, and core samples were taken for laboratory adhesion pull tests. Such methods often cover specifically small areas and may not expose hidden failures. Some tests are also labor-intensive and destructive, especially that of coring. An innovative, nondestructive, broad coverage joint seal tester that yields quick results has been designed and developed for evaluation of pavement joint seal performance. The Iowa vacuum joint seal tester (IA-VAC) applies a low vacuum above a joint seal that has been spray-covered with a foaming water solution. Any unsealed area or leak that exists along the joint will become quickly and clearly visible by the development of bubbles at the leak point. By analyzing the results from the IA-VAC tests, information on the number and types of leaks can be obtained; such information will help identify the source of the problem and direct efforts toward a solution.

Use of Longitudinal Subdrains in the 3R Program, HR-509, Progress Report #2, 1981

The main consideration for base construction under the pavement, in the design of Iowa's interstate, was structural capacity. The material was dense graded with the aim of supporting the pavement and distributing the load as it is transferred to the underlying grade. The drainage characteristics of the base was apparently not given adequate consideration. On jointed portland cement concrete pavement, the water that is trapped immediately beneath the pavement causes severe problems. The traffic causes rapid movement of the water resulting in the hydraulic pressures or "pumping" (movement and redeposit of base fine material), further resulting in faulting between individual slabs. The objective of this evaluation is to determine if longitudinal subdrains are effective in preventing or reducing pumping, faulting and related deterioration. Results suggest that, based upon the flow from the outlets observed during periodic checks and evidence of water flow at the outlets, it appears that to date the subdrains are effective in draining the subbase and subgrade. Because of the limited data available at this time, however, the pavement condition and faulting results are inconclusive.

High Molecular Weight Methacrylate Sealing of a Bridge Deck, HR-2031, 1988

The Iowa Department of Transportation used a high molecular weight methacrylate (HMWM) resin to seal a 3,340 ft. x 64 ft. bridge deck in October 1986. The sealing was necessary to prevent deicing salt brine from entering a substantial number of transverse cracks that coincided with the epoxy coated top steel and unprotected bottom steel. HMWM resin is a three component product composed of a monomer, a cumene hydroperoxide initiator and a cobalt naphthenate promoter. The HMWM was applied with a dual spray bar system and flat-fan nozzles. Initiated monomer delivered through one spray bar was mixed in the air with promoted monomer from the other spray bar. The application rate averaged 0.956 gallons per 100 square feet for the tined textured driving lanes. Dry sand was broadcast on the surface at an average coverage of 0.58 lbs. per square yard to maintain friction. Coring showed that the HMWM resin penetrated the cracks more than two inches deep. Testing of the treated deck yielded Friction Numbers averaging 33 with a treaded tire compared to 36 prior to treatment. An inspection soon after treatment found five leaky cracks in one of the 15 spans. One inspection during a steady rain showed no leakage, but leakage from numerous cracks occurred during a subsequent rain. A second HMWM application was made on two spans. Leakage through the double application occurred during a rain. Neither the single or double application were successful in preventing leakage through the cracks.