Evaluation of Deterioration on US 20 in Webster County, MLR-91-1, 1991

Ten miles of U.S. Highway 20 in Webster County began to show deterioration in 1990. Any deterioration was unexpected, since the road was just constructed in 1986 and 1987. The deterioration looked much like the staining and cracking of D-cracking. Cracking was found on 391 joints throughout the 10 mile four lane divided highway. Evaluation of cores from the project reveal low air contents at those locations where cracking is occurring. The cause of the low air contents can only be speculated on. A possible cause may be the vibration from the paver coupled with the additional vibration at the joints. Other projects constructed in 1986 and 1987 with the same equipment show no signs of distress.

Retrofit Methods for Distortion Cracking Problems in Plate Girder Bridges, TR-436, 2003

This report is formatted to independently present four individual investigations related to similar web gap fatigue problems. Multiple steel girder bridges commonly exhibit fatigue cracking due to out-of-plane displacement of the web near the diaphragm connections. This fatigue-prone web gap area is typically located in negative moment regions of the girders where the diaphragm stiffener is not attached to the top flange. In the past, the Iowa Department of Transportation has attempted to stop fatigue crack propagation in these steel girder bridges by drilling holes at the crack tips. Other nondestructive retrofits have been tried; in a particular case on a two-girder bridge with floor beams, angles were bolted between the stiffener and top flange. The bolted angle retrofit has failed in the past and may not be a viable solution for diaphragm bridges. The drilled hole retrofit is often only a temporary solution, so a more permanent and effective retrofit is required. A new field retrofit has been developed that involves loosening the bolts in the connection between the diaphragm and the girders. Research on the retrofit has been initiated; however, no long-term studies of the effects of bolt loosening have been performed. The intent of this research is to study the short-term effects of the bolt loosening retrofit on I-beam and channel diaphragm bridges. The research also addressed the development of a continuous remote monitoring system to investigate the bolt loosening retrofit on an X-type diaphragm bridge over a number of months, ensuring that the measured strain and displacement reductions are not affected by time and continuous traffic loading on the bridge. The testing for the first three investigations is based on instrumentation of web gaps in a negative moment region on Iowa Department of Transportation bridges with I-beam, channel, and X-type diaphragms. One bridge of each type was instrumented with strain gages and deflection transducers. Field tests, using loaded trucks of known weight and configuration, were conducted on the bridges with the bolts in the tight condition and after implementing the bolt loosening retrofit to measure the effects of loosening the diaphragm bolts. Long-term data were also collected on the X-diaphragm bridge by a data acquisition system that collected the data continuously under ambient truck loading. The collected data were retrievable by an off-site modem connection to the remote data acquisition system. The data collection features and ruggedness of this system for remote bridge monitoring make it viable as a pilot system for future monitoring projects in Iowa. Results indicate that loosening the diaphragm bolts reduces strain and out-of-plane displacement in the web gap, and that the reduction is not affected over time by traffic or environmental loading on the bridge. Reducing the strain in the web gap allows the bridge to support more cycles of loading before experiencing fatigue, thus increase the service life of the bridge. Two-girder floor beam bridges may also exhibit fatigue cracking in girder webs.

Impact of Deck Cracking on Durability, TR-405, 2000

Concrete bridge decks subjected to corrosive environment because of the application of de-icing chemical could deteriorate at a rapid rate. In an effort to minimize corrosion of the reinforcement and the corresponding delaminations and spalls, the Iowa Department of Transportation started using epoxy-coated rebars (ECR) in the top mat of reinforcing around 1976 and in both mats 10 years later. The overall objective of this research was to determine the impact of deck cracking on durability and estimate the remaining functional service life of a bridge deck. This was accomplished by conducting a literature review, visually inspecting several bridge decks, collecting and sampling test cores from cracked and uncracked areas of bridge decks, determining the extent to which epoxy-coated rebars deteriorate at the site of cracks, and evaluating the impact of cracking on service life.

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.

Strength-Temperature Study of Fly Ash Concrete, MLR-84-6, 1984

Class A, B, and C concrete paving mixes were tested for compressive strength at 40°F and 73°F, both with and without fly ash substitution for 15% of the portland cement. Two Class C ashes and one Class F ash from Iowa approved sources were examined in each mix. The purpose of the study was to provide data on cool weather strength development of concrete paving mixes utilizing Iowa materials. In all cases except one, the fly ash concretes exhibited lower 7 and 28- day compressive strengths at 40°F than control mixes. The continuation of the October 15 cut-off date for the use of fly ash concrete is recommended.

Correlation of Locally-Based Performance of Asphalts with their Physicochemical Parameters, Task 1 Report, HR-298, 1988

This is the first report of 6 tasks to be performed in an effort to establish locally-based quality and performance criteria for asphalts, and ultimately to develop performance-related specifications based on simple physicochemical methods. Three of the most promising chemical methods (high performance liquid chromatography (HPLC), thermal analysis, and X-ray diffraction were selected to analyze 4 different types of samples. The results will indicate the fundamental asphalt property variables that directly affect the field performance in Iowa. The details of the materials and procedures employed are described, and the results of the tests are presented.

Ultrathin Portland Cement Concrete Overlay Extended Evaluation, Construction Report, TR-432, 2000

In recent years, ultra-thin whitetopping (UTW) has evolved as a viable rehabilitation technique for deteriorated asphalt cement concrete (ACC) pavement. Numerous UTW projects have been constructed and tested, enabling researchers to identify key elements contributing to their successful performance. These elements include foundation support, interface bonding condition, portland cement concrete (PCC) overlay thickness, synthetic fiber reinforcement usage, joint spacing, and joint sealing. The interface bonding condition is the most important of these elements. It enables the pavement to act as a composite structure, thus reducing tensile stresses and allowing an ultra-thin PCC overlay to perform as intended. The Iowa Department of Transportation (Iowa DOT) UTW project (HR-559) initiated UTW in Iowa. The project is located on Iowa Highway 21 between Iowa Highway 212 and U.S. Highway 6 in Iowa County, near Belle Plaine, Iowa. The objective of this research was to investigate the interface bonding condition between an ultra-thin PCC overlay and an ACC base over time, considering the previously mentioned variables. This research lasted for five years, at which time it was extended an additional five years. The new phase of the project was initiated by removing cracked panels existing in the 2-inch thick PCC sections and replacing them with three inches of PCC. The project extension (TR 432) will provide an increased understanding of slab bonding conditions over a longer period, as well as knowledge regarding the behavior of the newly rehabilitated areas. In order to accomplish the goals of the project extension, Falling Weight Deflectometer (FWD) testing will continue to be conducted. Laboratory testing, field strain gage implementation, and coring will no longer be conducted. This report documents the planning and construction of the rehabilitation of HR 559 and the beginning of TR 432 during August of 1999.

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.

Accelerated Testing Track, HR-7, 1951

In May 1950 a proposal for a research project was submitted to the newly formed Iowa Highway Research Board for consideration and action. This project, designated RPSl by the Board, encompassed the study, development, preparation of preliminary plans and specifications for the construction of a wheel track to be used in the accelerated testing of highway pavements. The device envisioned in the proposal was a circular track about seventy-five feet in diameter equipped with a suitable automobile-tired device to test pavements about five feet in width laid into the track under regular construction practices by small scale construction equipment. The Board, upon review, revised and expanded the basic concepts of the project. The project as revised by the Board included a study of the feasibility of developing, constructing and operating an accelerated testing track in which pavements, bases and subgrades may be laid one full lane, or at least ten feet, in width by full size construction equipment in conformity with usual construction practices. The pavements so laid are to be subjected, during test, to conditions as nearly simulating actual traffic as possible.

Service Correlation of the Traffic Simulator, HR-100, 1967

A study was undertaken by the Bituminous Research Laboratory of the Engineering Research Institute at Iowa State University, under the sponsorship of the Iowa Highway Research Board, project HR 100, to ascertain the effects of a number of characteristics and properties of asphaltic concrete mixes upon the service behavior of the mixes as evaluated by the Traffic Simulator and by field observations. The study included: Investigations of the relations, of gradation, fraction and resistance to wear of aggregates; of stability, cohesion, per cent voids and asphalt content: of a number of laboratory and field mixes to service behavior as indicated by the Traffic Simulator under various test conditions. Based upon the results of the tests and the relationships noted, tentative criteria for the Traffic Simulator test were devised, subject to verification by observations and measurements of field service behavior of the mixes.

Soil Erosion Control for Secondary Roads, HR-155

Research project HR-155 was initiated to study soil erosion problems along the secondary road system in Iowa and to find a substitute for straw for the control of soil erosion during the period of seed establishment. Accordingly, six field research sites were established to test the ability of commercial soil conditioners to control soil erosion. The six field research sites were selected on the basis of terrain and type of soil material exposed on the cut-slope areas.

Experimental Use of Calcium Magnesium Acetate, Addendum, HR-253, 1984

The Iowa Department of Transportation Materials Laboratory personnel developed a process to produce a road deicer consisting of sand grains coated with calcium magnesium acetate (CMA). Research project HR-253 was established to explore commercial production of the CMA/sand deicer by an independent contractor. About 60 tons of the deicer was produced at a ready-mix concrete facility and evaluated in the field during the 1983-1984 winter season. The initial contracted production of CMA/sand deicer under research project HR-253 identified two major problems: (1) excessive unreacted lime in the final product, and (2) formation of spherical lumps within the product requiring subsequent size reduction. It was recommended in the HR-253 report that additional deicer be produced as a continuation of the project in order to address these problems and further develop the production process. A contract was negotiated with W. G. Block Co. to produce and deliver 50 tons of additional deicer. This addendum report covers this production effort including descriptions and results of all modifications of equipment and process procedures used.

Pavement Instrumentation, HR-293, 1988

The report documents the development and installation of an instrumented pavement on I-80 in Iowa for the purposes of demonstration and answering current pavement questions. Its two primary objectives include documentation of the installation and verification of existing design procedures through monitoring of the continuous traffic stream reactions in the pavement. Some 120 instruments were installed in a forty foot segment of reconstructed pavement. The instruments included concrete strain gages, weldable strain gages on dowels, LVDT-deflection gages and temperature sensors in the concrete and base material. Five tubes were placed under three joints and two midslabs to measure the relative moisture and density at the interface between the pavement and base with atomic equipment. The instruments were placed ahead of the paving and over 92% of the instruments responded after paving. Planning requirements, problems encountered and costs of installation are presented. The site will use piezoelectric cables in a weigh-in-motion arrangement to trigger the data collection, a microcomputer controlled data acquisition system to analyze multiple sensors simultaneously, and telemetry to monitor the site remotely. Details provide the first time user of instrumentation with valuable information on the planning, problems, costs and coordination required to establish and operate such a site.

Asphalt Cement Containing AC-13, HR-522, Construction Report, 1985

Stopping and turning maneuvers on high traffic volume asphalt cement concrete surfaced roads and streets often causes distortion of the pavement. Distortion may show up as excessive rutting in the wheel path, shoving of the pavement and/or rippling of the surface. Often times repeated corrective work such as cold milling or heater planing is required in these areas to maintain the pavement surface in a reasonable condition. In recent years polymer additives have been developed for asphalt cement concrete paving mixes that show promise in improving the inplace stability of the pavements. AC-13 (Styrelf 13) available from Bitucote Products Company, St. Louis, Missouri is an asphalt cement that has been modified by an additive to exhibit characteristics of very high stability in asphalt mixes.

Recycling of Cass County I-80 Asphalt Concrete, Progress Report, HR-1011, 1977

Approximately 40,000 tons of slightly damaged asphalt concrete has been removed from Interstate 80 in Cass and stockpiled. Laboratory tests had indicated that this material had 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 new material. Follow~up evaluations will be made to determine the effects of traffic and environment. Preliminary data indicate that plans should be made to incorporate the stockpiled material in projects near the stockpile site.