Evaluation of Microcracking and Chemical Deterioration in Concrete Pavements, October 31, 1995

The major objective of this research project was to investigate the chemistry and morphology of portland cement concrete pavements in Iowa. The integrity of the various pavements was evaluated qualitatively, based on the presence or absence of microcracks, the presence or absence of sulfate minerals, and the presence or absence of alkali-silica gel(s). Major equipment delays and subsequent equipment replacements resulted in significant delays over the course of this research project. However, all these details were resolved and the equipment is currently in place and fully operational. The equipment that was purchased for this project included: (I) a LECO VP 50, 12-inch diameter, variable speed grinder/polisher: (2) a Hitachi S-2460N variable pressure scanning electron microscope; and (3) a OXFORD Instruments Link ISIS microanalysis system with a GEM (high-purity germanium) X-ray detector. This study has indicated that many of the concrete pavements contained evidence of multiple deterioration mechanisms: and hence, the identification of a single reason for the distress that was observed in any given pavement typically had to be based on opinion rather than empirical evidence.

Evaluation of Microcracking and Chemical Deterioration in Concrete Pavements Final Report, October 31, 1995

The major objective of this research project was to investigate the chemistry and morphology of portland cement concrete pavements in Iowa. The integrity of the various pavements was evaluated qualitatively, based on the presence or absence of microcracks, the presence or absence of sulfate minerals, and the presence or absence of alkali-silica gel(s). Major equipment delays and subsequent equipment replacements resulted in significant delays over the course of this research project. However, all these details were resolved and the equipment is currently in place and fully operational. The equipment that was purchased for this project included: ( I ) a LECO VP 50, 12-inch diameter, variable speed grinder/polisher: (2) a Hitachi S-2460N variable pressure scanning electron microscope; and (3) a OXFORD Instruments Link ISIS microanalysis system with a GEM (high-purity germanium) X-ray detector. This study has indicated that many of the concrete pavements contained evidence of multiple deterioration mechanisms: and hence, the identification of a single reason for the distress that was observed in any given pavement typically had to be based on opinion rather than empirical evidence.

Evaluation of Low Cost Traffic Calming for Rural Communities – Phase II, April 2013

The main goal of the research described in this report was to evaluate countermeasures that agencies can use to reduce speeds as drivers enter rural communities located on high-speed roadways. The objectives of this study were as follows: * Identify and summarize countermeasures used to manage speeds in transition zones * Demonstrate the effectiveness of countermeasures that are practical for high- to low-speed transition zones * Acquire additional information about countermeasures that may show promise but lack sufficient evidence of effectiveness * Develop an application toolbox to assist small communities in selecting appropriate transition zones and effective countermeasures for entrances to small rural communities The team solicited small communities that were interested in participating in the Phase II study and several communities were also recommended. The treatments evaluated were selected by carefully considering traffic-calming treatments that have been used effectively in other countries for small rural communities, as well as the information gained from the first phase of the project. The treatments evaluated are as follows: * Transverse speed bars * Colored entrance treatment * Temporary island * Radar-activated speed limit sign * Speed feedback sign The toolbox publication and four focused tech briefs also cover the results of this work.

Age vs. Experience: Evaluation of a Video Feedback Intervention for Newly Licensed Teen Drivers, TPF-5(207), 2013

This project examines the effects of age, experience, and video-based feedback on the rate and type of safety-relevant events captured on video event recorders in the vehicles of three groups of newly licensed young drivers: 1. 14.5- to 15.5-year-old drivers who hold a minor school license (see Appendix A for the provisions of the Iowa code governing minor school licenses); 2. 16-year-old drivers with an intermediate license who are driving unsupervised for the first time; 3. 16-year-old drivers with an intermediate license who previously drove unsupervised for at least four months with a school license. METHODS: The young drivers’ vehicles were equipped with an event-triggered video recording device for 24 weeks. Half of the participants received feedback regarding their driving, and the other half received no feedback at all and served as a control group. The number of safety-relevant events per 1,000 miles (i.e., “event rate”) was analyzed for 90 participants who completed the study. RESULTS: On average, the young drivers who received the video-based intervention had significantly lower event rates than those in the control group. This finding was true for all three groups. An effect of experience was seen for drivers in the control group; the 16-year-olds with driving experience had significantly lower event rates than the 16-year-olds without experience. When the intervention concluded, an increase in event rate was seen for the school license holders, but not for either group of 16-year-old drivers. There is strong evidence that giving young drivers video-based feedback, regardless of their age or level of driving experience, is effective in reducing the rate of safety-relevant events relative to a control group who do not receive feedback. Specific comparisons with regard to age and experience indicated that the age of the driver did not have an effect on the rate of safety-events, while experience did. Young drivers with six months or more of additional experience behind the wheel had nearly half as many safety-relevant events as those without that experience.

Evaluation of Low Cost Traffic Calming for Rural Communities – Phase II [Updated], TR-630, October, 2013

The main goal of the research described in this report was to evaluate countermeasures that agencies can use to reduce speeds as drivers enter rural communities located on high-speed roadways. The objectives of this study were as follows: * Identify and summarize countermeasures used to manage speeds in transition zones * Demonstrate the effectiveness of countermeasures that are practical for high- to low-speed transition zones * Acquire additional information about countermeasures that may show promise but lack sufficient evidence of effectiveness * Develop an application toolbox to assist small communities in selecting appropriate transition zones and effective countermeasures for entrances to small rural communities The team solicited small communities that were interested in participating in the Phase II study and several communities were also recommended. The treatments evaluated were selected by carefully considering traffic-calming treatments that have been used effectively in other countries for small rural communities, as well as the information gained from the first phase of the project. The treatments evaluated are as follows: * Transverse speed bars * Colored entrance treatment * Temporary island * Radar-activated speed limit sign * Speed feedback sign The toolbox publication and four focused tech briefs also cover the results of this work.

A Further Evaluation of Concrete Bridge Deck Surfacing in Iowa, MLR-79-1, 1979

The Iowa Department of Transportation has overlaid 446 bridge decks with low slump dense concrete from 1964 through October 1978. The overall performance of these decks has been satisfactory. Nineteen bridges that were resurfaced with either low slump dense concrete (LSDC) or latex-modified concrete were analyzed for chloride content, electrical corrosion potential, delaminations or debonding, and deck surface condition. The resurfacing ages of these bridges range from 5 to 13 years. None of the bridges showed any evidence of surface distress and the chloride penetration into the resurfacing concrete is relatively low. There are delaminations in the original decks below the resurfacing on the majority of bridges examined. The delaminations are concluded to be caused by either (A) reinforcing steel corrosion, (B) not removing all delaminated concrete prior to placing the resurfacing concrete, or (C) creating an incipient fracture in the top surf ace of the original deck through the use of scarification equipment. The active corrosion of the reinforcing steel is predominately in the gutter line on the majority of bridges evaluated. Recommendations for future deck repairs include removal of concrete to the top layer of reinforcing steel in areas where an electrical corrosion potential of -0.35V or more is detected, providing more positive methods of locating delaminated concrete, and treating the curb and gutter line to reduce the potential damage from salt water.

Evaluation of Gap-Graded Asphalt Concrete Mixtures, Vol. 1. Physical Properties (Part I: Mechanical Properties), HR-157, Volume 1, 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper-combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100(d/D)^n is not justified. It is recommended that the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Evaluation of Gap-Graded Asphalt Concrete Mixtures Vol. 3. Appendix, HR-157, Volume 3 (Part 3), 1972 (1973)

This report presents the results of a comparative laboratory study between well- and gap-graded aggregates used in asphalt concrete paving mixtures. A total of 424 batches of asphalt concrete mixtures and 3,960 Marshall and Hveem specimens were examined. There is strong evidence from this investigation that, with proper combinations of aggregates and asphalts, both continuous- and gap-graded aggregates can produce mixtures of high density and of qualities meeting current design criteria. There is also reason to believe that the unqualified acceptance of some supposedly desirable, constant, mathematical relationship between adjacent particle sizes of the form such as Fuller's curve p = 100 (d/D)n is not justified. It is recommended that. the aggregate grading limits be relaxed or eliminated and that the acceptance or rejection of an aggregate for use in asphalt pavement be based on individual mixture evaluation. Furthermore, because of the potential attractiveness of gap-graded asphalt concrete in cost, quality, and skid and wear resistance, selected gap-graded mixtures are recommended for further tests both in the laboratory and in the field, especially in regard to ease of compaction and skid and wear resistance.

Field Evaluation of Engineering Fabrics for Asphalt Concrete Resurfacing - Audubon County, HR-360, Final Report, 2001

An 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. • ProGuard, Phillips Fiber Corporation The data indicated a statistically significant decrease in reflective crack formation in the ProGuard fabric sections compared to control. There was little evidence of a similar effect from the PavePrep fabric sections compared to control. However, the rate of cracking (the rate of formation of new cracks) for both fabrics and control tended to be similar after three years. The benefits of using these fabrics (possible delay of some crack formation by two years) on this project did not outweigh the costs of up to $4200.00 per mile.

Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials, HR-1069, 2003

Transverse joints are placed in portland cement concrete pavements to control the development of random cracking due to stresses induced by moisture and thermal gradients and restrained slab movement. These joints are strengthened through the use of load transfer devices, typically dowel bars, designed to transfer load across the joint from one pavement slab to the next. Epoxy coated steel bars are the materials of choice at the present time, but have experienced some difficulties with resistance to corrosion from deicing salts. The research project investigated the use of alternative materials, dowel size and spacing to determine the benefits and limitations of each material. In this project two types of fiber composite materials, stainless steel solid dowels and epoxy coated dowels were tested for five years in side by side installation in a portion of U.S. 65 near Des Moines, Iowa, between 1997 and 2002. The work was directed at analyzing the load transfer characteristics of 8-in. vs. 12-in. spacing of the dowels and the alternative dowel materials, fiber composite (1.5- and 1.88-in. diameter) and stainless steel (1.5-in. diameter), compared to typical 1.5-in. diameter epoxy-coated steel dowels placed on 12-in. spacing. Data were collected biannually within each series of joints and variables in terms of load transfer in each lane (outer wheel path), visual distress, joint openings, and faulting in each wheel path. After five years of performance the following observations were made from the data collected. Each of the dowel materials is performing equally in terms of load transfer, joint movement and faulting. Stainless steel dowels are providing load transfer performance equal to or greater than epoxy-coated steel dowels at the end of five years. Fiber reinforced polymer (FRP) dowels of the sizes and materials tested should be spaced no greater than 8 in. apart to achieve comparable performance to epoxy coated dowels. No evidence of deterioration due to road salts was identified on any of the products tested. The relatively high cost of stainless steel solid and FRP dowels was a limitation at the time of this study conclusion. Work is continuing with the subject materials in laboratory studies to determine the proper shape, spacing, chemical composition and testing specification to make the FRP and stainless (clad or solid) dowels a viable alternative joint load transfer material for long lasting portland cement concrete pavements.

Evaluation of Iowa's Driver Improvement Program, 2009

This study examines the effectiveness of Iowa’s Driver Improvement Program (DIP), measured as the reduction in the number of driver convictions subsequent to the DIP. The analysis involved a random sample of 9,055 drivers who had been instructed to attend DIP and corresponding data on driver convictions, crashes, and driver education training history that were provided by the Iowa Motor Vehicle Division. The sample was divided into two groups based on DIP outcome: satisfactory or unsatisfactory completion. Two evaluation periods were considered: one year after the DIP date (probation period) and the period from the 13th to 18th month after the DIP date. The evaluation of Iowa’s DIP showed that there is evidence of effectiveness in terms of reducing driver convictions subsequent to attending the DIP. Among the 6,790 (75%) drivers who completed the course satisfactorily, 73% of drivers had no actions and 93% were not involved in a crash during the probation period. Statistical tests confirmed these numbers. However, the positive effect of satisfactory completion of DIP on survival time (that is, the time until the first conviction) was not statistically significant 13 months after the DIP date. Econometric model estimation results showed that, regardless of the DIP outcome, the likelihood of conviction occurrence and frequency of subsequent convictions depends on other factors, such as age, driver history, and DIP location, and interaction effects among these factors. Low-cost, early intervention measures are suggested to enhance the effectiveness of Iowa’s DIP. These measures can include advisory and warning letters (customized based on the driver’s age) sent within the first year after the DIP date and soon after the end of the probation period, as well as a closer examination of DIP instruction across the 17 community colleges that host the program. Given the large number of suspended drivers who continued to drive, consideration should also be given to measures to reduce driving while suspended offenses.

Evaluation of Corrosion Resistance of Different Steel Reinforcement Types, 2006

The corrosion of steel reinforcement in an aging highway infrastructure is a major problem currently facing the transportation engineering community. In the United States alone, maintenance and replacement costs for deficient bridges are measured in billions of dollars. The application of corrosion-resistant steel reinforcement as an alternative reinforcement to existing mild steel reinforced concrete bridge decks has potential to mitigate corrosion problems, due to the fundamental properties associated with the materials. To investigate corrosion prevention through the use of corrosion-resistant alloys, the performance of corrosion resistance of MMFX microcomposite steel reinforcement, a high-strength, high-chromium steel reinforcement, was evaluated. The study consisted of both field and laboratory components conducted at the Iowa State University Bridge Engineering Center to determine whether MMFX reinforcement provides superior corrosion resistance to epoxy-coated mild steel reinforcement in bridge decks. Because definitive field evidence of the corrosion resistance of MMFX reinforcement may require several years of monitoring, strict attention was given to investigating reinforcement under accelerated conditions in the laboratory, based on typical ASTM and Rapid Macrocell accelerated corrosion tests. After 40 weeks of laboratory testing, the ASTM ACT corrosion potentials indicate that corrosion had not initiated for either MMFX or the as-delivered epoxy-coated reinforcement. Conversely, uncoated mild steel specimens underwent corrosion within the fifth week, while epoxy-coated reinforcement specimens with induced holidays underwent corrosion between 15 and 30 weeks. Within the fifth week of testing, the Rapid Macrocell ACT produced corrosion risk potentials that indicate active corrosion for all reinforcement types tested. While the limited results from the 40 weeks of laboratory testing may not constitute a prediction of life expectancy and life-cycle cost, a procedure is presented herein to determine life expectancy and associated life-cycle costs.