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Project Details
STATUS

Completed

PROJECT NUMBER

17-634, TR-735

START DATE

11/01/17

END DATE

11/30/20

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, AMPP
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Chris Williams

Director, AMPP

About the research

Low-volume rural roads are generally low funding priorities compared to the roads that are part of the National Highway System (NHS). Therefore, low-volume rural roads tend to deteriorate to a point where traditional pavement preservation and maintenance techniques no longer have the desired effect or sufficient funding is not available.

As a potential solution, the Iowa Department of Transportation (DOT) constructed 10 test sections with various base and surface treatments on a 13 mi low-volume asphalt road segment in northeast Iowa in 2013, which were studied as part of the first phase of this research project. The aim of the project was to develop holding strategies beyond pavement preservation as a solution to low-volume roads that are in poor condition when there are not resources available for a complete rehabilitation. Due to the success of this first phase, a second phase was proposed in 2018.

This second phase study focused on surface treatments and was intended to treat highly distressed composite pavements that have asphalt overlays on portland cement concrete (PCC) pavements. Eight test sections were constructed on US 65, between Hubbard and Zearing in Iowa. The holding strategies evaluated were a combination of cold in-place recycling with various surface mixes, 1 in. profile milling with various surface courses, 2.5 in. profile milling with interlayer and surface course, and double coats of microsurfacing with and without additional spot grinding.

Based on the evaluation of the test sections and follow-up surveys, recommendations are given regarding the selection of the most advantageous strategy for the conditions of the studied pavement.

Project Details
STATUS

In-Progress

PROJECT NUMBER

20-728, TR-784

START DATE

05/01/20

END DATE

06/30/22

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, AMPP, CTRE
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Omar Smadi

Director, CTRE

About the research

Selecting the right treatment for the right pavement at the right time has been a fundamental principle to pavement preservation success. The objective of this project is to develop “Iowa’s Pavement Preservation Guide,” a document tailored to serving the needs of Iowa practitioners who have active pavement preservation programs or plan to implement a pavement preservation program.This proposal outlines a research approach based on national-best practices for pavement preservation program implementation. Many states have developed pavement preservation manuals. The research addresses six areas including: (1) project selection, (2) anticipated benefit/costs of pavement preservation treatments at the network-and project-level, (3) implementing pavement preservation into system-wide strategic planning, (4) preservation treatment considerations, (5) construction/specifications, and (6) materials training. It is important that pavement preservation guidance include project-level and system-level selection strategies project-level decisions have a network-wide impact. Practitioners who use this guidance will be able to communicate pavement preservation benefits at the project-and network-levels, identify candidate roadways for preservation treatments, and utilize the guide to enhance project delivery of pavement preservation treatments.

Project Details
STATUS

In-Progress

PROJECT NUMBER

20-739, TR-789

START DATE

05/01/20

END DATE

05/31/23

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, PROSPER
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Halil Ceylan

Director, PROSPER

Co-Principal Investigator
Sunghwan Kim

Associate Director, PROSPER

Co-Principal Investigator
In-Ho Cho

About the research

Snow and ice removal operations in winter road maintenance are essential for the Iowa Department of Transportation (DOT) as well as counties and cities in Iowa to ensure the safety, mobility, and efficiency of their transportation infrastructure systems. As an innovative snow and ice removal alternative, the researchers at Iowa State University (ISU) have developed (1) new mix design and production methods of heated concrete (dubbed electrically conductive concrete [ECON], hereafter) and (2) new structural and system design approaches for a heated pavement system (HPS) using the new ECON developed. Based on successful real-world implementation of ECON HPS recently demonstrated by the ISU research team for airport pavement and roadway construction projects, the City of Iowa City has expressed strong interest to the Iowa DOT and ISU research team in implementing ECON HPS for their new bus stop stations as well as the bus stop loading area under an upcoming pedestrian crossing and bus stop enhancement project at Muscatine Avenue in the City of Iowa City. This research is proposed in response to such keen interest by the City of Iowa City. A set of proposed research tasks (to implement ECON HPS for the bus stop station application) include the development of ECON mix design and ECON HPS system design options for construction, comprehensive performance monitoring and evaluation, as well as economic analysis of the constructed full-scale ECON HPS at least over two consecutive winter cycles, and a survey and interview on the implementation of heated pavements for winter maintenance and management practices. The primary outcome of this research will be the draft of a technical guide/specification (comparable with the current Iowa DOT specifications and Iowa Statewide Urban Design and Specifications [SUDAS]) that Iowa DOT and Iowa’s counties and cities could use for future ECON HPS implementation projects under their public works departments for enhancing sustainable and resilient winter maintenance and management practices.

Project Details
STATUS

In-Progress

PROJECT NUMBER

20-740, TR-787

START DATE

08/01/20

END DATE

07/31/22

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, AMPP
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Chris Williams

Director, AMPP

Co-Principal Investigator
Eric Cochran

About the research

Iowa State University (ISU) has assembled a team of experts in Civil, Chemical, and Industrial and Manufacturing Systems Engineering to address the challenges of integrating scrap and end-of-life rubbers to supplant the use of up to 140,000 tons/year of virgin polymer used in asphalt pavements. The team proposes the use off-specification polybutadiene to modify ground tire rubber (GTR) particles, from recycled tires, and use them as an asphalt modifier to replace widely used SBS elastomers. GTR is currently being used as a modifier, which offers comparable improvements with respect to SBS polymers such as rutting resistance and elastic recovery, with advantages such as improved traction and reduced noise. However, because of the difference in density with asphalt it suffers from inadequate storage stability, rendering it an unpreferred material in asphalt modification. ISU has developed a technology that density matches GTR with asphalt with simple compounding techniques, producing a GTR product that meets storage stability specifications and would be accepted by the market. If 100% of virgin polymer were replaced with recycled GTR, up to 140,000 tons/year could be reclaimed nationwide. Moreover, asphalt pavements are 100% recyclable, including as a major component of new roadways, which means that GTR used in pavements will continue to be reused.

Project Details
STATUS

In-Progress

PROJECT NUMBER

19-726, TR-781

START DATE

11/01/19

END DATE

10/31/22

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, CTRE, PROSPER
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Halil Ceylan

Director, PROSPER

Co-Principal Investigator
Sunghwan Kim

Associate Director, PROSPER

Co-Principal Investigator
In-Ho Cho

About the research

Iowa state law limits weight of vehicles by axle and gross (total) weight. While these laws standardize traditional vehicles by size and weight, the agricultural implement industry is a vehicle sector that has changed substantially in recent years, most notably in terms of manufacturing larger vehicles. This has resulted in heavier farm implements that, if filled to capacity, are substantially overweight in terms of current law. Similarly, there are other superloads and heavy traffic generators (non-divisible vehicles, trucks carrying wind turbines, transport from-to concentrated animal feeding operations, and other industries) that can potentially become overweight. Local law enforcement typically does not have the equipment necessary to measure overweight vehicles, so most counties report overloaded vehicles to their Department of Transportation (DOT) Motor Vehicle Enforcement Agency. However, response from DOT Vehicle Enforcement is not always timely, and many reports receive no response at all. Given this legal and enforcement environment, when designing and constructing county roads, counties must adapt by accounting for the percentage of traffic overweight vehicles traveling on the county road system. Currently, since this percentage (i.e., % superloads) is more or less subjective based on guesswork, there is a need for a better way of determining more accurate traffic types and counts that take into account the presence of superloads.

Project Details
STATUS

In-Progress

PROJECT NUMBER

19-717, TR-779

START DATE

07/15/19

END DATE

03/31/22

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, BEC
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Justin Dahlberg

Acting Director, NCWTS

Co-Principal Investigator
Brent Phares

Bridge Research Engineer, BEC

About the research

A709 Grade QST 65 Steel has been recently introduced to the Standard Specification for Structural Steel for Bridges. Its strength characteristics and ductility meet or exceed those of more conventionally used steels (30% higher strength) for bridges leading to potential cost savings (3% higher cost). Testing of the material to assess the ability to meet the design provisions set forth by the American Association of State Highway and Transportation Officials is needed to further the case for regular adoption into bridge construction projects. Laboratory testing of this steel in composite action with a concrete deck and fatigue testing will be performed as part of this project. Additionally, live load testing of a newly constructed bridge in Buchanan County, Iowa, using this steel will be completed.

Project Details
STATUS

In-Progress

PROJECT NUMBER

19-694, TR-766/TR-776

START DATE

05/01/19

END DATE

12/31/21

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, BEC
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Katelyn Freeseman

Acting Director, BEC

Co-Principal Investigator
Zhengyu Liu

Research Engineer, BEC

Co-Principal Investigator
Brent Phares

Bridge Research Engineer, BEC

About the research

The American Association of State Highway and Transportation Officials (AASHTO) has revised the design guidelines over the years to impose greater design/rating earth pressures on buried structures. This is one of the major reasons that many old culverts designed with allowable stress design (ASD) or load factor design (LFD) do not pass load and resistance factor ratings (LRFR) although they have performed satisfactorily for many years. Currently, the Iowa Department of Transportation (DOT) Office of Bridges and Structures uses the lateral earth pressure of 36/18 pcf specified for LFD and ASD and the 60/30 pcf for load and resistance factor design (LRFD). It would be helpful to understand which load pressure is more realistic for Iowa soil conditions and typical construction methods. This understanding is very important for culvert load rating so as to avoid unnecessary load postings of many older culverts.

A culvert located in Ida County, which consists of multiple 8×12 ft concrete boxes was selected during the initial phase of this project and has been monitored for two years (Stage 1 of Design #1115). The monitoring system consists of six strain gauges and five pressure cells, and was installed on 1/28/2016. After two full seasonal cycles, and with the amount of the accumulated data, a systematic analysis of the acquired data is now necessary. The goal of this project is to analyze the collected data from the Ida County culvert and develop practical Iowa-specific earth pressure recommendations that can be used in culvert design and load rating.

Project Details
STATUS

Completed

PROJECT NUMBER

15-559, TR-698

START DATE

11/01/15

END DATE

05/31/19

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, CP Tech Center, PROSPER
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Peter Taylor

Director, CP Tech Center

Co-Principal Investigator
Halil Ceylan

Director, PROSPER

Student Researcher(s)
Rabindra Pariyar

About the research

The objective of this project was to determine the optimum joint spacing for thin concrete overlays based on different concrete overlay thicknesses, support systems, and concrete overlay types with and without structural macro-fibers.

In thin concrete overlays, field observations have sometimes shown that not all contraction joints activate initially and, in some cases, do not activate until many years after construction. Contraction joints that do not activate may be considered an inefficient design that may lead to unnecessary maintenance efforts and costs. The optimum joint spacing design may need to be determined based on factors other than those that are currently considered.

This project included an analysis for recommended joint spacing using pavement design software as well as a field review of joint activation in existing concrete overlays using nondestructive testing. Test sections were also constructed to analyze a wider range of variables and to study early-age joint activation behavior.

The data showed that joint spacing was the most significant factor affecting joint activation. A design parameter, slab length over the radius of relative stiffness (L/ℓ), was identified to have a correlation with joint activation percentage and timing.

The data showed that use of macro-fibers did not affect the percentage or rate of joint activation compared to overlays without macro-fibers.

Project Details
STATUS

Completed

PROJECT NUMBER

19-693, TR-773

START DATE

04/01/19

END DATE

09/30/21

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, BEC
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Behrouz Shafei

Structural Engineer, BEC

Co-Principal Investigator
Brent Phares

Bridge Research Engineer, BEC

Co-Principal Investigator
Peter Taylor

Director, CP Tech Center

About the research

Ultra-high performance concrete (UHPC) provides superior properties in strength and durability for the long-term performance of bridges. Despite these desirable properties and the potential to be applicable in the majority of projects, UHPC is still not widely used, mainly because of the cost associated with it.

This report details a study performed on the design of non-proprietary UHPC mixes that provide comparable strength properties to that of commercially available mixtures. A set of base mixtures were explored by varying the ratios for various constituents and investigating their durability, strength, and transport properties, including volume stability and freeze-thaw resistance.

In the later stage of the project, the selected non-proprietary mixes were evaluated for their flexural strength. The flexural strength in UHPC comes mainly from the fibers used in the mix. Bearing in mind the role of fibers, the effects of various types of steel fibers (i.e., variation in shape, size, and dosage) were evaluated. The role of fibers on strength and post-cracking behavior was carefully examined using laboratory testing and image analysis utilizing digital image correlation techniques. The efforts found that an optimal combination of micro- and macrofibers can enhance the flexural strength of UHPC mixtures.

Steel fibers contribute to more than a third of the cost of UHPC mixtures, so the possibility of utilizing less expensive and more environmentally friendly synthetic fibers—polypropylene, polyvinyl alcohol, nylon, alkali resistant glass, or carbon—to partially replace the steel fibers could reduce the cost of UHPC. The steel fibers were partially replaced by the different synthetic fibers to see their effect on the UHPC’s fresh properties and flexural strength. Utilizing digital image correlation, the synthetic fiber contribution to post-cracking behavior was evaluated, especially from the crack width control and crack propagation aspects. The replacement of steel fibers with synthetic fibers showed promise for flexural strength and post-cracking behavior.

This report provides recommendations for the preparation of cost-effective, non-proprietary UHPC mixtures that could be used for various transportation infrastructure applications. Further recommendations are also made for the optimal combination of different types of steel micro- and macrofibers to get the best flexural response. Recommendations are then extended for the use of different types of synthetic fibers and the optimum percentage of dosage replacement for steel fibers.

Project Details
STATUS

Completed

PROJECT NUMBER

15-540, TR-690

START DATE

07/01/15

END DATE

04/30/19

FOCUS AREAS

Infrastructure

RESEARCH CENTERS InTrans, BEC
SPONSORS

Iowa Department of Transportation
Iowa Highway Research Board

Researchers
Principal Investigator
Kejin Wang

PCC Engineer, CP Tech Center

Co-Principal Investigator
Scott Schlorholtz

Faculty Affiliate

Co-Principal Investigator
Sri Sritharan

Faculty Affiliate

About the research

This Phase II research project on the shrinkage behavior of high-performance concrete (HPC) used in Iowa bridge decks and overlays evaluated several concrete mixes, building off or modifying mixes developed in Phase I. Based on shrinkage behavior and mechanical properties, the mixes studied in Phase I were characterized as having either high, medium, or low cracking potential. In the Phase II study, three concrete mixes (Mixes 6, 8, and 2, characterized in Phase I as having high, medium, and low cracking potential, respectively) were selected for further investigation. The selected mixes were modified using three shrinkage control technologies: shrinkage-reducing admixtures (SRAs), cementitious materials (CM), and internal curing (IC) agents, respectively. The modification methods were first studied in a laboratory until the optimal shrinkage behavior of each concrete mix was achieved. Two pairs of the tested concrete mixes (Mixes 6 and 8 with and without modification) were then used in a field investigation on the US 20 over I-35 dual bridge. The mixes were placed side by side for the bridge overlays, which were monitored for about one year with strain gages, temperature and moisture sensors, and regular visual examinations.

The laboratory investigation confirmed positive effects for the concrete shrinkage control technologies used. The laboratory test results also provided specific details for the concrete mix modifications, ensuring optimal concrete performance and shrinkage control. The modifications included the addition of 1.0/1.25 gal/yd3 of SRA in Mix 6, the use of 10% CM reduction for Mix 8, and the use of lightweight fine aggregate as an IC material in Mix 2. The results of the field investigation suggest that environmental conditions on the casting day and the first few days of curing play an important role in the development of concrete properties. Future studies could benefit from a comprehensive stress analysis to better understand the long-term effects of the shrinkage control technologies, as well as further field tests and an extended monitoring time.

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