Institute for Transportation

About the research

Accelerated bridge construction (ABC) has been implemented with greater frequency over the last decade, with successful projects geographically spread across the country. As these initial deployments of ABC methods age, it becomes necessary to inspect the structures for both maintenance decision making and for assurance of adequate service life performance. This data collection in the form of detailed inspection information allows for active management of the infrastructure and assessment of performance via key metrics. As such, it would be useful to broadly assess the performance of past ABC projects across the nation using consistent and effective inspection methods and metrics. This effort is further strengthened by the national presence of the ABC-UTC partner universities who are collaborating on this project.

About the research

Many transportation organizations have embraced Accelerated Bridge Construction (ABC) to reduce both the traffic impacts and societal costs. One of the most common means to achieve ABC is to utilize prefabricated elements that are connected on site to construct a bridge. ABC will not be effective if the barrier requires cast-in-place construction. The purpose of this report is to present details of a precast barrier and two connection alternatives between the deck and precast barriers. In addition, a new connection between two adjacent prefabricated barriers was presented. All three connections were tested using full-scale precast barriers and a video summarizing the test can be found at https://youtu.be/up6sMEeqfaU.

One barrier-to-deck connection used inclined reinforcing bars with threaded ends that were connected to bar splicers embedded in the bridge deck. The other barrier-to-deck connection used U-shaped bars that were inserted into the barrier from the underside of the bridge deck overhang. Factors that were considered when designing the connections were minimal damage to deck, easy replacement of barrier, constructability, durability, and cost.

The barrier-to-barrier connection utilized headed reinforcement in the longitudinal and transverse directions. The connections were designed to meet TL-4 loads as per the Manual for Assessing Safety Hardware (MASH) and Load and Resistance Factor Design (LRFD) Bridge Design Specifications.

This report presents results from various tests and shows that all proposed connections are viable for accelerated construction of concrete barriers, although some refinement to the tested details will be needed.

About the research

Accelerated Bridge Construction (ABC) has grown tremendously over the past several years, due in part to the maturation of new materials that have properties conducive to working in an ABC environment. In recent years, Caterpillar Inc. has developed several formulations of a cementitious material for building purposes called CEMPOSIT, which is a variation of macro-defectfree (MDF) concrete.

This material is unlike any cement-based material currently available and is much more closely related to various types of rubber—although with vastly different properties than rubber. These favorable properties include high strength (comparable to ultra-high-performance concrete), rapid early strength, extremely low permeability, and the ability to be extruded on-site to fit specific project needs.

The goal of this work was to assess important material characteristics of MDF concrete and to develop conceptual uses for the material with a specific focus on accelerated/robotic bridge construction. The findings from the material tests are presented, along with discussion of applicability for usage in the accelerated bridge construction field, in this report.

About the research

The effectiveness of cast-in-place joints and other connections are of critical importance for ABC projects. While high strength materials are being used for these in-field connections, there is a general lack of existing research regarding inspection of joint quality and performance prior to opening to traffic. While these joints are intended to be constructed quickly, poor quality performance/construction will be detrimental to the equally important longevity of construction.

This report evaluates the capabilities of existing nondestructive testing technologies that could be used to determine bond and joint strength between pre-formed deck panels and the cast-in-place joint strips, and other ABC components of interest. The results of the information collection will be used to assess the feasibility of various techniques for further implementation in QA/QC efforts relating to ABC projects.

About the research

As accelerated bridge construction (ABC) has gained the attention of the bridge community, certain bridge types, such as integral abutment bridges, have seen limited use. Integral abutments eliminate the expansion joint from the bridge superstructure by rigidly connecting the superstructure and foundation. The integral abutment is therefore often large and heavily reinforced, which presents challenges for ABC projects.

This research investigated integral abutment details for use in ABC projects through mechanical splicing of the integral diaphragm and the pile cap. Two ABC details, the grouted reinforcing bar coupler detail and the pile coupler detail, were evaluated in the laboratory for constructability, strength, and durability. A typical cast-in-place detail was also constructed and tested as a baseline.

For the grouted reinforcing bar coupler detail, a plywood template was used to “match cast” the pile cap and the integral diaphragm. The template was simple to construct and resulted in the successful alignment of 17 spliced steel bars and grouted couplers over an 8 foot specimen. Though the grouting of two couplers was obstructed, more than adequate strength was created by the connection, and the crack width at the precast joint was comparable to that of the cast-in-place specimen.

The pile coupler reduced the number of spliced connections between the pile cap and integral diaphragm sufficiently to facilitate adequate construction tolerances. The splicing system worked well during construction, but the detail’s strength and durability was less than ideal. Several lessons were learned from these tests that could improve the structural performance of the pile coupler detail.

About the research

The use of precast elements and prefabricated bridge segments along with accelerated construction techniques, known as accelerated bridge construction (ABC), has allowed for increased efficiency of construction, reduced safety concerns, and converted month-, or even year-, long closures into a matter of weeks, or at times, days. This tactic is growing in popularity within the bridge community, and research projects have been initiated to investigate how the construction of bridge elements can be expedited.

One such element being investigated is the integral abutment. This structural connection for bridges was introduced to eliminate the need for expansion joints between the substructure and superstructure, where the presence of water and other deteriorating chemicals caused long-term and frequent maintenance issues. Due to this area needing to be heavily reinforced, congestion issues arise when attempting to apply ABC methods. In addition to the reinforcing congestion, the construction tolerances and weight of the integral abutments cause some problems for ABC projects.

These issues are the basis for this project, which was intended to investigate the use of mechanical couplers to splice the foundation elements to the superstructure elements of bridges while applying ABC techniques. Since this was a Phase II project, the methodologies and laboratory setup for evaluating the ABC connection details were the same as that of Phase I. From the results of Phase I, three connection details were developed for investigation in Phase II. Of which, two were a revised design of the two mechanical coupler connection details tested in Phase I, and the third was a new connection detail designed through the Iowa Department of Transportation (DOT) to be used on an upcoming bridge project.

With this project completed, further investigations about integral abutment connection details for ABC applications should be conducted to provide more literature on the subject. Such investigations would be further revisions to the designs of the connection details and field monitoring of real-world applications of the connections.

About the research

Accelerated bridge construction (ABC) techniques are rapidly gaining acceptance as an alternative to conventional construction methods to reduce construction duration and minimize the impact of closures at the network level. There are different types of ABC, and each technique has its limitations and its own speed of completion. The choice of using ABC depends on a host of different factors, including the availability of capital funds for its implementation, its impact on the traveling public, and socio-economic considerations. While many states have implemented a multitude of different ABC techniques, the decision making process for choosing ABC over conventional construction, the costs of ABC, the type of ABC techniques used, and the associated timelines and incentives for faster completion are not clear.

This report aims to address this lack of clarity through a review of the available literature and interviews with a few states that have implemented ABC at different levels. It appears that the major factors impacting the timelines for ABC projects are the impacts the closures might have on the socio-economic aspects of the community. While most states acknowledge the importance of indirect costs, there is no mathematical formulation to account for these costs in the final decision making process. Most decisions are made based on qualitative input from the districts and discussions with the public. For the establishment of incentives, a procedure similar to that followed for conventional construction and that follows the Federal Highway Administration (FHWA) guidelines is suggested by most of the states.