APPENDIX
UHPC Properties and the Bridge Delivery Process
A.1 UHPC Properties
Conventional concrete has been used for centuries and has been widely adopted for infrastructure, including buildings, bridges, and roads, because of its high compressive strength. Recently, advancements in the science of concrete materials led to the development of an improved class of concrete called UHPC. UHPC is a concrete mixture consisting of formulations that often combine portland cement, fine sand, silica fume, HRWR, fibers (usually steel), water, and various chemical admixtures. Table A-1 displays the typical composition of Ductal, a proprietary UHPC mix.
The two main advantages of UHPC over conventional concrete are increased strength and durability. The higher cement content of UHPC (approximately 30% compared with 15% to 20% in conventional concrete) and the use of chemical admixtures and steel fibers contribute to these improved properties. UHPC is stronger than conventional concrete and has a compressive strength of at least 21.7 ksi compared with 3–6 ksi in conventional concrete and a tensile strength greater than 0.72 ksi compared with around 0.5 ksi in conventional concrete. UHPC also has a discontinuous pore structure and a slightly lower porosity, leading to lower permeability and significantly reduced water infiltration. Reducing water infiltration protects the steel fibers from corrosion and reduces cracking caused by the freeze–thaw cycle when concrete is exposed in cold-weather climates.
A.2 Bridge Delivery Process
There are two main bridge delivery methods: the design-bid-build process and the design-build process. In the design-bid-build process, the owner agency contracts the bridge design to a firm that designs the bridge in coordination with the owner agency. The owner agency then solicits bids from contractors to complete construction. In the design-build process, the owner agency contracts out design services and construction at the same time and usually to the same company. Although the owner agency determines the location and sets general requirements for the bridge design and construction, the contractor(s) create(s) a bridge delivery process that aligns with the needs and concerns of the contractor(s).
Most bridge construction and repair projects in the United States are commissioned by federal, state, or local owner agencies. It is typically the owner agency that decides to build a bridge using ABC methods and PBEs. Owner agencies can specify the use of certain materials or construction processes, potentially including the mandated use of UHPC-C and even UHPC mix performance specifications or proprietary UHPC mix specifications naming a preferred brand. In the absence of such specifications, contractors may not be as inclined to use UHPC-C because of the increased cost and other factors that make it more difficult to use in the field.
Table A-1. Typical Ductal UHPC composition.
| Material | lb/yd3 | Percentage by Weight |
|---|---|---|
| Portland cement | 1,200 | 28.5% |
| Fine sand | 1,720 | 40.8% |
| Silica fume | 390 | 9.3% |
| Ground quartz | 355 | 8.4% |
| HRWR | 51.8 | 1.2% |
| Accelerator | 50.5 | 1.2% |
| Steel fibers | 263 | 6.2% |
| Water | 184 | 4.4% |
SOURCE: Russell and Graybeal, 2013.
The contractor is typically responsible for securing the concrete needed for bridge construction. If the bridge is built using conventional construction methods and conventional concrete, the contractor often serves as the concrete supplier. If the owner agency specifies the use of PBEs, these are produced in dedicated facilities, and few contractors can self-supply the material. Similarly, if the owner agency specifies the use of UHPC-C, the contractor is typically unable to self-supply the needed UHPC. As of August 2021, there were four providers of commercial UHPC blends in the United States.
In most cases, owner agencies either contract out or conduct inspection and materials-testing services throughout the process of bridge construction as concrete is placed. If the project uses UHPC-C, the inspection and testing technicians need to be trained on the proper procedures of UHPC-C use, on conducting tests on samples in the field, and on conducting the proper laboratory tests on the samples collected in the field.
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Abbreviations and acronyms used without definitions in TRB publications:
| A4A | Airlines for America |
| AAAE | American Association of Airport Executives |
| AASHO | American Association of State Highway Officials |
| AASHTO | American Association of State Highway and Transportation Officials |
| ACI–NA | Airports Council International–North America |
| ACRP | Airport Cooperative Research Program |
| ADA | Americans with Disabilities Act |
| APTA | American Public Transportation Association |
| ASCE | American Society of Civil Engineers |
| ASME | American Society of Mechanical Engineers |
| ASTM | American Society for Testing and Materials |
| ATA | American Trucking Associations |
| CTAA | Community Transportation Association of America |
| CTBSSP | Commercial Truck and Bus Safety Synthesis Program |
| DHS | Department of Homeland Security |
| DOE | Department of Energy |
| EPA | Environmental Protection Agency |
| FAA | Federal Aviation Administration |
| FAST | Fixing America’s Surface Transportation Act (2015) |
| FHWA | Federal Highway Administration |
| FMCSA | Federal Motor Carrier Safety Administration |
| FRA | Federal Railroad Administration |
| FTA | Federal Transit Administration |
| GHSA | Governors Highway Safety Association |
| HMCRP | Hazardous Materials Cooperative Research Program |
| IEEE | Institute of Electrical and Electronics Engineers |
| ISTEA | Intermodal Surface Transportation Efficiency Act of 1991 |
| ITE | Institute of Transportation Engineers |
| MAP-21 | Moving Ahead for Progress in the 21st Century Act (2012) |
| NASA | National Aeronautics and Space Administration |
| NASAO | National Association of State Aviation Officials |
| NCFRP | National Cooperative Freight Research Program |
| NCHRP | National Cooperative Highway Research Program |
| NHTSA | National Highway Traffic Safety Administration |
| NTSB | National Transportation Safety Board |
| PHMSA | Pipeline and Hazardous Materials Safety Administration |
| RITA | Research and Innovative Technology Administration |
| SAE | Society of Automotive Engineers |
| SAFETEA-LU | Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) |
| TCRP | Transit Cooperative Research Program |
| TDC | Transit Development Corporation |
| TEA-21 | Transportation Equity Act for the 21st Century (1998) |
| TRB | Transportation Research Board |
| TSA | Transportation Security Administration |
| U.S. DOT | United States Department of Transportation |
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