Recommended AASHTO Guide Specifications for ABC Design and Construction (2018)

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NCHRP Project 12-102 165 C H A P T E R 6 ABC Construction Specification Development 6.1 Approach This project is essentially a large-scale synthesis of past work. No formal laboratory research was complete under this project. Questionnaires were sent to each State Transportation agency. The questionnaire included a request for ABC construction specifications. Many were received. The project team strove to incorporate the appropriate sections of these specifications into the ABC Guide Specifications. 6.2 Specification Section and Article Development The team was charged with developing guide specifications in AASHTO format. This is not a stand- alone design specification, but a supplement the AASHTO LRFD Bridge Construction Specifications. The key features of AASHTO Guide Specifications include: 1. Two-column format: Specifications in the left column, commentary in the right column. 2. A “section” is akin to a chapter in other documents. 3. Articles are numbered using number headings (1.1, 1.1.1, 1.1.1.1, etc.) 4. Commentary headings start with a Capital C. 5. Tables of Contents are generated for each section as opposed to an overall document Table of Contents. 6. The first article in each section contains the scope of that section. 7. Notations for each section are included in the front of each section. Reference to the applicable articles is also identified. 8. References to current AASHTO provisions do not include the actual provision number, just the provision title. This is done to address possible re-organization of AASHTO documents. 9. Where appropriate, articles covering “Measurement and Payment” were included in each section to be consistent with the AASHTO LRFD Bridge Construction Specifications. Number There is a hierarchy in the use of AASHTO documents. Standard AASHTO specifications are mandatory specifications (unless overridden by agency specifications). Guide Specifications are different, but similar to standard AASHTO specifications. They differ in that they are not mandatory. Guide specifications are written to be similar to a full specification. The guide specifications make use of the terms “shall”, “should”, “may”, and “recommended”. The following describes how these terms should be interpreted: • The term “shall” denotes a requirement for compliance with the specifications. • The term “should” indicates a strong preference for a given criterion.

NCHRP Project 12-102 166 • The term “may” indicates a criterion that is usable, but other local and suitably documented, verified, and approved criterion may also be used in a manner consistent with the LRFD approach to bridge design. • The term “recommended” is used to give guidance based on past experiences. It should be noted that the AASHTO LFRD Bridge Construction Specifications do not typically contain the level of detail that a state agency specification might include. This is due to the fact that state specifications contain references to applicable other state specifications. The goal of this specification development was to use the same level of detail as in the current AASHTO LFRD Bridge Construction Specifications. The outline of the construction specifications is similar to the AASHTO LFRD Bridge Construction Specifications. Sections are separated based on materials and specific construction processes such as temporary works. The following sections contain information on the development of each specification section. 6.3 Section 1 – Introduction The provisions in this section serve as an introductory section of the overall construction guide specification. Section 1 references Part 1 of the document for definitions of common prefabricated elements and systems. This section notes that U.S. Customary Units are used, which is consistent with the current AASHTO LFRD Bridge Construction Specifications. 6.4 Section 2 – Temporary Works This section supplements Section 3 of the AASHTO LFRD Bridge Construction Specifications. The supplementary materials include special provisions for ABC projects. Temporary works play a significant role in ABC projects. Certain projects required large temporary works that support portions of the bridge or the entire bridge, requiring a high level of care with respect to temporary works. The construction of temporary works falls under the realm of “contractor means and methods”. Bridge system designs often include schematic details for the temporary works required to construct the bridge. The roles and responsibilities for these types of projects should not differ from conventional construction. The responsibilities for the design engineer and the contractor are defined in this section. 6.5 Section 3 – Fabrication and Assembly Planning This section covers recommendations for specifications that require the contractor to demonstrate, through careful planning, that the fabrication, shipping and assembly of a bridge can be accomplished on schedule. Without careful planning, there is a potential for problems to arise, leading to construction delays, which are contrary to the goals of ABC. A portion of this section covers quality control in the fabrication facility. The section also covers temporary precast concrete fabrication facilities. The quality control specifications include the use of multiple checklists including inspections for pre-pour, casting, curing, post-pour, dry fit of assemblies, and prior to shipping. Repair of damaged precast elements is also covered in this specification. Provisions are also included for shipping and handling calculations.

NCHRP Project 12-102 167 Assembly of a prefabricated bridge or a bridge system requires careful planning. These guide specifications include provisions for development of assembly plans, which are more detailed than conventional erection plans. The concept is to have the contractor develop a step-by-step assembly sequence, demonstrating to the engineer that they have an understanding of the sequences that are necessary to accomplish the construction. This concept was first used by the New Hampshire DOT on an early prefabricated bridge project. It has since been adopted by the PCI Northeast Bridge Technical Committee, and used by a number of agencies across the country. This section also includes a step-by-step procedure for post-tensioning of precast concrete full-depth deck panels. The sequence of this work is critical to the proper performance of this ABC technology. This sequence was developed from work by the PCI Northeast Bridge Technical Committee. 6.6 Section 4 – Layout and Tolerances Tolerance specifications for prefabricated elements are being developed under NCHRP Project 12-98. Michael Culmo, the PI for Project 12-102 is also the PI for Project 12-98. Project 12-98 includes the development of a guideline for tolerances for prefabricated elements and systems. It is anticipated that the guideline will be published in 2017, therefore the majority of that document is not replicated in this guide specification. Instead, it is referenced by the applicable provisions in this section. At some point in the future, the AASHTO T-4 Technical Committee for Construction may integrate the recommended tolerances into this document. The importance of proper layout and geometry control are covered in this section. To date, the most significant lessons learned with prefabricated bridge elements is a lack of control of tolerances and geometry during construction. 6.7 Section 5 – Concrete Structures The current AASHTO LRFD Bridge Construction Specifications cover concrete construction in significant detail. There are several features of ABC that are not covered in adequate detail. The provisions in this section fill the gaps in the current AASHTO provisions. The following are several of the more significant provisions in this section. 1. Non-shrink Grouts: Non-shrink grouts are commonly used in prefabricated construction. Existing provisions for non-shrink grouts have been found to be inadequate to ensure proper construction and long-term durability. The provisions in this section are a performance-based specification. They are based on work completed by the FHWA. 2. High Early Strength Concrete: High early strength concretes are common in prefabricated bridges. The rapid pace of construction leads to a need for rapid strength gain in closure joint concretes. High early strength concrete has been used on a number of ABC projects; however excessive shrinkage and cracking have been observed. The goal is to get rapid strength gain, without excessive shrinkage and with durability. Similar to non-shrink grouts, a performance specification is recommended. Since most closure joints are cast in a restrained position, small scale and a full-scale restrained shrinkage tests are recommended. These test are used to develop a mix that minimizes the potential for shrinkage cracking in high early strength closure joints. The specifications included in this section have proven to give good results for strength and durability. 3. UHPC: The provisions for UHPC are based on work completed by FHWA. The material portion of this specification is a performance specification. Currently, it is believed that only one manufacturer can meet this specification, therefore notes have been added to the commentary regarding the potential

NCHRP Project 12-102 168 proprietary nature of this concrete. The placement, finishing and curing of UHPC requires special care, therefore provisions were developed to cover all aspects of UHPC construction. 4. Surface Preparation of Concrete Joints: Several research projects at FHWA have identified a need to prepare the surface of joints that are to receive non-shrink grout, concrete, or UHPC. The use of an exposed aggregate surface at the interface of the fill material and the concrete element has proven to provide better bond and less potential for leakage at the interface. 5. GC: Grouted reinforcing bar couplers are common in prefabricated bridges. Detailed specifications for installation of GC do not exist in the current AASHTO LRFD Bridge Design Specifications. Specifications were developed based on manufacturer’s recommendations and several agency special provisions. 6.8 Section 6 – Steel Structures The construction of steel elements in ABC is similar to conventional construction. There are a few elements that are in use that require specifications. These specifications include provisions for: • Simple spans made continuous for live load: Fabrication fit-up • Modular Deck Beams: Coordination with precast fabrication • Link Slabs: Top flange surface preparation in link slab region 6.9 Section 7 – Geosynthetic Reinforced Soil / Integrated Bridge System This section contains a significant level of detail with regard to construction of geosynthetic reinforced soil / integrated bridge system (GRS/IBS). The provisions are based on the FHWA document entitled Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide (2012). This guide contains more detail regarding the construction of a GRS/IBS bridge, therefore it is referenced.