Long-Term Performance of Epoxy Adhesive Anchor Systems (2013)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

1 The objective of this project was to develop recommended standard test methods and specifications, design guidelines and specifications, and quality assurance guidelines and con- struction specifications for the use of adhesive anchor systems in transportation structures. Development of these tests, specifications, and guidelines was founded on the results of a program of experiments to determine, predict, and verify the sustained-load performance of these systems under sustained load in their different applications and environments. This project was divided into several phases; literature review, experimental program, and development of AASHTO standards and specifications. The following provides a summary of this report. The literature review investigated the current state of art of adhesive anchors. Extensive dis- cussion was devoted to the behavior of adhesive anchors in concrete as well as the many factors that can affect their short-term and sustained-load strength. Existing standards and specifica- tions for the testing, design, construction, and inspection of adhesive anchors were covered. A triage was conducted on many parameters identified as possibly affecting the sustained- load performance of adhesive anchors and the highest priority parameters were investigated in this project. A stress versus time-to-failure approach with tests performed at 110°F (43°C) was used to evaluate sensitivity of three adhesive anchor systems meeting the acceptance cri- teria of International Code Council Evaluation Service (ICC-ES) AC 308. The experimental stress versus time-to-failure relationship was compared to an expected relationship derived from the reduction in strength from short-term tests. Of all the various parameters inves- tigated only elevated service temperature [>120°F (49°C)] and manufacturer’s minimum cure time were shown to influence the sustained-load performance more than predicted by short-term tests of fully cured adhesive. It was recommended that anchors under sustained load exposed to temperatures of 120°F (49°C) or greater for significant portions of their service life should be tested and evaluated according to Temperature Category B in Ameri- can Concrete Institute (ACI) 355.4 §8.5. Additionally, it was recommended that adhesive anchors for sustained-load applications be allowed to cure an additional 24 hours beyond manufacturer’s minimum recommended cure time prior to loading or torquing. Various tests were conducted on the adhesives alone (time-temperature superposition, time-stress superposition, and dogbone tensile tests) to investigate the existence of a cor- relation with long-term anchor pullout testing in concrete. No consistent correlations were detected for the adhesives in the study. Tests were also conducted on the effect of early-age concrete strength on adhesive anchor bond strength. For the three adhesives investigated, one product (a vinyl ester) did not exhibit any significant increase in bond strength in concrete older than 14 days and the other two products (epoxies) did not exhibit any significant increase in bond strength in concrete older than 7 days. S U M M A R Y Long-Term Performance of Epoxy Adhesive Anchor Systems

2The project also developed suggested recommended standards and specifications for AASHTO pertaining to adhesive anchors in concrete. The following standards and specifi- cations were developed: • Test methods and specifications and material specifications and commentary for inclu- sion in the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, • Design guidelines, • Design specifications and commentary for inclusion in the AASHTO LRFD Bridge Design Specifications, • Quality assurance guidelines, and • Construction specifications and commentary for inclusion in the AASHTO LRFD Bridge Construction Specifications. The testing and material specifications made reference to the extensive and well-vetted testing program found within ACI 355.4 with a proposed exception for sustained-load test- ing. Design provisions for adhesive anchors in tensile loading were developed for AASHTO under given limitations. For cases that fall outside those restrictions, the designer was referred to ACI 318-11. Construction specifications were drafted for incorporation into the existing Section 29 “Embedment Anchors” of the AASHTO LRFD Bridge Construction Specifications, which previously addressed adhesive anchors. Quality assurance guidelines were drafted to orient construction and inspection personnel to adhesive anchor installation.