International Concrete Abstracts Portal

Adhesive and mechanical concrete anchor systems today are typically tested in concrete mix designs containing no fly ash. This paper investigates the influence of a certain amount of fly ash as a cement replacement on the short term resistance of common adhesive anchor systems. The result shows no significant influence for the tested conditions.

Bonded anchors are frequently used for connections between structural or non-structural elements to concrete members. These connections are loaded by long-term and short-term loads respectively. The evaluation of the long-term behavior in the current approval guidelines in the U.S. and Europe is established by sustained load tests having a minimum duration of 1,000 hours in the U.S. and 2,000 hours in Europe. The results of these tests are extrapolated to approximately 450,000 hours (50 years) for tests at standard temperature and to roughly 90,000 hours (10 years) for tests at elevated temperature. The extrapolation technique and the evaluation criteria are developed to allow for an evaluation on the safe side. The paper presents results of tests on anchors installed using a proprietary adhesive anchor system that were subjected to sustained loads for up to approximately 21,000 hours (2.4 years). In these tests not only the time of testing but also the load level were beyond the requirements of the current approval guidelines. Based on these results the current evaluation method is analyzed and the conservatism associated with several aspects of the testing and evaluation methods is discussed.

This paper describes an experimental investigation on the long-term creep behavior of adhesive anchors under sustained tensile loads in combination with different environmental exposures. The experimental program comprises of 36 pull-out test specimens. The specimens consist of a cylindrical shape concrete block of 300 mm (12 inch) in diameter and 200mm (8 inch) in depth, with 15M (No. 5) deformed steel bars post-installed to an embedment depth of six times the bar diameter or 125mm (5 inch). Three types of adhesives were used: Type A - Fast setting two component methyl methacrylate adhesive, Type B - Fast setting two part epoxy adhesive and Type C - Standard set two part epoxy adhesive. The study is divided into four phases. Phase I consists of static pullout tests to determine the yield strength (fy) and the maximum capacity of each anchor system. Phase II consists of sustained load tests under load levels of 40%fy at normal laboratory conditions. Phases III and IV are sustained load tests under load levels of 40%fy with moisture exposure and freeze/thaw cycling, respectively. All sustained load tests lasted for a period of at least 90 days. The results of the static pullout testing showed that specimens with epoxy based adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. As for the sustained load test results, specimens with standard set epoxy based adhesive showed insignificant creep displacement under room conditions, however, when exposed to moisture noticeable creep displacements were recorded. Specimens with both fast setting epoxy and methyl methacrylate based adhesives showed higher creep displacements under environmental exposure versus those kept at room temperature.

ASTM E488 and ASTM E1512 as well as ICC-ES AC308 and ACI 355.4 have extensive testing protocols for the short-term and long-term evaluation of adhesive anchor systems. Currently the sustained load testing procedures establish residual load and displacement criteria on projected displacements from a 1000 hour sustained load test. An anchor is considered approved for sustained load if it meets these pass/fail criteria. In an NCHRP research project conducted at the University of Florida, an AASHTO standard (AASHTO TP 84-10) was developed to evaluate the sustained load performance of adhesive anchor systems based on a stress versus time-to-failure approach common with many testing protocols. Adhesive anchors are loaded to failure at various percentages of the mean static load as determined from static load tests. The resulting stress versus time-to-failure relationship generated from this test method is very useful to an engineer designing with adhesive anchors under sustained load. A subsequent NCHRP research project conducted in partnership at the University of Florida and the University of Stuttgart will utilize this test method to evaluate the long-term performance of adhesive anchor systems under sustained load coupled with various installation and in-service conditions (temperature, moisture, etc).

Adhesive anchors are used worldwide for structural and non-structural connections. Because their structural behavior is influenced by many factors, adhesive anchors must be prequalified. In the US this is done according to ICC-ES AC308 and ACI 355.4-10. Design provisions for bonded anchors are stated in ICC-ES AC308 and the ACI 318-11, Appendix D. Only prequalified adhesive anchor systems are covered by the ACI Standard. In this paper the testing procedure, assessment criteria and design provisions with respect to sustained tension loading are described and – based on test results – the validity of the design provisions is discussed. It is concluded, that adhesive anchors qualified according to ACI 355.4-10 and designed according to the ACI 318-11, Appendix D can safely be used to resist sustained tension loading provided that they are installed properly. The design provisions given in ICC-ES AC308 and ACI 318-11, Appendix D should be applied to all anchors that must resist sustained tension loads and not only to anchors installed overhead.