Creep Behaviour of Post-Installed Adhesive Anchors under Various Sustained Load Levels and Environmental Exposures

Abstract

This thesis describes an experimental study on the long-term creep behaviour of adhesive anchors under sustained tensile loads in combination with different environmental exposures. A comprehensive background and literature review is presented, focusing on various bond stress models for adhesive anchors, factors affecting their bond behavior, and an overview of available testing standards and evaluation criteria. The experimental program comprises of 82 test specimens. The specimens consist of a cylindrical shaped concrete block of 300 mm (12 inch) in diameter and 200mm (8 inch) in depth, with 15M (No. 5) deformed steel bar post-installed to an embedment depth of six times the bar diameter or 125mm (5 inch). Three types of adhesives were used for anchor installation: Type-A a fast setting two component methyl methacrylate adhesive, Type-B a fast setting two part epoxy adhesive, and Type-C a standard set two part epoxy adhesive. The study is divided into four phases. Phase I consists of 27 static pullout tests to determine the yield strength (fy) and the maximum tensile capacity of each anchor system under three exposure conditions. Phase II and Phase III consist of 36 specimens tested under sustained load levels of 40%fy (32kN) and 60%fy (48kN)under normal laboratory conditions (room temperature) and moisture exposure, respectively. Phase IV consists of 9 specimens tested under sustained load with a load level of 40%fy (32kN) with exposure to freeze/thaw cycling. 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. Under sustained load testing, 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 (moisture, freeze/thaw) versus those kept at room temperature. Displacement data from creep testing were analysed and projected over a service life span of 50 years for room temperature exposure, and for 10 years for moisture and freeze/thaw exposures. Based on the analysis results, the service life of different anchor systems was estimated. An integrated qualification and testing protocol is proposed for the creep behavior of adhesive anchors under various environmental exposures.