Developing Guidelines for Epoxy Grout Pourback Systems for Controlling Thermal/Shrinkage Cracking at Post-Tensioning Anchorages: Full-Scale Testing and Numerical Analysis

Abstract

Epoxy grout pourbacks at end anchorages of post-tensioning tendons provide an essential level of corrosion protection. The tendon may fail because of strand corrosion, within a few years of installation, if it is not properly protected with epoxy grout pourbacks. Recently, the Florida Department of Transportation (FDOT) found cracking on larger epoxy grout pourbacks, possibly as a result of the exothermic nature of the epoxy grout curing, causing thermal stresses that increase the potential for pourbacks cracking. Coordinated laboratory and numerical investigations were undertaken to develop best practice guidance for eliminating cracking in epoxy grout pourbacks. Potential factors were determined to be the pourback size, shapes, and temperature of the concrete substrate. An epoxy grout pourback material was used to construct full-scale pourback systems consisting of rectangular (R-type) and irregular (S-type) pourbacks with volume to surface, V/ S ratios of 80, 98, and 113 mm. The full-scale specimens were instrumented with multiple thermocouples and a vibrating wire strain gauge, to capture the temperature profile and localized strain respectively. An ANSYS finite element model was developed to perform a parametric study to better understand the cracking mechanism and the influence of the V/ S ratio. The model was calibrated and validated using the data obtained from the full-scale test. Based on the research findings, it is recommended that the maximum value of the V/ S ratio of the epoxy grout pourbacks be limited to 91 for S-type and 107 mm for R-type shapes.