Develop Epoxy Grout Pourback Guidance and Test Methods to Eliminate Thermal/Shrinkage Cracking at Post-Tensioning Anchorages: Phase II.

摘要

This research report contains guidance for eliminating thermal and shrinkage cracking in epoxy grout pourbacks used in post-tensioned anchorages. In this study, an experimental investigation of a selected epoxy grout pourback material and finite element analysis on the full-scale pourback specimens using the same pourback material were conducted. The study was undertaken to better understand the pourbacks’ failure mechanisms and provide guidelines and methods for eliminating them. Additionally, field investigation of epoxy grout pourbacks cracking was made at two bridge sites in Tampa and Miami. Based on a comprehensive literature review, manufacturer and contractor feedbacks, field investigation, and full-scale testing potential factors affecting epoxy grout pourback were determined to be the pourback size, shapes (particularly shapes with obtuse corner), ambient condition and concrete substrate’s temperature. The results of the full-scale testing and finite element analysis indicated that the primary cause of pourback failure was due to thermal cracking. The manufacturer-provided peak exothermic temperature did not reflect what was measured in the full-scale specimens as well as in the researchers’ own laboratory test, which were significantly higher. It was found that both the peak exothermic temperature and the maximum thermal stress increased as the volume-to-surface (V/S) ratio increased. It should be noted that the V/S ratios calculated in this report were based on the volume divided by the area of the exposed surfaces (the face of the epoxy grout not in contact with the concrete) in ft. The shapes also played a significant role particularly shapes with obtuse corners. The thermal cracks found in the field and full-scale specimens were full-depth cracks that penetrated through the epoxy grout. Therefore, it is recommended that these cracks should be immediately sealed. To avoid the thermal cracks, it is highly recommended, based on the findings of this study, that the V/S ratio of the epoxy grout be limited to 0.30 ft and 0.35 ft for irregular (S-type) and rectangular (R-type) shaped pourbacks, respectively.