The Effects of Alkali-Silica Reaction and Delayed-Ettringite Formation on the Structural Performance of the Dapped End Region of Prestressed Concrete Trapezoidal Box Beams

Tests were conducted on the dapped end sections of two beams that had undergone significant concrete cracking due to alkali-silica reactions (ASR) and delayedettringite formation (DEF). The purpose of the tests was to determine the effects of the cracking on the structural performance of the dapped ends of the beams. The beams were full-scale prestressed trapezoidal box beams. The beams were rejected because of fabrication errors and remained in a casting yard for over 14 years during which time the cracking damage occurred. The beams were transported to the laboratory for testing. Loading was applied to the beams to produce high shear forces at the dapped ends. Shear strength in the dapped end regions is critical and the effects or ASR/DEF damage on such beams has not been studied.

The observed strength of the dapped ends was compared with calculated strength using the provisions of the PCI Design Handbook, ACI 318-08, and AASHTO LRFD Specifications. The observed strengths were greater than the computed strengths. Additional testing is underway.