Effects of alkali-silica reaction and delayed ettringite formation on anchorage of prestressing strands in trapezoidal box beams with dapped ends

Abstract

Concern about the effects of alkali-silica reaction (ASR) and delayed ettringite formation (DEF) on dapped prestressed concrete trapezoidal box beams in Houston, Tex., prompted an investigation of their shear strength. Beams originally intended for a highway bridge project were stored in a local precast concrete yard and were exposed to the environment for 15 years. During that period, ASR/DEF deterioration of varying severity occurred. Load tests were conducted on five specimens (two of which are discussed in this paper) with varying levels of distress to study the performance of the dapped end and to assess the effect of the ASR/DEF deterio- ration on the in-service beams. The strength of each specimen was governed by shear-induced anchorage failure confirmed both by the formation of cracks in the development region and slip of the prestressing strands. The length available for the development of the flexural reinforcement was limited, and ASR/ DEF cracking along the development length exacerbated the problem.