Structural Assessment of "D" Regions Affected by Premature Concrete Deterioration: Technical Report (0-5997-1)

The effects of ASR/DEF on the D-regions of structures are investigated by means of a dual experimental and analytical modeling program. Four near full scale specimens that represent cantilever and straddle pier bents, that are representative of typical bridges in Texas, are constructed, conditioned over time, and tested to failure. The undamaged first specimen serves as the control specimen, while the next two are tested after eight months and two years of field conditioning through the Texas heat along with supplemental water aimed at promoting ASR/DEF. The fourth remains to be tested within the next three years. In the two specimens subjected to deterioration, early formation of ASR gel is observed, and with time load-induced cracks along with other additional cracks are observed. These additional cracks are a result of the continued formation of ASR gel, which causes the concrete to swell, and in turn puts the reinforcing steel into a state of active prestress. It is observed that the failure mechanism in all the specimens is a brittle shear failure through the beam-column joint. Specimens with ASR/DEF deterioration show greater stiffness and strength, and slightly greater ductility. A Compatibility Strut-and Tie (C-STM) technique is developed as a suitable minimalist analysis technique to model the force-deformation behavior of reinforced concrete bridge piers with significant D-regions that may be deteriorated through ASR/DEF effects. The C-STM simulates the overall and the internal behavior of the structure very well. In spite of the disturbing appearances of the ASR/DEF damage arising from concrete swelling and cracking, the performance and strength of the specimens are not impaired. Damage that appears in the cover concrete region is offset by the mild level of confinement to the core concrete induced by the reinforcing steel.