Dean Deschenes

As part of a large-scale experimental study of ASR/DEF-affected bridge bent caps, the accuracy and conservatism of two structural assessment techniques were examined. The crack width summation and elastic rebound techniques were selected for their potential to provide fast, sufficiently accurate estimates of the expansion due to ASR/DEF. These expansion estimates are ultimately valued for their ability to provide clear insights into the behaviour of affected structures. Comparison of the estimates with measured expansions revealed that the crack width summation technique was best suited to the estimation of moderate expansion levels (above 0.2 percent). Conversely, implementation of the elastic rebound test resulted in excellent accuracy at low levels of expansion (below 0.2 percent). It is believed that further refinement of both techniques could lead to an invaluable pair of techniques for the practical assessment of ASR/DEF-affected structures.

The rapid pace of infrastructure growth in the State of Texas is responsible for the recent increase in the number of concrete structures prematurely damaged by alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). Common use of `high-sack' early strength concrete accelerated construction schedules, but also resulted in elevated alkali loadings, high curing temperatures, and substantially increased chances for ASR and DEF deterioration. The consequences of accelerated construction practices are apparent in the Houston District of the Texas Department of Transportation (TxDOT). A number of reinforced concrete bent caps, constructed within the last ten to fifteen years, have developed map cracking and spalls characteristic of ASR and DEF (Figure 1). Outdated material specifications were only recently updated to address the deficiencies and more cases are likely to be discovered in the future. Concerned that future damage may result in a loss of strength and require substantial resources for remediation, the Houston District commissioned the University of Texas at Austin to investigate the structural safety of bridge bents subjected to ASR and DEF.