Alkali-Aggregate Reaction in the Roads and Traffic Authority Bridges, NSW, Australia


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Title: Alkali-Aggregate Reaction in the Roads and Traffic Authority Bridges, NSW, Australia

Author(s): A. Shayan and H. Morris

Publication: Special Publication

Volume: 170


Appears on pages(s): 597-616

Keywords: Alkali-aggregate reactions; alkali carbonate reactions; basalt; bridges (structures); cracking (fracturing); expansion.

Date: 7/1/1997

Nine bridges under the control of the Roads and Traffic Authority (RTA), in New South Wales (NSW), were inspected in two different regions of the State, and seven with various degrees of cracking and/or repair were selected for examination, particularly with respect to alkali-aggregate reaction (AAR). Twenty-eight cores were drilled from four bridges in the north-east coastal area and 14 cores from three bridges in the same area but 250 km inland. Detailed petrographic examination and scanning electron microscopy of the cores has shown that of the three inland bridges, definite signs of AAR are present in two bridges but the third bridge has a less clear diagnosis, although the aggregate is the same. For the bridges in the coastal area the glassy basalt may have reacted, although typical visual signs of AAR products were not evident. Clay alteration products in the basalt used for two of the bridges may have caused some dimensional instability. For one of the bridges, signs of alkali-carbonate reaction (ACR) were seen in some cores, but the contribution of this reaction to cracking of the bridge is not clear. This is the first report of ACR in Australia. The expansive behavior of cores and alkali levels are also discussed. subjected to elevated temperature, humidity,