2011 – Searching for Solutions to ASR

Bob Wark, Louise Thomas, Andrew Peek

Alkali Silica Reaction (ASR) has been by far the dominant cause identified in the deterioration of concrete caused by expansion of the pastes from an interaction with the aggregates. However the path to the identification of the presence of the deleterious effects of ASR is not always straightforward. In a recent example, the concrete spillway slabs and walls at South Dandalup Dam exhibited classic craze cracking symptoms of ASR. However when subjected to more detailed analysis the driving process was found to be delayed ettringite formation (DEF).

ASR and DEF are chemically different concrete deterioration mechanisms with physically similar manifestation, causing slow concrete expansion in the presence of moisture. ASR has been reported mostly in concrete structures constructed prior to the early 90’s when the DEF deterioration mechanism was not fully recognised. However it is possible that ASR and DEF can take place simultaneously and more extensive damage due to DEF could have occurred and remain undetected.

The paper will also describe a recent case using basalt aggregate for Stirling Dam in which the use of an accelerated mortar bar test gave an extreme reaction but the ASTM concrete prism expansion test gave a negative result. Further detailed petrographic examination provided the clues to the real cause.

The paper will describe the occurrence of the problems, compare the causes and outline the methods undertaken to investigate the issues. Alternative concrete mix designs, incorporating a high flyash content to replace ordinary Portland cement as the main pozzolanic material, have been investigated and successfully implemented. This paper describes the investigations undertaken to develop these alternate mixes, the resultant properties of the concrete and its resistance to deterioration.

2011 – Searching for Solutions to ASR