Correlation of Alkali Silica Reaction with Petrographic Examination

The alkali–silica reaction, more commonly known as “concrete cancer”, is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive non-crystalline (amorphous) silica found in many common aggregates in the presence of sufficient moisture.

This reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium silicate [Na₂SiO₃· n H₂O, or Na₂H₂SiO₄· n H₂O, or N-S-H (sodium silicate hydrate)]. This hygroscopic gel swells and increases in volume after absorbing water, it exerts an expansive pressure inside the siliceous aggregate, causing spalling and loss of strength of the concrete, finally leading to its failure.

ASR can lead to serious cracking in concrete, resulting in critical structural problems that can even force the demolition of a particular structure. The expansion of concrete through reaction between cement and aggregates was first studied by Thomas E. Stanton in California during the 1930s with his founding publication in 1940.

In many parts of the world, precautions must be taken to avoid excessive expansion due to alkali-aggregate reactivity (AAR) in many types of concrete construction. AAR may involve siliceous aggregates (alkali-silica reactivity, ASR) or carbonate aggregates (alkali-carbonate reactivity, ACR) and failure to take precautions may result in progressive deterioration, requiring costly repair and rehabilitation of concrete structures to maintain their intended function.

The correlation between the results of ASR and petrographic examination has been presented in this paper.