Diagnosis of chemical attack of concrete structures: The role of microscopy

Microscopical analysis of concrete in a deteriorating structure involves investigative techniques that make use of various analytical methods to solve specific problems related to the concrete. The technique is quick and particularly useful for diagnosing concrete deterioration and damage problems such as alkali-silica reactions, sulphate attack, frost damage, fire damage and also for assessing the quality of aggregate for use in concrete. This paper deals with the use of stereomicroscopy, polarising and fluorescent microscopy and scanning electron microscopy to diagnose deterioration of the concrete in concrete structures caused by chemical attack. It is based on several years of experience with the use of microscopy in solving concrete problems. Three mechanisms of chemical deterioration namely alkali-silica reaction, sulphate attack and pop-outs formation due to oxidation of iron sulphide are described for the purposes of illustrating the microscopical techniques. In each case, the vital role played by microscopy in analysing the specific problem is emphasise