SEDL / STP / STP1215-EB / STP12648S

The Identification and Measurement of Entrained Air in Concrete using Image Analysis

Cahill, J
Scientist, Unilever Research, Port Sunlight Laboratory, Bebington, Wirral

Dolan, JC
Research and Development Manager, Cormix Construction Chemicals, Warrington,

Inward, PW
Scientist, Unilever Research, Port Sunlight Laboratory, Bebington, Wirral

Pages: 14    Published: Jan 1994

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Abstract

The use of ASTM C457 (“linear traverse” or “modified point-count methods”) for microscopical determination of air-void content and parameters of the air-void system, in hardened concrete has become widespread in the prediction of the durability of concrete in freeze-thaw conditions, and in assessing concrete that has failed in service. More recently a new European Standard, based on linear traverse measurements has been adopted as an efficacy test for air entraining agents. The linear traverse method described in both standards involves identification, counting and, in the Euro Standard, measurement of air-voids. It is laborious, tedious and subjective and the error of the method has not been rigorously assessed. We have explored the possibility of using Image Analysis in conjunction with the linear traverse method to develop less laborious and subjective measurement methods. A number of methods of visualisation of air-voids have been applied to polished samples of hardened concrete which had previously been assessed by the standard linear traverse method. The quality of the surface preparation required for Image Analysis was found to be even more critical than for the standard manual method.