Abstract
The alkali silica reaction (asr) occurs in concrete when certain siliceous minerals in an aggregate react with the alkaline pore solution in the hardened cement paste. The reaction is expansive and may crack and damage structural components constructed from reinforced and prestressed concrete. This report looks at non-destructive methods for detecting and mapping cracks caused by asr. The aim was to identify a method whch could determine the extent of internal cracking and the orientation and depth of cracks in reinforced concrete. The selected system would be able to scan the surface of the concrete, discriminate between cracks, reinforcement and other embedded materials, and be robust and portable. The investigation took the form of a literature survey and a laboratory demonstration of techniques with potential for development. The report concludes that there are a number of techniques which might be able to provide all or some of the information required. The practical demands for a portable robust instrument rules out x-ray or gamma-ray radiography and tomography which are capable of mapping internal cracks. Ultrasonic time-of-flight methods appear to have the greatest potential for measuring the depth of surface breaking cracks, although radar, acoustic emission, thermography and electrical continuity are thought to be worth exploring in the longer term. (Author/TRRL)
Published Version
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