New Concern over Alkali-Aggregate Reaction.

There are three reasons why there is new concern over alkali-aggregate reaction 1 The simple cheap precaution of specifying low-alkali cement, and obtaining it at no increase in price over cement not required to be low-alkali, will no longer be widely available. 2 Aggregates not previously regarded as reactive are being found to have reacted in concrete in old structures and to be associated with significant cracking and damage. 3 Serious early damage to concrete structures has occurred in places where it was previously unknown, especially in north Germany. Aggregate sources and rock type are discussed. A re-examination is made of the state of knowledge and the state of the use of knowledge in this area.