sexta-feira, 29 de abril de 2011

ALKALI-AGGREGATE REACTIVITY- DURABILITY

Figure 11-20.Cracking of concrete from alkali-silica reactivity.


Figure 11-21. Indication of potential alkali-silica reaction is provided by the classic map cracks on the surface of the concrete.
ASR should be verified by petrographic examination



Figure 11-22. Popouts caused by ASR of sand-sized particles. 

Aggregates containing certain constituents can react with alkali hydroxides in concrete. The reactivity is potentially harmful only when it produces significant expansion. Alkali-aggregate reactivity (AAR) has two forms – alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). ASR is of greater concern than ACR because the occurrence of aggregates containing reactive silica minerals is more widespread.

Alkali-silica reactivity has been recognized as a potential source of distress in concrete since the late 1930s. The reduction of ASR potential requires understanding the ASR mechanism; properly using tests to identify potentially reactive aggregates; and, if needed, taking steps to minimize the potential for expansion and related cracking.

PCA's Concrete Technology E-briefing

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