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PETROGRAPHIC CONSIDERATION ON ALKALI-SILICA REACTIVITY OF CORES TAKEN FROM CONCRETE STRUCTURESコンクリート構造物から採取したコアによるアルカリシリカ反応性の岩石学的検討

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Abstract

Using concrete cores taken from the abutments of K and T bridges in Toyama Prefecture, the judgement of potential expansion capacity by accelerated expansion test in 1N-NaOH sol. was verified from the ASR reactivity of the used aggregate and the results of detailed texture observation of the concrete. Fine aggregates used in K bridge has a high content of andesite showing a high ASR reactivity and ASR-gel filled cracks were observed in andesite. By contrast, fine aggregates used in T bridge has a high content of rhyolitic welded tuff showing a low ASR reactivity and no cracks due to ASR were observed. As a result of the alkali solution immersion test, the concrete of K bridge was assessed as “harmful” and that of T bridge was as “innocuous”. From microscopic observations, it was considered that accelerated expansion in T bridge was not promoted due to original absence of cracks in concrete and the progress of carbonation in cement paste.

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