異常ひび割れが発生した構造物コンクリートの鉱物学的考察

概要

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Currently, there are many reports on unusual cracking of concrete structures attributable to alkali aggregate reaction. A mineralogical survey was conducted on concrete specimens from various concrete structures throughout the country. The resuts indicated the unusual cracking of concrete might be influenced by alkali aggregate reaction or the leaching of some constituents of the aggregate and identified the following characteristics. (1) The amount of active minerals to alkali contained in the aggregate is not necessarily related to the cracking. (2) The component radio of SiO/(Na_2O + K_2O)is low in andesite aggregate subject to the cracking. (3) In cured cement, ettringite and portlandite are prevalent or 3CaO・Al_2O_3・8〜12H_2O and 4CaO・Al_2O_3・13H_2O are found to be generated. The so-called alkali aggregate reaction may be an abnormal reaction of cement largely caused by inadequate curing during concrete placement and the leaching of some constituents of the aggregate in concrete.
2006-03-06