CHARACTERISTICS OF AGGREGATES IN CONCRETE AND ALKALI-SILICA REACTIONS IN JAPAN --PROCEEDINGS OF THE 7TH INTERNATIONAL CONFERENCE ON CONCRETE ALKALI-AGGREGATE REACTIONS, OTTAWA, CANADA, 1986

Visual examination of and sampling of test pieces were carried out on 21 concrete structures in Japan in which map-like cracks had occurred. Measurements of length changes were performed on these test pieces. In addition, measurements of the alkali reactivities of the coarse aggregates separated from the test pieces and analysis of their mineral assemblages by means of x-ray diffraction were undertaken. The results showed that in 20 structures the cracks were due or possibly due to alkali silica reactions. The rocks which were the cause of these reactions were aphyric bronzite andesite (so-called sanukitoids) and other andesites and cherts.(a) for the covering abstract of the conference see IRRD 811982.