THE SUBJECT OF ALKALI-CARBONATE ROCK REACtivity (ACR) was discussed for the first time as a distinct and separate chapter-length topic in ASTM STP 169B by H. N. Walker [1]. Prior to that, W. C. Hansen, in ASTM STP 169A in 1966 [2], discussed the reactivity of dolomitic limestones, along with the reactivity of other rocks and minerals, under the general heading of chemical reactions. Previous editions of Significance of Tests and Properties of Concrete and Concrete-Making Materials (ASTM STP 169, 1956) and its predecessors ASTM STP 22A, in 1943, and ASTM STP 22, in 1935, did not treat the subject of deleterious carbonate rock reactions because such reactions were not recognized as a distinct problem until identified as such by Swenson in 1957 [3], based on his investigations of expanded, cracked, and buckled concrete in the vicinity of Kingston, Ontario, Canada.