Physicochemical studies of the destructive alkali-aggregate reaction in concrete

Abstract

In a further stud.I' of t he a lka li-aggregate reaction in high-alkali cements, 11 reactiv e a nd nonreactive experimental aggregates were examined by several procedures. On com-paring t he results of each m ethod with th e standard expansion-bar test, it appears that eac h property studied has some bearing on the expansion characteristics of each aggregate. For exa,mple: (1) The chemical durabili ty as determined by the interferometer procedure was poor for t he aggregates t hat showed excessive expansion, but not a ll aggregates that are shown to be chemically reactive by this procedure will cause expansion, (2) all aggregates are suffi cie ntly hygroscopic to attract the water necessary for t he reaction if other properties arc also favorable, (3) s urface electrical-resistance measurements confirm the hygrosco picity determinations; however, fr ee ions in glasses may have considerably more effect on the sur-face resistance of certain glasses than do thei r hygroscopic properties, and (4) the uneve n di stribution of migratable ions bet\\'een the aggregate surface and the outer phase offers a mechan ism for the' osmotic swellin g of individual aggregate grains, with accompany ing cxp,wsioll in CO Il CI' l'{l' members.