The effect of the silica content of silica fume on its ability to control alkali-silica reaction

The use of silica fume (SF) has been instrumental in the development and utilization of high-strength and high-performance concrete. In the interests of economics, questions have been raised regarding the possible use and effectiveness of lower grade SFs with SiO2 contents less than 85%. Such materials do not meet current CSA and ASTM standards for SF. In this study, the performance of two SFs from the same U.S. plant but with different silica contents (68% and 88% SiO2) were compared by examining the effect of the materials on the expansion due to alkali-silica reaction (ASR) and the composition of the pore solution. The mixtures tested with these procedures included 0%, 4%, 8%, and 12% SF replacement by mass of cement. Results show that the SF with lower than standard silica contents cannot control ASR at the levels of replacement examined in this program. (C) 2003 Elsevier Science Ltd. All rights reserved.