The effect of product form of silica fume on its ability to control alkali–silica reaction

Abstract

Various alternative product forms of silica fume (SF), such as densified, compacted, and slurried, have been developed and employed to improve transport and handling properties over those of as-produced undensified SF. However, few data exist on the dispersibility of these forms in concrete to ascertain whether there is equivalent performance. The effects that the form of SF have on resistance to alkali–silica reaction (ASR) expansion were investigated by: (1) concrete prism expansion; (2) mortar bar expansion; and (3) paste pore solution analysis. The mixtures tested included 4%, 8%, and 12% SF replacement by mass of cement, and ordinary Portland cement mixtures for control purposes. At low replacement levels of SF (i.e. 4%), performance was found to vary with product form. At higher levels of replacement (i.e. 8% and 12%), there are no discernible differences in the results from the concrete prism expansion (up to 1 year) or paste pore solution analysis of mixtures made with the various forms of SF tested. The accelerated mortar bar test results at all levels of replacement indicate that under these conditions undensified and slurried SFs are significantly better at controlling the expansion of a reactive siliceous limestone aggregate than are densified or pelletized SFs.