Effects of low-level silica fume replacement in ASTM C 1260 and ASTM C 227 mortar-bar testing

Replacement of a percentage of cement by supplementary cementing materials (SCM) can control deleterious alkali-silica reaction. Silica fume, a commonly used SCM, and can be used to mitigate alkali-silica reaction (ASR). As-produced, silica fume is very small (0.1 μm) and requires densification for economical distribution. The densification, transportation and storage process may produce larger agglomerated silica fume (up to mm in size). Recently there have been some discrepancies in data reported in the literature as to the effect of these silica fume agglomerates on alkali-silica reaction in laboratory and field experiments. These results led to an investigation of the root causes of these differences. This thesis presents finding from an extensive investigation into the effects of silica fume replacement on alkali-silica reaction. Three different silica fumes (two densified and one undensified) were tested in various combinations with four different aggregates (two non-reactive, one reactive, and one highly-reactive). Results from ASTM C 1260 and preliminary results from ASTM C 227 mortar bar expansion tests are presented. Scanning electron microscopy was used to analyze epoxy-impregnated 28-day mortar samples from the ASTM C 1260 tests. It was observed that one type of silica fume agglomerates was alkali-silica reactive, while another neither increased nor decreased alkali-silica expansion. The undensified silica fume effectively controlled alkali-silica expansion with all aggregates except the highly-reactive aggregateCivil, Architectural, and Environmental Engineerin