Silica Fume, Bond Strength, and the Compressive Strength of Mortar

ABSTRACTThe strength and strain-rate sensitivity of cement paste and mortar is studied as a function of water-cementitious material ratio (W/C) and silica fume content. W/C's of 0.30 and 0.35 are used for materials without silica fume, while W/C's ranging from 0.336 to 0.436 are used for material containing silica fume. The volume fractions of cement paste matrix and sand are held at 63 and 37 percent, respectively, for all mortars. Strain rates of 30, 3000, and 300,000 microstrain per second are used. The results indicate that materials with silica fume are less strain-rate sensitive of than materials without silica fume. The replacement of cement by silica fume appears to (1) reduce rather than increase the bond strength between cement paste and sand and (2) increase the compressive strength of mortar primarily by increasing the strength of the cement paste matrix.