Bond of self-compacting concrete incorporating silica fume: Top-bar effect, effects of rebar distance from casting point and of rebar-to-concrete relative displacements during setting

Abstract

This study investigates the effect of different silica fume levels of cement replacement on the bond capacity of Self-Compacting Concrete (SCC).Specifically, the top-bar effect, the bond variation as a function of the rebar distance from the casting point and the effect of a rebar-to-concrete relative displacement during setting on bond are examined. Vertical and horizontal specimens with transverse rebars distributed over height (600mm) and length (1780mm), respectively, were cast and tested by pull-out. Six SCC mixtures with various replacement levels were investigated and compared to one reference SCC mixture (without silica fume) and three Normally Vibrated Concrete (NVC) mixtures of different workability classes.It was found that the top-bar effect of SCC mixtures incorporating silica fume is less intense than in NVC and it is almost eliminated for replacement levels between 8.9% and 10.6% (by weight). No bond loss is evident up to at least 1.60m from the casting point. Finally, the effect of a rebar-to-concrete relative displacement during setting on bond is similar between SCC and NVC. Although higher initial setting times are observed in SCC, bond is not prone to reduction due to a rebar-to-concrete relative displacement during this period.