Influence of supplementary cementitious materials on microstructure and transport properties of spacer-concrete interface

Reinforcement spacers are a critical component of concrete structures. Their presence affects microstructure and transport properties cover though this is not widely appreciated. This paper presents the first study to determine whether negative effects can be mitigated through use supplementary cementitious materials such as silica fume, fly ash blast-furnace slag. Concrete samples (>200) with different spacers, binders, curing drying regimes were prepared tested for diffusion, permeation, absorption, electrical conductivity, carbonation microstructure. It was found that increase all properties, extent depending on type spacer, regime mechanism. The spacer-concrete interface weak, porous micro-cracked, lowers resistance ingress aggressive agents. beneficial SCMs (strength enhancement densification) prolonged (120-day) insufficient overcome spacers. Implications durability discussed.