Abstract:
Corrosion of rebar in concrete is commonly associated with, and to a large degree influenced by, the free chloride concentration in
the pore water. It is standard industry practice to add various mineral admixtures such as pulverised fuel ash (PFA), or fly ash,
ground granulated blast furnace slag (GGBS) and silica fume (SF), to concrete mixtures to increase the corrosion resistance of the
reinforcement in the matrix and its subsequent design life span. Various investigations have reported on the effect of mineral
admixtures and additions on chloride binding in cementitious matrices, and the current study contributes further to knowledge
in this field. Unlike previous investigations, this study attempted to make a clear distinction between the contributions of the
two components in a blended cement consisting of ordinary Portland cement (OPC) and ground blast furnace slag (BFS). These
contributions of each component have been quantified. Relationships between the total amount of chloride bound, the level of
BFS additions, and the levels of initial chloride content present in the matrix were determined. It was found that the OPC/BFS
blended cement with partial BFS replacements of up to 50%displayed a lower binding capacity than that of the OPC on its own.
This observation was derived based on the assumption that theOPCand slag reactions were treated as competing and equivalent
and did not take any potential time delays into account, nor the degree of cement hydration. The chloride-binding efficiency by
the BFS is dependent on both the BFS partial replacement addition level as well as the initial amount of chloride present in the
matrix. It is shown that both the OPC and BFS contribute to chloride binding in cement pastes, depending on the amount of BFS
that replace the OPC component in the matrix.
