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South African Journal of Chemistry

On-line version ISSN 1996-840X
Print version ISSN 0379-4350

S.Afr.j.chem. (Online) vol.64  Durban  2011




Chloride-binding effect of blast furnace slag in cement pastes containing added chlorides



J.H. PotgieterI; D.J. DelportII, *; S. VerrynIII; S.S. Potgieter-VermaakIV

IChemistry and Materials Division, School of Biology, Chemistry and Health Sciences, Manchester Metropolitan University, All Saints Campus, Oxford Road, Manchester, Ml 5GD, UK
IIDepartment of Chemical & Metallurgical Engineering, Tshwane University of Technology, Private Bag X680, Pretoria, 0001, South Africa
IIIDepartment of Geological Sciences, University of Pretoria, Lynnwood Road, Brooklyn, Pretoria, 0002, South Africa
IVDivision of Chemistry & Environmental Science, School of Science & the Environment, Manchester Metropolitan University, All Saints Campus, Oxford Road, Manchester, Ml 5GD, UK




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 the OPC and 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 ofBFS that replace the OPC component in the matrix.

Keywords: Chloride binding, granulated blast furnace slag, pore solution, permeability, corrosion



Full text available only in pdf format.



The authors express their gratitude to the NRF (National Research Foundation) for financial assistance and Tshwane University of Technology (TUT) for equipment and facilities to conduct the work.



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Received 8 June 2010
Revised 28 May 2011
Accepted 1 July 2011



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