GGBS is primarily a binder used as an addition to cement which uses the latent hydraulic properties of GGBS to produce Portland blastfurnace cement (6-35% of GGBS) or blastfurnace cement (36-90% GGBS) produced by blending at the concrete mixer, or as a factory blend at the cement factory. When produced at the concrete plant mixer these cements will have the designation CII or CIII, and when produced as a cement factory blend, they have the designation CEM II or CEM III.
GGBS is produced by grinding Granulated Blastfurnace Slag to a controlled fineness. There are a number of different methods of grinding granulated blastfurnace slag. Traditionally, standard ball mills have been used, but since the early 2000s the use of roller presses and vertical mills has increased.
Granulated blastfurnace slag is a very hard material and as a result necessitates the use of high wear resistant materials in the grinding process. The grinding process takes account of mean particle size, grading (particle size distribution), fineness and the particle shape in order to ensure that when used in concrete performance is maximised. Typically, GGBS is ground to a specific surface area of 450-550 m2/kg, similar to that of cement.
GGBS concrete is significantly less permeable to aggressive elements such as chlorides than comparable CEM I concrete it also has significant capacity bind any chloride that are present.
GGBS at the appropriate addition level, is suitable for every designed chemical class of aggressive ground and is the only cement type suitable for DC-4m where the Thaumasite form of attack is a risk.
GGBS is internationally recognised as being effective in reducing the risk of alkali silica (ASR) reactions. No cases of ASR have occurred in concrete containing suitable proportions of ggbs and that high addition rates in excess of 50% are effective controlling expansion with reactive aggregates.
GGBS reactions rates are slower than CEM I and produce different proportions of hydration products which evolve less heat than CEM I. As such it is very effective for reducing the risk of thermal cracking in thick sections such as foundations.
GGBS is off white and as a result produces a much lighter coloured concrete.
GGBS is covered by European Standard BS EN 15167. For further information on the use of Ground granulated blast furnace slag refer to: CSMA - The Cementitious Slag Makers Association.
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