Effect of blast furnace slag on the strength development of concrete

Blast furnace slag cements generally give a higher durability of the concrete compared to that of other types of cements. Therefore, slag cements should be very suitable for concrete structures in severe environments. Depending on the slag content, however, concrete based on slag cements may show a very low early age strength compared to that of other types of cement. In order to provide more information about the effect of slag on the strength development of concrete, an experimental program was carried out, where the ordinary Portland cement was successively replaced by blast furnace slag of up to 80%. The water/binder ratio of the concrete was 0.40, and the Blaine fineness of the slag was 600 m²/kg. For some of the concrete mixtures, the cement replacement was also combined with other supplementary materials such as silica fume and fly ash. The combination of the slag with silica fume significantly increased the early age strength of the concrete, and therefore, a proper incorporation of silica fume may effectively counteract the reduced early age strength caused by high volumes of slag. By combining the slag with silica fume, also the durability of the concrete will be further enhanced.