This paper investigated cements consisting of 60 percent ground granulated blast furnace slag and 40 percent fly ash activated by 7 percent sodium hydroxide. Various slags were used, including some laboratory-made synthetic slags. The influence of additives like superplasticizers and defoaming agents has been examined. The most favorable composition with respect to strength development has been subjected to a durability testing program. A negative aspect appeared to be the carbonation resistance, which is low in comparison with portland cement. Carbonation leads to a decrease in strength. Other properties were favorable.