Durability of Portland Cement- Silica Fume Mixes in Tidal Zone

In the past couple of decades the use of Silica Fume (S.F.) as a supplementary cementing materials has been extensively increased in concretes used for marine structures in the Persian gulf regions. The reason for this is claimed to be for improving the durability of coastal structures (including within the tidal zone) by the consultant engineers. In this research the performance of cement paste and concrete mixes incorporating 7 and 10 percent of silica fume as a cement replacement have been investigated in three exposure conditions, i.e. in fresh portable water, in coastal tidal zone and in laboratory simulation ponds. The performance of both plain and blended cements was evaluated by measuring the compressive strength, reduction in compressive strength and capillary absorption. The results show that plain type II Portland cement performs better than S.F. incorporated mixes under cyclic wetting and drying condition. The results also indicate that silica fume incorporated specimens under cyclic wetting and drying condition exhibit higher strength loss when compared with plain type II Portland cement or/and when cured under potable water. Inaddition the greater silica fume amount used in the mixes, the more water absorption bycapillary when exposed within tidal zone or/and under wetting and drying simulation. Further, the effect on incorporating GGBS (Ground Granulated Blast furnace Slag) on theperformance of the S.F. mixes in the three different exposure conditions was also investigated. The blended GGBS mix was the worst performing mix in the all three exposure conditions. This paper summarises the investigations conducted to assess the durability of plain and blended type II Portland cement exposed to marine tidal environments.