The Impact of Tidal Conditions, Supplementary Cementitious Material and Marine’s Material on Some of Concrete's Durability Parameters

The use of dredged-marine-sand and seawater for concrete production is practically more justified in marine environments due to the primary sources of these materials. Also, it is very crucial to examine the durability parameters of concrete structures in marine environments, especially in tidal conditions, because in these area, consecutive dry/wet cycles, temperature and humidity gradients over time, intensify carbonation and diffusion of conductive ions, therefore physical and chemical deterioration accelerated accordingly. The aim of this research is to investigate the effect of metakaolin, silica fume, and slag on the mechanical properties and microstructure Seawater-seasand concrete in tidal conditions. The results showed that the use of seawater and sand in concrete, due to the presence of chloride ions as well as the filling of voids by ettringite caused by the sulfates attacks, led to the improvement of mechanical properties in the early ages, but after that, a significant drop was occurred. Due to the high source of SiO2 and its high reactivity, silica fume accelerated the consumption of calcium hydroxide, prevented carbonation progress, and formed a dense calcium-silicate-hydrate gel in the microstructure of Seawater-seasand-concrete, and in the presence of magnesium sulfate, better than slag and metakaolin, prevented the formation of ettringite and therefore, propagation of pores and microcracks.