An investigation of using seawater as mixing water for alkali-activated slag pastes

Recently, freshwater is under stress due to population growth, change of climate, urbanization and industrialization. World Meteorological Organization expected that 5 billion people will be in a shortage of even freshwater for drinking. In fact, it is difficult to get freshwater in some areas. In the construction field, concrete consumes about 2 billion tonnes of freshwater annually. Among possible ways to mitigate the demand of freshwater, seawater (SW) can be used as mixing water for concrete, mortar and paste instead of tap water (TW). This research is an attempt to use SW as mixing water for alkali-activated slag paste mixtures activated by different concentrations of NaOH. Mixing TW was partially replaced with SW at ratios of 50%, 75% and 100%, by weight. The flowability of different mixtures containing different contents of SW was determined. Compressive strength ranging from 3 days up to 365 days was measured. The results showed high flowability and compressive strength when SW was used as mixing water. The rates of enhancement of compressive strength at the early ages were higher than those at the later ages. The process of polymerization of the samples mixed with SW was accelerated as confirmed by thermogravimetric analysis, while the microstructure was modified as confirmed by scanning electron microscopy analysis.