Utilization of seawater in high calcium fly ash alkali-activated paste cured at ambient temperature

The influence of seawater upon high calcium fly ash alkali activated paste (AAP) on setting time and strength was studied. The materials included high calcium fly ash, sodium hydroxide (NaOH), sodium silicate (NS) and seawater. Setting time and compressive strength of the mixes were tested. The variables included seawater content, liquid to fly ash ratio, NaOH concentration, and NS/NaOH ratio. All mixes were cured at ambient temperature. Seawater was used instead of distilled water to prepare NaOH solution. The incorporation of seawater resulted in the shortening of setting time and increasing compressive strength. The strength enhancement was highly significant when the seawater is used with low NaOH concentration of 5 molar which is cost attractive. The use of seawater with short setting time and sufficiently high strength AAP is useful in applications such as patch repair of pavement and sidewalk, precast sections and other applications in places such as remote coastal areas and islands where fresh water is scarce.