Pore and strength characteristics of alkali-activated slag paste with seawater

This study investigates the pore and strength characteristics of alkali-activated slag paste, using seawater (SW) and tap water (TW) as the mixing water. During the investigation, the water/binder ratio was 0·45 and the activator used was sodium hydroxide (NaOH). Activator concentrations of 2, 4 and 6% of the binder weight were used. The compressive strength was measured and X-ray diffraction, mercury-intrusion porosimetry (MIP) and scanning electron microscopy analyses were conducted to determine the cause of the change in strength and pore structure. The results indicate that the compressive strength for early and later ages improved with the use of SW instead of TW. When SW was used, calcium–silicate–hydrate gel and Friedel's salt were identified as the hydration reactants. Based on the MIP measurements, when the sodium hydroxide concentration was increased, the pore size and number of pores decreased to form a denser matrix. In particular, samples containing SW had an increased number of gel pores (<0·01 μm).