An Exploratory Study on Alkali-Activated Slag Blended with Microsize Metakaolin Particles Under the Effect of Seawater Attack and Tidal Zone

In general, building materials exposed to the marine environment are more prone to deteriorates than others. There are three main zones of the marine environment named atmospheric zone, tidal zone and submerged zone. This article investigated the effect of different curing conditions named water curing, air curing, seawater curing and wet/dry curing on the compressive strength and microstructure properties of alkali-activated slag (AAS) pastes with and without microsize metakaolin (mK) particles over a period of up to one year. The wet/dry curing was used to simulate the effect of the tidal zone, of which the specimens were submerged in seawater for 18 h followed by 6 h of air drying per day. The slag was partially replaced with mK at ratios fluctuated from 0 to 12% with a step of 2%, by weight. A fixed concentration of sodium silicate was used as an alkaline activator. After initial curing, the specimens were exposed to the aforementioned treatment conditions for 3, 6 and 12 M. The phase composition and microscopic structure of the neat AAS and AAS/mK samples were tested by X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG) and scanning electron microscopy (SEM). The results showed that the deterioration in the specimens exposed to the simulated tidal zone is more severe than those submerged in seawater. The neat AAS pastes showed better strength and microstructure than those blended with mK.