Characteristics of alkali-activated slag powder mixing with seawater: Workability, hydration reaction kinetics and mechanism

Abstract

Marine engineering is faced with the problem of shortage of engineering materials. The local use of marine raw materials, such as seawater and sea sand, can greatly promote the development of marine engineering construction. In order to explore the application potential of seawater in marine engineering materials, in this paper, the influences of seawater on the physical & mechanical properties, hydration kinetics and microstructure of alkali-activated slag powder (AAS) were investigated compared with deionized water. The results show that seawater can reduce the hydration exothermic rate and cumulative heat of AAS. From analysis of hydration kinetics, seawater delays AAS from crystal nucleation and growth (NG) stage into the phase boundary reaction (I) stage and diffusion (D) stage. And the reaction rate of NG and I decrease by seawater, which is manifested by the increase in setting times and fluidity of AAS. Compared with the deionized water mixing, the compressive strength at curing age 3 d to 28 d of the alkali-activated slag mortar mixed with seawater decreases by about 6%. The volume of harmless or less-harmful pores decreases and the porosity of AAS paste increases after seawater mixing, which explains the decrease of strength for AAS with seawater. In additional, AAS can bound chloride ions in seawater.