Influence of seawater on alkali-activated slag concrete

Abstract

This study examines the use of natural seawater as mixing water for alkali-activated slag concrete and reports the characteristics of alkali-activated slag concrete with exposure to seawater. Preliminary experiments were conducted on pastes in order to measure pH and select optimum activator content under the experimental conditions. Wet-sieved pastes from fresh concrete were used to evaluate the mineralogical and microstructural characteristics of reaction products. Compressive strengths and chloride contents were measured with the hardened concrete samples. The activators used in alkali-activated slag concrete were sodium hydroxide (5% weight of slag) and liquid sodium silicate (5% weight of slag). The alkali-activated slag samples showed the carbonation of calcium silicate hydrate (C–S–H), which resulted in the reduction in strength with time. The seawater-mixed alkali-activated slag samples produced additional reaction products, C4AH13, and chloride-bearing hydrocalumite, and they improved the strength. The seawater-mixed alkali-activated slag samples exposed in seawater exhibited improved mechanical performance compared to other samples. C–S–H carbonation did not occur, refinement of the pore structure was confirmed, and the compressive strength increased after exposure to seawater. The release of partial chloride ions, which were bound in solid phases, occurred; however, such slight leaching did not affect the strength of the samples. The investigation within the experimental conditions of this study showed a positive result regarding the use of seawater as mixing water in alkali-activated slag concrete.