Long-term investigation of alkali-silica reaction behaviors in seawater sea-sand concrete

The potential sustainability and cost-effectiveness of seawater sea-sand concrete (SWSSC) have sparked widespread research interest and prompted extensive applied studies. However, the understanding of the alkali-silica reaction (ASR) in SWSSC is still lacking. In this work, the long-term ASR of SWSSC and the characterization of ASR gel was investigated. The result illustrated that the specimens mixed with either seawater or NaCl solution would show long-term ASR expansion, degrading the pore structure and forming ASR cracks. With the increase of sodium ion concentration, higher expansion and larger crack width were observed. Nanoindentation tests further revealed the evolution of ASR damage. The ASR gel produced in SWSCC had a white appearance and consisted of numerous interwoven sheet-like structures forming a honeycomb-like network. Its elastic modulus and hardness were 14.77 GPa and 0.35 GPa, respectively. In addition, the increase of sodium ion concentration would promote the formation of ASR gel but reduce the polymerization degree and the average chain length of the C–S–H, increasing the amount of gel pores.