Beneficial Influence of Nanoparticles on the Strengths and Microstructural Properties of Non-dispersible Underwater Concrete

This paper describes research into the effectiveness of using various nanomaterials, admixtures, and fibers as concrete additives to increase the compressive strength of non-dispersible underwater concrete (NUC). The suitable content of nanomaterials, admixtures, and fibers was determined based on slump tests, cement mass loss, and compressive strength tests for specimens. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) were used to identify the crystalline composition and microstructure characteristics of the modified NUCs. The results showed that the addition of nano-SiO2 or nanometakaolin significantly increased the compressive strength of the NUC. The compressive strength of the NUC containing 3% nano-SiO2 or 5% nano-metakaolin increased by 33.5% or 26.4% at 3 days, respectively, and by 52.1 % or 32.6% at 28 days, respectively. XRD, MIP and SEM showed that the nano-SiO2 and nanometakaolin filled internal pores and initiated a pozzolanic effect, making the NUC more complex and increasing its density. The nanomaterials altered the internal structure of the NUC and thus increased its compressive strength. The recommended additives to NUC will make NUC better able to resist a damaging seawater environment, and they have usage potential for real projects.