Microstructural characterization of ultra-high performance concrete further hydrating in the marine environment

Further hydration as the origin of self-healing in ultra-high performance concrete (UHPC) is highly concerned. However, UHPC generally serves in the marine environment. The effects of the chloride ions on this process have not been sufficiently considered. Herein, the effects of water and chloride ions on the further hydration of the cement paste with silica fume (C5SF1) used in UHPC were evaluated, respectively. To simulate the further hydration in marine environment, the UHPC specimens were immersed in 3.5 wt.% NaCl solution after 28 days of standard curing. The microstructural changes of UHPC during further hydration were analyzed by mercury intrusion porosimetry (MIP), thermogravimetric/differential thermogravimetric (TG/DTG) analysis and calorimetry test. The results showed that the porosity of C5SF1 further hydrated in water fluctuated certainly, which was dominated by the repairing effects of hydration products. Although increasing the porosity of C5SF1, the chloride ions would improve the further hydration degree. While during the further hydration of UHPC in NaCl solution, the porosity showed a dropping trend in the period of 1 ~ 7 and 28 ~ 45 days. © 2022, RILEM.