Effect of moisture content on tunnel fire resistance of self-compacting concrete coated with aerogel mortar

Self-compacting concrete (SCC) is widely used in tunnel linings that are subject to fire risks. During tunnel fires, personnel and structural safety are commonly threatened by the explosive spalling of SCC due to its high strength and high moisture content. Recent studies have suggested that a coating of fire-resistant material can efficiently prevent SCC from spalling during a tunnel fire. In this study, SCC samples coated with a 6 mm thick layer of silicon dioxide aerogel-cement mortar (SiO₂-ACM) were prepared and compared with uncoated samples. The effects of different moisture contents (0%, 25%, 50%, 75% and 100%) on the fire resistance of SCC were investigated. The results show that SiO₂-ACM exhibited excellent mechanical and durability performances as well as low thermal conductivity. During exposure to mimetic tunnel fire, the degree of spalling of SCC increased as moisture content increased. The SCC samples with the SiO₂-ACM coating exhibited much less spalling than those without such coating. After the mimetic tunnel fire, the uncoated SCC samples had almost completely failed in terms of compressive strength, whereas the residual compressive strength of the coated SCC samples was more than 68·6% even for the SCC with 100% moisture content. Therefore, a SiO₂-ACM coating provides an attractive means by which to enhance the behaviour of SCC during a tunnel fire.