Effect of Curing Temperature on Tunnel Fire Insulation of Aerogel Cement Paste Coatings

Abstract

To further strengthen the protective effect of aerogel cement paste (ACP) coating on self-compacting concrete (SCC) in tunnel fire under the optimal mix proportion, the effect of curing temperature (from 5 to 80 °C, based on site construction curing temperature and surrounding rock temperature) on fire insulation of ACP was investigated. The mechanical properties, thermal conductivity and porosity of ACP were tested. The microstructure of ACP was characterized by means of SEM, XRD and TG/DTG. The results reveal that 50 °C is the optimal curing temperature for ACP with good mechanical properties and fire insulation. Relatively high curing temperature can facilitate hydration and pozzolanic reactions, contributing to the generation of more stable substances (such as C-S-H gels, tobermorite and thenardite, etc). ACP under excessive low curing temperature brings inhomogeneous microstructure with coarse pores, leading to producing wider and longer microcracks when it is exposed to tunnel fire. The microcracks make the heat convection and thermal radiation more significant and thus accelerate the damage of ACP under fire. In case of the less than 7% difference of thermal conductivity, dense microstructure and stable substances are more conducive to strengthening fire insulation of ACP. In practical engineering applications, the thickness of protective layer of ACP can be further optimized when ACP is cured under about 50 °C.