Review of concrete performance at elevated temperature and hot sodium exposure applications in nuclear industry

The Influence of Nanomaterials on the Thermal Resistance of Cement-Based Composites—A Review

“…Concrete is widely used as a material for high-rise buildings, tunnels, drilling platforms, as well as nuclear facilities (having both satisfactory thermal and shielding properties) [ 5 , 6 , 7 , 8 ]. However, recent accidents involving existing structures have revealed that there is still a strong need to continue studies, in order to understand the effects of high temperature on cement-based materials, as well as to find methods for improving their thermal resistance.…”

“…In general, aggregates usually remain stable up to 500–600 °C, although some siliceous aggregates, such as flint [ 9 , 11 ], are stable only up to 300–350 °C [ 2 , 12 ]. It has been reported that siliceous aggregates (i.e., quartzite, granite), have worse thermal resistance than carbonatic aggregates (such as limestone or dolomite) [ 3 , 5 , 11 ]. This is attributable to the higher thermal expansion of carbonatic aggregates, as well as to the quartz crystal transition, which takes place at around 573 °C (low to high quartz), resulting in volume expansion [ 11 ].…”

“…This is attributable to the higher thermal expansion of carbonatic aggregates, as well as to the quartz crystal transition, which takes place at around 573 °C (low to high quartz), resulting in volume expansion [ 11 ]. In the case of calcareous aggregates, a temperature range of 700 °C to 900 °C seems to be disruptive, as a result of the decomposition of calcium carbonate; CaCO 3 decomposes into CaO (lime) and CO 2 (carbon dioxide) [ 2 , 5 , 13 ].…”

“…In addition to the alternation of the pore structure while heating, when the temperature exceeds 200 °C the first cracks in the cement matrix can be noticed; however, a significant increment in cracks is observable only when the temperature exceeds 400 °C. Above a temperature of 400 °C, the number of cracks increases drastically with temperature [ 3 , 5 ]. Moreover, when the temperature rises, thermal incompatibilities between aggregate and cement paste arise, leading to propagation of micro-cracking in the interfacial transition zone (ITZ) between the cement paste and the aggregate [ 3 ], resulting in significant strength loss.…”

“…As reported by Arioz [ 16 ], exposure to a temperature of 500 °C causes irreversible changes in concretes. A further temperature increment leads to the second phase of C–S–H gel decomposition at 560 °C and formation of β-C 2 S at 600–800 °C, as well as the decomposition of poorly crystalized CaCO 3 to CaO and CO 2 [ 2 , 3 , 5 , 13 ]. A temperature of 600 °C seems to be critical for concrete, resulting in an extreme increase in cracks observed on the surface of the concrete, as well as significant growth of porosity, resulting in a dramatic strength loss in the concrete [ 5 , 9 ].…”