Fire resistance properties of heavyweight magnetite concrete in comparison with normal basalt- and quartz-based concrete

Nowadays application of radiation shielding structures grows over the world. Nuclear buildings represent one of the most complicated radiation shielding structures; that is why a particular type of concrete is required to withstand different conditions during their lifespan. Unique properties such as the behaviour under elevated temperatures, radiation shielding, and thermal stability properties are essential to guarantee the fire resistance safety of nuclear buildings. However, some gaps are still there, warranting further investigation, particularly the thermal stability and fire-resistance properties of the heavyweight concrete. The properties are mechanical, physical, and deformation properties of concrete after being subjected to elevated temperature. This paper investigated the fire resistance properties of three concrete mixes. There were magnetite-based concrete, basalt-based concrete, and quartz-based concrete. Compressive and flexural strength, spalling, mass loss, porosity, and scanning electron microscopy were measured for the three concrete types after being subjected to different temperature steps at 20, 150, 300, 500, and 800 °C. The three types of concrete showed different fire resistance properties. Magnetite-based concrete has better heat/fire resistance than basalt- and quartz-based concrete; there was no significant change up to 500 °C, and explosive spalling occurred at 800 °C. Correspondingly, the maximum change in porosity and reduction in the compressive and flexural strength occurred at 300 °C, which indicates the good thermal stability of magnetite-based concrete. Concerning basalt-based and quartz-based concretes, cracks were observed at 500 °C, and cracks with colour change and small spalling were initiated at 800 °C. Therefore, the maximum growth in the porosity and the high reduction in the compressive and flexural strength in basalt-based concrete occurred at 800 °C. Likewise, the extreme change in the porosity occurred at 500 °C, and the drastic reduction in the compressive and the flexural strength in the quartz-based concrete was relatively high at 500 °C and 800 °C. The SEM observations and analysis obtained the appearance of microcracks, voids and degradation of C-S-H in different concrete mixes at 500 and 800℃.