Mechanical and thermal properties of a heavy radiation-proof concrete exposed to high temperature

Concrete radiation-shielding capability is one of the most sought after properties (together with its mechanical performance) in certain specific structures close to the core of the reactor in nuclear power-plants or aimed to confine X rays in medical facilities. To increase the attenuation properties against X rays, dense concretes with barite aggregates (based on barium sulphate) are often used in order to give the material a mass per unit volume from 25 to 50% higher than that of ordinary concrete. While the attenuation properties of barite-based and other heavy concretes have been extensively investigated in the past, information on their mechanical and thermal properties at high temperature (up to 750°C) is scanty even though fire is one of the most dangerous occurrences in any secluded compartment containing high-tech irradiation devices. A rather typical heavy concrete containing barite aggregates, kept in different environmental conditions after the usual 28-days curing (three years in air or in a moist environment, target strength on cylinders = 30 MPa, nominal mass per unit volume = 3100- 3200 kg/m3) has been recently investigated at high temperature in Milan, with reference to the residual strength in tension and in compression, as well as to the mass loss and to the thermal diffusivity (Tmax = 750°C). After a concise examination of the available literature on heavy concretes exposed to high temperature, some results are presented and discussed. Compared to ordinary concrete, baritic concrete is shown to have better insulation properties and a slightly better heat resistance above 500°C, most probably thanks to the very good thermal compatibility between the coarse aggregate and the cementitious matrix, both based on barite.