Thermo-mechanical behavior of baritic concrete exposed to high temperature

A number of structures close to the core of the reactor in nuclear power plants or designed to confine X rays in medical facilities are required to have radiation-shielding capabilities. To this aim, dense concretes are used, and – among them – baritic concretes containing barite aggregates, with a mass per unit volume from 25% to 50% higher than that of ordinary concrete.Information on their mechanical and thermal properties at high temperature – however – is scarce and rather outdated, something that should be looked at, as required by the ongoing revamping of several nuclear power plants and by the increasing use of heavy concrete in waste repositories and in medical facilities.A research project on the high-temperature behavior of a rather typical baritic concrete (target strength on cylinders = 30 MPa, mass per unit volume = 3100–3200 kg/m3) has been recently completed in Milan. After the usual curing period, the specimens were kept for three years either in air or in a moist environment. The strength in tension/compression and the elastic modulus after heating and cooling down to room temperature (= residual mechanical properties), as well as the mass loss, the thermal diffusivity and the porosity were investigated up to 750 °C, and damage indices were introduced to quantify the mechanical damage.Compared to ordinary concrete (as indicated in ACI and European documents, and by previous tests performed by the authors), baritic concrete is shown to have better insulation properties, a slightly better residual compressive strength above 500 °C, a similar tensile strength by splitting and a slightly lower stiffness (elastic modulus). In general, however, the high-temperature performance of baritic concrete is similar to that of any good ordinary concrete, thanks to the closeness of the thermal coefficients of baritic aggregate and baritic mortar.