Packing coupled post-fire behavior of ultra-heavy-weight concrete

Heavy-weight concrete (HWC) made with heavy-weight aggregate (HWA) is recently widely used in the nuclear industry due to its superior radiation shielding capacity. A new-type HWC containing iron sand (IS) and steel slag coarse aggregate (SSCA) simultaneously, renamed as ultra-heavy-weight concrete (UHWC) due to its ultra-high unit weight, has been proposed in this paper. A total of 16 mixes were fabricated, in which IS and SSCA were selected to replace natural fine and coarse aggregates, respectively with volumetric replacement ratio of 50 % and 100 %. In the meanwhile, fly ash (FA) was adopted to replace 15 %, 25 % and 35 % cement. The heating test with target temperatures of 400–1000°C was conducted and the heating curve, mass loss, surface change, residual compressive strength and elastic modulus after fire were studied. Besides, the chemical phases were detected by X-ray diffraction (XRD) before and after exposure to elevated temperatures. Results revealed that the heat-insulation capacity of UHWC was greatly enhanced by adding SSCA due to its lower thermal conductivity . Satisfactory flowability and pre- and post-fire mechanical properties of UHWC could be achieved. Lastly, it is evident that the pre- and post-fire performance of UHWC could be explicable by the change of packing structure. • Iron sand (IS) and steel slag coarse aggregate (SSCA) are used to produce ultra-heavy-weight concrete (UHWC). • The pre- and post-fire behavior of UHWC was correlated with its packing structure. • The heat-insulation capacity of UHWC was greatly enhanced by adding SSCA. • A fitting curve with high prediction accuracy on the residual strength of UHWC under elevated temperatures up to 1000°C was proposed.