ABSTRACT
The use of recycled concrete aggregates in the casting of concrete elements is one of the ways to achieve more sustainable buildings. Nowadays, these new concretes are more and more characterized, allowing their incorporation in construction projects. However, the fire behavior remains a research area that has seen limited attention. This chapter aims to characterize the behavior of two specific concretes with 30% and 100% recycled coarse aggregate replacement rate (with 30% and 0% recycled sand replacement rate, respectively). It goes from the characterization of heated recycled concrete behavior up to the spalling occurrence assessment and fire resistance of large-scale elements. The spalling of concrete was evaluated in a comparative way on four slabs: 20 cm thick, 4.6 m long, and 1.5 m wide. In addition to the two formulas with recycled aggregate (RA) concretes (RAC), two other slabs with natural aggregates (NA, siliceous or limestone) were made. The thermal profiles within these slabs were also measured during the tests carried out under the conventional temperature time curve (commonly called ISO 834). The concrete mix with RAs has a higher moisture content than with NA (+ 0.5 to + 1.5%), which may explain some few localized spalling that are not detrimental to fire resistance. Furthermore, the thermal gradients inside the specimens show a lower thermal diffusivity for RAC, which has been confirmed by 254transient plane source (TPS) measurements through a lower thermal conductivity. Hot and residual thermomechanical characteristics were determined for the two concretes tested with RA on samples of diameter 10 cm and length 30 cm at 300°C and 600°C (according to the recommendations of RILEM). Lastly, the fire resistance of two beams with a total length of 4.2 m was also evaluated and analyzed in a comparative way with a design according to Eurocode 2-1-2 (the tests were carried out according to the reference NF EN 1365-3). The results show good agreement with the Eurocode 2-1-2 requirements.
