ABSTRACT
Once the temperatures and the strength properties are assessed, simplified calculations based on EN 1992-1-2 may be used to determine the residual capacity of concrete elements.
2 RESIDUAL STRENGTH
2.1 Compressive strength reduction
Table 1 summarizes the mix design of a Self-Compacting Concrete (SCC), a traditional vibrated concrete with siliceous aggregates (TC) and calcareous aggregates (TCk), as well as a High Strength Concrete (HPC). Cubes (150 × 150 × 150 mm) are cured for 4 weeks in an air-conditioned room at a RH > 90% and a temperature of 20 ± 1°C, after which they are stored at 60% RH and 20 ± 1°C for drying until testing age (>17 weeks). Two cubes are heated for each of the examined temperature levels (till 800°C), occurring at a heating rate of 3.5°C/min. The target temperature is kept constant for 750 minutes to obtain a uniform temperature distribution. The cubes are allowed to cool slowly in an oven (0.5°C/min), after which they are immediately tested for compression. It is noticed that higher heating rates will influence the compressive strength as thermal strains will be introduced due to difference in expansion between the outer and inner concrete.
