Improvement of Post-fire Properties of Concrete with Steel Slag Aggregate

In this paper electric arc furnace (EAF) steel slag as by-products from the steel production industry is considered as an aggregate which could improve post-fire properties of concrete due to the fact that it is the material that is made at the temperatures of up to 1650 °C. For this purpose five high-strength concrete (HSC) mixtures were prepared: reference mixture with dolomite aggregate and four concrete mixtures with two types of steel slags available from Croatian steel plants as a coarse aggregate. Two slag based concrete mixtures were prepared with the slags that were previously thermally treated. At the age of 56 days concrete specimens have been exposed to high temperatures up to 800 °C. Upon cooling of the specimens their residual properties (compressive strength, modulus of elasticity, weight loss and ultrasonic pulse velocity) were tested and compared with the same properties of the reference concrete. Microstructural analysis based on SEM observations was also done. To clarify the impact of each individual component of concrete mixtures on the behaviour of concrete under high temperatures the dilatometer analysis of cement paste and all aggregate types used in studied mixtures was conducted. The obtained results showed that slag could improve fire performance of concrete in the temperature range up to 400 °C. This improvement is especially observable in the case of concrete made with the previously thermally treated slag.