Effect of high temperature on properties of steel slag aggregate concrete

Abstract

The use of slag as a fire-resistant aggregate was investigated in concrete and in structural members. Three mixtures of three-fractional concrete with type CEM I 52.5N cement were prepared: the reference mixture (dolomite fractions of 0–4mm, 4–8mm and 8–16mm) and two mixtures with coarse slag fractions (4–8mm and 8–16mm) and a fine dolomite fraction (0–4mm). At 56 days the specimens were exposed to high temperatures. Their residual mechanical properties (flexural strength, compressive strength and static modulus of elasticity) and residual mass were tested after cooling, and results were compared among specimens. To determine the fire resistance of a structural member with slag in the concrete mixture, fire resistance of reinforced-concrete beams with slag was compared with that of reinforced-concrete beams with dolomite. In these experiments, concrete beams were exposed to high temperature according to the ISO 834 temperature curve for 60min. The temperature increase within the beams during their exposure to high temperature in the furnace was also observed. Bearing capacity was tested after fire exposure and compared with bearing capacity of the beams at room temperature. The results showed that slag in combination with Portland cement did not increase fire resistance of concrete and its structural members. In order to create a structural member with improved fire resistance, slag should be combined with a binder that can better adapt to slag expansion under high temperature or be used as a partial replacement for coarse aggregate in concrete.