Durability of steel fiber reinforced concrete with coarse steel slag aggregates including performance at elevated temperatures

Abstract

The present study investigates the performance of concrete with Electric Arc Furnace (EAF) steel slag as coarse aggregate and steel fiber reinforcement. EAF slag was tested for suitability as concrete aggregate regarding chemical properties, granulometry, apparent specific density, water absorption and flakiness index. Test concrete mixtures were prepared with EAF slag as coarse aggregate with either no reinforcement, or with 30 mm or 60 mm steel fibers at a volume ratio of 0.7%. The test concretes were compared to reference concretes with natural limestone coarse aggregates to determine potential improvement due to the use of EAF slag or due to the use of different steel fiber sizes. The testing program consisted of measuring fresh concrete properties, as well as mechanical properties and toughness of the hardened concrete. The results on fresh concrete showed that water absorption of EAF slag needs to be considered at the design stage, otherwise there is a workability loss in fresh concrete, and that EAF slag use leads to considerable increase in density. However, the mechanical properties of concrete with EAF slag aggregates were significantly higher compared to the reference concrete. This increase was also recorded regarding the toughness and impact resistance of Steel Fiber Reinforced Concrete (SFRC). Durability measurements regarding drying shrinkage, abrasion resistance and freeze-thaw resistance showed that the use of EAF slag as coarse aggregate improved the performance of SFRC. Regarding thermal behavior, the thermal conductivity of the test concretes was measured, while hardened SFRC specimens were subjected to elevated temperatures up to 870 °C. After heating, the microstructure of the concrete was investigated, and the specimens were tested for compressive strength and ultrasonic pulse velocity. The results show that although EAF slag aggregates tend to form micro cracks at temperatures higher than 600 °C and the rate of strength loss is increased, there is a reduced risk of spalling.