Improving the post-fire behaviour of steel slag coarse aggregate concrete by adding GGBFS

Steel slag is a waste by-product from steelmaking industry but has potential for concrete industry due to its specific physical and chemical properties. Even though the effect of steel slag on the strength, workability and durability of concrete at ambient temperature has been investigated extensively, there were limited research on the behaivour of steel slag concrete (SSC) at and upon exposure to elevated temperatures. To understand and improve the post-fire behaviour of SSC, this paper firstly uses steel slag coarse aggregate (SSCA) to replace natural coarse aggregate (NCA) with replacement ratio of 50% and 100% by volume to make SSC. Then ground granulated blast furnace slag (GGBFS) was adopted to substitute ordinary Portland cement with different volumetric ratios (0%, 15%, 25% and 35%). Nine concrete mixes were designed and after 28-day curing, a series of experiments were conducted: heating test with target temperatures of 400, 600, 800 and 1000 & DEG;C, compressive test, mass loss calculation and surface change comparison. In addition, the chemical composition of concrete at different temperatures was tested using X-ray diffraction. Results showed that the heat resistance of concrete was enhanced for concrete mixes containing SSCA and/or GGBFS. Besides, the post-fire relative strength (post-fire residual strength to the ambient temperature strength ratio) of concrete containing steel slag reduced while adding GGBFS could mitigate this problem effectively. Lastly, EC2 Model was proved to be conservative when estimating the post-fire residual strength of SSC.