Behavior of SSFA high-strength concrete at ambient and after exposure to elevated temperatures

Owing to the higher strength-to-weight ratio and elastic modulus as well as more cost-effective, high-strength concrete (HSC) is now becoming increasing popular. However, the huge demand of HSC results in over-exploitation of river sand (RS) and other raw materials, which impairs the environment. Steel slag, a waste by-product of steel-making process, has been reported to be a great substitute for RS. However, up to now, relatively few research studies investigated the post-fire behavior of steel slag fine aggregate (SSFA) HSC. To promote the practical application of SSFA as the RS substitute in HSC, its behavior at ambient and after exposure to elevated temperatures should be studied thoroughly. Thus, 27 HSC mixtures with different SSFA and / or silica fume (SF) volumetric replacement ratios, and different amounts of superplasticizer (SP) were designed and a series of experimental tests were conducted, including slump-flow, wet packing density (WPD), X-ray diffraction, compressive strength and heating tests at target temperatures of 600, 800and 1000°C. Results revealed that the physical and chemical characteristics of SSFA could enhance the compressive strength of HSC but impair its flowability, which could be mitigated by adding suitable amount of SF and SP. Besides, adding SSFA and SF may be disadvantageous to the post-fire behavior of HSC owing to the enhanced WPD, whose relative strength index was reduced from 0.185~0.199 to 0.084~0.127 by fully replacing RS with SSFA upon 1000°C.