Effect of ferrosilicon and silica fume on mechanical, durability, and microstructure characteristics of ultra high-performance concrete

This paper presents a new material that can be used as a partial substitute for cement in the production of ultra high-performance concrete (UHPC). This material is an industrial waste product of ferrosilicon (FS) alloy, which is available as furnace slag. It is used as a partial substitute for cement after grinding until it reaches the stage of microparticles with a surface area of 12,850 (cm2/gm). UHPC mixtures are designed with cement replacement ratios of 5%, 10%, 15%, 20% and 25% by FS, and same proportions of silica fume (SF). Fresh concrete properties are assessed by applying tests of air content and workability. Mechanical properties are assessed by applying tests of compressive strength, split tensile strength, flexural strength and modulus of elasticity. Moreover, transport properties are assessed by chloride penetration resistance and initial sorptivity water permeability test. Microstructure analyses are carried out by SEM-EDX and XRD tests. Results show that the increase in cement replacement rates by SF and FS by 25% of cement mass reduces slump flow to 345 and 356 mm, respectively, whereas it is 385 for the control mixture. Inclusion up to 20% FS enhances compressive strength by 210.4 MPa compared with 178.6 for the control mix at 90 days. In addition, including up to 25% FS improves the transport properties of UHPC by increasing permeability resistance compared with the control mixture.