This study presents the results of an experimental evaluation of the performance of high strength concrete (HSC) with basic oxygen steel-making (BOS) slag and nano-silica respectively used as a partial replacement of sand and cement. The properties of fresh and hardened concrete specimens containing 25%, 50%, 75%, and 100% BOS as partial replacement of sand and 2% of cement replaced with nano-silica were evaluated. According to the results, concrete samples containing nano-silica with higher BOS percentages, demonstrated improvements in strength and durability properties, while workability was reduced. For example, at 50% BOS content, about 18% increase in compressive strength and 50% reduction in water absorption was observed, while slump was reduced by 40%.
Concrete is one of the most widely used construction materials in all around the world due to its ease of access, durability, and proper mechanical properties. The global concrete consumption is estimated about 25 billion tons yearly. The large consumption volume of this construction material has raised many environmental issues including depletion of natural raw materials, problems associated with extraction of natural sand from river beds , and a great decrease in resources of fine aggregates in the past 15 years . Furthermore, the greenhouse effect caused by ordinary Portland cement (OPC) production is the main source of CO2 emissions , being responsible for 5–7% of global CO2 emissions . These problems have led many researchers to investigate alternative materials for partial or full replacement of natural aggregates or cement to reduce environmental impacts . One alternative is to replace fine aggregates with some by-products, which can be categorized as: 1) agricultural such as rice husk ash [6,7], 2) industrial such as fly ash [8–11], cement kiln dust , silica fume , granulated blast furnace slag (GBFS) , and bagasse ash , and 3) municipal wastes including glass, plastics , and paper . Rashad provided a general review on using different types of wastes in mortar and concrete . Regarding the industrial wastes, steel-making slag, especially Basic Oxygen Steel-making (BOS) slag, which is produced during the iron/ steel manufacturing process, has attracted the attention of researchers due to its environmentally safe applications . BOS is a non-metallic ceramic material produced from the reaction between flux such as calcium oxide and inorganic non-metallic components in the steel scrap. Typically, 130–200 kg of slag is obtained from one ton of steel depending on the composition and manufacturing process . BOS slag usually contains large clusters, coarse and very fine particles [20,21]. Water is typically poured over slag as it is channeled out of the furnace, providing rapid cooling. This process causes a series of chemical reactions to occur within the slag and causes the material to behave similar to rocks. The chemical composition of slag depends on furnace type, steel grades, and pretreatment method, but generally it consists of SiO2, CaO, Fe2O3, FeO, Al2O3, MgO, MnO, and P2O5 . Furthermore, the grind ability index of steel slag is 0.7, compared to the value of 0.96 and 1.0 for blast furnace slag and standard sand, respectively .