Cement, Energy and Environment

18 Keywords: EOF Slag, Circularity, Sustainability, Cement, Concrete. 1.0 INTRODUCTION AND LITERATURE REVIEW The necessity of shelter for living is the prime driving factor for gradual evolution of the civilized society. Hence the effort to make a safe space for living is still on the track of evolution. The journey of today’s gigantic skyscrapers started from natural narrow caves and holes in ancient times. The biggest breakthrough in the field of construction of houses and monuments is the invention of Portland cement and concrete. Portland cement is a hydraulic binder that offers excellent fast irreversible binding properties by simple chemical processes like hydration. The conventional Ordinary Portland Cement (OPC) is composed of two components clinker (~95%) and gypsum (~5%). Clinker is the principal component of conventional Portland cement which provides the hydraulic binding property. Conventionally clinker is manufactured by pyro-treatment (~ 1450 °C) of lime-stone and some other supplementary raw materials (to maintain a certain chemical stoichiometry) in a rotary kiln. Primarily, limestone undergoes calcination at the temperature range of 800-900 °C to form calcium oxide (lime) and carbon dioxide [1]. Beyond that temperature range (900-1450 °C) lime reacts with available other oxides (i.e SiO2, Al2O3, Fe2O3) to form different cementitious phases including tri-calcium silicate (C3S, elite), di-calcium silicate (C2S, belite), tri-calcium aluminate (C3A), tetra-calcium aluminoferraite (C4AF) etc [2]. As one mole of CO2 is generated by the calcination of one mole of calcium carbonate, the process of clinkerization causes severe CO2 emission. As a consequence, the cement sector solely contributes ~8 % of global CO2 emissions [3]. Hence the reduction of clinker factor in cement is the most common and relevant challenge for cement and concrete research. Blended cement has been introduced to the market to address this concern. Blended cement are composed of clinker, gypsum, and some supplementary cementitious materials (SCM). Hence the usage of SCM directly reduces the clinker content in cement. SCMs are not able to provide any binding properties individually. However these materials exhibit some pozzolanic or hydraulic reactivity while blended with OPC and provide excellent binding properties [4]. Fly ash, ground granulated blast furnace slag (GGBS), calcined clay, etc. are well-known SCMs, which are already in practice to make blended cement. Slag is a byproduct of metallurgy. The high melting oxide impurities (silica, alumina, etc.) present in the molten metals react with added flux materials (limestone, dolomite, etc.) and generate a low melting as well as low-density floating material. This material is being separated from the molten metal physically and is termed as slag. Iron and steel industries generate several types of slags. Although the iron-making slag (blast furnace slag) is a proven SCM for cement making the steel making slags are still almost unexplored from the aspect of Circular Economy. Almost 150-200 Kg of steel-making slags are generated from 1 ton of liquid steel [5]. This significant amount of slag is usually being dumped or used for landfilling. This demands a huge land space and draws severe environmental pollution concerns. Hence an efficient scope to reuse those steel-making slag may promote a circular economy as well as address the concern about environmental hazards. Energy Optimizing Furnace (EOF) is a primary steel-making furnace where the carbon content of hot metal gets oxidized by efficient O2 blowing through sub-merged tuyeres and supersonic lances. After oxidation of carbon, CO comes out from the hot metal bath and is further burnt in the presence of atmospheric O2 to form CO2. Slags are also generated from the reaction of remaining impurities and added flux materials. The slag generated by the steel refining process from EOF is termed EOF slag. This slag is alsoalmost untouched to date from the aspect of circular economy. There are few reports available in the existing literature on the utilization of EOF slag. Sabapathi et al. (2017) have reported the utilization of surface modified EOF slag as a coarse aggregate for concrete [6]. Malathy et al. (2021) have reported the surface- modified EOF Slag aggregates for concrete and their performance in corrosive environments [7]. But to date the development of any value-added material from EOF slag is yet to be explored. This article deals with the exploration of EOF slag as a potential SCM to make blended cement. Initially, EOF slag has been characterized with different analysis techniques including Optical microscope, XRF, and XRD analyses. Based on the results, different compositions of blended cement (ingredients: clinker, GGBS, ground EOF slag, and