# Physical-Mechanical Properties of Cupola Slag Cement Paste
## 1 Introduction  
The changes introduced in the iron and steel manufacturing processes of ferrous alloys have generated, in recent years, new types of industrial waste which, given the unavoidable requirements of sustainability, must be reused as much as possible. In particular, steel slag has recently been the subject of numerous valorisation studies [1; 2; 3] that have accredited its suitability for different uses depending on its origin and characteristics; these range from being used as a raw material in the production of cement to its use as aggregates for concrete or bituminous mixtures [4; 5]. Slags can be produced from a wide range of metallurgical sources, such as iron, steel, nickel, manganese, copper, etc. The various types of slags have similar metallurgical functions, although they vary widely in their physical and chemical properties. The most commonly used slag in the construction industry is steel slag, which comes from steelmaking and smelting. Traditional steel production takes place in blast furnaces and the raw materials used are iron ore, coke and lime, limestone or dolomite as fluxes. The slag thus generated is called blast furnace slag, defined as \"a non-metallic product consisting essentially of silicates and aluminosilicates of calcium and other bases, which was developed under liquid conditions together with iron in the blast furnace\". Currently, other options have been established based on three types of processes: electric arc furnace, basic oxygen furnace and ladle furnace. The raw materials for steelmaking are iron and blast furnace slag, in varying proportions depending on the furnace, lime and limestone or dolomite. Blast furnace slag has been used in the binder industry for a long time, and it is interesting to note that as early as 1862 the first known tests on the granulation of slag were carried out, showing that this basic slag, ground and mixed with hydraulic lime, gaverise to a material which, without reaching the quality of Portland cement, was superior to systems which only used lime as a binder. This waste is also used in mining technologies such as backfilling, which is desirable for environmental reasons [6]. In the case of electric arc furnace slag, the existence of certain previous experiences related to its reuse as a construction material, carried out without prior control of the quality of the waste, and which in some cases have posed serious problems for the safety of the construction site and/or the environment, highlight the need to carry out a specific and detailed investigation to guarantee the suitability of the proposed application. Cupola slag (CS) is an industrial by-product generated in the production of parts after a casting process in cupola furnaces. In general, for each tonne of molten metal, between 50-60 kg of CS are generated [7], which, in Spain, is mostly sent to landfill. It is a waste that is easily separated from the metal by flotation when both are in a liquid state due to the considerably lower density of the slag. The properties of these slags will depend, to a large extent, on the cooling process, since the faster the cooling process, the more chemical compounds will present an amorphous structure, i.e., the more susceptible the slag will be to pozzolanic, active behaviour. Concrete is the most widely used material in construction and is estimated to be responsible for 10% of man-made CO\({}_{2}\) emissions [8; 9; 10]. For this reason, many solutions have been proposed over the years to reduce the environmental impact of concrete manufacture [11; 12; 13]. One of these options is to recover waste by using it as aggregates for the manufacture of concrete. Although the most commonly used waste is construction and demolition waste [14; 15; 16; 17], there are also a large number of studies in which industrial by-products, such as slag, are incorporated as aggregates [2; 18].