**2.2. Characteristics of steelmaking wastes and their influence on clay brick properties**

The steel industry generates a huge variety of wastes in the course of its process, mainly in the case of integrated mills. In relation to the solid wastes generated, the transformation of iron ore into steel can be classified into slags, sludges, and dusts, which together represent between 2 and 4 tons per ton of steel produced. The composition of these wastes varies according to the source of generation but usually contains iron, carbon, calcium, magnesium, silicon, manganese, zinc, and lead. Besides that, some slag and sludge contain a notable amount of heavy metals, and their improper deposition can negatively impact the environment [3, 14–19].

So, the disposals of these wastes in landfills are becoming less attractive which not only occupy plenty of land but also increase the costs. Therefore, it is desirable to identify productive cycles capable of using the steelmaking wastes as raw material. In this way, this will lead to a better evolution of sustainable development. The following will be analyzed as to how the incorporation of these wastes in clayey bodies for production of ceramics for civil construction affects the properties and microstructure of these products.

#### *2.2.1. Slag*

The slag originated at the steelmaking refining process, denoted as steel slag (SS), may vary in chemical composition as a function of the raw materials used and the technology and equipments employed. Currently, this residue is recycled in cement production as well as a base for pavements and composition for aggregates.

The difficulty of using the steel slag as raw material for construction products is its capability to enlarge. This is a consequence of the presence of free CaO and MgO as well as the polymorphism of the dicalcium silicate combined with the oxidation and corrosion of the metallic iron [20].

In relation to the characterization of this waste, the particle sizes with no crush processing present a wide distribution range varying from 20 to 30 × 103 μm and mean particle sizes of 7.860 μm. This is an undesirable feature for traditional ceramic production, in which it typically uses raw material with particles having sizes lower than 2.000 μm. Aiming its application in an industrial way, it would be necessary to comminute this residue before it is added to the ceramic clayey body [14].

**Table 1** presents the chemical composition and the loss on ignition (LoI) of the steel slag, which is predominantly composed of Ca, Fe, Mg, and Si. Ca is present in the form of silicates as well as carbonate. Mg occurs mainly as free oxide and Fe as reduced oxides such as wustite and magnetite. Si occurs as silica and also as complex silicates. The loss on ignition may be attributed to carbonate decomposition and also to the dehydration of hydroxides such as brucite (Mg(OH)<sup>2</sup> ). The chemical composition results also in identified traces of K, V, Ni, Cu, Zn, Nb, Rh, and I.

The incorporations of 0 (C0SS), 5 (C5SS), 10 (C10SS), 20 (C20SS), and 30 (C30SS) wt.% of SS into clayey body, sieved at 20 mesh (0.840 μm), were evaluated by `Vieira and Monteiro (2010) [14]. The specimens were sintered at 700, 900, and 1000°C at heating rate of 3°C/min.

The extrusion prognostic is an important parameter to production of ceramics for civil construction, since this property is related to the workability and productivity of the pieces. In **Figure 1**, it can be observed that the clayey body without waste incorporation is located within the limits of the acceptable and non-recommended regions, and in practice, the results indicate that the incorporation of SS did not practically present significant variation at the workability of the clay.

The results of the technological properties evaluated are represented in **Figures 2**–**4**. In relation to the influence of the steel slag incorporation, the incorporation of higher up to 10 wt.% impairs the water absorption (**Figure 2**), while adding up to 5% has improved this property. This slight improvement in water absorption may be due to the better packaging provided by the addition of the residue. It may be noted that the temperature elevation of 700–900°C increased the water absorption; this can be explained by the combustion of coke fines at temperatures close to 800°C. The linear shrinkage (**Figure 3**) almost does not change with SS incorporation at sintering temperatures of 700 and 900°C. From another point of view, at temperature of 1100°C, the linear shrinkage significantly decreases with the SS incorporation. The flexural rupture strength is represented in **Figure 4**, and the results suggest that the incorporation

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 29

**Figure 2.** Water absorption of the clay as a function the amount of the SS incorporated [14].

**Figure 1.** Extrusion prognostic through Atterberg limits [14].


**Table 1.** Chemical composition of the SS (wt.%) and loss on ignition (LoI) [14].

**Figure 1.** Extrusion prognostic through Atterberg limits [14].

incorporation of these wastes in clayey bodies for production of ceramics for civil construc-

The slag originated at the steelmaking refining process, denoted as steel slag (SS), may vary in chemical composition as a function of the raw materials used and the technology and equipments employed. Currently, this residue is recycled in cement production as well as a base for

The difficulty of using the steel slag as raw material for construction products is its capability to enlarge. This is a consequence of the presence of free CaO and MgO as well as the polymorphism of the dicalcium silicate combined with the oxidation and corrosion of the metallic

In relation to the characterization of this waste, the particle sizes with no crush processing

7.860 μm. This is an undesirable feature for traditional ceramic production, in which it typically uses raw material with particles having sizes lower than 2.000 μm. Aiming its application in an industrial way, it would be necessary to comminute this residue before it is added

**Table 1** presents the chemical composition and the loss on ignition (LoI) of the steel slag, which is predominantly composed of Ca, Fe, Mg, and Si. Ca is present in the form of silicates as well as carbonate. Mg occurs mainly as free oxide and Fe as reduced oxides such as wustite and magnetite. Si occurs as silica and also as complex silicates. The loss on ignition may be attributed to carbonate decomposition and also to the dehydration of hydroxides such as

The incorporations of 0 (C0SS), 5 (C5SS), 10 (C10SS), 20 (C20SS), and 30 (C30SS) wt.% of SS into clayey body, sieved at 20 mesh (0.840 μm), were evaluated by `Vieira and Monteiro (2010)

The extrusion prognostic is an important parameter to production of ceramics for civil construction, since this property is related to the workability and productivity of the pieces. In **Figure 1**, it can be observed that the clayey body without waste incorporation is located within the limits of the acceptable and non-recommended regions, and in practice, the results indicate that the incorporation of SS did not practically present significant variation at the

[14]. The specimens were sintered at 700, 900, and 1000°C at heating rate of 3°C/min.

45.10 23.62 10.29 5.40 0.54 0.34 2.90 1.81 10.33 12.96

). The chemical composition results also in identified traces of K, V, Ni, Cu,

**O3 P2**

**O5 MgO LoI\***

μm and mean particle sizes of

tion affects the properties and microstructure of these products.

28 Current Topics in the Utilization of Clay in Industrial and Medical Applications

present a wide distribution range varying from 20 to 30 × 103

**CaO Fetotal SiO2 MnO SO3 TiO2 Al2**

**Table 1.** Chemical composition of the SS (wt.%) and loss on ignition (LoI) [14].

pavements and composition for aggregates.

to the ceramic clayey body [14].

brucite (Mg(OH)<sup>2</sup>

Zn, Nb, Rh, and I.

workability of the clay.

\*Loss on ignition.

*2.2.1. Slag*

iron [20].

**Figure 2.** Water absorption of the clay as a function the amount of the SS incorporated [14].

The results of the technological properties evaluated are represented in **Figures 2**–**4**. In relation to the influence of the steel slag incorporation, the incorporation of higher up to 10 wt.% impairs the water absorption (**Figure 2**), while adding up to 5% has improved this property. This slight improvement in water absorption may be due to the better packaging provided by the addition of the residue. It may be noted that the temperature elevation of 700–900°C increased the water absorption; this can be explained by the combustion of coke fines at temperatures close to 800°C. The linear shrinkage (**Figure 3**) almost does not change with SS incorporation at sintering temperatures of 700 and 900°C. From another point of view, at temperature of 1100°C, the linear shrinkage significantly decreases with the SS incorporation. The flexural rupture strength is represented in **Figure 4**, and the results suggest that the incorporation

At temperature of 1.100°C, the mechanical strength suddenly decreases with the amount of SS incorporation. At this temperature, the sintering mechanisms are highly intensified; in this sense, the clay minerals are extremely reactive during the sintering stages in temperatures higher than 950°C due to their morphology, constitution, and particle size [17], promoting both solid-state and liquid-state sintering. Thus, the reduction in the content of clay minerals due to the incorporation of residue reduces the reactivity of the ceramic clayey body; therefore, there will be fewer points of contact formed during the sintering, and as a consequence, the mechanical strength of the product will be impaired. For this reason, the deleterious effect of the SS addition on the open porosity and mechanical strength of the clay

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 31

**Figure 5.** SEM micrographs of the fractured region of the clay (a) fired at 700°C; (b) fired at 1100°C [14].

The microstructure of the fracture region of the ceramics containing 0 and 30% of residue is shown in **Figures 5** and **6**, respectively. At these micrographs, it may be noted that the two ceramics presented rougher texture. As expected, the ceramics sintered at higher temperatures produced samples with finer texture, but the cracks and voids are still present. It can be noted that the C30SS ceramic has typical regions in which the materials were plucked out at

**Figure 6.** SEM micrographs of the fractured region of the clay with 30% of SS incorporated (a) fired at 700°C; (b) fired

is more pronounced.

at 1100°C [14].

the moment of the mechanical resistance tests.

**Figure 3.** Linear shrinkage of the clay as a function the amount of the SS incorporated [14].

**Figure 4.** Flexural rupture strength of the clay as a function the amount of the SS incorporated [14].

of 10% SS (C0SS) sintered at 900°C is feasible for the reddish ceramic production since the values for this property are compatible with the products containing 0% of residue. At the lower temperatures investigated, 700 and 900°C, the clayey body (with no SS incorporation) supports SS addition up to 10 wt.% without significant changes on its properties.

Recycling of Steelmaking Plant Wastes in Clay Bricks http://dx.doi.org/10.5772/intechopen.74431 31

**Figure 5.** SEM micrographs of the fractured region of the clay (a) fired at 700°C; (b) fired at 1100°C [14].

At temperature of 1.100°C, the mechanical strength suddenly decreases with the amount of SS incorporation. At this temperature, the sintering mechanisms are highly intensified; in this sense, the clay minerals are extremely reactive during the sintering stages in temperatures higher than 950°C due to their morphology, constitution, and particle size [17], promoting both solid-state and liquid-state sintering. Thus, the reduction in the content of clay minerals due to the incorporation of residue reduces the reactivity of the ceramic clayey body; therefore, there will be fewer points of contact formed during the sintering, and as a consequence, the mechanical strength of the product will be impaired. For this reason, the deleterious effect of the SS addition on the open porosity and mechanical strength of the clay is more pronounced.

The microstructure of the fracture region of the ceramics containing 0 and 30% of residue is shown in **Figures 5** and **6**, respectively. At these micrographs, it may be noted that the two ceramics presented rougher texture. As expected, the ceramics sintered at higher temperatures produced samples with finer texture, but the cracks and voids are still present. It can be noted that the C30SS ceramic has typical regions in which the materials were plucked out at the moment of the mechanical resistance tests.

**Figure 6.** SEM micrographs of the fractured region of the clay with 30% of SS incorporated (a) fired at 700°C; (b) fired at 1100°C [14].

of 10% SS (C0SS) sintered at 900°C is feasible for the reddish ceramic production since the values for this property are compatible with the products containing 0% of residue. At the lower temperatures investigated, 700 and 900°C, the clayey body (with no SS incorporation)

supports SS addition up to 10 wt.% without significant changes on its properties.

**Figure 4.** Flexural rupture strength of the clay as a function the amount of the SS incorporated [14].

**Figure 3.** Linear shrinkage of the clay as a function the amount of the SS incorporated [14].

30 Current Topics in the Utilization of Clay in Industrial and Medical Applications

In this context, it is possible to predict that the SS particles do not react with the clay compounds. The insufficient level of chemical bonding leads the SS particles to stay loose from matrix and therefore generates defects such as voids and cracks in the product.
