Arch. Metall. Mater.

67 (2022), 1, 209-214

DOI: https://doi.org/10.24425/amm.2022.137491

Noor Amira Sarani 1, Azini Amiza Hashim 1, Aeslina Abdul Kadir 1*

,
Nur Fatin Nabila Hissham 1, Mohd Ikhmal Haqeem Hassan 1,
M. Nabiałek 2, B. Jeż 2

Assessment on the Physical, Mechanical Properties and Leaching Behaviour

of Fired Clay Brick Incorporated with Steel Mill Sludge

The disposal of industrial steel mill sludge in landfills has frequently received significant concern as the sludge has a very
notable potential to contaminate soil surface and groundwater in the long run. Recently, the incorporation of industrial steel mill
sludge into fired clay brick has become one of the promising alternative methods as it could produce a lightweight product while
minimizing the environmental impact of the waste used. In this study, fired clay bricks as the most common building material were
incorporated with 0%, 5%, 10% and 15% of steel mill sludge and fired at 1050°C (heating rate of 1°C/min). The manufactured
bricks were subjected to physical and mechanical properties such as firing shrinkage, dry density, and compressive strength while
the Toxicity Characteristic Leaching Procedure (TCLP) was conducted to analyze leaching behavior from the manufactured bricks.
The results demonstrated that incorporation up to 15% of steel mill sludge reduces the properties up to 27.3% of firing shrinkage,
8.1% of dry density and 67.3% of compressive strength. The leaching behavior of Zn and Cu from steel mill sludge was reduced
up to 100% from 7414 to 9.22 ppm (Zn) and 16436 to 4.654 ppm (Cu) after 15% of sludge incorporation. It was observed that high
temperature during the firing process would improve the properties of bricks while immobilizing the heavy metals from the waste.
Therefore, recycling steel mill sludge into construction building materials could not only alleviate the disposal problems but also
promote alternative new raw materials in building industries.
Keywords: building materials; leachability; fired clay brick; steel mill sludge; brick properties

1. Introduction of oil presence in the steel mill sludge has minimized the abil-
ity of the heavy metal in the sludge to be recycled through the
With the rapid development in industrial activity, the de- sintering process. This situation has resulted in the only option
mand for steel production to meet the winding of flat products left for the steel mill sludge is to be treated and disposed of at
continues to increase. Due to the high demand for the product, the designated landfill site [4]. The hazardous metal present in
a large amount of industrial waste has been generated. There is the sludge could have an adverse impact on the environment
no denying that industrial waste is the largest contributor to solid especially if it is being disposed of. Other viable options for
waste generation in landfills. the management of steel sludge must therefore be critically
Over the past few decades, the contamination of heavy investigated.
metal has become a worldwide issue due to its toxic charac- Furthermore sustainable development has promoted the
teristics and abundant production especially from the industry recycling or reuse of sludge to maintain environmental safety.
[1]. The major concern is on the heavy metal components in the One of the alternatives for the recycling of sludge, which offers
wastewater and sludge due to their harmful potential of being enormous potential, is the recycling of sludge into building
released to the surrounding [2]. For instance, the steel industry materials, namely clay brick, ceramic and concrete [5]. This
contributed a large amount of heavy metal sludge. In particular, method provides a long-term approach to sludge disposal for
0.90 tons of steel mill sludge is generated for every 1000 tons economic and environmental sustainability. A few studies have
of rolling steel production [3]. To make it worse, a high level produced a positive result on the use of heavy metal sludge in
1
Universiti Tun Hussein Onn Malaysia, Faculty of Civil Engineering and Built Environment, 86400 Parit Raja, Batu Pahat, Johor, MALAYSIA
2
Częstochowa University of Technology, Faculty of Production Engineering and Materials Technology, Department of Physics, 19 Armii Krajowej
Av., 42-200 Częstochowa, Poland
* Coressponding author: aeslina@uthm.edu.my

© 2022. The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCom-
mercial License (CC BY-NC 4.0, https://creativecommons.org/licenses/by-nc/4.0/deed.en which permits the use, redistribution of
the material in any medium or format, transforming and building upon the material, provided that the article is properly cited, the
BY NC use is noncommercial, and no modifications or adaptations are made.
210
ceramics [6,7]. Another study that has extensively examined the Table 1
possible encapsulation of heavy metal in the fired clay brick, Mixture amount of raw material for SMSB production
found that the temperature increase associated with the firing
of bricks could prevent heavy metals from leaking to the sur- Percentage Amount Amount of Total
Amount of
of steel mill of clay soil steel mill mixture
rounding area [8]. water (mL)
sludge (%) (kg) sludge (kg) amount
The wide usage and versatility of bricks in the building 0 3.00 0.00 3.00 450
industry as well as the structural composition of bricks provide 5 2.85 0.15 3.00 480
a distinctive alternative for sludge recycling [9,10]. The type 10 2.70 0.30 3.00 510
of industrial mill sludge that has been incorporated in bricks 15 2.55 0.45 3.00 540
includes wastewater treatment sludge [5], sewage sludge [11],
mosaic sludge [12], paper sludge [13] and electroplating sludge
[14], with varying sludge composition. The varying composition 2.2. Physical and mechanical testing
of clay and sludge as raw materials showed that bricks can accept
the introduction of high sludge percentage and still maintain to The physical and mechanical properties of bricks that were
be a viable construction option [15]. The physical and mechani- tested in this study are firing shrinkage, dry density, initial rate of
cal properties of these bricks were analyzed, and the findings suction and compressive strength. The procedures of testing were
revealed that the sludge content used in the brick manufacturing carried out following BS 3921:1985 [16]. In each testing, three
plays a crucial role in influencing the brick quality. brick samples for each percentage were used and the properties
This study presents the influence of steel mill sludge value was obtained from an average value.
as a partial replacement of clay soil as a raw material of brick
on the physical and mechanical characteristics of fired clay
bricks as well as their leaching behaviour. The amount of 2.3. Toxicity characteristic leaching procedure testing
steel mill sludge incorporated into fired clay brick is 0%, 5%,
10% and 15%. The mobility of inorganic contaminants present in a brick
sample was tested using the Toxicity Characteristic Leaching
Procedure (TCLP) based on USEPA Test Method 1311. This
2. Materials and methods procedure is essential for the understanding of the leaching
behavior and also for the verification of whether the generated
The methodology involved in this study is mainly divided leachate from brick would classify the material as hazardous.
into three stages which are the manufacturing process, physical The crushed samples from the previous compressive strength
and mechanical properties testing and leaching behavior of steel test were collected and sieved through 9.5 mm sieve. About
mill sludge-brick (SMSB). 20 g of the sieved sample was placed in a 500 mL high-density
polyethylene plastic bottle with 400 mL of predetermined extrac-
tion fluid. The sample was agitated in a rotatory end-to-end at
2.1. Raw materials preparation 30 rpm for 18 ± 2 hours (at 22 to 24°C). Then, the sample was
filtered through a 0.7 µm glass fiber filter and sent for metals
Raw materials for SMSB which are clay soil and steel mill analysis using atomic absorption spectrometry (AAS) analysis.
sludge were collected from the industry located at Sedenak and
Kluang, respectively. Upon arrival, both raw materials were
oven-dried for a day at 105°C. After the drying process, the raw 3. Result and discussion
materials were crushed and sieved to ensure that the particle
size of the materials is less than 500 µm. This step is crucial to In this section, chemical characteristics of clay soil and
make certain of the homogeneity of the sample size for the brick steel mill sludge were discussed. Besides, the results of physical,
manufacturing process. Apart from that, X-Ray Fluorescence mechanical properties and leaching tests were also elaborated
(XRF) analysis was done to determine the chemical elements and compared to the standard brick.
present in the raw material. Four percentages (0%, 5%, 10% and
15%) of steel mill sludge were used as a clay replacement and
mixed with a predetermined amount of water, as per shown in 3.1. Chemical composition of raw materials
Table 1. Next, the brick mixture was compacted into the mould
(210 mm × 102 mm × 65 mm) at pressure 2000 kPa. The brick Table 2 summarized the chemical composition of raw mate-
was then removed and dried in the oven for 24 hours before be- rials obtained from the XRF analysis. From Table 2, clay soil in
ing fired in the furnace at 1050°C with a firing rate of 1°C/min. this study mainly consists of silicon dioxide (SiO2), aluminium
Then, the fired brick samples were left cooled for at least a day oxide (Al2O3) and iron oxide (Fe2O3) with minor content of
at room temperature before being tested for physical, mechanical sodium oxide (Na2O) and calcium oxide (CaO). High silica
and leaching tests. content in the raw material is beneficial to increase the strength
 211
of brick after the firing process. Meanwhile, the presence of 3.2. Firing shrinkage of SMSB
a significant amount of iron oxide influences the reddish colour
of the brick, giving an aesthetic value to the brick. Table 2 also Firing shrinkage is related to the expansion or shrinkage of a
shows that steel mill sludge contains a high amount of iron oxides hardened mixture due to the loss of moisture content throughout
and magnesium oxides. The significant content of iron oxides in the firing stage [17]. In the case of brick, several parameters
steel mill sludge is related to the main materials used to make affect its shrinkage, such as the characteristics and ratio of the
steel bar products. brick components, the method of mixing and the moisture con-
tent of the surroundings. The effect of the amount of steel mill
Table 2 sludge incorporated into fired clay brick on the firing shrinkage
is exhibited in Figure 1. From the trend, it can be observed that
Chemical composition of raw material
the firing shrinkage was decreased with the increasing addition
Concentration (%) of steel mill sludge. The control brick has the highest shrinkage
Chemical
Clay soil Steel mill sludge value with 2.56% followed by 5% SMSB with 2.37%.
Metal content as oxides, dry basis (wt.%) Meanwhile, the shrinkage value for both 10% and 15%
Silicon oxide (SiO2) 60.7 3.2 SMSB is 1.86%. The shrinkage value for all percentages is far
Aluminium oxide (Al2O3) 24.4 0.68 below the standard which is 8%. Apart from that, the result shows
Iron oxide (Fe2O3) 4.46 70.9 that the addition of steel mill sludge has increased the ability of
Sodium oxide (Na2O3) 0.3 5.2 the brick to comply with the standard brick size. Thus, the intro-
Magnesium oxide (MgO) 1.2 4.28 duction of steel mill sludge into fired clay brick could enhance the
Manganese oxide (MnO) 0.05 0.57 shrinkage value while producing brick with excellent properties.
Calcium oxide (CaO) 0.25 1.59
Titanium oxide (TiO) 0.09 0.15
Lead oxide (PbO) 0.04 0.28
Heavy metal, dry basis (ppm)
Chromium (Cr) 19.5 345.5
Scandium (Sc) 14.5 5.0
Vanadium (V) 67.0 33.5
Cobalt (Co) 5.5 11.0
Nickel (Ni) 6.0 102.0
Copper (Cu) 15.0 6932.5
Zinc (Zn) 97.5 15654
Gallium (Ga) 20.0 23.5
Arsenic (As) 15.0 —
Rubidium (Rb) 108.5 35
Strontium (Sr) 47.5 63.5
Yitrium (Y) 57.5 16.5
Fig. 1. Firing shrinkage of steel sludge mill-brick
Zirconium (Zr) 344.5 130.5
Niobium (Nb) 14 6.0
Molybdenum (Mo) 1 9.0
Tin (Sn) 7.5 615.5
3.3. Dry density of SMSB
Antimony (Sb) 2.50 —
Caesium (Cs) 11.5 10.5 Dry density of brick refers to the ratio between the mass
Barium (Ba) 293 195.0 and volume after the drying and firing process. Dry density
Lanthanum (La) 37.5 28.0 value of SMSB is presented in Figure 2. From the figure, it
Cerium (Ce) 80.5 5.0 should be noted that the dry density is inversely proportional
Lead (Pb) 20.5 4121.5 to the amount of steel mill sludge added during manufacturing
Thorium (Th) 26 75.0 process. The control brick was found to have the highest density
value of 1935 ­kg/m3 followed by 5% SMSB with a density value
Uranium (U) 6.5 3.0
of 1890 kg/m3 while the dry density value of 10% SMSB is
1823 kg/m3. The lowest density value of brick was obtained by
In addition, when comparing the concentration of heavy the addition of 15% steel mill sludge (1779 kg/m3). The addition
metals in clay soil and steel mill sludge, the concentration of of more than 15% of steel mill sludge has resulted in lower dry
heavy metals in steel mill sludge is much higher. The elements density due to the presence of porosity in brick. The relationship
present in steel mill sludge arranged in descending order are as between the dry density and sludge percentage acquired from this
follows: Zn (16436 mg/L), Cu (7414 mg/L), Pb (4391 mg/L), study manifested the same agreement with the outcome obtained
Sn (657 mg/L), Cr (351 mg/L) and Ni (104 mg/L). from the previous study [18,19].
212
In general, the dry density values of brick must be between in this study are relatively close to the previous study in which
1500 kg/m3 to 2000 kg/m3 [9]. Therefore, it was found that both the increase of waste content into clay bricks will potentially
control brick and SMSB were complying with the average den- increase the suction rate (Kizinievič et al., 2018). Based on the
sity value of common brick. Furthermore, it has also appeared brick specification set out in British Standard 3921:1985, the low
that the incorporation of steel mills sludge has produced a light- value of the SMSB-possessed IRS allowed it to be classified as
weight brick which could minimize the cost of transporting the a damp-proof brick [16].
brick.

3.5. Compressive strength of SMSB

Compressive strength is one of the important properties

to ensure the engineering quality of bricks to withstand loads.
Based on Figure 4, 15% of SMSB has the lowest compressive
strength value, 7.43 N/mm², followed by 10% of SMSB with the
strength value of 11.45 N/mm². Meanwhile, control brick has the
highest value of compressive strength (22.72 N/mm²), followed
by 5% of SMSB with the value of 16.8 N/mm². It shows that
the compressive strength was reduced by the increasing amount
of steel mill sludge incorporated into the brick. The presence of
porosity due to the complete combustion of organic matter in clay
soil has resulted in a lower compressive of brick.
This finding is identical to the previous study results, which
Fig. 2. Dry density of steel sludge mill-brick implied that higher addition of sludge had reduced the compres-
sive strength value [20]. It was determined from the compres-
sive strength test that all measured bricks complied with the
BS 3921:1985 standard ranging from 7 N/mm² to 100 N/mm²,
3.4. Initial rate of suction of SMSB
however not strong enough to be classified as Engineering Brick
A or Engineering Brick B [16].
By referring to the results obtained in Figure 3, the control
brick was found to have the lowest value of the initial rate of
suction (IRS) with an average value of 3.12 g/mm2, followed
by 5% of SMSB with an average value of 3.80 g/mm2. Mean-
while, the value of IRS for 10% of SMSB is 5.04 g/mm2. It
was also determined that 15% of SMSB dominates the highest
value of IRS with an average value of 7.12 g/mm2. The result
showed that the IRS of each brick sample was much lower than
the standard IRS value. The addition of steel mill sludge has
literally modified the clay characteristic. The results collected

Fig. 4. Compressive strength of steel sludge mill-brick

3.6. Leachability of Heavy Metals

The results in Table 2 show that the concentration of heavy

metals in steel mill sludge is much higher than the concentra-
tion of heavy metals in clay soil. Therefore, the leachability of
fired clay bricks with steel mill sludge would also be studied.
In this analysis, two of the most critical heavy metals, Zn and
Fig. 3. Initial rate of suction of steel sludge mill-brick Cu, are chosen.
 213
3.6.1. Zn concentration in leachate metals contained in the steel mill sludge were found to be high
during the chemical characterization. It is also explained that,
Figure 5 shows the results of the leaching behavior of Zn due to the re-dissolution of Zn at a strong base condition, the
contained in the extraction fluid of the sludge brick. From the concentration of Zn will increase due to the increasing sludge
result, the concentration of Zn in all specimens is consistent content. Meanwhile, Cu is a low-activity element that is compara-
with the standard set by USEPA which is limited to less than tively difficult to vaporize and easy to accumulate in the sludge.
500 mg/L. It is shown that the increments in steel mill sludge The leachability study resulted in an acceptable value,
in the brick cause the Zn leaching. This showed that the leachate although Zn and Cu showed the highest heavy metals concen-
concentration of Zn is increasing as the amount of steel mill tration contained in steel mill sludge. Therefore, the incorpora-
sludge that is added to the production of clay brick. tion of steel mill sludge up to 15% into fired clay brick would
produce an acceptable amount of leachate and secure to be used
as a building material.

4. Conclusion

Overall, it can be inferred that the corresponding chemical

composition of steel mill sludge to the clay soil has great potential
to be used as a raw material replacement for brick production.
The optimum percentage of steel mill sludge incorporated into
fired clay brick is limited up to 5%. The results show that the
brick with the suggestion percentage has the highest compressive
strength and low initial rate of suction.
The study also identified that all specimens produced
leachate concentrations of heavy metals below the permissible
Fig. 5. Leachate concentration of Zn limit that USEPA has regulated. For Zn and Cu case focused
on this research, which is the higher concentrations in the XRF
results, their concentrations in the leachate of all specimens are
3.6.2. Cu concentration in leachate not a concern as their value is still below the permissible limit
of USEPA.
Figure 6 shows the results of the leaching behavior of Cu The results from the physical and mechanical properties
contained in the sludge brick extraction fluid. Based on the figure, evaluation deduced that the recycling of steel mill sludge into
the increase in steel sludge had an impact on the leaching behav- fired clay brick could serve as a desirable alternative to replace
ior of Cu in brick where leachate concentration increased from the disposal method of the sludge while producing good quality
0.034 mg/L to 4.654 mg/L. Furthermore, the Cu was found below brick.
the permissible limit set by USEPA which is below 100 mg/L.
The level of heavy metals leached from the manufactured
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