Articulo cientifico sobre los ladrillos como se fabricna

Apuntes pwerdon

1. Improvement of engineering
properties and environmental
impact of fired clay bricks utilizing
industry sludge waste
Amir Detho
1
, Aeslina Abdul  Kadir
1
, Ahmad  Shayuti
1
, Bin Abdul  Rahim
1
, Nejib  Ghazouani
2,3
,
Abdelkader Mabrouk
2,3
, Ahmed Babeker Elhag
4,5
& Hesham Hussein Rassem
6
The increasing generation of industrial waste sludge poses a serious worldwide problem with
detrimental effects on the environment and the economy. Effective utilization of waste sludge in
sustainable construction practices offers a universal solution to mitigate environmental impacts. As
the mining industry continues to extract clay from clay mines, the demand for sustainable practices
in both clay mineral extraction and brick production is growing. Bricks are fundamental in masonry
construction, and current research is exploring the integration of industrial waste materials into fired
clay bricks to enhance their properties and mitigate environmental impacts. This study investigates the
incorporation of waste sludge in brick manufacturing to assess its potential for reducing environmental
burdens while maintaining technical performance. X-ray Fluorescence Spectrometry (XRF) analysis
reveals that both clay soil and mosaic sludge contain high levels of silicon dioxide (SiO₂) and aluminum
oxide (Al₂O₃), supporting their suitability as partial substitutes for clay soil. Incorporating up to 30% of
body mill sludge (BS) and polishing sludge (PS) into the brick mix significantly enhances physical and
mechanical properties, resulting in reduced shrinkage, increased porosity, and improved compressive
strength, reaching up to 25 N/mm². Initial rate of suction tests shows values below 5 g/mm², indicating
optimal water absorption characteristics. Various leachability assessments, including the Toxicity
Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), and
Static Leachate Test (SLT), confirm that bricks containing up to 30% BS and PS comply with United
States Environmental Protection Agency (USEPA) and Environment Protection Authority Victoria
(EPAV) standards for heavy metals, making them environmentally safe for use. Additionally, indoor air
quality assessments confirm that these bricks meet Industry Codes of Practice on Indoor Air Quality
(ICOP-IAQ) guidelines. This study demonstrates that using BS and PS as alternative raw materials
offers a sustainable, cost-effective solution aligned with Sustainable Development Goals (SDGs),
promoting cleaner production practices in brick manufacturing.
Keywords  Mosaic sludge, Clay minerals, Brick strength, Leachability, Mine sustainability
Sludge is frequently associated with industrial waste that comes from urban areas. Yet, it can also originate from
industrial and medical waste, wastewater processing plants, street drainage, farming zones, and occasionally
from the leachate of landfills. Typically, sludge usually derived from residential regions is organic in nature
1
.
Hence, this refuse inflicts lesser damage and has a reduced effect on the ecosystem in contrast to industrial
byproducts. Conversely, industrial sediment may exist in either an organic or inorganic state
2,3
. The primary
concern with industrial sludge is its inorganic constituents, particularly heavy metals, which need specialized
treatment to avoid harming the environment.
In Malaysia, mosaic tiles are among the sectors responsible for generating sludge waste production.
Approximately 66 mosaic industries are officially recorded with the Construction Industry Development
1
Faculty of Civil Engineering and Built Environment, University Tun Hussein Onn Malaysia (UTHM), Parit Raja,
Batu Pahat, Johor, Malaysia.
2
Mining Research Center, Northern Border University, Arar 73222, Saudi Arabia.
3
Department of Civil Engineering, College of Engineering, Northern Border University, Arar 73222, Saudi Arabia.
4
Department of Civil Engineering, College of Engineering, King Khalid University, Abha 61413, Saudi Arabia.
5
Center
for Engineering and Technology Innovations, King Khalid University, Abha 61421, Saudi Arabia.
6
Faculty of Science,
University of Hodeidah, Hodeidah, Yemen.

email: [email protected]; [email protected]
Scientific Reports | (2025) 15:4820 1| https://doi.org/10.1038/s41598-025-89147-1
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2. Board Malaysia. According, Malaysian Mosaics Berhad (MMB), each factory generates about 5–8 tonnes of
mosaics sludge daily for every mosaic batch they produce. The mosaic industry, classified as a non-metal sector,
generates roughly 250 tonnes of waste per month, included concrete, mosaics, ceramics, and stone body waste
4
.
Huge volume and toxicity of the wastes, mosaic sludge can cause significant harm to both landfills and the
environment
4
.
According to Department of Environment (Malaysia Environmental Quality Report, 2012) claimed
that Malaysia, in 2012, a total of 2,854,516.78 metric tonnes of scheduled wastes were generated, reflecting a
13.01% reduction compared to the 3,281,569.73 metric tonnes reported in 2011
5
. The primary categories of
waste included dross/slag/clinker/ash, gypsum, mineral sludge, oil and hydrocarbons, heavy metal sludge, and
e-waste. Among the states, Terengganu contributed the largest share of scheduled waste (20.9%), followed by
Johor (20.14%), Perak (14.23%), Selangor (12.87%), and Pulau Pinang (8.58%), while the remaining 10 states
collectively accounted for 23.28% of the total waste generated. In Malaysia, approximately 1.6 million metric
tonnes of industrial sludge are generated annually, with 0.81  million metric tonnes disposed of in sanitary
landfills
6
.
In addition, the general public concern and the limited land resources will heighten the relevance of the
industrial sludge disposal issues
7
. Furthermore, landfills are recognized as a significant contributor to adverse
environmental effects in Malaysia
8
. Huge quantities of industrial sludge have piled up, and there is a pressing
need for alternative disposal techniques since landfills are no longer a suitable solution for such waste.
Currently, Malaysia faces problems in finding adequate disposal sites
9
, even though having over 165 active
sites and 131 that have been decommissioned (PPSPPA, 2014). Landfills are largely utilized open dumps
10
.
Moreover, the sludge from the mosaic industry is rich in heavy metals such as Copper (Cu), Zinc (Zn),
Iron (Fe), and Chromium (Cr). These metals can pose risk to both human health and the surrounding
environment
11,12
. High concentrations of heavy metals present significant risks to human health, potentially
leading problems such as anemia, digestive disturbances, lung cancer, bone conditions like osteoporosis, damage
to the nervous system, and harm to the liver and kidneys
13
.
The reuse of textile mill sludge in fired clay bricks. The textile mill sludge was mixed in different proportions
(5–35%) as a raw material in this study. The brick was fired at 600ºC to 800ºC and for 8, 16 and 24 h. Based on
the results, textile sludge can be added up to 15% as it gives a compressive strength above 3.5 MPa and the water
absorption ratio is also less than 20%
14
.
The author investigated the brick durability of cast brick with industrial sludge. The results showed that the
earth brick can be replaced with sludge up to 40% by weight with satisfactory value in strength. The compressive
strength of brick without sludge and 5% sludge were 11.7  MPa and 17.6  MPa respectively. The compressive
strength decreased with addition of sludge beyond 5% from 17.6 MPa to 10.5 MPa. For water absorption, when
the sludge added was more than 10% by weight, the water absorption gradually increases. In this study, the
addition of sludge into brick gave dual benefits of safe disposal of sludge and also conservation of brick making
15
.
The author incorporation of water treatment sludge and Rice Husk Ash (RHA) in clay bricks. In this study
25%, 50% and 75% by weight of water treatment sludge were added to produce clay bricks. Each brick series was
fired at 900ºC to 1200ºC. The compressive strength of brick value was 5.7 MPa to 6.8 MPa for the control brick
and 2.82 MPa to 7.84 MPa for the Sludge-RHA brick. Meanwhile, for the water absorption test, the results were
9.94–11.18% of control brick and 17.41–73.33% for sludge-RHA brick respectively. From the obtained results, it
was concluded that under the common temperature used in brick kilns, 75% addition was the optimum sludge
to produce the bricks
16
.
The incorporation of three sludge percentages which are 6%, 8% and 10% shows that the compressive
strength decreased to 20.22% but at the same time the flexural strength increased. The compressive strength
of 10% of sewage sludge was 21.8 MPa whereas the flexural strength was 4.6 MPa. Autoclaved sludge fly ash
was incorporated in brick when a pH of 6.9 was obtained which is close to normal pH. The heavy metals were
solidified during the curing process so that they will not pollute the environment
17
.
The author used 5%, 10%, 15%, 20%, 25% and 30% of sewage sludge incorporated into soft mud bricks with
12 specimens for each sludge percentage. From the results obtained there was no sign of alteration in colour or
odour. Bricks with 35% sludge are very brittle and there are some dimensional reductions between 1 mm and
7 mm. Based on the result, the brick mass reduced significantly according to the percentage of sludge
18
.
According to the results demonstrated that the appropriate percentage of ash sludge to produce good quality
bricks is in the range of 20–40% by weight with 13–15% optimum moisture content prepared in the moulded
mixture. Firing was conducted at 1000ºC for six hours. Utilization of 10% of sludge ash in bricks exhibited higher
compressive strength than normal bricks
19
.
The study examined clay bricks incorporating 10%, 20%, 30%, 40%, 50% and 60% stone sludge waste and
fired them at 1050ºC. The compressive strength ranged from 2.11 MPa to 4.2 MPa, with the water absorption
ratio between 8% and 12%. The optimal mix was 30% stone sludge, yielding the highest compressive strength of
4.2 MPa. This approach not only enhances brick properties but also addresses stone sludge disposal, a byproduct
of the mining industry. By integrating stone sludge with clay minerals, this method promotes eco-friendly and
sustainable construction practices
20
.
The author investigated clay bricks incorporating 2–16% industrial sludge, fired at temperatures up to 1050
°C. The compressive strength of these bricks ranged from 12 MPa to 31 MPa, demonstrating strong mechanical
performance. The study highlighted the reuse of marine clay-industrial sludge mixtures as a viable solution for
waste disposal and resource recovery, supporting sustainable construction practices
21
.
Recently, numerous researchers have been effectively incorporated different kinds of sludges into fired clay
bricks. These sludges include those from marble, stone
20
, water treatment processes
15,22
, sewage
23,24
, and textile
industry, mining industry
14,25
. The use of waste in clay brick manufacturing often enhances the properties of the
bricks, resulting in lighter, better stronger, and have improved shrinkage, porosity, and thermal characteristics.
Scientific Reports | (2025) 15:4820 2| https://doi.org/10.1038/s41598-025-89147-1
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3. Lighter bricks are more desirable as they can decrease transportation and handling expenses. Additionally,
incorporating waste into bricks lowers the clay requirement, which can in turn lower production costs
26
.
Many experts have researched the inclusion of mosaic sludge into fired clay bricks. Using various sludges in
this manner can improve the bricks characteristics and provide an environmentally responsible way to dispose
of the waste. However, the majority of researchers in earlier studies mainly paid attention to the physical and
mechanical characteristics. There has been insufficient research conducted on how using sludge waste in terms
of its effects on the environment.
So, in this research, a study was conducted to find the appropriate proportions of mosaic sludge may
effectively incorporated into fired clay bricks. This research examines physical and mechanical characteristics
like compressive strength, shrinkage, density, and initial suction rate, along with the environmental effects
concerning leachability and indoor air quality.
Experimental procedures
Stage I: raw material formulation
Preparation and collection of mosaic sludge and clay
Mosaic sludge was sourced from Malaysian Mosaic Berhad (MMB) based in Kluang Johor. The sludge composed
in a semisolid state. According to MMB the mosaic production and sludge evaluation remained the same and
was not affected by the processing of mosaic. Clay soil used in the study was supplied by the Hap Seng Brick
Company in Sedenak, Johor. The sludge and clay were dried at 105 ºC in an oven for 24 h. They were then
manually pulverized and sifted using sieves with a size ranging of 3 to 5 mm. All these processes were done in
the RECESS and Geotechnic laboratories.
Characterization of raw materials
The clay and sludge were cleaned up before being subjected to X-ray fluorescence analysis. Raw materials were
subjected to 24 h of oven drying. Subsequently, the sludge was grounded to crush with appropriate apparatus.
Before the XRF analysis, the sludge was formed in pellet shapes. The chemical content and heavy metal levels
of the raw materials in sludge and clay were determined using XRF equipment in Environmental Analytical
Laboratory. Samples should be in fine powder condition because XRF can penetrate only in few millimetres from
the sample surface. Meanwhile, the soil’s moisture-density relationship is determined by the compaction test
experiment, Atterberg limits are the basic method to measure critical water content in clay and silt soil, specific
gravity analysis experiment. All the experiment was done in the RECESS and Geotechnic laboratories, UTHM.
Analytical analysis
Testing procedure was carried out according to the British standard BS3921 in order to determine the compressive
strength, shrinkage, initial rate of suction and density. On the other hand, the heavy metals leachability testing
was conducted by using TCLP, SPLP and SLT method according to the United States Environmental Protection
Agency (USEPA, 1996) and Environmental Protection Agency Victoria (EPAV, 2005a). Table 1 illustrates the
instruments and equipment used in the experimental procedures.
Stage II: brick manufacturing
Two types of bricks (control brick and sludge brick) were produced, control bricks made of clay and bricks
incorporated with mosaic sludge. Bricks were made without sludge (0% or control bricks) and with varying
sludge proportions (1%, 5%, 10%, 20%, and 30%) were manufactured in the RECESS Laboratory. The brick
manufacturing process was carried out accordance with BS EN 771-1:2011 and BS 3921:1985.
The control brick was produced by blending soil and water in a specific proportion using a mechanical mixer.
Once the soil was thoroughly mixed, it was placed in a mould and manually compacted at a pressure of 2500
psi. The bricks were produced with standard dimensions of 100 mm × 210 mm × 70 mm, in a rectangular shape,
which is typical for conventional fired clay bricks. The curing process involved drying the bricks in an oven at
105 °C for 24 h to remove moisture before firing at temperature ranging from 0.7 ºC/min until 1050 °C
27
. The
bricks were then cooled gradually to room temperature. The same procedure and process were done for the
mosaic sludge bricks by incorporating the mosaic sludge (bodymill sludge and polishing sludge), clay soil and
water in different percentages ratio by weight made based on specific gravity and optimum moisture content.
Instrument/equipment Model Purpose
X-Ray Fluorescence SpectrometerS4 Pioneer Bruker-AXS, GermanyChemical composition analysis
Scanning Electron Microscope (SEM)ZEISS EVO LS10, Germany Microstructural analysis
BET Machine Micromeritics ASAP 2020, USASurface area characterization
Indoor Air Quality Monitor IAQ Monitor Measurement of indoor air quality parameters
Toxicity Gas Test Instrument GrayWolf Detection of toxic gases
Gas Detector Aeroqual Series 500 Ozone and other gases measurement
ICP-MS PerkinElmer Elan9000, USA Heavy metal analysis
Table 1. Instruments and equipment used in experimental procedures.

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4. Stage III: physical and mechanical analysis
Fired shrinkage experiment
Shrinkage is the measure of any changes or variations occurred in the brick’s dimensions during drying and
firing operation. Ten specimens were picked randomly and measured after the firing process in the furnace by
using the following Eq. 1.

Ls=
(
Lwet−Ldry
L
)
×100(1)
Density test
Density refers to the mass of a substance per its volume unit and it varies depending on the material’s temperature
and pressure. Ten specimens were picked randomly for each percentage and density of the brick can be calculated
using follow Eq. 2.

ρ=
m
/
v(2)
Compressive strength analysis
Compressive strength indicates the highest stress a brick can endure when subjected to a crushing load. The
brick’s compressive strength is determined by dividing the load by its cross-sectional area. The bricks were tested
for compressive strength to find out their strength until they fail. According to the BS3921:1985 test procedures,
the strength must be between <  28  N/mm
2
and >  42  N/mm
2
. Ten specimens were picked randomly to fulfil
the BS3921:1985 requirements. Results from each specimen were divided with the area of the bed face can be
measured with the follow Eq. 3.

C=
F
/
A(3)
Initial rate of suction analysis
The initial rate of suction (IRS) measures brick capacity to permit water flow through it. Several approaches were
employed to evaluate water absorption. Based on BS3921:1985, the bricks have to be prepared accordingly before
they could be tested. Based on BS3921:1985 requirements three specimens were picked randomly for every
percentage. These procedures were repeated for other bricks of different percentages of sludge. Equation 4 was
used to calculate the IRS based on the total immersion area which is expressed in in kg/m
2
.min.

Initial rate of suction(IRS)=
1000 (m2−m1)
A
(4)
Microstructure characteristic analysis
The Scanning Electron Microscopy (SEM) was employed to examine the microstructure of the bricks surface.
SEM is an electron microscope that forms a three-dimensional visualization with focus on the electron beams
and moves across the object. SEM instrument is made up of two components (electronic console and electron
column) and enables to investigate samples at a nanometer-scale resolution. The important signal is by the
interaction of the primary electrons (PE) of the electron beam and secondary electrons (SE) with the specimens.
Specimens with different diameter consume different energies used.
Surface area characterization analysis
Brunauer Emmett Teller (BET) method is one of the techniques used to evaluate a material surface area by using
nitrogen multilayer adsorption, which is measured in relation to pressure employed fully automated analyzer. It
helps in the analysis of the effects of particle size and surface porosity in various applications. BET surface area
measurements were conducted using a Micromeritics ASAP 2020 analyzer, with nitrogen adsorption at 77 K, to
evaluate the porosity and surface area characteristics.
Stage IV: leachability analysis
The TCLP and SPLP method are designed to evaluate the movement of both organic and inorganic constituents
present in liquid, solid, and mixed-phase samples. The TCLP and SPLP analysis for this research was carried out
in the Wastewater Laboratory at UTHM. Brick samples were divided into four segments and then pulverized to
provide a suitable sample for the investigation. The static leachate test (SLT) was first defined by
28
, is designed
to identify highest leachate concentration under static conditions without the need to replace or altering the
leachate. Typically, SLT test was performed in long term duration, from over three-month period to one year
and data was composed continuously.
Stage V: indoor air quality
The term “indoor air quality” (IAQ) pertains to the quality of air inside a building and way its impact on the
occupant’s health and comfort of those inside. This encompasses concerns related to chemical, physical, and
biological pollutants. Nowadays, ensuring a safe, healthy, and comfortable IAQ is not only a necessity but also
a significant priority. Improved AIQ boosts focus, productivity and harmonies. The Walk-in Stability Chamber
(WiSC) was used for IAQ testing for determining the area-specific emission rate of volatile organic compounds
(VOCs) from newly manufactured building materials or furnishings under specified climatic conditions
according to method (ISO-16000-9:2006). This method can also potentially be used for older products. WiSC
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5. was built in many sizes and depended on the purpose of the test. It is also designed to controlled temperature-
humidity chamber
29
. The research was carried out at the Thermal Environment Laboratory (TEL) in the Faculty
of Mechanical and Manufacturing Engineering at UTHM. The experiment used three different dimensions and
the arrangement of samples was in cube, column and wall.
Result and discussion
Analysis of chemical constituents and their concentrations
The composition of clay and sludge resulting from both the BS and PS processes is significantly impacted by
the type of raw materials used and the production method. The data provided in Table 2 demonstrates that
silicon dioxide (SiO
2
) and aluminum oxide (Al
2
O
3
) make up the largest portions of the clay, with proportions
varying between 55.77% and 24.40%. The analysis of the mosaic sludge showed that SiO
2
and Al
2
O
3
were the
predominant elements, with concentrations between 61.83 and 62.37% and 15.50–20.55%, respectively. The Loss
on Ignition (L.O.I) results indicated that both the BS and PS sludge had low organic content, ranging from 7.01
to 7.92%, classifying as inorganic sludges.
Table 3 displays the concentrations of heavy metals in the clay soil and mosaic sludge. The results indicate
that both the clay soil and mosaic sludge generated from the BS and PS processes contain measurable quantities
of heavy metals. Zr shown the highest concentration among the heavy metals, reaching 2738 ppm in PS sludge
and 2507 ppm in BS sludge. Ba followed with levels of 1242 ppm in PS sludge and 1232 ppm in BS sludge.
Furthermore, the concentrations of heavy metals such as Fe (ranging from 105 to 136 ppm), Cu (from 234 to
255 ppm), Zn (from 195 to 210 ppm), and Mn (from 89 to 97 ppm) were higher in the PS sludge compared to
the BS sludge, except for Cr which showed levels of 915 to 971 ppm. Conversely, the concentrations of Fe and V
were notably higher in clay soil compared to both PS and BS sludges.
Compaction test analysis
The compaction analysis was performed at the RECESS Laboratory, UTHM where the water content of each
blend was determined. The optimal moisture content (OMC) is a critical parameter in the brick manufacturing
process, as it directly affects the compaction and density of the bricks. Higher OMC values facilitate better particle
arrangement, leading to improved mechanical strength and reduced porosity. However, excessive moisture can
result in shrinkage and cracking during the drying and firing stages. In this study, OMC values ranged from
12 to 24%, with higher sludge percentages requiring higher moisture content due to the finer particle size and
increased surface area of the sludge. OMC for both the control brick and mosaic sludge brick. The OMC which
greatly influences brick properties, was determined using a combination and test method based on BS1377:1990.
Atterberg limits analysis
Atterberg limit was performed accordance with BS1377-2:1990. The result showed that the type of soil in this
research was silty clay or clayey silt with 13.4% within the range of Plastic Index which is between 7 and 17%.
The specific gravity (SG) result shows there was no significant different between clay soil and mosaic sludge with
2.6 kg/m³ and 2.4 kg/m³. Thus, the mosaic sludge could be replacing clay soil in terms of percentages by weight.
Firing shrinkage analysis
Shrinkage rate of bricks with 5% BS displayed the smallest shrinkage, measuring at 0.34%. This is succeeded by
the bricks with 1%, 10%, 20%, and 30% BS, which showed shrinkage rates of 0.43%, 0.56%, 0.57%, and 0.69%
respectively. Particularly, the brick with 30% BS had the highest shrinkage at 0.69%. The shrinkage rate for PS
bricks is highest for the 30% PS brick at 0.60%. Subsequently, the shrinkage rates for the 20%, 1%, 10%, and 5%
Heavy metal Formula
Composition (%)
BS PS Clay soil
Carbon Dioxide CO
2
0.10 1.80 1.00
Silicon Dioxide SiO
2
62.3761.8355.77
Aluminum Oxide Al
2
O
3
20.5515.5024.40
Sodium Oxide Na
2
O 1.40 2.30 0.30
Potassium Oxide K
2
O 1.02 2.06 1.93
Iron Oxide Fe
2
O
3
1.05 2.28 5.06
Calcium Oxide CaO 1.08 1.18 0.25
Magnesium Oxide MgO 1.35 1.45 1.20
Zirconium DioxideZrO
2
1.00 1.35 0.00
Phosphorus PentoxideP
2
O
5
0.39 0.46 0.00
Titanium Oxide TiO
2
0.56 1.07 0.94
Barium Oxide BaO 0.15 0.17 0.00
Manganese Oxide MnO 0.01 0.01 0.04
Chromium Cr 0 < LLD 0 < LLD 0 < LLD
Loss on ignition (LOI) 7.01 7.92 8.72
Table 2. Chemical composition (BS, PS & Clay).

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6. PS bricks are 0.56%, 0.50%, 0.49%, and 0.34%, respectively. Similar findings were documented by
30,31
, when they
combined sludge into fired clay bricks. According to previous studies, in order to yield a good quality brick, the
shrinkage value should not be more than 8%
32,33
.
Density test analysis
The density of BS bricks of 30% displays the least density, at 1665.24 kg/m
3
. There’s a gradual increase in density
for the 20%, 10%, 5%, 1%, and 0% BS bricks, with values being 1677.43  kg/m
3
, 1679.89  kg/m
3
, 1683.28  kg/
m
3
, 1688.06 kg/m
3
, and 1698.24 kg/m
3
respectively. PS bricks findings reveal that the brick with 1% PS sludge
recorded the maximum density of 1690.03 kg/m
3
. This is followed closely by the 5% sludge brick with a density
of 1689.73 kg/m
3
. Bricks containing 10% and 20% sludge had a density of 1687.99 kg/m
3
and 1678.52 kg/m
3
.
The trend observed in PS brick that of BS brick, where increasing higher proportions of sludge to the fired clay
brick leads to a reduction in density. The brick with the low density was the one combined with 30% PS sludge
with1661.49  kg/m
3
. Overall, the density values typically fall within the range of 1500  kg/m
3
to 2000  kg/m
3
.
Consequently, the bricks’ densities fall within this range and adhere to the standard weight for common bricks
34
.
Thus, the bricks align with the standard weight of common bricks. As per author
35
, bricks with a lighter weight
are practicable, and such lightweight bricks can lead to reduced manufacturing and transportation expenses.
Compressive strength analysis
The outcomes of the compressive strength testing for BS brick are revealed the highest recorded compressive
strength was achieved by the BS brick with 30% sludge content, with 26.58 N/mm
2
. Following this, the strengths
for the 20%, 10%, 5%, and 1% BS bricks were 26.17 N/mm
2
, 25.81 N/mm
2
, 24.80 N/mm
2
, and 17.91 N/mm
2
,
respectively. On the other hand, the PS brick shows the highest compressive strength with 30% of PS brick
incorporation with 23.45 N/mm
2
and followed by PS brick 20%, 10%, 5% and 1% with 21.91 N/mm
2
, 19.81 N/
mm
2
19.50 N/mm
2
, and 15.43 N/mm
2
discretely. The control brick showed the lowest results compared to the
other samples, with a measurement of 15.32 N/mm
2
. This is because BS and PS are categorized as inorganic
material compared to organic. clay soil is burned during the firing process, it results in weak inter-particle bonds
within the manufacturing brick
14,36
. Other than that, the BS brick 30% obtained slightly higher compressive
strength compared to PS brick 30%. This could happen due to the reaction of silicon dioxide and aluminum
oxide that was higher in BS sludge that assisted good bonding
37
.
Initial rate of suction
Figure 1 illustrates that the initial rate of suction for the BS brick drops as sludge waste increases from 0 to 30%.
The peak value is observed in the BS brick (1%) at 12.65 g/mm
2
, while the lowest average rate is seen in the BS
brick (30%) at 3.94 g/mm
2
. The control brick results revealed an initial rate of suction highest at 12.96 g/mm
2
.
Nevertheless, for PS brick, based on Fig. 1, the PS brick displayed its lowest value at PS brick (30%) averaging
3.75 g/mm2, succeeded by PS brick (20%) with an average of 4.35 g/mm
2
. The peak value was observed in (1%)
PS brick with an average measurement of 11.64 g/mm
2
. This was categorized according to the initial rate as
defined by BS3921:1985. The initial water rate for both the control brick and mosaic sludge (BS and PS) in the
Heavy metals
Formula
Concentration (ppm)
USEPAE PAV
BSPSClay soil
Original-g 9 9 9
Added-g 3 3 3
Titanium Ti 667066 - -
Vanadium V 353657 - -
Chromium Cr 97191530 5 20
Manganese Mn 978990 - -
Iron Fe 105136556 - -
Cobalt Co 32335 - -
Nickel Ni 29295 1.3 8
Copper Cu 23425515 100 800
Zinc Zn 19521022 500 1200
Gallium Ga 202221 - -
Arsenic As 302611 5 2.8
Strontium Sr 13313534 - -
Zirconium Zr 25072738358 - -
Niobium Nb 272914 - -
Caesium Cs 9 119 - -
Barium Ba 12321242179 100 280
Cerium Ce 565753 - -
Lead Pb 151714 5 4
Table 3. Concentration of heavy metals (BS, PS & Clay).

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7. range of 1–10% were not satisfied. According to
38,39
, a lower IRS can build strong bonds in brick because the
lower IRS will not allow moisture to infiltrate into a brick. From the results, it was observed that the initial value
was high compared to the standard value.
Microstructure analysis
Figure 2a and l present the comparative views of the control brick and the brick with mosaic sludge (BS and
PS). These images reveal that the bricks containing mosaic sludge have a more refined surface structure than the
control brick. Additionally, the images depict rough surfaces for bricks containing 0%, 1%, 5%, and 10% sludge
compared to those with 20% and 30% sludge. The pore sizes of the control brick ranged from 45 μm to 50 μm.
Bricks with a sludge content of 1–10% exhibited pore sizes ranging from 18 μm to 44 μm. In contrast, bricks with
20% and 30% sludge had pore sizes between 1.9 μm and 3 μm. Conversely, PS bricks display a similar pattern,
with bricks made of 1–10% sludge having bigger pore sizes than those with 20% and 30% sludge content. This
occurs because the granularity of mosaic sludge powder is more refined than clay soil, allowing the mosaic
sludge to fill the spaces between the clay particles in the mixture. Currently, the mosaic sludge bricks with 20%
and 30% content possess a smooth texture, though they display a lighter texture and reduced soil cohesion. The
author
15
suggests that incorporating sludge can lead to variations in the plasticity and the filler properties of
the sludge. Moreover, during the initial tests, BS and PS bricks with up to 40% incorporated showed noticeable
affects. This observation aligns with the findings of
18
, who indicated that bricks with up to 35% sludge content
were quite brittle and broke upon removal.
Surface area characterization
The BET experiment results revealed that mosaic sludge bricks had considerably smaller average pore sizes.
Specifically, the BS brick 30% had a pore size of 13.40 nm and the PS brick 30% had a size of 15.92 nm, in
contrast to the control brick which had a pore size of 123.22 nm. The BS brick 30% and PS brick 30% fall into the
mesoporous category with pore sizes ranging from 2 nm to 50 nm, as per
40
. On the other hand, the control brick
is characterized as microporous with pore sizes exceeding 50 nm. Nevertheless, the total pore volume in BS and
PS bricks was greater at 0.005 cm
3
/g, while the control brick had a volume of just 0.002 cm
3
/g. The formation
of mesopores makes the bricks lighter and when combined with 30% BS and PS sludge, they exhibit greater
strength compared to the control brick.
Toxicity characteristics leaching Procedure (TCLP)
The concentration of heavy metals present in BS brick were Cd, Mn, Fe, Cr, Cu, Pb, Co, Ba, Ni, Zn, As and
Vanadium. All heavy metal levels were below the permissible limits for example Fe for 10% BS brick was
0.65 mg/L, the highest among other heavy metals. Other metals like Mn, Ba, Zn, As and Vanadium also showed
visible low concentration within acceptable range limits. The concentration of heavy metals for PS brick has
low metal concentration such as Cd, Cr, Cu, Co, Ni, Hg compared to Mn, Fe, Ba, Zn, As and Vanadium.
However, TCLP results were compared with the specific limits set by USEPA (e.g., Pb  ≤ 5.0 mg/L, Cd  ≤ 1.0 mg/L,
Cr ≤ 5.0 mg/L) and EPAV guidelines (e.g., Pb  ≤ 5.0 mg/L, Cd  ≤ 0.5 mg/L, Cr  ≤ 1.0 mg/L). Therefore, fired clay
brick incorporated with mosaic sludge brick is safe to be discarded to landfill and no special caution is needed.
Fig. 1. Initial rate of suction proportions of BS and PS brick.

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8. Synthetic precipitation leaching Procedure (SPLP)
Synthetic Precipitation Leaching Procedure (SPLP) is one of the leachate tests that haves been used to determine
the potential for soil contamination leachability into groundwater. SPLP was designed for in-situ (ground surface
of the landfill) purposes, which is exposed to rainfall with the assumption that the rainfall is slightly acidic. In
the SPLP test, nitric acid and sulfuric acid (40/60) are used to simulate synthetic rain in order to depict the
actual situation. The concentration of heavy metals in BS brick detected using SPLP. Lead, Pb element was the
highest in BS brick (1%) with 2.307 mg/L, followed by 5% and 10% with 2.173 mg/L and 1.821 mg/L respectively.
Other elements like Cd, Mn, Fe, Cr, Co, and Ni showed lower concentration. However, V, Zn, As and Ba showed
moderate concentration. The author
41
found that bricks made from sludge produced lower amounts of leachate
elements. However, the concentration of metals in these bricks comply USEPA guidelines which is 5 mg/L.
Fig. 2. SEM result of (BS and PS) brick materials.

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9. Meanwhile, heavy metal leaching from the PS brick. The findings revealed that using SPLP resulted in an
extremely low leaching of all heavy metals from the PS brick. Lead, Pb element was the highest in PS brick (1%)
with 0.902 mg/L, followed by 5% and 10% with 0.802 mg/L and 0.194 mg/L respectively and it comply USEPA
guidelines which is 5 mg/L. Other elements like V, Zn, As and Ba showed values between 0.113 and 0.229 mg/L.
Static leachate test (SLT)
Figure 3 depicts the heavy metal concentration in the control brick between day-4 and day-95. The data indicates
that iron (Fe) reached its peak level on day-16 at 2.07 mg/L. This was closely followed by V, which reached
1.790 mg/L on day-28, when compared to the other heavy metals. On day-16, Ba recorded its peak concentration
at 1.73 mg/L and then gradually decreases to 0.25 mg/L by day-95. Other metals like Cr, Ni, Cu, Zn, As, Cd, and
Pb were present in small quantities and met both USEPA and EPAV guidelines.
Figure 4 presents the heavy metal concentration in a 1% BS brick. The data indicates that vanadium had the
higher concentration at 2.14 mg/L on day-32. This was closely followed by Fe with 2.11 mg/L on day-28. Both
of these metal concentrations remained unchanged from day-81 through day-95. Zn reached its highest level on
day-8 and then rapidly declined until day-95. The concentrations of other heavy metals were consistently below
1 mg/L and far within acceptable boundaries. However, it’s important to note that all heavy metal concentrations
within the 1% BS brick within the prescribed standard.
Figure 5 illustrates the heavy metal concentration in a 5% BS brick. The data reveals that Fe concentration
in the 5% BS brick peaked at 2.26 mg/L on day-20, then gradually dropped until day-74, remain constant at
0.52 mg/L by day-88. V concentration was observed at 1.99 mg/L on day-24, which then consistently decreased
to 0.10 mg/L by day-95. All other heavy metals were detected at levels below 1 mg/L and were within acceptable
standards.
Figure 6 displays the concentration of heavy metals in a 10% BS brick from day-4 to day-95. The data
indicates that iron (Fe) concentration peaked at 2.34 mg/L on day-20, then dropped to 1.81 mg/L by day-24.
However, from day 60 to day 95, the concentration remained constant. After Fe, V was observed to be the next
most concentrated heavy metal, reaching 2.11 mg/L on day-32. By day-95, its level had reduced to 0.10 mg/L. All
other heavy metals had values under 1 mg/L. Therefore, all the heavy metals were within and met the standard
guidelines.
Figure 7 displays the elevated levels of heavy metals in a 20% BS brick. On day-46, there was a significantly
increased in V at 3.36 mg/L. But from day-53 to day-95, the concentration of V gradually decreased. On day-28,
Fe showed a high level of 2.19 mg/L, but by day-95, its level had substantially decreased to 0.21 mg/L. Conversely,
the Zn reading reached its highest point on day-12 at 1.28 mg/L, after which it remained constant from day-46
and above, at a level of 0.04 mg/L. Consequently, all the heavy metal concentrations remained low and within
the limits.
Fig. 3. Heavy metal concentration for control brick.

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10. Figure 8 depicts the heavy metal levels in 30% BS bricks. Fe illustrated the highest concentration among all
metals on day-8 with 2.79 mg/L and then steadily decreased to 0.23 mg/L by day-95. V reached a higher value
of 2.52 mg/L on day-60 and remained stable through day-95. On day-95, Pb had the lower concentration at
0.0008 mg/L, which is below the USEPA level of 5 mg/L. Nonetheless, all the other heavy metals tested met the
USEPA standards.
Figure 9 displays the data for the 1% PS brick. Ba recorded the maximum level at 2.27 mg/L on day-12, but
this level decreased, reaching 0.21 mg/L by day-95. Fe had a relatively high level at 2.15 mg/L on day-28 but
decreased to 0.50 mg/L by day-95. Meanwhile, V was peaked at 2.06 mg/L on day-60 and then stabilized through
day-95. Zn also showed a notable concentration of 1.71  mg/L on day-20. Consequently, all the heavy metal
concentrations remained low and within the limits prescribed by the USEPA.
Figure 10 presents the outcomes of heavy metal concentration in a 5% PS brick. The graph illustrates the
variation in brick concentration from day-4 to day-95. The data revealed that V reached its highest concentration
at 2.99  mg/L on day-46, while Fe followed at 1.88  mg/L on day-28. On day-20, Zn revealed a peak level of
1.17 mg/L, while Ba reached 0.88 mg/L on day-16. As the study progressed to day-95, all heavy metal levels
declined and remained within the acceptable level.
Figure 11 depicts the concentration of heavy metals in a 10% PS brick, measured in mg/L, from day-4 to
day-95. Fe reached a higher value of 3.29 mg/L on day-32. This began to decrease by day-39, and remain stable
at 1.51 mg/L until day-95. V the second highest value of heavy metal with 2.13 mg/L on day-32. Ba, on the other
hand, reached its highest value of 1.01 mg/L on day-16 and remained stabilized at 0.07 mg/L from day-67 to
day-95. The concentrations of Cr and Zn ranged from 0.60 mg/L to 0.85 mg/L throughout the study period. All
other heavy metals had values under 0.40 mg/L up to day-95. Therefore, all the heavy metals were within and
met the standard guidelines.
Figure 12 displays the concentration of heavy metals in PS brick (20%). On day-24, Fe had the maximum
concentration at 2.36 mg/L, while V was the next highest at 2.18 mg/L on day-67. By day-81, the concentrations
of Fe and V remained stabilized at 0.12 mg/L and 2.16 mg/L, respectively. On day-28, Ba reached its highest
concentration at 1.10 mg/L, but it decreased to 0.19 mg/L by day-95. Zn and Cr had higher levels on day-16 and
day-46, with 0.91 mg/L and 0.89 mg/L, respectively. The remaining heavy metals stayed under 0.35 mg/L until
day-95. Consequently, all the heavy metal concentrations remained within the limits prescribed by the USEPA.
Fig. 4. Heavy metal concentration for BS brick (1%).

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11. Figure 13 data reveal the concentration of heavy metals in the PS brick (30%) from the day-4 to the day-
95. The day-28 recorded the higher concentration of Fe at 3.64 mg/L, other heavy metals. This concentration
began to decrease from the day-32 and continued to do so until the day-95. As for Vanadium, it reached a
concentration of 1.78 mg/L on the day-53, but this level stabilized and remained constant from the day-88 to day-
95. The concentrations of Zn and Ba peaked on the day-24, registering at 0.92 mg/L and 0.88 mg/L, respectively.
However, all the concentrations of these heavy metals remained satisfied and followed to the standards limits.
Apart from that, the most appeared elements that were most frequently observed in both short- and long-
term tests were Vanadium, Iron (Fe), Arsenic (As), Barium (Ba), and Zinc (Zn). Hence, by adding mosaic sludge
to the fired clay bricks, all heavy metal results satisfied and followed to the standards set by the USEPA and EPAV.
Total volatile organic compound (TVOC)
Figure 14 shows the TVOC values against types of bricks. The findings indicated that the control brick recorded
the lowest emissions when arranged in wall and column designs, with values of 0.667 ppm and 0.576 ppm
respectively. In the cube design, control bricks emitted the maximum level at 0.917 ppm compared to other
bricks. From the graph, the pattern appears to increase from 0 to 30% for wall and column pattern, while the
cube form shows a decreasing trend from 0 to 30%.
The values for BS brick 5% and 30% for the wall are 0.715 ppm and 0.912 ppm, higher than the control
brick. The values for column patterns were 0.675 ppm for BS (5%) and 0.800 ppm for BS (30%). PS brick also
demonstrated an increasing pattern at 0.690 ppm for 5% and 0.819 ppm for 30% in the form of a wall. On the
other hand, the cube form of PS brick showed very minimal differences in the comparison between 5% and 30%
PS brick which is 0.002 ppm. Compared to the limit for Empty Room (ER), the TVOC level for control brick
appeared to be slightly higher in every pattern except for the cube pattern.
In conclusion, the result shows that the amount of TVOC has no significant difference between control, BS
and PS brick. This might happen as a result of the organic compounds present in the brick being removed during
Fig. 5. Heavy metal concentration for BS brick (5%).

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12. the firing process. Nevertheless, the increasing value of TVOC is still below the limit which is 3 ppm based on the
standard and BS and PS bricks are safe to be used as an indoor brick in terms of the volatile organic compound.
Carbon dioxide (CO2)
The emission of carbon dioxide (CO
2
) for both control bricks and mosaic sludge bricks (BS and PS) for 5% and
30%. The findings shows that control brick (0%) obtained the highest emissions compared to BS brick and PS
brick. CO
2
was measured in unit ppm by using Yes monitor, based on the standard for CO
2
which is 1000 ppm
according to the ICOP-IAQ (2010).
The results obtained showed that the control brick had highest emission of CO
2
for the wall design at 381
ppm and trailed by column and cube design at 357 ppm and 349 ppm. For BS bricks, the 5% sludge had a higher
emission compared to 30% sludge for wall design at 342 ppm and 323 ppm. Cube pattern for BS brick (5%)
showed a higher reading at 342 ppm compared to BS brick (30%) at 340 ppm. For the column pattern, both BS
bricks show equal readings of 330 ppm. On the other hand, PS brick with 5% sludge incorporation obtained the
highest emission of CO
2
compared to 30% sludge in the wall pattern (337 ppm and 329 ppm) and column (334
ppm and 329 ppm) pattern. The ER results indicated a lower value compared to the other bricks, confirming that
all bricks released CO
2
throughout the ER process.
From all the results, it was determined that control bricks emitted the maximum level of CO
2
whereas
the levels were lower for bricks incorporated with mosaic sludge. Thus, control bricks appeared to emit more
CO
2
than bricks with mosaic sludge (BS and PS). The BS brick with 30% composition is recommended, as it
consistently displayed lower concentration values across all patterns when compared to other brick samples.
Nevertheless, it is important to note that all the bricks produced in this study are considered safe for use as
Fig. 6. Heavy metal concentration for BS brick (10%).

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13. building materials within enclosed structures. They meet the requirement of being below the limit of 1000 ppm
set by the ICOP-IAQ (2010).
Carbon monoxide (CO)
Overall, the findings indicated that control bricks emitted the most CO when compared to other types (BS and
PS) of bricks in the form of wall, column, and cube. These phenomena occur when the control brick carries CO
after the firing process. Other than that, the control brick was higher with the organic content compared to BS
and PS brick.
Control brick for column shows the higher values 0.200 ppm while both wall and cube with the same result
(0.180 ppm). In the meantime, BS brick (5%) showed a higher emission compared to BS brick (30%) for all wall
patterns (0.080 ppm and 0.010 ppm), columns (0.010 ppm and 0.050 ppm) and cubes (0.080 ppm and 0.040
ppm). The results obtained for PS brick showed a similar trend with the BS brick. PS brick (5%) obtained higher
emissions compared to PS brick (30%) in all forms of wall, column and cube. Empty Room (ER) findings was
0.005 ppm and slightly lower compared to BS brick and PS brick 30%.
Furthermore, the CO values were lower in BS brick and PS brick that have been incorporated with 30%
sludge. Thus, the incorporation of mosaic sludge has the potential to reduce the CO content in fired clay bricks.
Nonetheless, all the bricks followed to the CO standard, ensuring levels remained below the 10 ppm.
Ozone (O3)
The values of O
3
were obtained from control bricks and mosaic sludge (BS and PS) bricks in wall, column and
cube patterns. The result shows that control bricks have the lowest emission among the others with 0.009 ppm for
wall, 0.011 ppm for column and 0.013 ppm for cube. Meanwhile, for BS bricks, the result for wall pattern showed
that 30% of sludge had the highest emission at 0.012 ppm compared to 5% sludge at 0.011 ppm. The same trend
was obtained for the column and cube which were 0.013 ppm and 0.023 ppm for BS brick (30%) compared to BS
brick (5%) which are 0.012 ppm and 0.013 ppm respectively. The result measurements for PS brick also showed
the same trend with PS brick (30%) having higher O
3
emissions compared to PS brick (5%). On the other hand,
PS brick (30%) showed that the cube pattern was the highest with 0.026 ppm, trailed by column and wall designs
with 0.023 ppm and 0.019 ppm. In the experimental phase, the concentration of O
3
value for ER appeared lower
Fig. 7. Heavy metal concentration for BS brick (20%).

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14. possibly because of the empty state of room conditions. Nonetheless, when the brick was placed inside the
chamber, both types of fired clay bricks indicated a rise in the O
3
concentration within the room.
The data revealed that incorporating sludge into fired clay bricks increases the release of ozone emissions.
Among all brick samples tested, the BS brick with a 5% composition revealed the most favourable result,
emitting the least amount of gases. However, all the bricks followed to the ICOP-IAQ (2010) standards, ensuring
emissions stayed below the 0.050 ppm. Thus, mosaic sludge bricks are safe to be used.
Formaldehyde (HCHO)
Generally, there is no significant difference in the HCHO emission between control bricks and mosaic sludge
bricks. The ER value was determined lower with 0.001 ppm as expected.
The control bricks show the lowest emission values compared to other bricks i.e., wall, column and cube
(0.018, 0.013 and 0.015 ppm). BS brick showed that 5% sludge bricks showed lower HCHO emissions compared
to 30% sludge bricks in all forms. The results showed that the HCHO emissions for BS brick (5%) for wall was
0.019 ppm for cube and column form at 0.016 ppm and 0.014 ppm. BS brick (30%) also showed similar results
whereby the highest was obtained for wall (0.021 ppm), followed by cube (0.018 ppm) and column (0.017 ppm).
On the other hands, PS brick (5%) has a lower value at 0.023 ppm (wall) compared to PS brick (30%) at 0.025
Fig. 9. Heavy metal concentration for PS brick (1%).

Fig. 8. Heavy metal concentration for BS brick (30%).

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15. Fig. 12. Heavy metal concentration for PS brick (20%).

Fig. 11. Heavy metal concentration for PS brick (10%).

Fig. 10. Heavy metal concentration for PS brick (5%).

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16. ppm, followed by cube at 0.016 ppm for PS brick (5%) and 0.017 ppm for PS brick (30%). Furthermore, PS brick
for column pattern had a similar trend with PS brick (5%) which is 0.012 ppm compared to PS brick (30%) at
0.015 ppm.
However, the wall pattern utilizing BS brick (5%) emitted lower HCHO emissions in contrast to the other
patterns. Nevertheless, all bricks adhered to the standards and can be considered suitable for use as indoor
building materials. Other than that, the finding indicates that HCHO emission for all bricks did not exceed 0.100
ppm based on the ICOP-IAQ (2010) standards required.
Particulate matter (PM10)
PM
10
levels of various types of fired clay bricks. While the ER result was at a lower level of 0.015 mg/m
3
, the
measurements for the bricks (control, BS and PS) revealed slightly higher PM
10
levels, but they still remained
within the accepted standards. The results obtained showed that the wall, column and cube pattern values for BS
brick increased with the increasing sludge percentages with 0.115 mg/m
3
(0% sludge), 0.127 mg/m
3
(5% sludge)
and 0.133 mg/m
3
(30% sludge) for wall, 0.111 mg/m
3
(0% sludge), 0.124 mg/m
3
(5% sludge) and 0.136 mg/
m
3
(30% sludge) respectively for column. As for cube it showed 0.1403 mg/m
3
(0% sludge), 0.147 mg/m
3
(5%
sludge) and 0.149 mg/m
3
(30% sludge) respectively. Meanwhile, for PS brick there was an increase for the wall
pattern at 0.115 mg/m
3
(0% sludge), 0.120 mg/m
3
(5% sludge) and 0.127 mg/m
3
(30% sludge) each.
However, for the column and cube pattern, the lowest PM
10
value was shown by 5% sludge brick with column
(0.104 mg/m
3
) and cube (0.129 mg/m
3
). Overall, this finding shows that PS (5%) emitted the lowest PM
10
value
for all patterns compared to other bricks. Nevertheless, all bricks satisfied the standard ICOP-IAQ (2010) limit
which is below 0.150 mg/m
3
.
In terms of emission due to IAQ, the BS brick containing 5% sludge was considered safer and more suitable
than other variants. Consequently, it is recommended to employ the BS brick (5%) as a building material since
it released lower gases emission into the environment and adhered to the ICOP-IAQ standard. It also has lower
emissions than the control brick. However, for full utilization of mosaic sludge as raw material it could use up to
30% mosaic sludge. As all parameters in each pattern closely aligned with the standards set by ICOP-IAQ, every
pattern is considered suitable from a design perspective. However, based on the overall findings suggest that the
wall pattern is the most advisable choice for construction purposes.
Nevertheless, the overall results obtained show that the wall pattern is most recommended to be used in
construction work.
Conclusion
In conclusion, all the characteristics, sludge percentages, physical and mechanical properties, leachability, and
indoor air quality of bricks incorporated with BS sludge and PS sludge waste were determined. The results from
the XRF analysis revealed that the chemical properties of both clay soil and mosaic sludge were rich in SiO
2
and
Al
2
O
3
. The analysis indicated that the elements in clay were SiO
2
and Al
2
O
3
, comprising between 55.77% and
24.40%. Similarly, the mosaic sludge waste revealed its highest proportion in SiO
2
and Al
2
O
3
, ranging from 61.83
to 62.37% and 15.50–20.55% respectively.
The incorporation of mosaic sludge improved the physical and mechanical properties of bricks, achieving
a compressive strength of up to 25 N/mm², reduced microporosity, and satisfactory density (1600 kg/m³) and
shrinkage (<  8%) values. Leachability tests (TCLP, SPLP, SLT) confirmed compliance with USEPA and EPAV
guidelines for heavy metals, ensuring environmental safety. While 5% sludge bricks offered the safest choice
for indoor air quality under ICOP-IAQ standards, higher sludge content (up to 30%) effectively minimized
environmental waste and enhanced material properties without exceeding IAQ limits. The TCLP employs acetic
acid, which has a more acidic reagent, leading to a greater release of heavy metals than the SPLP. The results of
the SLT test demonstrated that the inclusion of mosaic sludge in fired clay bricks, up to a 30% proportion, led
to an initial increase in concentration up to 3 mg/L. Subsequently, the concentration decreased and remained
Fig. 13. Heavy metal concentration for PS brick (30%).

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17. constant until day 95. In summary, the integration of mosaic sludge into fired clay bricks ensured that heavy
metal results complied both the USEPA and EPAV guidelines. It can be concluded that BS sludge and PS sludge
can be effectively used up to 30% in the production of fired clay bricks, resulting in satisfactory physical and
mechanical characteristics. These bricks meet the standard criteria for heavy metals and offer improved indoor
air quality in line with ICOP-IAQ standards. Thus, these sludges present an eco-friendly and economical
alternative for disposal.
Data availability
The datasets used and/or analyzed during the current study available from the corresponding author on reason-
able request.
Received: 13 November 2024; Accepted: 3 February 2025
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Acknowledgements
The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid Uni-
versity for funding this work through a Large Research Project under grant number RGP 2/163/45. The authors
extend their appreciation to the Deanship of Scientific Research at Northern Border University, Arar, KSA for
funding this research work through the project number NBU-FFMRA-2025-2105-02.
Author contributions
Amir Detho: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Validation, Exper-
imental work, Writing and original draft preparation.Aeslina Abdul Kadir, Ahmad Shayuti Bin Abdul Rahim,
Nejib Ghazouani, Abdelkader Mabrouk, Ahmed Babeker Elhag, Hesham Hussein Rassem: Writing-Reviewing
and Editing.
Scientific Reports | (2025) 15:4820 18| https://doi.org/10.1038/s41598-025-89147-1
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19. Declarations
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