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Chemical Durability of Concrete Containing Pyrolyzed Waste Tyre
Wires: A Mechanical and Microstructural Investigation

Audu, U. D., Mamman, M., Dahiru, D. D.

Department of Building, Ahmadu Bello University, Zaria, Nigeria.

DOI: https://doi.org/10.51583/IJLTEMAS.2025.1410000064

Received: 10 October 2025; Accepted: 17 October 2025; Published: 10 November 2025
Abstract- The depletion of natural resources and need for advancements in industrial waste management have motivated
researchers to focus on identifying innovative strategies to lower carbon emissions within the construction industry. Concrete’s
inherent brittleness limits its ductility. To enhance this property, researchers have explored the incorporation of fibres in concrete.
This research evaluates the durability of concrete containing Pyrolyzed Waste Tyre Wires (PWTW) under chemical erosion.
Specimens with PWTW dosages of 0%, 0.5%, 1%, and 1.5% by weight were prepared and exposed to H2SO4 and MgSO4 solutions
for up to 56 days. Compressive strength evolution and microstructural changes (SEM) were assessed. After 56 days, PWTW
inclusion significantly mitigated strength loss due to chemical attack. Compared to the control (0% PWTW), the 1% PWTW mix
showed the lowest strength loss in H2SO4 (11.65% vs 15.93%), while the 1.5% PWTW mix performed best in MgSO4 (20.9% vs
28.88% loss). SEM analysis revealed denser microstructures in PWTW-reinforced samples after chemical exposure. Findings
demonstrate that PWTW enhances concrete's resistance to sulfuric acid and magnesium sulphate attack, supporting their use in
durable and sustainable construction.

Keywords- End of Life Tyres, Concrete, Durability, Environment, Acid Attack, Sulphate Attack

I. Introduction

Concrete, a fundamental construction material, is widely used in buildings and infrastructure due to its strength, workability, and
cost-effectiveness. However, its inherent weaknesses, including high self-weight, low tensile strength, and brittleness, limit its
applicability in specialized projects [1], also previous research show concrete's vulnerability to biological and physical damage.
Therefore, it must be improved to achieve higher strength, toughness, workability, and durability. To address these weaknesses,
researchers have proposed distributing reinforcing fibres throughout the concrete's cross section [2]. This new material called Fibre
Reinforced Concrete (FRC) has become widely adopted in industrial infrastructure including industrial floors, sewage and
wastewater tunnels, agricultural silos, fermenters, and power plant cooling towers, due to its enhanced strength and ductility.
However, these applications are prone to chemical deterioration, underlining the importance of studying the performance of FRC
under various chemical attacks [3]. When cementitious composites come into contact with acidic solutions, the main phases of the
hardened cement paste begin to break down and dissolve. This chemical reaction diminishes the alkalinity of the pore solution,
leads to increased porosity, and consequently reduces the mechanical strength of the concrete. This degradation process is
commonly referred to as chemical erosion of concrete [4].

There are different types of chemical erosion of concrete, including acid and sulphate chemical erosion of concrete. Solid sulphates
typically have little impact on concrete, but in liquid form, they migrate into the concrete's voids and react with its hydrated cement
products. This chemical reaction, known as sulphate attack, involves sulphate ions breaking down the cement paste. The process is
driven by water-soluble sulphate salts particularly those of alkali-earth metals (like calcium and magnesium) and alkali metals (such
as sodium and potassium) which react with the concrete components. Below is a detailed depiction of the chemical process [5].

MgSO4 + Ca(OH)2 + 2H2O = CaSO4.2H2O + Mg(OH)2 (1)

Cementitious composites are inherently highly alkaline, with pH levels exceeding 12. When cement paste comes into contact with
acids, its components begin to break down, a process termed acid attack. As the pH drops below the stability limits of cement
hydrates, these hydrates lose calcium and decompose into an amorphous hydrogel [4]. The final products of this acid attack are the
calcium salts corresponding to the attacking acid, along with hydrogels comprising silicon, aluminium, and ferric oxides. As the
pH of the acid decreases below approximately 6.5, concrete becomes increasingly vulnerable, leading to the dissolution of both its
hydrated and un-hydrated cement compounds as well as calcareous aggregates [6]. The chemical reactions involved in a typical
acid attack on cementitious composites can be given as follows:

Ca(OH)2 + H2SO4 = CaSO4.2H2O (2)

3CaO.2SiO2.3H2O + H2SO4 = CaSO4.2H2O + Si(OH)4 (3)

Dsouza et al., 2018 [7] investigated the strength and durability of Steel Fibre Reinforced Concrete (SFRC) produced using M25-
grade concrete with steel fibres of aspect ratio 60 at dosages of 0.5%, 1%, and 1.5% by weight. In their study, concrete cubes were
immersed in a hydrochloric acid solution of pH 2, with concentration of 5% water weight, for the acid attack test, and in both
sodium sulphate and magnesium sulphate solutions each at 5% water weight concentration for the sulphate attack test. Their findings

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revealed that SFRC exhibits improved resistance to both acid and sulphate attacks compared to conventional concrete with the 1.5%
steel fibre mixture demonstrating the highest resistance.

Vegesana and Killamsetty, 2020 [8] investigated the compressive strength of SFRC exposed to chemical attack using M30 grade
concrete. In their study, hooked-end steel fibres with an aspect ratio of 50, were incorporated at 0% and 3% of weight of cement
and were randomly dispersed throughout the mix. Cube specimens were then immersed in 5% concentrated solutions of H2SO4 and
MgSO4 for a period of 30, 60, 90, 120, 150 and 180days. The results indicated that steel fibres improved the concrete's resistance
to acid attack and sulphate attack.

Zhang et al., 2022 [9] studied the microscopic properties of SFRC under chemical erosion using M30 grade concrete with steel
fibre contents of 0%, 1%, and 2%. Specimens were immersed in a 5% sulphuric acid solution and a 10% sodium sulphate solution
for 28 days. After immersion, both the microstructural properties and the axial bearing capacity were measured. The results
indicated that adding steel fibres significantly improved the axial bearing capacity, and chemical erosion accelerated the concrete's
failure, although SFRC had greater resistance. The study identified an optimal steel fibre content of 1% for a sodium sulphate
environment and 2% for a dilute sulphuric acid environment.

This research’s significance is to explore alternative materials to enhance concrete properties while also sourcing an eco-friendly
material from industrial waste. The paper examines the durability of steel fibre reinforced concrete under various adverse
environmental conditions. By incorporating pyrolyzed waste tyre wires, the study evaluates both the mechanical and microstructural
properties of the concrete.

II. Materials and Methods

A. Materials

The materials used for this study are as follows; cement, fine aggregate, coarse aggregate, water and steel fibre. Details of the
materials are as follows:

1) Ordinary Portland cements: All mixes employed locally manufactured Dangote brand 3X 42.5 cement, whose chemical,
physical, and mechanical properties adhere to the standards set by EN 197-1:2000 [10].

2) Aggregates: The aggregates used in the experiment consisted of both fine and coarse materials that comply with BS EN
12620:2013 [11]. The fine aggregate was sharp river sand with a maximum particle size of 4.75 mm, while the coarse aggregate
was crushed gravel with a maximum size of 20 mm. Both types were sourced from Zaria, as shown in Figure 1.

3) Water: Pipe-borne water sourced from Ahmadu Bello University in Zaria, which adheres to the specifications of BS EN
1008:2015 [12], is used.

4) Steel Fibres: Steel fibres were sourced from Zango Abattoir in Sabon Gari LGA, Zaria, Kaduna State. At this facility, waste
tyres are used as fuel during meat processing, which produces steel wires; thus, the fibres are a product of the pyrolysis process.
Tyre wires of 1.67mm diameter obtained from heavy-duty truck tyres were used, these steel wires were then cut into 50mm length
and used as discrete steel fibres in concrete. Preliminary tests conducted at the Department of Metallurgical and Material
Engineering Laboratory, Ahmadu Bello University, Zaria, confirmed that the fibres meet the tensile strength requirements specified
in ASTM A820 [13] and BS EN 14889-1 [14]. The results are presented below in Table 1.

Table 1: Properties of Recycled Steel Fibre

Specimen Breaking Force (N) Tensile Strength (MPa) Elongation at break (%)

Maximum 4300 1938.01 21.5

Minimum 1870 844.5 6.96

Mean 3005 1350.84 10.67

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Figure 1: Particle Size Distribution of Aggregates

B. Mix design

Concrete Grade 25 was utilized in this study, with the mix design carried out according to the Building Research Establishment
(BRE) design method. The quantities of materials prescribed by the mix design are detailed in Table 2.

Table 2: Quantity of Materials

Materials Cement Water Aggregate Fibre

Fine Coarse 0.5% 1% 1.5%

Quantity
(Kg/m3)

370 210 675 1150 12 24 36

A total of 180 specimens were produced, using four mix designs with varying steel fibre dosages: a control mix, alongside mixes
containing 0.5%, 1%, and 1.5% fibre by volume of concrete.

C. Methods

The study was carried using the following processes which include;

1) Test on fresh properties of concrete: Fresh property test carried out on concrete containing various dosages of the fibre include:

Workability Test: Slump values were measured in accordance with BS EN 12350-2:2019 [15], using a slump cone with a height of
300 mm, a bottom diameter of 200 mm, and a top diameter of 100 mm.

2) Test on harden properties of concrete: To evaluate the compressive strength of concrete, a uniaxial compression test was
performed on 100 mm × 100 mm × 100 mm cubes in accordance with BS EN 12390-3:2019 [16].

Resistance to sulphuric acid (H2SO4): The resistance to external acid attack was assessed following ASTM C267-01 [17]. Initially,
100 × 100 × 100 mm cubes were cast and cured in water for 28 days. After curing, the samples were removed, allowed to reach a
saturated surface-dry condition. Subsequently, the specimens were immersed in a 5% sulfuric acid solution for additional curing
periods of 28 and 56 days.

Resistance to Magnesium Sulphate (MgSO4) Solution: The resistance to external sulphate attack was assessed according to ASTM
C1012 [18]. Cubes measuring 100 × 100 × 100 mm were cast and water-cured for 28 days. Once cured, the specimens were
removed, allowed to reach a saturated surface-dry condition. They were then immersed in a 5% magnesium sulphate solution
(prepared by dissolving MgSO4 salts in water) for additional curing periods of 28 and 56 days.

Microstructure: The microstructure of the specimens, was examined using a Scanning Electron Microscope (SEM). This analysis
was carried out at the National Steel Raw Materials Exploration Agency (NSRMEA) Laboratory in Malali, Kaduna, following the
procedures specified in ASTM C1723-16 [19].

100

0.1 1 10 100

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Logarithmic Scale (Sieve Size)

Logarithmic Sieve Analysis of aggregates

Fine Aggregate Coarse Aggregate BS 882 Zone 1 Upper Limit BS 882 Zone 1 Lower Limit

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III. Results

A. Properties of Fresh Concrete Specimen

1) Slump: Figure 2 presents the results of the slump test conducted on fresh concrete specimens. It displays the slump values
obtained from concrete mixes with varying fibre dosages of 0%, 0.5%, 1%, and 1.5%. As expected, the results reveal a decline in
workability as the fibre content increases. The presence of fibres restricts the mobility of the concrete mix, leading to reduced
workability, a finding that is consistent with the observations reported by ACI Committee 544 (2002) [20].

Figure 2: Slump Values at Fresh stage

B. Effect of Chemically Aggressive Environment on Hardened Concrete

1) Resistance to sulphuric acid (H2SO4) attack: Figure 3 shows the compressive strength of concrete specimens that were cured in
a 5% H₂SO₄ solution for 28 days, while Figure 4 displays the compressive strength after 56 days of acid curing. Overall, all samples
experienced a decline in compressive strength following exposure to the acid solution.

After 28 days of acid curing, the percentage reduction in compressive strength relative to normally cured specimens was 7.22% for
the control mix, 4.38% for the mix with 0.5% fibre, 1.32% for the 1% fibre mix, and 12.46% for the 1.5% Pyrolyzed Waste Tyre
Wires (PWTW) mix. Although all specimens demonstrated some strength loss due to acid exposure, the mixes with 0.5% and 1%
fibre content showed considerably better acid resistance compared to the control, while the mix with 1.5% fibre did not perform as
well.

After 56 days of acid curing, the decreases in compressive strength compared to normally cured specimens were 15.93% for the
control sample, 14.37% for the 0.5% PWTW mix, 11.65% for the 1% fibre mix, and 15.18% for the 1.5% PWTW mix. Notably,
the control sample exhibited severe deterioration, resulting in all fibre-reinforced concrete (SFRC) mixes outperforming it. The
incorporation of pyrolyzed waste tyre wires led to an optimal reduction in strength deterioration of 5.9% and 4.28% at 28 and 56
days, respectively, which aligns with the results reported by [7] and [3].

Figure 3: Effect of H2SO4 curing on Compressive strength of Concrete with PWTW after 28days

98
93

100

120

0 0.5 1 1.5

S
lu

m
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(
m

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Fibre Dosages (%)

Slump Test

0% Control 0.5% Dosage 1% Dosage 1.5% Dosage

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28days Normal curing 28days Sulphuric acid curing

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Figure 4: Effect of H2SO4 curing on Compressive strength of Concrete with PWTW after 56days

2) Resistance to magnesium sulphate (MgSO4) attack: Figure 5 presents the compressive strength of concrete specimens exposed
to a magnesium sulphate (MgSO4) solution after 28 days of curing. All specimens showed a reduction in compressive strength
when cured in the MgSO4 solution. Specifically, after 28 days, the control mix experienced a reduction of 24.93%, while the mixes
with 0.5%, 1%, and 1.5% fibre dosages exhibited decreases of 12.19%, 16.28%, and 19.09%, respectively.

Figure 5: Effect of MgSO4 curing on Compressive strength of Concrete with PWTW after 28days

Figure 6 displays the compressive strength after 56 days of MgSO4 curing. Here, all specimens experienced a further, albeit slight,
loss in strength. The control mix showed a 28.88% reduction compared to its normal 56-day strength. Meanwhile, the fibre-
reinforced concrete, referred to here as PWTW concrete with 0.5%, 1%, and 1.5% fibre dosages recorded compressive strength
losses of 22.2%, 22.9%, and 20.9% respectively. Notably, the overall strength loss between the 28-day and 56-day curing periods
was relatively minimal across all specimens.

Figure 6: Effect of MgSO4 curing on Compressive strength of Concrete with PWTW after 56days

0% Control 0.5% Dosage 1% Dosage 1.5% Dosage

C
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56days Normal curing 56days Sulphuric acid curing

0% Control 0.5% Dosage 1% Dosage 1.5% DosageC
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28days Normal curing 28days Magnesium Sulphate curing

0% Control 0.5% Dosage 1% Dosage 1.5% Dosage

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56days Normal Curing 56days Magnesium Sulphate curing

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C) Microstructural analysis of concrete exposed to Chemically aggressive environment

Sulphuric acid (H2SO4): Figure 7 illustrates the SEM micrographs of 0% PWTW concrete and 1.5% PWTW concrete specimens,
captured both before and after exposure to an acid solution. In both cases, the cement paste, which appeared dense prior to acid
immersion, becomes noticeably loose afterward, with dislodged fragments, enlarged pore sizes, and numerous discernible cracks
evident in the post-exposure images.

Figure 7: SEM Images of Concrete Samples before and after exposure to H2SO4, a) Control Sample Before; (c) 1.5% PWTW

Concrete before exposure; (d) 1.5% PWTW Concrete after exposure

Magnesium sulphate (MgSO4): Figure 8 displays the microscopic morphology of specimens with 0% and 1.5% fibre dosage after
immersion in a 5% MgSO4 solution for 56 days. The dense cement paste, initially observed in both the 0% and 1.5% PWTW
concrete samples has deteriorated, becoming loose and highly porous. Additionally, more microcracks are apparent after exposure.
In the 1.5% PWTW concrete, the cracks predominantly occur along the aggregate-cement interfacial transition zone (ITZ) rather
than along the steel fibre, which indicates a stronger bond in the steel-cement ITZ compared to the aggregate-cement ITZ. Prior to
MgSO4 immersion, the 1.5% PWTW concrete exhibited a strong bond between the steel fibre and the cement paste; however, after
immersion and during sample preparation for SEM the cement paste tends to separate from the steel fibre.

Figure 8: SEM Images of Concrete Samples before and after exposure to MgSO4, a) Control Sample Before; b) Control Sample

after; (c) 1.5% PWTW Concrete before exposure; (d) 1.5% PWTW Concrete after exposure

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IV. Conclusions

Based on the experimental findings, the following conclusions can be deduced:

1. An increase in the steel fibre content significantly reduces the workability of the concrete. Specifically, the slump
decreased by 64.3% from 98 mm in the 0% fibre dosage to 35 mm at a 1.5% fibre dosage.

2. The incorporation of steel fibres was found to significantly enhance the compressive strength of SFRC. Notably, at 56
days, a 1.5% fibre dosage resulted in a 45.7% increase in compressive strength compared to the control mix.

3. Specimens exposed to the H2SO4 solution demonstrated a loss in compressive strength. However, SFRC proved to be more
resistant to acid attack. Specifically, the concrete mixes with fibre dosages of 0%, 0.5%, 1%, and 1.5% experienced
compressive strength losses of 15.93%, 14.37%, 11.65%, and 15.18%, respectively, highlighting enhanced durability with
fibre incorporation.

4. The results indicate that SFRC exhibits enhanced resistance to sulphate attack compared to conventional concrete. When
immersed in a MgSO4 solution, the compressive strength reductions for concrete with fibre dosages of 0%, 0.5%, 1%, and
1.5% were recorded as 28.88%, 22.2%, 22.9%, and 20.9%, respectively. This clearly demonstrates that incorporating steel
fibres improves sulphate resistance, with the SFRC mixes suffering significantly lower strength losses.

Acknowledgements

The authors wish to sincerely thank the Petroleum Technology Development Fund (PTDF), Nigeria, for their generous financial
support that enabled this research.

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