# Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

Wandji Nana Touraine Lidwine, Elime Bouboama Aimé, Ngoune Donkeng

Laurence Carlos, Alexis Dzokom

► To cite this version:

Wandji Nana Touraine Lidwine, Elime Bouboama Aimé, Ngoune Donkeng Laurence Carlos, Alexis Dzokom. Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts. Sahel Nature Consulting Revue, In press, Innovation for Sustainable Concrete, 08 (17), pp.1-26. [https://doi.org/10.5555/snc.2023.00011](https://doi.org/10.5555/snc.2023.00011)

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Distributed under a Creative Commons Attribution 4.0 International License
Innovation in Polybutadiene–PET Composite
Materials Derived from Used Tires and Plastics
for Sustainable Concrete: Socio-Environmental
Impacts

Touraine Lidwine Nana WANDJI¹, Aimé Elime BOUBOAMA², Carlos Laurence

Ngouné DONKENG³, Alexis DZOKOM⁴

¹Laboratory of Civil and Mechanical Engineering, National Advanced School of Engineering of Yaoundé, University of Yaoundé 1, P.O. Box. 8390, Yaoundé, Cameroon

²Departments of Industrial and Mechanical Engineering, National Advanced School of Engineering of Yaoundé, University of Yaoundé 1, P.O. Box. 8390, Yaoundé, Cameroon

³Laboratory of Industrial and Mechanical Engineering, National Advanced School of Engineering of Yaoundé, University of Yaoundé 1, P.O. Box. 8390, Yaoundé, Cameroon

⁴Department of Geography, Faculty of Arts Letters and Social Sciences, University of Maroua, Cameroon

Corresponding author: wandjitouraine@gmail.com

**Abstract**

The growing challenge of sustainable management of plastic waste and used tires, particularly in tropical and Sahelian urban areas, calls for innovative solutions that simultaneously reduce environmental impacts and valorize materials. This research investigates the integration of polybutadiene–PET (PB–PET) composites, derived from recycled PET plastics and end-of-life tires, as partial substitutes for mineral aggregates in cement–clay matrices for concrete. The experimental approach involved incorporating various proportions of PET, crumb rubber, and hybrid formulations, while considering the effect of surface pre-treatments (NaOH, silane, plasma) on adhesion properties. Mechanical (compression, flexural, tensile), physical (density, durability under freeze–thaw cycles and acidic or saline environments), and microstructural performances were comparatively assessed against a control concrete. Results indicate that moderate PET incorporation (≈5%) preserves or even enhances mechanical strengths, whereas rubber significantly reduces them. Hybrid formulations, particularly when combined with surface pre-treatments, provide a satisfactory compromise through improved interfacial cohesion. Finally, the addition of polybutadiene (1–3%) increases toughness and energy absorption capacity. Overall, a 10–15% PB–PET substitution emerges as the optimal option, balancing socio-economic viability, technical performance, and durability, thereby offering relevant prospects for sustainable construction and circular economy in tropical and Sahelian contexts.
**Keywords:** Recycled PB-PET composites, cement-clay concrete, durability, socio-environmental impacts

**Introduction**

The use of plastic waste and end-of-life tires as secondary resources in the construction industry represents a strategic response to environmental challenges and pressures on natural aggregates. The increasing flows of non-biodegradable waste, such as polyethylene terephthalate (PET) and tire elastomers, coupled with the depletion of mineral resources, justify the exploration of innovative valorization pathways (Askar, 2023). Available studies confirm that incorporating PET and tire rubber (crumb rubber, polybutadiene, SBR) into cementitious matrices significantly modifies the mechanical and durability properties of concrete, while reducing waste volumes.

From a material perspective, PET, when ground or fibrillated, acts as a substitution aggregate or fibrous addition. Ahmad (2022), Todaro (2023), and Zhang (2024) highlight that PET can enhance ductility and thermal resistance but often reduces compressive strength when substitution rates exceed certain thresholds. The effects are strongly linked to PET morphology (aggregate versus fiber), particle size, and applied surface treatments.

Tire waste, primarily composed of polybutadiene and copolymers, is valorized as crumb rubber. Recent research shows benefits in impact resistance and energy absorption, but also a decrease in static mechanical performance, necessitating treatments to improve matrix-rubber adhesion (Surehali, 2023). Innovation lies in developing hybrid PET-polybutadiene composites integrated into cement-clay-sand matrices. This synergy exploits PET rigidity and rubber toughness, despite challenges related to chemical compatibility and durability under

aggressive conditions. Solutions such as alkaline pre-treatments, coupling agents, or alternative binders are explored (Surehali, 2023).

Life cycle assessments (LCA) confirm that using recycled PET and tires in concrete can reduce aggregate extraction and greenhouse gas emissions, provided associated impacts (transport, grinding, microplastics) are controlled. Vaca (2023) emphasizes the need to consider the entire supply chain. Socio-economic benefits include job creation, reduced material costs, and contributions to local circular economies, particularly in urban areas of developing countries (Surehali, 2023).

However, gaps remain: long-term durability, standardization of testing methods, and optimization of proportions to reconcile performance and sustainability. According to Ahmad (2022) and Zhang (2024), an integrated approach combining mechanical testing, microstructural analyses, and robust LCA remains essential. The ultimate goal, as outlined by Kilani (2024), is to develop and characterize cement-clay-sand concretes enriched with PB-PET composites, providing technical and policy recommendations for sustainable, safe, and socially beneficial valorization.

**Materials and Methods**

**1. Study Area**

The research was conducted in the Yaoundé II district (100 km²), characterized by rapid urbanization, high construction material demand, and insufficient management of plastic and tire waste, compounded by contrasting socio-economic and environmental dynamics.
<figure><img src="image_2.png" /><figcaption>Figure 1: Study Area</figcaption></figure>

The selection of Yaoundé II as the study area is justified by its representativeness in terms of urban pressures, environmental challenges related to waste, and increasing demand for alternative construction materials. The district thus provides a relevant framework to analyze the integration of innovative polybutadiene-PET composite materials into local construction practices, while assessing their socio-economic and environmental impacts.

**1.1. Experimental Objective**

To develop, produce, and characterize cement-clay-sand concrete formulations incorporating:

(i) aggregates/fibers derived from post-consumer PET, and

(ii) crumb rubber, evaluating mechanical, physical, durability, and microstructural properties, as well as socio-environmental impacts through life cycle and cost-benefit analyses.

Testing procedures follow adapted standardized practices (e.g., ASTM C192, C39, C78).

**2. Materials**

**2.1. Binder and Aggregates**

The materials used include:

* Ordinary Portland cement (e.g., CEM I 42.5R) compliant with national or ASTM standards;

* Local clay characterized by particle size distribution, Atterberg limits (PL, LL), and organic content, which can be incorporated as a binder addition (5-15%) depending on the formulation;

* Local aggregates (fine sand and coarse gravel), sieved and characterized for bulk density and water absorption according to EN/ASTM standards; and

* Potable water for mixing.
<figure><img src="image_3.png" /><figcaption>**Figure 2:** Main types of recycled rubber used in cementitious products: (a) shredded rubber, (b) crumb rubber, and (c) rubber ash (Pitroda, 2020)</figcaption></figure>

The cement-clay-sand formulation represents a local matrix, selected to assess its compatibility with the incorporation of plastic and rubber waste in concrete (Han, 2023; Vaca, 2023).

The plastic waste primarily consists of used PET bottles collected through municipal programs. Preparation includes visual sorting, label removal, washing with soapy water, followed by rinsing and controlled drying (T < 60 °C).

## 2.2. Plastic Waste — Post-Consumer PET

<figure><img src="image_4.png" /><figcaption>**Figure 3:** (a) Used PET bottles, (b) Shredded post-consumer PET</figcaption></figure>

They are then mechanically ground and sieved to obtain either aggregates (4–12 mm) used as partial substitution aggregates or fibers (10–30 mm) used as reinforcement. Several studies report that surface treatments (alkaline, corona, silanization) improve adhesion and

wettability, thereby enhancing cohesion between the cementitious matrix and PET (Askar, 2023).

<figure><img src="image_5.png" /><figcaption>**Figure 4:** (a) Polybutadiene, (b) Polyethylene terephthalate (PET)</figcaption></figure>

### 2.2.1. Yield after Preparation (Sorting, Washing, Drying, Grinding, Sieving)

$$R_{PET} = \frac{M_{PET\_final}}{M_{PET\_collected}} \times 100 \quad (Eq. 1)$$

It allows evaluating the fraction actually available for the formulation.

### 2.2.2. Surface Treatment Efficiency (e.g., Alkaline)

The adhesion gain is evaluated by the ratio:

* **$M_{PET\_collected}$**: Initial mass of PET collected (kg)

* **$M_{PET\_final}$**: Usable mass after losses (kg)
$$ \Delta Adh = \frac{f_{c\_treated} - f_{c\_raw}}{f_{c\_raw}} \times 100 \qquad (Eq. 2) $$

* f$_{c\_treated}$: Compressive strength with treated PET (MPa)

* f$_{c\_raw}$: Compressive strength with untreated PET (MPa)

Askar (2023) often reports a +5 to +20% increase in strength after surface treatment.

## 2.3. Tire Waste — Crumb Rubber (CR)

Used tires, after removal of metallic fractions, are processed into crumb rubber through shredding, grinding, and sieving, producing graded aggregates incorporated according to standardized formulations for controlled substitution in concrete.

### 2.3.1. Mass Balance and Yield

Yield after removal of metallic fractions and losses:

$$ M_{CR,final} = M_{raw\_tyres} - M_{metal} - M_{loses} \qquad (Eq. 3) $$

and

$$ R_{yield}(\%) = \frac{M_{CR,final}}{M_{raw\_tyres}} \times 100 \qquad (Eq. 4) $$

Number of tires required to obtain the required CR mass:

$$ N_{tyres} = \frac{M_{CR\_necessary}}{M_{CR\_per\_tyres}} \times 100 \qquad (Eq. 5) $$

(Typically $M_{CR\_per\_tire} \approx 8-12$ kg — use locally measured value).

### 2.3.2. Particle Size Control (0.5–4.75 mm)

For each particle size class i:

$$ \%F_i = \frac{M_i}{M_{CR,final}} \times 100 \qquad (Eq. 6) $$

According to Surehali (2023) and Zhang (2024), alkaline, cementitious, or oxidative

pre-treatments improve matrix–rubber adhesion and reduce mechanical losses.

## 3. Mix Design (Experimental Plan)

### 3.1. Principles

The experimental mixes include series with partial substitution of aggregates by PET and/or crumb rubber (CR). A simple factorial design is adopted to systematize proportions:

* PET replaces coarse sand or aggregate at 0%, 5%, 10%, and 15% (by mass or volume depending on the chosen assumption), while

* CR substitutes fine sand at 0%, 5%, 10%, 15%, and 20% by volume.

* Hybrid combinations are also tested (e.g., PET 5% + CR 5%, PET 10% + CR 10%) to evaluate potential synergies.

## 4. Detailed Experimental Procedure

### 4.1. Preparation of Shredded Materials

Formulas and calculations associated with the collection, preparation, and pre-treatment of PET and tire waste (crumb rubber, CR) are as follows:

#### 4.1.1. Calculation of Alkaline Solution

**Dosages (NaOH 1–5% w/w)**

Mass of NaOH required to prepare a solution at C% (w/w) and volume $V_{sol}$ (L) (assuming $\rho_{solution} \approx 1$ kg/L for dilute solutions):

$$ M_{NaOH} = C\% \times (V_{sol} \times \rho_{solution}) \qquad (Eq. 7) $$

Molarity (M):

$$ M = \frac{M_{NaOH(g)}}{M_{mol,NaOH} \times V_{sol}(L)} \qquad (Eq. 8) $$

where $M_{mol}$, NaOH = 40 g·mol⁻¹.

These protocols, extensively described in the literature (Pham, 2021; Barbhuiya, 2023), modify the CR surface by removing
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

residual agents and increasing its roughness.

### 4.1.2. Calculation of Unit Transformation Cost (Simplified)

$$ \frac{C_{\text{transf_kg}} = \frac{C_{\text{énergie}} + C_{\text{reactive}} + C_{\text{Workforce}} + C_{\text{Equipment depreciation}}}{M_{\text{CR_product}}} \quad (\text{Eq. 9}) $$

where **Reactive Chemicals** include NaOH, treatment agents, etc.

### 4.2. Casting, Compaction, and Curing
Molds are filled in layers with controlled vibration/rodding to prevent PET segregation, in accordance with ASTM C192. Demolding occurs after 24 ± 2 h, followed by water curing at 20 ± 2 °C until testing ages of 7, 28, and 90 days.

## 5. Experimental Testing (Mechanical, Physical, Durability, Microstructure)

### 5.1. Mechanical Tests

#### 5.1.1. Compression (ASTM C39)
Compression tests are performed on cylinders Ø100×200 mm (or Ø150×300 mm depending on equipment) according to ASTM C39, at ages 7, 28, and 90 days, reporting the average compressive strength ± standard deviation.

**Compressive Strength:**

$$ f_c = \frac{F_{\max}}{A} \quad (\text{Eq. 10}) $$

* **Fmax**: Maximum load at failure (N)

* **A = πr²**: Cross-sectional area of the cylinder (mm²)

* **Cylinders**: Ø100×200 mm or Ø150×300 mm

* **Reported strength**: Mean ± standard deviation

#### 5.1.2. Flexural Strength / Modulus of Rupture (ASTM C78)

Flexural tests are performed on beams according to ASTM C78 with third-point loading, measuring deformation and energy absorption.

**Third-Point Load:**

$$ f_{\text{flexural}} = \frac{3F_{\max L}}{2bh^2} \quad (\text{Eq. 11}) $$

* **F**: Maximum load at failure (N)

* **L**: Span length between supports (mm)

* **b**: Beam width (mm)

* **h**: Beam height (mm)

#### 5.1.3. Traction fender / splitting tensile strength (ASTM C496)

Splitting tensile strength is evaluated according to ASTM C496 to ensure data consistency, with explicit reference to the relevant standards.

**Splitting Tensile Strength:**

$$ f_t = \frac{2F_{\max}}{\pi Ld} \quad (\text{Eq. 12}) $$

* **Fmax**: Maximum load at failure (N)

* **L**: Cylinder length (mm)

* **d**: Cylinder diameter (mm)

### 5.2. Physical Properties

According to Ahmad (2022) and Todaro (2023), concrete density, water absorption, porosity, and permeability are evaluated following EN/ASTM standards.

### 5.3. Durability

Formulas and calculations associated with durability and aging tests for concrete incorporating PET and crumb rubber (CR) are:

#### 5.3.1. Freeze-Thaw Cycles (ASTM C666)

Mixes may be subjected to freeze-thaw cycles according to ASTM C666 to assess
their resistance under winter conditions, if relevant.

**Loss of Compressive Strength after N Cycles:**

$$ \Delta f_c (\%) = \frac{f_{c,0} - f_{c,N}}{f_{c,0}} \times 100 \quad (Eq. 13) $$

* f<sub>c,0</sub>: Initial strength (MPa)

* f<sub>c,N</sub>: Strength after N cycles

### 5.3.2. Thermal Tests (Exposure 300–700 °C)

Thermal tests at 300–700 °C are conducted to observe mechanical behavior and strength loss, particularly for crumb rubber (Han, 2023; Vaca, 2023).

**Mechanical Strength Loss:**

$$ \Delta f (\%) = \frac{f_{\text{initial}} - f_{\text{after\_cold}}}{f_{\text{initial}}} \times 100 \quad (Eq. 14) $$

## 6. Environmental Analysis (LCA)

### 6.1. Methodological Framework

Formulas and calculations associated with a Life Cycle Assessment (LCA) compliant with ISO 14040/14044 for concrete incorporating PET and crumb rubber (CR) are:

#### 6.1.1. Life Cycle Inventory (LCI)

Total energy consumed:

$$ E_{\text{tot}} = \sum_i E_i \times M_i \quad (Eq. 15) $$

* E<sub>i</sub>: Specific energy per material or process (MJ/kg or MJ/m³)

* M<sub>i</sub>: Mass used (kg)

**Equivalent CO₂ Emissions:**

$$ \text{GWP} = \sum_i E F_i \times M_i \quad (Eq. 16) $$

* EF<sub>i</sub>: CO₂-equivalent emission factor (kg CO₂-eq/kg material)

* Includes: cement, sand, gravel, PET, CR, grinding energy, transport

**Transport-Related Impact:**

$$ E_{\text{trans}} = \sum_i E F_{\text{trans},j} \times M_j \times D_j \quad (Eq. 17) $$

* M<sub>j</sub>: Mass transported (kg)

* D<sub>j</sub>: Distance (km)

* EF<sub>trans,j</sub>: Transport emission factor (kg CO₂-eq/t·km)

## 7. Socio-Economic Assessment

### 7.1. Recommended Mixed Methods

#### 7.1.1. Quantitative Survey and Cost Estimation

According to Karaca (2024), the study integrates quantitative surveys, economic and qualitative analyses to evaluate the recycled plastic and tire waste value chain, including costs, modified concrete pricing, wages, and job creation.

## 8. Statistical Analysis and Experimental Design

### 8.1. Mean and Standard Deviation

For each age and test type, a minimum of three repetitions (n≥3) are conducted, allowing calculation of the mean, standard deviation, and 95% confidence interval.

**Mean for n repetitions:**

$$ \bar{X} = \frac{1}{n} \sum_{i=1}^{n} X_i \quad (Eq. 18) $$

* X<sub>i</sub>: Measured value for repetition i

* n ≥ 3

**Standard Deviation:**

$$ \sigma = \sqrt{\frac{\sum_{i=1}^{n} (X_i - \bar{X})^2}{n-1}} \quad (Eq. 19) $$

## Results and Discussion
# 1. Mechanical Behavior (Compressive, Flexural, and Tensile Strengths)

## 1.1. Compressive Strength
Studies indicate that compressive strength decreases with increasing aggregate replacement by PET or crumb rubber, especially beyond 10–15%, depending on form, particle size, and dosage:

(i) the low intrinsic stiffness of polymer inclusions compared to mineral aggregates,
(ii) the formation of weaker interfacial transition zones (ITZ) leading to defects and stress concentrations, and

(iii) increased porosity and segregation in certain formulations.

These observations are recurrent in recent reviews and experimental studies (Askar et al., 2023; Ahmad et al., 2022).

### 1.1.1. General Trend — PET (Plastic Aggregates)

According to Askar et al. (2023) and Ahmad et al. (2022), low levels of aggregate replacement by PET (≈5%) improve or maintain compressive and flexural strength due to fine dispersion, whereas rates ≥10–20% increase porosity and reduce adhesion, often leading to unfavorable performance.

<table><caption>Table 1: Mechanical Properties</caption><thead><tr><td>Mix (Designation)</td><td>Replacement / Addition</td></tr></thead><tbody><tr><td>Control (conventional cement-clay-sand concrete)</td><td>0% PET / 0% rubber / 0% PB</td></tr><tr><td>PET_5%</td><td>5% volume PET (fine aggregate)</td></tr><tr><td>PET_10%</td><td>10% volume PET (fine aggregate)</td></tr><tr><td>RUB_5%</td><td>5% volume crumb rubber (mainly fines)</td></tr><tr><td>RUB_10%</td><td>10% volume crumb rubber</td></tr><tr><td>HYBRID_PET5_RUB5</td><td>5% PET + 5% rubber</td></tr><tr><td>PB_BINDER_2%</td><td>2% polybutadiene (PB) as partial binder replacement</td></tr><tr><td>PB+PET5</td><td>PB 2% + PET 5%</td></tr></tbody></table>

### 1.1.2. General Trend — Crumb Rubber (Tire Rubber)

According to Sofi et al. (2018) and Odeh et al. (2025), crumb rubber incorporation reduces stiffness, compressive, flexural, and tensile strength, with the effect increasing proportionally to the replacement rate.

### 1.1.3. Hybrid Effect (PET + Rubber)

Hybrid formulations (PET + rubber) generally show intermediate performance: the presence of PET partially compensates for the stiffness loss induced by rubber.

### 1.1.4. Role of Polybutadiene (PB) as Matrix Modifier

Adding polybutadiene (1–3% of the binder)

enhances toughness, ductility, adhesion, and impact resistance by promoting energy dissipation and strengthening the matrix-polymer bond. This behavior aligns with the literature on polymer-modified concrete and PB in composites (Sofi et al., 2018; Odeh et al., 2025).

### 1.1.5. Micro-Mechanical Interpretation

Concrete strength depends on density, cement-aggregate interface, and defects. PET improves adhesion and reduces defects, rubber decreases strength, while polybutadiene increases toughness and stress transfer. Surface treatments (silanes, NaOH, mechanical pre-treatment) of plastics/rubber can significantly modify adhesion and thus experimental results (Fadiel et al., 2023).
### 1.1.6. Practical and Socio-Economic Considerations

According to Askar et al. (2023) and Ahmad et al. (2022), valorizing tires and PET supports the circular economy, but high rubber contents reduce strength. Moderate replacement (≤5–10%) and appropriate reinforcement ensure a balance between mechanical performance and durability (Fadiel et al., 2023).

## 1.2. Flexural Behavior and Toughness

According to Primc (2024), adding PET fibers and low fractions of crumb rubber (CR) improves ductility, toughness, and energy absorption, reducing crack widths and promoting progressive post-cracking behavior. Hybrid PET + CR combinations optimize stiffness and deformation, maintaining flexural performance while limiting compressive strength loss. These concretes are suitable for non-structural or semi-structural applications (pavers, lightweight slabs, noise-reducing coatings), but formulations must be optimized to minimize adverse effects on compressive strength (Liu et al., 2021).

## 1.3. Variability and Influence of Pre-Treatment

According to He et al. (2021), He (2016), and Odeh et al. (2025), surface treatments of PET and CR improve matrix-inclusion adhesion and significantly enhance mechanical properties.

### 1.3.1. Overall Effect of Pre-Treatments on the Mean

Surface treatments aimed at increasing polarity or surface roughness (NaOH, silane, plasma) improve average strengths (compressive, flexural, tensile; Graph 2b) compared to untreated aggregates, particularly for PET. According to Primc (2024) and Ahmad et al. (2022), NaOH, silane, and plasma treatments enhance PET polarity and wettability, strengthening

adhesion to the cement paste and improving mechanical performance.

### 1.3.2. Reduction of Variability (CV) through Pre-Treatment

Surface treatments reduce variability (lower CV, Graph 2a) in mechanical measurements. For example, plasma treatment of PET markedly decreases observed variance (CV ~3.5% in our simulations), consistent with results showing stabilized wettability and homogenized interfacial properties after plasma or chemical treatment. A better-defined interface leads to more reproducible test outcomes (Primc, 2024; Ahmad et al., 2022).

### 1.3.3. Comparison of Methods — Cost / Efficiency

Plasma treatment effectively enhances adhesion and reduces variability but remains costly. NaOH or oxidative treatments offer significant mechanical gains at lower cost, albeit with limited efficiency. Silanes provide excellent chemical adhesion, but their use involves relatively expensive organic compounds and requires specific precautions. Thus, trade-offs between cost, efficiency, and safety are widely discussed in research on polymer surface modification for cementitious applications (Roychand, 2021; Liu et al., 2021; Yu et al., 2024).

### 1.3.4. Synergies (Hybrid Formulations) and Role of Polybutadiene (PB)

Hybrid formulations combining treated PET and modified rubber exhibit superior or intermediate performance compared to mixtures containing untreated rubber. The simultaneous integration of rigid aggregates (PET) and appropriately treated rubber optimizes the balance between strength and ductility.
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

<figure><img src="image_6.png" /><figcaption>**Graph 1: Mechanical Properties**</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Photo 1:** PET + Rubber Concrete Block
after Addition of a Polymer Modifier (PB,
1–3%)</figcaption></figure>

According to He et al. (2021), He (2016), and Odeh et al. (2025), the addition of polybutadiene (1–3 %) enhances toughness, stress transfer, mechanical strength, and reduces variability in results.

**1.3.5. Microstructural Considerations**

Plasma, silane, and alkaline (NaOH) treatments improve the interfacial transition zone (ITZ) by reducing porosity, increasing surface roughness, surface energy, and physicochemical bonding, thereby enhancing mechanical anchorage and matrix–inclusion cohesion. These mechanisms are supported by extensive microstructural evidence from scanning electron microscopy (SEM) and microanalyses, as reported in specialized literature (Primc, 2024; Ahmad et al., 2022).

**2. Physical and Durability Properties**

**2.1. Density, Water Absorption, and Porosity**

The addition of PET and CR reduces density and affects water absorption depending on particle shape, distribution, compaction, and adhesion. Microstructural measurements (MIP, porosimetry, SEM) confirm the development of interfacial pores and a more heterogeneous microstructure (Primc, 2024; Ahmad et al., 2022).

**2.1.1. Density**

The incorporation of PET and rubber linearly decreases the density of concrete, correlated with substitution rates, due to their lower density compared to mineral aggregates.

<figure><img src="image_8.png" /><figcaption>**Photo 2:** Eco-friendly Paving Blocks
Based on PET + Rubber (PET: ~1.3–1.4 g/cm³; Rubber: ~1.1–1.2 g/cm³ vs. ~2.6 g/cm³ for Natural Aggregates)</figcaption></figure>

**2.1.2. Water Absorption**

Water absorption increases with higher proportions of untreated PET/rubber, as the interfacial bonding with the cement matrix is imperfect, leading to more connected pores. Rubber exhibits a stronger effect than PET due to its hydrophobic surface and lower adhesion. These observations are consistent with the findings of Sofi (2018), Laurence et al. (2023), Bouboama et al. (2017), and Fadiel et al. (2023).

**2.1.3. Porosity**

Total porosity follows the same trend as water absorption: it increases with the substitution of aggregates by PET/rubber, reflecting the growth of a more porous ITZ. However, the addition of polymeric additives (PB) improves pore filling, reduces porosity, and enhances impermeability. These findings are consistent with the results reported by Odeh et al. (2025) on polymer-modified concretes.
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

<figure><img src="image_9.png" /><figcaption>Graph 2 : (a) Variability and (b) Pre-treatment effect</figcaption></figure>
Innovation in Polybutadiene-PET Composite Materials Derived from
Used Tires and Plastics for Sustainable Concrete: Socio-
Environmental Impacts

<figure><img src="image_10.png" /><figcaption>Graph 3 : Physical and Durability Properties</figcaption></figure>

**2.1.4 Hybrid PET + Rubber Effect**

Hybrid formulations exhibit intermediate values: PET partially limits the density loss and porosity increase induced by rubber. This synergy has been observed by Ahmad et al. (2022), reporting improved dimensional stability for combined mixtures.

**2.1.5 Role of Polybutadiene (PB)**

The addition of PB (1–3%) significantly reduces water absorption and porosity through matrix modification. This effect is well-documented in the polymer-modified concrete literature, where the durability gain is more pronounced than the mechanical strength improvement.

**2.2 Durability: Freeze-Thaw Cycles, Permeability, Chemical Attack**

Increased porosity and absorption make concrete more vulnerable to aggressive agents. Surface treatments (NaOH, silanes, plasma) improve the interface, limiting

water uptake and fragility. Reduced density lightens non-structural elements but requires careful compaction control. Crumb rubber enhances impact resistance and energy absorption, while freeze-thaw behavior remains sensitive to porosity and inclusion distribution. Thermal tests also reveal increased susceptibility of polymer inclusions at high temperatures (partial degradation or melting), reducing post-exposure properties (Primc, 2024; Ahmad et al., 2022).

**2.2.1 Freeze-Thaw Durability**

The incorporation of PB-PET progressively reduces mass loss over freeze-thaw cycles. This improvement is attributed to the elastomeric effect of polybutadiene and the low thermal conductivity of recycled PET, which limit internal cracking. According to Li et al. (2019), recycled polymers in cementitious matrices enhance freeze-thaw resistance through their energy absorption capacity and micro-filling role.
Innovation in Polybutadiene-PET Composite Materials Derived from
Used Tires and Plastics for Sustainable Concrete: Socio-
Environmental Impacts

<figure><img src="image_11.png" /><figcaption>**Graph 4 :** Freeze-Thaw Durability and Water Permeability (10<sup>-12</sup> m/s)</figcaption></figure>

**2.2.2 Water Permeability**

Water permeability decreases with
increasing PB–PET content, reflecting
improved microstructural compactness. The
polymer chains create a hydrophobic barrier
that hinders capillary water migration
(Akinyemi & Omoniyi, 2020; Laurence et
al., 2023; Bouboama et al., 2017).

**2.2.3 Resistance to Chemical Attacks**

Mass loss in acidic (H₂SO₄) and saline
(NaCl) environments decreases with higher
PB–PET content. PET acts as a barrier
phase, reducing the diffusion of aggressive

ions. This aligns with the findings of
Siddique & Naik (2004), demonstrating that
recycled polymers mitigate chemical
degradation in concrete.

**2.2.4 Optimization**

The optimal PB–PET content lies between
10–15%, balancing durability and
mechanical performance. Higher additions
(≈20%) further enhance durability but may
compromise compressive strength (see
previous tables).

<figure><img src="image_12.png" /><figcaption>**Graph 5 :** Resistance to Chemical Attacks in Acidic (H₂SO₄) and Saline (NaCl) Environments</figcaption></figure>

A rigorous durability protocol (LCA,
freeze-thaw cycles ASTM C666,
permeability, chloride diffusion tests) is
essential to validate concrete intended for
exterior or aggressive environments.

**3. Microstructure and Matrix–Inclusion Interaction Mechanisms**

SEM/EDS and FTIR observations generally
show:
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

* a weaker interfacial transition zone (ITZ) between hydrated matrix and untreated polymer particles (low wettability),

* microcrack concentration around poorly bonded inclusions,

* viscoelastic behavior of inclusions (CR) affecting energy dissipation under dynamic loading.

<table><caption>Table 5: Microstructure and Matrix-Inclusion Interaction Mechanisms</caption><thead><tr><td>Formulation</td><td>Microstructural Observation (SEM/EDS)</td></tr></thead><tbody><tr><td>Control concrete (without PB-PET)</td><td>Abundant capillary pores, standard paste-aggregate interface</td></tr><tr><td>Concrete + 5% PB-PET</td><td>Good dispersion of PET particles, initial barrier effect</td></tr><tr><td>Concrete + 10% PB-PET</td><td>Dense interfaces, reduced microcracks, polymer-cement bonding observed</td></tr><tr><td>Concrete + 15% PB-PET</td><td>Strong barrier effect, almost no microcracks, improved transition zones</td></tr><tr><td>Concrete + 20% PB-PET</td><td>High density but risk of segregation, slightly reduced adhesion due to polymer excess</td></tr></tbody></table>

**3.1 Pore Distribution**
The average pore size decreases with PB-PET incorporation, indicating a filling and hydrophobic effect. Silva et al. (2013) reported that recycled polymers act as a physical barrier, reducing capillary porosity.

<figure><img src="image_13.png" /><figcaption>**Photo 3:** (a) Concrete microstructures and (b) slabs with PB-PET incorporation</figcaption></figure>

**3.2 Microcrack Density**
A significant reduction in microcracks is observed from 10% PB-PET incorporation, as polybutadiene absorbs local stresses and limits crack propagation. Pelisser et al. (2011) report that rubberized materials exhibit improved microstructural toughness.

**3.3 Matrix-Inclusion Adhesion**
Adhesion increases up to 15% incorporation due to chemical-physical interactions between PET functional groups (esters) and the cementitious matrix. Beyond 20%, the matrix becomes overloaded with polymer inclusions, slightly reducing internal cohesion (Benazzouk et al., 2007; Manfo et al., 2025a,b).
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

<figure><img src="image_14.png" /><figcaption>Graph 6: Microstructure and Matrix-Inclusion Interaction Mechanisms</figcaption></figure>

## 3.4 Microstructural Observations (SEM/EDS)

Analyses reveal a progressive improvement of the interfacial transition zone (ITZ), with formation of polymeric bridges. The barrier effect limits water and aggressive ion penetration, enhancing durability (cf. Siddique & Naik, 2004). These mechanisms explain the observed combination of reduced static strength, increased ductility, and improved resistance under dynamic or impact loading. Surface pretreatments can transform the ITZ into a rougher, chemically reactive zone, improving adhesion and mitigating performance loss (Primc, 2024; Ahmad et al., 2022).

## 4. Life Cycle Assessment (LCA) Results – General Trends

## 4.1 Potential Gains

LCA results indicate that incorporating PET and tires into concrete reduces raw material extraction, landfill disposal, and emissions, thereby improving the carbon footprint:

(i) collection and preparation (grinding, pretreatment) are optimized,

(ii) transport distances remain low, and

(iii) partial substitution avoids energy-intensive steps.

Certain studies report decreased global warming potential (GWP) in well-managed “local circular” scenarios (He et al., 2021; Odeh et al., 2025; He, 2016; Dzokom, 2023a,b).

<table><caption>Table 6: Life Cycle Assessment (LCA) Results – Environmental Impact and Potential Gains</caption><thead><tr><th>Formulation</th><th>CO<sub>2</sub> Emissions (kg eq-CO<sub>2</sub>/m<sup>3</sup>)</th><th>Primary Energy Consumption (MJ/m<sup>3</sup>)</th><th>Eutrophication Potential (g PO<sub>4</sub><sup>3-</sup> eq/m<sup>3</sup>)</th><th>Landfill Potential (kg waste/m<sup>3</sup>)</th></tr></thead><tbody><tr><td>Control concrete (no PB-PET)</td><td>385 ± 15</td><td>5,200 ± 180</td><td>190 ± 15</td><td>42 ± 5</td></tr><tr><td>Concrete + 5% PB-PET</td><td>355 ± 12</td><td>4,850 ± 160</td><td>175 ± 13</td><td>36 ± 4</td></tr><tr><td>Concrete + 10% PB-PET</td><td>330 ± 10</td><td>4,600 ± 150</td><td>160 ± 12</td><td>30 ± 3</td></tr><tr><td>Concrete + 15% PB-PET</td><td>315 ± 9</td><td>4,420 ± 145</td><td>155 ± 11</td><td>26 ± 3</td></tr><tr><td>Concrete + 20% PB-PET</td><td>310 ± 8</td><td>4,350 ± 140</td><td>150 ± 11</td><td>25 ± 2</td></tr></tbody></table>
# Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

## 4.1.1 CO₂ Emission Reduction

Incorporating PB-PET reduces emissions by up to ~20% compared to control concrete. This is due to partial substitution of virgin aggregates and the valorization of plastic and rubber waste (Shen et al., 2011; Dzokom & Kodji, 2025a,b).

## 4.1.2 Primary Energy Consumption

Energy consumption decreases by ~15-20% as substitution rates increase. This trend results from savings in extraction and transportation of natural aggregates (Geyer et al., 2017; Dzokom et al., 2025a,b).

<figure><img src="image_15.png" /><figcaption>Graph 7: Primary Energy Consumption (MJ/m³) and CO₂ Emissions (kg eq-CO₂/m³)</figcaption></figure>

## 4.1.3 Eutrophication

Life-cycle releases (industrial effluents and leachates) are reduced by approximately 20%. The hydrophobic barrier effect of PET limits the leaching of soluble elements during the service life phase (Tardif et al., 2019).

leads to a significant reduction in landfill flows, reaching up to ~40% for 20% incorporation. This positive impact aligns with circular economy principles and sustainable waste management practices (Mohajerani et al., 2020; Dzokom, 2024).

## 4.1.4 Landfilling

The valorization of waste tires and plastics

<figure><img src="image_16.png" /><figcaption>Graph 8: CO₂ Emissions, Eutrophication Potential, and Landfilling</figcaption></figure>
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

## 4.2 Limits and Dependencies

The LCA indicates that an optimal addition of 10–15% PB-PET balances performance,

durability, and environmental benefits, while higher contents may degrade mechanical properties.

<table><caption>Table 7: Life Cycle Assessment (LCA) — Environmental Limits and Dependencies</caption><thead><tr><th>Formulation</th><th>Energy Dependence on PB-PET Treatment (MJ/m³)</th><th>Emissions from Chemical Pre-treatment (%)</th><th>Transport Sensitivity (kg CO₂ eq/m³)</th><th>Risk of Leaching or Local Pollution (%)</th></tr></thead><tbody><tr><td>Reference Concrete (0% PB-PET)</td><td>0 ± 0</td><td>0 ± 0</td><td>12 ± 1</td><td>0 ± 0</td></tr><tr><td>Concrete + 5% PB-PET</td><td>80 ± 10</td><td>3.5 ± 0.5</td><td>14 ± 1.2</td><td>2 ± 0.3</td></tr><tr><td>Concrete + 10% PB-PET</td><td>150 ± 12</td><td>5 ± 0.6</td><td>16 ± 1.5</td><td>3 ± 0.4</td></tr><tr><td>Concrete + 15% PB-PET</td><td>220 ± 15</td><td>6.5 ± 0.7</td><td>18 ± 1.7</td><td>4 ± 0.5</td></tr><tr><td>Concrete + 20% PB-PET</td><td>280 ± 18</td><td>8 ± 0.8</td><td>21 ± 2</td><td>5 ± 0.6</td></tr></tbody></table>

### 4.2.1 Energy Dependence on PB-PET Treatment

Pre-treatment (grinding, washing, sometimes alkaline treatment) increases energy consumption. According to Ramarad et al. (2015), PET and rubber recycling processes may require up to 20–25% additional energy per m³ of recycled concrete.

### 4.2.2 Emissions from Chemical Pre-treatment

The use of alkaline solutions or silanes to enhance matrix-inclusion adhesion generates indirect chemical emissions, representing a limitation in overall carbon footprint reduction (Silva et al., 2014).

### 4.2.3 Transport Sensitivity

The collection and transport distance of PB/PET waste significantly affects emissions. For transport distances exceeding 50 km, CO₂ impacts can offset

part of the environmental gains (Mohajerani et al., 2020).

### 4.2.4 Risk of Leaching or Local Pollution

Excessive incorporation (>20%) without adequate treatment can lead to migration of chemical additives or microplastics into the environment. This emphasizes the importance of rigorous life-cycle management, from pre-treatment to end-use (Siddique & Naik, 2004).

Overall, environmental benefits obtained through substitution of natural aggregates and waste valorization are offset by the energy and chemical costs of pre-treatment, as well as transport dependencies. The optimal formulation, balancing environmental gains and practical constraints, remains 10–15% PB-PET.
Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

<figure><img src="image_17.png" /><figcaption>Graph 9: Life Cycle Assessment (LCA)</figcaption></figure>

To maximize environmental benefits, the preferred strategy involves local valorization (reducing transport distances), the use of energy-efficient pretreatments, and optimization of dosages (low to moderate replacement levels).

## 5. Socio-Economic Impacts and Sectoral Challenges

<table><caption>Table 8: Socio-economic impacts and sectoral outcomes</caption><thead><tr><td>Mix Design / PB-PET Integration Level</td><td>Direct Jobs Created</td><td>Indirect Jobs / Value Chain</td><td>Local Annual Economic Gain (USD/m³)</td><td>Reduction in Raw Material Costs (%)</td></tr></thead><tbody><tr><td>Control concrete (0% PB-PET)</td><td>0 ± 0</td><td>0 ± 0</td><td>0 ± 0</td><td>0 ± 0</td></tr><tr><td>Concrete + 5% PB-PET</td><td>4 ± 1</td><td>6 ± 2</td><td>12 ± 2</td><td>3 ± 0.5</td></tr><tr><td>Concrete + 10% PB-PET</td><td>7 ± 2</td><td>10 ± 3</td><td>25 ± 3</td><td>6 ± 0.7</td></tr><tr><td>Concrete + 15% PB-PET</td><td>10 ± 2</td><td>14 ± 3</td><td>38 ± 4</td><td>8 ± 1</td></tr><tr><td>Concrete + 20% PB-PET</td><td>12 ± 3</td><td>18 ± 4</td><td>45 ± 5</td><td>10 ± 1.2</td></tr></tbody></table>

### 5.1.1 Direct Job Creation

PB-PET integration generates new local employment opportunities in sorting, shredding, washing, and conditioning of plastic and rubber wastes. Each 5% incorporation level corresponds to 3-4 additional direct jobs per production site (cf. Mohajerani et al., 2020).

### 5.1 Job Creation and Local Value Chain

The circular economy literature highlights that structured collection and processing chains for tires and plastics generate local jobs and formalized income. Case studies demonstrate net socio-economic benefits when appropriate infrastructures and local markets are integrated (Primc, 2024; Ahmad et al., 2022).

### 5.1.2 Indirect Jobs and Value Chain

Indirect jobs include transportation, logistics, shredder maintenance, distribution, and marketing of PB-PET concrete. The multiplier effect on the local economy is estimated at 1.5 times direct employment (Geyer et al., 2017).
# Innovation in Polybutadiene-PET Composite Materials Derived from Used Tires and Plastics for Sustainable Concrete: Socio-Environmental Impacts

## 5.1.3 Economic Gains

Partial substitution with recycled PB-PET reduces costs (≈3-10%), generates annual savings, and strengthens community economic resilience.

## 5.1.4 Boosting the Local Sector

The valorization of plastic and tire waste stimulates selective collection, supports circular economy dynamics, and alleviates pressure on landfills and urban environments. African and Asian case studies show that PB/PET supply chains can become profitable starting from 10% integration (Shen et al., 2011).

The combination of social, economic, and environmental impacts makes PB-PET

particularly attractive for sustainable development and circular economy policies, especially in Sahelian and tropical urban areas with high levels of plastic and tire waste generation.

## 5.2 Costs, Acceptability, and Barriers

Cost-benefit analyses indicate savings in aggregates and waste management, offset by initial costs and variability. Acceptance depends on standardization, performance guarantees, and user feedback. Perceived health risks (dust generation during shredding) and long-term uncertainties may hinder adoption in the absence of regulatory frameworks and certification protocols (Primc, 2024; Ahmad et al., 2022).

<table><caption>**Table 9. Socio-economic impacts: Costs, acceptability, and barriers**</caption><thead><tr><td>Mix Design / PB-PET Level</td><td>Additional Cost (USD/m³)</td><td>Artisan/User Acceptability (%)</td><td>Main Identified Barriers (score 1-5)</td></tr></thead><tbody><tr><td>Control concrete (0% PB-PET)</td><td>0 ± 0</td><td>95 ± 2</td><td>1 ± 0</td></tr><tr><td>Concrete + 5% PB-PET</td><td>5 ± 1</td><td>88 ± 3</td><td>2 ± 0.5</td></tr><tr><td>Concrete + 10% PB-PET</td><td>10 ± 2</td><td>80 ± 4</td><td>2.5 ± 0.6</td></tr><tr><td>Concrete + 15% PB-PET</td><td>15 ± 3</td><td>72 ± 5</td><td>3 ± 0.7</td></tr><tr><td>Concrete + 20% PB-PET</td><td>20 ± 3.5</td><td>65 ± 6</td><td>3.5 ± 0.8</td></tr></tbody></table>

### 5.2.1 Additional Costs

The addition of PB-PET entails expenses related to pretreatment (shredding, washing, chemical treatment) and collection logistics. These costs remain moderate (≈5-20 USD/m³), but increase with higher incorporation rates (cf. Mohajerani et al., 2020).

### 5.2.2 Acceptability of Artisans and Users

Acceptability slightly decreases with higher PB-PET incorporation, mainly due to unfamiliarity with performance and prejudices against recycled materials. Field

surveys show that training and practical demonstrations substantially increase user confidence (Shen et al., 2011).

### 5.2.3 Main Barriers

Identified barriers include:

1. Availability and quality of PB-PET waste

2. Uncertainty regarding durability and strength

3. Logistics and transport costs

4. Local regulations and standards
Innovation in Polybutadiene-PET Composite Materials Derived from
Used Tires and Plastics for Sustainable Concrete: Socio-
Environmental Impacts

Optimal integration at 10–15% PB–PET
balances environmental benefits,
employment creation, and costs. Beyond
this threshold, economic constraints hinder
large-scale adoption. Incentive policies and
business models integrating training, safety,
and R&D are necessary for widespread
deployment.

**Conclusion and Recommendations**

Conclusion

The incorporation of recycled PB–PET
composites into sand–clay–cement concrete
valorizes plastic and tire wastes, reducing
natural aggregate consumption. Moderate
substitution levels (≤10%) preserve
acceptable mechanical performance while
enhancing ductility, toughness, and impact
resistance. Density reduction and ITZ
variability remain challenges, but adequate
surface treatments improve bonding and
mitigate strength losses.

Environmental impacts are positive: reduced waste disposal, lower aggregate extraction, and carbon footprint, provided that local, low-energy logistics chains are established—supporting circular economy transitions in urban and peri-urban contexts. Recycling supply chains create local jobs and foster inclusive development, though adoption remains limited by perceived variability, lack of standardization, high initial setup costs, and quality control requirements, despite their socio-economic potential in waste-critical regions.

Technical Recommendations Based on
Results

1. Limit replacement of aggregates with CR/PET to test levels (≤10 vol.%) for structural uses; higher percentages should be reserved for non-structural applications (Shukur

et al., 2023; Li et al., 2023; Saeed,
2024; Abdi et al., 2024).

2. Favor PET fiber forms to improve toughness and crack control where post-cracking performance is targeted (Purchase, 2021; Han, 2023; Askar, 2023).

3. Apply cost-effective pretreatments (diluted NaOH, mechanical abrasion, light cementitious coating) to improve ITZ and reduce strength losses (Mousavimehr, 2020; Araujo-Morera, 2021; Jiao, 2024).

4. Optimize logistics chains (local collection, shared shredding, centralized pretreatment) to maximize LCA benefits and minimize costs and transport-related emissions (Mousavimehr, 2020; Araujo-Morera, 2021; Jiao, 2024).

5. Implement certification protocols (standardized tests, durability requirements) to overcome regulatory barriers and facilitate market acceptance (Purchase, 2021; Han, 2023; Askar, 2023).

Credit Author Statement

* Touraine Lidwine Nana WANDJI: *Conceptualization, Original Draft, Investigation, Formal analysis*

* Aimé Elime BOUBOAMA, Carlos Laurence Ngouné DONKENG: *Writing – Review & Editing.*

* Dzokom Alexis: *Methodology, Writing–Supervision, Project administration, Data curation, Validation,*

Conflict of Interest

The author declares that there is no conflict
of interest related to this article with any
individual or institution.

Acknowledgements
Innovation in Polybutadiene-PET Composite Materials Derived from
Used Tires and Plastics for Sustainable Concrete: Socio-
Environmental Impacts

The author wishes to express deep gratitude
to all individuals and institutions who,
directly or indirectly, contributed to the
completion of this article. Special thanks go
to the local communities of the
Cameroonian Sahel for their invaluable
collaboration and the sharing of their
indigenous knowledge, which greatly
enriched this study.

The author also extends sincere thanks to
environmental experts, officers from
decentralized technical services of the State,
and leaders of farmers' organizations for
their insightful contributions during the
field surveys.

Gratitude is particularly extended to
academic and research institutions that
supported this endeavor, notably by
providing data, infrastructure, and high-
quality scientific guidance.

Finally, the author expresses appreciation to
the technical and financial partners, without
whom this research would not have been
possible. Their support helped strengthen
local capacities in sustainable
environmental management and socio-
ecological resilience.

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