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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,

MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)

ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026

Development and Analysis of Eco-Friendly Composite Materials for

Low-Load Structural Applications Using Plastic Waste and PET

ABSTRACT

Rapid urbanization in Kenya triggers explosive demand for precast concrete products. Conventional production

relies heavily on natural river sand. Over-exploitation causes scarcity and environmental destruction.

Simultaneously, uncontrolled plastic waste accumulation worsens environmental health. This study investigates

developing eco-friendly composite materials to produce interlocking paving blocks, partition blocks, and

landscaping tiles. We replace natural fine aggregates with postconsumer recycled Polyethylene Terephthalate

(PET) waste. We replace river sand with shredded PET bottles at volumetric mass equivalent levels of 0, 5, 10,

15, and 20 percent in standard cementitious mixes. We evaluated physical and mechanical properties including

workability, density, water absorption, and compressive strength per standard BS EN and ASTM protocols.

Results indicate systematic reduction in density and workability with increasing PET content. Compressive

Paving Blocks, Circular Economy, Compressive Strength.

INTRODUCTION

Rapid urbanization in Kenya triggers explosive demand for precast concrete products. These include interlocking

paving blocks and non-load-bearing partition blocks. Conventional production relies heavily on natural river

sand. Intense unregulated mining of sand from major river basins causes severe environmental consequences.

These include lowered water tables and destruction of riparian ecosystems. You face a dual crisis in Kenya.

Over-exploitation of natural aggregates causes scarcity and environmental destruction. Uncontrolled plastic

waste accumulation worsens the situation. You will find this research addresses this intersection by developing

and rigorously characterizing an optimized eco-composite for paving blocks, partition blocks, and landscaping

tiles. Postconsumer PET bottles serve as a partial replacement for natural fine aggregates. This study minimizes

toward using shredded plastic as a partial replacement for mineral aggregates in traditional Ordinary Portland

Cement matrices. Studies demonstrated replacing fine aggregate with PET flakes reduces compressive strength

linearly. The Interfacial Transition Zone governs this reduction. Natural aggregates are rigid. Plastics are

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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,

MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)

ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026

flexible. Under load the plastic deforms faster than the surrounding cement. This causes debonding. The

hydrophobicity of PET prevents capillary suction of the cement paste. This creates local voids with high water-

to-cement ratios. These act as stress concentrators. Current literature lacks systematic optimization using real-

world unrefined municipal waste streams targeting specific geometry and performance requirements of East

African standards. This study fills this gap by utilizing locally collected unsorted PET waste for low load

applications.

MATERIALS AND METHODOLOGY

mixing and curing.

Mix Design and Preparation

We employed a mass-based replacement method. We replaced specific percentages of the fine aggregate mass

with PET flakes. We formulated five mix designs. These include a Control mix with 0 percent PET and four

experimental mixes with 5, 10, 15, and 20 percent PET replacement. We homogenized the dry constituents in a

pan mixer for 3 minutes. We introduced water gradually to achieve desired workability. We subjected fresh

concrete to the slump test prior to casting into standard 150 mm steel cube moulds. We achieved compaction

using a vibrating table at 3000 vibrations per minute for 60 seconds. We demoulded specimens after 24 hours

and submerged them in a water curing tank at 20 degrees Celsius until the designated testing age.

Testing Protocols

Physical Properties - Workability

The workability of fresh concrete influences placement. Results revealed a clear inverse relationship between

PET content and workability. The control mix achieved a slump of 90 mm. As PET replacement increased to 20

percent the slump dropped to 40 mm. This represents a 55.6 percent reduction. We attribute this to the flaky

irregular shape of the shredded PET. It increases inter-particle friction. The hydrophobic nature of the plastic

prevents the formation of a stable lubricating water film. All mixes remained within the acceptable BS EN

12350-2 workable range for paving applications.

Density and Unit Weight

Density testing demonstrated a consistent linear reduction with increasing PET content. The control mix

exhibited a normal-weight density of 2415 kg/m3. At 20 percent replacement the density decreased to 2090

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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,

MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)

ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026

interface generates micro-voids. This facilitates water ingress. The inherent zero-absorption characteristic of the

PET particles mitigates porosity increases. All experimental mixes successfully complied with the KS 2769:2018

maximum allowable limit of 7 percent.

Table 1. Physical Properties of PET-Modified Concrete

control strength. It achieved 14.49 MPa. Mix D saw a 79.2 percent strength loss. It dropped to 5.19 MPa.

Table 2. Compressive Strength Development

Discussion on Strength Degradation

The systematic strength reduction directly links to the degradation of the Interfacial Transition Zone. As a

inclusions. Internal physical discontinuities purely limit the mechanical performance. The current experimental

phase observes a severe 79.2 percent strength loss at a 20 percent PET replacement level. This limits the higher-

load structural viability of the material. The study identifies stiffness incompatibility and ITZ hydrophobicity as

the primary causes. We did not test mitigation strategies within this phase. We stopped mechanical testing at 28

days. Long-term durability and weather resistance remain unaddressed in the current scope.

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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,

MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)

ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026

for these materials. The control mix qualifies for light vehicular traffic. The 5 percent PET composite borders

on the 15 MPa threshold required for Class 15 pedestrian applications. We designate Mix A as the optimal

formulation for non-traffic environments. These include pedestrian walkways, garden paths, public plazas, and

internal non-load-bearing partition walls. We relegate mixes exceeding 10 percent replacement to decorative

landscaping features. Structural integrity is not a design constraint here. You apply these materials based on your

specific load requirements.

Standard vibration equipment remains sufficient for your compaction up to 20 percent replacement.

5 percent mass replacement mix is the structural optimum. It achieves 14.49 MPa at 28 days.

5. The 5 percent PET composite is feasible for commercial deployment in Class 15 applications like pedestrian

walkways. A production rate of 100 cubic meters per month sequesters approximately 60 tonnes of plastic waste

annually. This drives direct contributions toward UN Sustainable Development Goals 9, 11, and 12.

6. Future research phases must actively address the weaknesses found at the particle boundary layer. Researchers

should implement and test chemical surface treatments on the recycled PET flakes. Applying sodium hydroxide

etching or silane coupling agents will improve adhesion at the ITZ and mitigate compressive strength loss.

7. Future researchers must conduct extended durability testing beyond the initial 28-day curing period. They

need to assess material performance under continuous environmental exposure and physical wear.

8. Future researchers must explore alternative mix designs with supplementary cementitious materials. This will

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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,

MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)

ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026

6. Saikia, N., and de Brito, J. (2014). Mechanical properties and abrasion behaviour of concrete

containing shredded PET bottle waste as a partial substitution of natural aggregate. Construction and

Building Materials, 52, 236–244.

7. Thorneycroft, J., Orr, J., Savoikar, P., and Ball, R. J. (2018). Performance of structural concrete with

recycled plastic waste as a partial replacement for sand. Construction and Building Materials, 161,

63–69.