RE-BLOCKS: Modular Interlocking Building Systems Using Recycled Plastics for Affordable Urban Housin

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RE-BLOCKS: Modular Interlocking Building Systems Using Recycled Plastics for Affordable Urban Housing Jeeva Nandham E1, Sameer Mohamed2, Suriyavarsha T3 1Architect and Designer, Design Labo, Tokyo, Japan 2Architect and Designer, SAM & SAF, Chennai, Tamil Nadu, India

3Under-Graduate Student, PSG Institute of Architecture and Planning, Coimbatore, Tamil Nadu, India

---------------------------------------------------------------------***--------------------------------------------------------------------million tons of plastic waste are mismanaged, contributing to Abstract - This paper presents RE-BLOCKS, a modular

this environmental catastrophe. This crisis extends beyond typical packaging to include textiles and household items, indicating a pervasive problem that demands innovative and scalable solutions.

interlocking building system developed using recycled plastic waste and fly ash, designed to address two pressing global challenges: plastic pollution and affordable housing. Drawing inspiration from LEGO-like dry-stacking mechanisms, REBLOCKS offers a sustainable alternative to conventional bricks by minimizing the need for mortar, enabling rapid construction, and supporting material circularity. The study explores material properties of various thermoplastics, details the prototype fabrication process, and validates performance through finite element analysis using Abaqus CAE. Global precedents such as Conceptos Plasticos, Plana Bricks and PLAEX Building Systems are reviewed to position RE-BLOCKS within a broader innovation landscape. The findings highlight the potential of this system to contribute to low-cost, demountable, and disaster-resilient housing in the Global South.

The environmental impact of plastic pollution is profound and long-lasting. Plastic's non-biodegradable nature means it persists in the environment for hundreds of years, causing severe harm to wildlife, marine ecosystems, and human health. Improper disposal also contributes to greenhouse gas emissions during both the production and decomposition phases of plastic. The sheer volume of this persistent waste necessitates comprehensive strategies that extend beyond traditional recycling methods, emphasizing the need for advanced reprocessing technologies and novel applications.

The extensive data on plastic waste generation and the limited recycling capacity clearly indicate that incremental improvements in existing recycling infrastructure are insufficient. A radical, high-volume pathway for plastic at the end of its life cycle is not merely beneficial but essential. ReBlocks, by converting plastic into durable building materials, offers a direct, large-scale diversion from landfills and oceans.

This approach addresses the fundamental deficit in waste management capacity rather than simply attempting to improve recycling rates for a small fraction of the waste stream. This positions Re-Blocks as a critical component of a truly circular economy, transforming an environmental liability into a valuable resource on an industrial scale.

Key Words: Modular construction, Interlocking bricks, Sustainable housing, Plastic bricks, Dry-stacking, Architectural systems, Circular economy

1.INTRODUCTION This paper investigates Re-Blocks, an innovative approach to transforming plastic waste into sustainable building materials. The initiative is positioned within the critical global context of escalating plastic pollution and an urgent demand for affordable and environmentally responsible construction solutions. By repurposing a pervasive environmental pollutant into a valuable resource, Re-Blocks offers a pathway toward a more circular economy and greener infrastructure development.

1.2 The Demand for Sustainable and Affordable Building Materials Concurrently with the plastic waste crisis, the world faces a severe and growing housing shortage. Approximately 2.8 billion people globally currently lack adequate housing, a number projected to increase to 3 billion by 2030. This crisis is primarily characterized by a significant lack of affordable housing units, particularly for low- and middle-income populations. The challenge is exacerbated by rapid population growth and increasing urbanization, which place immense strain on existing housing infrastructure. In many regions, housing prices have dramatically outpaced income growth, highlighting the urgent need for cost-effective and rapidly deployable construction solutions.

1.1 Solving Two of the World's Biggest Crises The world is grappling with an escalating plastic waste crisis of unprecedented scale. Projections indicate that approximately 400 million tonnes of plastic waste will be generated in 2024, a figure anticipated to nearly triple by 2060. This immense volume presents a formidable challenge, especially given that only about 9% of global plastic waste is currently recycled. The vast majority of plastic ends up in landfills or pollutes natural environments, leading to significant ecological burdens. Annually, an estimated 69.5

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Traditional construction methods, while fundamental to building infrastructure, are inherently resource-intensive and environmentally damaging. These practices lead to significant resource depletion, including the unsustainable harvesting of timber and the extensive extraction of raw materials like sand and gravel for concrete production. The manufacturing and transportation of conventional building materials such as cement and steel require substantial energy inputs, contributing to a high embodied energy footprint for buildings. Cement production, in particular, is a major source of carbon dioxide emissions. Furthermore, the construction and demolition phases generate massive amounts of waste, contributing to pollution and landfill burdens. These conventional practices contribute to air and water pollution, habitat destruction, and an increased overall carbon footprint of the built environment. Beyond environmental concerns, the escalating costs of conventional building materials, coupled with a lack of awareness and skills in sustainable alternatives, present significant economic barriers to adopting greener construction practices. The project addresses not only the plastic waste crisis but simultaneously the critical demand for affordable, sustainable building materials, while also mitigating the environmental footprint of conventional construction. This creates a powerful synergy, demonstrating that the project has the potential for significant social (affordable housing) and environmental (waste reduction, lower carbon footprint) returns. This dual benefit makes RE-BLOCKS an appealing innovation for diverse stakeholders, ranging from environmental agencies to housing developers and governments.

Conceptos Plasticos A notable example is Conceptos Plasticos in Colombia, which has patented a system of interlocking bricks and pillars made from recycled plastic and rubber waste. These components are designed to assemble much like Lego pieces, enabling the rapid construction of multi-story homes within as little as five days. These bricks offer heat insulation, combustion retardation, thermoacoustic properties, and earthquake resistance, meeting stringent local building codes.

Plana Brick Similarly, Plana Brick in Indonesia utilizes all types of unsorted plastic waste to produce interlocking modular bricks. These bricks are claimed to be ten times stronger than conventional bricks, lighter, excellent insulators, and boast a 95% lower carbon footprint. The ability to process unsorted waste represents a significant advantage for efficiency and scalability.

PLAEX Building Systems In Canada, PLAEX Building Systems produces fully interlocking, mortarless blocks from over 90% recycled waste, branded as PLAEX-crete™. This system emphasizes circular economy principles, allowing for simple assembly and disassembly for true material reuse. It offers significant cost savings, estimated at 15-30% on project pricing, due to reduced labor and waste.

Furthermore, PLAEX-crete™ demonstrates superior impact and water resistance and is fire-resistant, undergoing rigorous third-party certifications.

2. LITERATURE REVIEW The concept of transforming plastic waste into building materials offers a promising pathway to address both environmental pollution and the escalating demand for construction materials. This approach diverts plastic from landfills and oceans, thereby reducing the need for virgin materials and promoting greener construction practices.

Various initiatives globally have explored and implemented this concept, providing valuable precedents for the REBLOCKS vision.

2.1 Lessons for Re-Blocks: The review of these diverse case studies reveals that "plastic building materials" is not a monolithic category. Different plastic types and processing methods yield vastly different properties and applications. This suggests that the REBLOCKS product line may need to be specialized based on the specific plastic waste stream available and the target application, whether load-bearing, non-load-bearing, insulation, or structural. The ability to process unsorted plastic, as demonstrated by Plana Brick, represents a particularly significant innovation that could dramatically improve the scalability and cost-efficiency of RE-BLOCKS manufacturing. The RE-BLOCKS vision aims to synthesize these advancements, focusing on developing a versatile range of sustainable building materials from plastic waste, optimized for structural integrity, environmental performance, and economic viability.

For instance, shredded plastic waste has been successfully incorporated with sand, cement, and aggregate to create durable paver blocks, effectively replacing coarse aggregate in the mixture. Beyond paver blocks, other applications include the transformation of low-density polyethylene (LDPE) plastic beads into building blocks, which, when sometimes combined with fly ash, have achieved compressive strengths greater than those of ordinary clay bricks. In Vietnam, a material known as RHPP (Recycled Plastic and Rice Husks) utilizes polypropylene and rice husks to produce lightweight, waterproof, fire-resistant, and sound-insulating blocks, particularly suitable for affordable housing and construction in disaster-prone areas.

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3. RESEARCH OBJECTIVES AND SCOPE OF THE STUDY

to its widespread availability established recyclability.

This research aims to investigate the optimal incorporation of plastic waste into RE-BLOCKs for enhanced mechanical and physical properties. It seeks to develop and analyse prototype designs for RE-BLOCKs. A combined experimental and software-based methodology will be employed to assess the structural performance of RE-BLOCKs in simulated building applications. The study will analyse the performance of REBLOCKs compressive load. Finally, it will identify the limitations, challenges, and future research directions for the widespread adoption of RE-BLOCKs. The scope of this study encompasses comprehensive material characterization and laboratory-scale experimental testing.

The research integrates advanced structural analysis using ANSYS for detailed material behaviour simulation and ETAB for evaluating multi-story building performance. By leveraging insights from existing research and global case studies, this study provides a comprehensive understanding of RE-BLOCKs' potential as a transformative sustainable building material.

4. PROTOTYPE DESIGN AND MATERIALS This section details the selection and characterization of materials used in RE-BLOCKS, emphasizing the crucial role of plastic waste and other components, and outlining the principles guiding the mix design.

and

PP (Polypropylene)

With a melting point of approximately 160°C, PP exhibits a Young's modulus of about 97.49 N/mm², a Poisson's ratio of around 0.420, a shear modulus of approximately 34.32 N/mm², a density of about 1121 kg/m³, and a compressive strength of roughly 5.45 N/mm². Like HDPE, PP is selected for plastic bricks due to its suitability for recycling and availability.

LDPE (LowDensity Polyethylene)

Characterized by its flexibility, LDPE is commonly used in applications such as plant packaging and is suitable for bricks and blocks.

PET (Polyethylene Terephthalate)

This plastic is hard and brittle, making it suitable for applications like rug fibers and as fibers in cementitious composites.

PC (Polycarbonate)

Known for being hard and either flexible or rigid, PC is suitable for use as fibers and aggregates in cementitious composites.

Polystyrene (PS)

A flexible plastic, PS is used for items such as laundry pegs, coat hangers, and insulation material.

Table 1

5. DESIGN AND FABRICATION CONSIDERATIONS FOR RE-BLOCK PROTOTYPES

Characterization of Plastic Waste Aggregates (HDPE, PP, LDPE, PET)

The design and fabrication of RE-BLOCK prototypes are tailored to their intended application and leverage features that enhance structural integrity and ease of assembly. For paver blocks, a zigzag shape was utilized in testing.

Waste plastic aggregate refers to shredded or crushed plastic materials that are utilized as a substitute for traditional aggregates such as sand, gravel, or crushed stone in various construction applications. These plastic aggregates can be derived from a wide array of waste plastic sources, including bottles, bags, containers, and packaging materials.

The properties of waste plastic aggregates vary depending on the type of plastic. Generally, waste plastic aggregates are characterized by a size greater than 4.75mm, a specific gravity of approximately 1.56, water absorption of about 1.70%, an angular and rough shape, and a relatively low density of around 520 kg/m³. More specifically, different plastic types exhibit distinct properties that influence their suitability for RE-BLOCKs: HDPE (HighDensity Polyethylene)

This plastic has a melting point of approximately 130°C, a Young's modulus of about 273.8 N/mm², a Poisson's ratio of around 0.406, a shear modulus of approximately 97.37 N/mm², a density of about 1129 kg/m³, and a compressive strength of roughly 13.68 N/mm². HDPE is particularly suitable for plastic bricks due

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Image 2: Assembly Views of RE-BLOCKS Modular Units General fabrication involves shredding plastic waste into small, manageable pieces, which are then thoroughly mixed with aggregate and binding agents. This mixture is subsequently compressed into moulds to form the desired block shapes.

Image 1: Prototype of Re-Blocks Interlocking Brick Based on Hydraform Geometry For interlocking bricks, the Hydra form shape was adopted.

This design incorporates tongue and groove joints on the sides, top, and bottom, enabling the bricks to interlock securely without the need for mortar in horizontal joints. The stability of walls constructed with Hydra form bricks is primarily derived from the width and inherent weight (massiveness) of the brick, rather than solely relying on the locking mechanism. During fabrication, sufficient compression is applied during moulding to ensure the fresh bricks can withstand the squeezing forces encountered when manually moved from the machine to the curing area.

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Image 3: 3D Printed Prototype Demonstrating RE-BLOCKS Corner Assembly The integration of 3D models and 3D printed prototypes in the design phase is crucial for optimizing the interlocking features, structural integrity, and material efficiency of REBLOCKs. These digital tools allow for precise visualization and iterative refinement of designs, ensuring that specific features enhance the blocks' performance or ease of assembly.

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6. Simulation and Finite Element Analysis of REBLOCK Prototypes 6.1 Software Platform: Abaqus CAE In this study, the finite element software Abaqus CAE (2022) was employed to simulate the mechanical behaviour of REBLOCK prototypes under compressive loads. Abaqus allowed for a detailed visualization of internal stress distributions, deformation zones, and principal strain patterns, thus validating and complementing the results from experimental compression testing.

Yellow

12 – 15 MPa

Mid wall — approaching moderate compression

Green

8 – 12 MPa

Central wall — moderate compressive region

Light Blue

4 – 8 MPa

Upper mid-wall — low stress

Dark Blue

0 – 4 MPa

Top rows — least stress (non-load-bearing region)

Table 3

Unlike traditional physical testing, the Abaqus simulation environment enabled controlled stress application, mesh discretization, and the assignment of real material properties (such as density, Poisson's ratio, elastic modulus, and compressive strength). This approach reduced costs, increased repeatability, and provided deeper insight into failure-prone regions of the 3m × 3m wall assemblies.

6.2 Material selection The RE-BLOCKs were modelled using measured and literature-backed properties for HDPE–fly ash composites, as detailed below: Property

Value

Units

Density

1129.85

kg/m³

Elastic Modulus

273.8 × 10⁶

Pa

Poisson’s Ratio

0.406

–

Compressive Strength

20 × 10⁶

Pa

Thermal Conductivity

0.48

W/m·K

Table 2

6.3 Simulation Setup and Boundary Conditions

Image 4: Finite Element Simulation of RE-BLOCKS Wall Under Compressive Loading

Each prototype wall was meshed using hexahedral (bricktype) elements with fine mesh resolution in critical stress zones. The bottom nodes of the wall were fixed in all degrees of freedom to simulate a rigid base, while a uniformly distributed load was applied vertically on the top surface to represent gravity and external compressive forces.

7. CONCLUSIONS The RE-BLOCKS project demonstrates a promising intersection of sustainability, material innovation, and modular construction for addressing global housing and waste management crises. By harnessing recycled plastic and fly ash composites through interlocking, mortarless design, this research offers a scalable and environmentally responsible alternative to conventional construction. The successful integration of experimental data with digital simulation validates the structural viability of RE-BLOCK prototypes. Future research will aim to optimize block geometry, thermal performance, and life cycle impacts.

Colour-based stress interpretation followed the legend: Colour Zone

Stress (MPa)

Red

18 – 20 MPa

Wall base — maximum load zone, full compression

Orange

15 – 18 MPa

Layer above base — high stress transition

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To further analyze the behavior of RE-BLOCKS in real-world scenarios, a 1:1 scale model will be developed. This full-scale prototype will help evaluate assembly techniques, thermal performance, user interaction, and practical challenges, bridging the gap between laboratory experimentation and on-site implementation.

Suriyavarsha T is a final year student of graduation with architecture from PSG Institute of Architecture and planning, Coimbatore. Her interests lie in public infrastructure, visual storytelling, and research-driven design.

REFERENCES [1]

D. D. Ahiwale, D.‑P. N. Kontoni, A. V. Jadhav & A. B. Bawale, “FEM analysis of the effect of various brick bond patterns on masonry walls under in‑plane cyclic loading,” Asian Journal of Civil Engineering, vol. 24, no. 7, pp. 2629–2643, Apr. 2023, doi:10.1007/s42107-02300668-4.

[2]

B. Haba, S. Djellali, Y. Abdelouahed, S. Boudjelida, F. Faleschini, and M. Carraro, “Transforming Plastic Waste into Value: A Review of Management Strategies and Innovative Applications in Sustainable Construction,” *Polymers*, vol. 17, no. 7, art. 881, Mar. 26, 2025.

[3]

Conceptos Plásticos, “Home,” ConceptosPlasticos.com, accessed: July 06, 2025.

Available: https://conceptosplasticos.com/

[4]

Plana, “Plana Brick,” Plana.co.id, accessed: July 08, 2025.

Available: https://plana.co.id/

[5]

PLAEX Building Systems Inc., “Product Overview,” PLAEX.ca, accessed: July 12, 2025. Available: https://plaex.ca/product-overview

BIOGRAPHIES Jeeva Nandham E is an architect and designer at the Design Labo, Tokyo.

Research Interest: Sustainable Design, 3D prototyping, Product design.

Sameer Mohamed holds a Master’s in Architecture from MEASI Academy of Architecture. He is a practicing architect with a passion for teaching and research. His interests include biomimicry, computational design, and 3D printing. He focuses on learning from nature to develop sustainable, technology-driven architectural solutions.

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