Mould Design
The brick manufacturing process utilized a custom-designed rectangular aluminium mold with precise dimensions of 230 mm × 120 mm × 150 mm. This mold comprised four meticulously crafted side plates, each measuring 230 mm × 150 mm with a thickness of 10 mm, ensuring structural integrity during the molding process. The base plate, strategically reduced to a 5 mm thickness, was engineered to minimize deflection and maintain a level surface. A notable feature of the mold was its top plate, equipped with an ingeniously designed knob-shaped component. This ergonomic addition served a dual purpose: facilitating easy application of pressure during the molding process and enabling effortless removal of the finished brick. The mold’s design was carefully optimized to ensure uniformity in brick dimensions and to streamline the manufacturing process, contributing to the overall quality and consistency of the produced bricks.
Materials
High-Density Polyethylene (HDPE)
The primary constituent of the eco-friendly bricks, High-Density Polyethylene (HDPE), was sourced from previously used containers and bottles, embodying the project’s commitment to waste recycling. The collected HDPE underwent a meticulous preparation process, beginning with a thorough cleansing using lukewarm water to remove any residual contaminants. Following the washing, the plastics were subjected to a comprehensive drying procedure to eliminate all moisture, ensuring optimal conditions for subsequent processing. The dried HDPE was then fed into a specialized shredding apparatus equipped with high-speed rotating blades. This crucial step transformed the bulky plastic waste into manageable fragments, ranging in size from 1 mm to 5 mm. The precise control over fragment size was essential for achieving the desired material properties and ensuring uniform distribution within the brick matrix.
Quartz Sand
Quartz sand, serving as the primary filler material, was carefully selected for its specific properties that complemented the plastic matrix. The sand used in this study exhibited a specific gravity of 2.5, indicative of its density and potential contribution to the overall weight and structural integrity of the bricks. Its water absorption rate of 5.2% was noteworthy, suggesting a moderate capacity to retain moisture, which could influence the brick’s behavior in various environmental conditions. The fineness modulus of 2.3 indicated a well-graded sand with a balanced particle size distribution, crucial for achieving optimal packing density within the brick structure. These properties, as detailed in Table 1, were instrumental in determining the sand's interaction with the plastic matrix and its impact on the final brick characteristics, including strength, durability, and thermal properties.
Bitumen
Bitumen, procured from BAUHAUS in Ludwigshafen, Germany, was incorporated as a binding agent to enhance the cohesion between plastic and sand particles. The study explored varying bitumen proportions of 1%, 2%, and 3% by weight to assess its optimal content for brick performance. The bitumen used exhibited a high specific gravity of 22.4, indicating its dense nature and potential to significantly influence the brick’s weight and structural properties. Its softening point ranged between 35°C and 70°C, a crucial parameter affecting the brick’s thermal behavior and stability under various temperature conditions. The ductility of 0.0264 m suggested moderate flexibility, potentially contributing to the brick’s ability to withstand stress without immediate failure. These properties, as outlined in Table 2, played a vital role in determining the bitumen’s effectiveness as a binding agent and its overall impact on the brick’s mechanical and thermal characteristics.
METHODOLOGY
Shredding and Mixing
The manufacturing process commenced with a critical mixing phase, where HDPE, quartz sand, and bitumen were combined in a specialized kneader. Operating at a carefully calibrated temperature of 180°C and a rotational speed of 40 rpm, this step ensured thorough blending and uniform distribution of components. The elevated temperature facilitated the melting of HDPE, allowing it to effectively encapsulate the sand particles and integrate with the bitumen. This melted mixture was then allowed to cool and solidify into lumps, a transitional state that facilitated subsequent processing. These solidified lumps underwent further refinement in a grinder, reducing them to fine particles. This granulation step was crucial in achieving a homogeneous mixture with consistent particle size, essential for the molding process and the final brick properties.
Molding
The molding process represented a critical phase in brick production, where the granulated mixture was transformed into the final product. The process began with carefully pouring the prepared granules into the custom-designed aluminium mold, ensuring even distribution. The filled mold was then subjected to a hot pressing procedure at temperatures exceeding 300°C for a duration of 1 hour. This elevated temperature, surpassing the melting point of HDPE, ensured complete fusion of the plastic matrix with the sand and bitumen. Concurrent with the heating, a substantial pressure of approximately 15 bar was applied, serving multiple purposes: it expelled air pockets, increased material density, and shaped the brick to the mold’s dimensions. Notably, this pressure was maintained during the cooling phase, a crucial step in preventing deformation and ensuring dimensional stability of the final product. The study explored various plastic-to-sand ratios (3:1, 3:2, 1:1, 2:3, and 1:3) and bitumen percentages (0%, 1%, 2%, and 3%) to comprehensively assess the impact of composition on brick properties.
Testing
A comprehensive suite of tests was conducted to evaluate the performance and characteristics of the produced bricks. Compression tests, adhering to DIN EN ISO 604 standards, utilized 20 brick specimens, each precisely cut to 10 mm × 10 mm × 10 mm dimensions. These samples were subjected to compressive forces using a Universal Testing Machine with a 100 kN capacity, applying load at a constant speed of 1 mm/min until deformation or fracture occurred. Water absorption tests involved a 24-hour immersion period, with initial dry weights (W1) and final wet weights (W2) meticulously recorded to calculate absorption rates. Efflorescence tests, crucial for assessing the presence of soluble salts, involved partial immersion (25 mm depth) in distilled water for 24 hours, followed by visual inspection after drying. The innovative temperature rise test exposed one face of the brick to a 410°C heat source for 3 minutes, with the temperature difference between the exposed and unexposed faces measured to evaluate thermal insulation properties. These diverse tests provided a comprehensive understanding of the bricks’ structural, hygroscopic, and thermal characteristics, essential for assessing their suitability for various construction applications. The results, particularly the relationship between compression strength, plastic content, and bitumen percentage, were visualized in Graph 1, offering valuable insights into optimal composition for desired brick properties.