Mechanical Strength Assessment of Eco-Friendly Bricks Produced Using Waste Marble Dust and Crushed Stone Dust as Partial Cement Replacements

Technical Summary: Mechanical Strength Assessment of Eco-Friendly Bricks Produced Using Waste Marble Dust and Crushed Stone Dust

Problem Statement
The construction industry faces a dual challenge: the generation of massive quantities of industrial waste, specifically marble dust (MD) and crushed stone dust (CSD), and the high environmental footprint of cement production. Marble processing in India generates approximately 12 million tons of waste annually, posing significant risks of soil and water contamination. Simultaneously, cement manufacturing contributes roughly 5% of global anthropogenic CO₂ emissions. While previous studies have explored the individual use of MD or CSD as partial cement replacements, the synergistic effect of combining these two waste materials in brick manufacturing remains a significant research gap. This study addresses the need to utilize these locally available waste materials to reduce cement consumption, mitigate environmental hazards, and produce sustainable construction materials without compromising mechanical performance.

Methodology
The research employed an experimental design to evaluate the suitability of MD and CSD as partial replacements for Pozzolanic Portland Cement (PPC) in brick production.

• Materials: The study utilized PPC (35% fly ash), natural sand (Zone I), marble dust, and crushed stone dust.
• Mix Design: Bricks were cast in a 1:4 (Cement:Sand) ratio with a water-cement ratio of 0.45. The control mix (M0) contained 100% cement. Experimental mixes replaced cement with equal proportions of MD and CSD at three levels:
  • M10: 10% MD + 10% CSD (Total 20% replacement).
  • M20: 20% MD + 20% CSD (Total 40% replacement).
  • M30: 30% MD + 30% CSD (Total 60% replacement).
• Specimen Preparation: Bricks measuring 230mm x 90mm x 80mm were cast in wooden molds, compacted using a table vibrator, and cured in water for 7, 14, and 28 days.
• Testing Protocols: The study conducted sieve analysis, specific gravity tests, silt content tests, water absorption tests, and density measurements. Compressive strength was evaluated using a Compression Testing Machine (CTM) at 7, 14, and 28 days.
• Statistical Analysis: Data were analyzed using descriptive statistics (mean, standard deviation, coefficient of variation) and One-Way Analysis of Variance (ANOVA) to determine the significance of curing age and replacement levels on strength (p < 0.05).

Key Results

• Compressive Strength: The control mix (M0) achieved the highest 28-day compressive strength of 24.56 MPa. The M10 mix (20% total replacement) recorded 20.62 MPa, representing a viable alternative. However, higher replacement levels resulted in significant strength reduction: M20 (40% replacement) dropped to 8.61 MPa, and M30 (60% replacement) fell to 6.37 MPa.
• Statistical Significance: ANOVA confirmed that both curing age and replacement level had a statistically significant effect on compressive strength (p < 0.001). The strength development over time (7 to 28 days) was significant for all mixes.
• Water Absorption: An inverse relationship was observed between strength and water absorption. As the replacement level increased, water absorption increased from 5.66% (M0) to 9.81% (M30), indicating increased porosity and reduced bonding at higher replacement levels.
• Density: The density of the bricks decreased gradually with increased replacement, ranging from 2698.87 kg/m³ (M0) to 2491.14 kg/m³ (M30). The M10 mix maintained a density consistent with standard construction materials.
• Material Properties: Marble dust exhibited a specific gravity of 2.63, and stone dust 2.57, both lower than cement (3.1), contributing to the observed density reduction.

Key Contributions and Claims
The paper claims that the partial replacement of cement with a combination of marble dust and crushed stone dust is a viable strategy for sustainable construction, provided the replacement level is optimized.

• Optimal Replacement Level: The study identifies the 20% total replacement level (10% MD + 10% CSD) as the optimal candidate. This mix achieved an average compressive strength of 20.62 MPa, which the authors argue is sufficient to compete with the control mix for specific construction applications, while offering environmental benefits.
• Synergistic Utilization: The research highlights the potential of utilizing two distinct industrial waste streams simultaneously, addressing a gap in literature regarding combined waste valorization.
• Environmental and Economic Impact: By substituting cement, the study claims a reduction in CO₂ emissions and energy consumption associated with cement manufacturing. Furthermore, utilizing locally sourced waste reduces transportation costs and disposal liabilities associated with marble and stone processing industries.

Significance
The authors position this work as a contribution to Sustainable Development Goals (SDGs) 9 (Industry, Innovation, and Infrastructure) and 11 (Sustainable Cities and Communities). The study demonstrates that industrial by-products can be engineered into functional construction materials, thereby reducing the carbon footprint of the built environment and managing solid waste. The paper concludes that while excessive replacement compromises durability and strength, a controlled, low-level substitution (specifically the 20% total replacement) offers a balanced approach to achieving cost savings, environmental sustainability, and acceptable mechanical performance. Future work is suggested to focus on long-term performance and the standardization of waste material properties.