Surreal cityscape with glowing recycled concrete beam.

Recycled Concrete: Is It Strong Enough for Our Buildings?

Jordan Keane in Tech & Innovation August 2025 • 4 min read.

"Discover how recycled concrete aggregates are changing construction, offering a sustainable yet structurally sound alternative to traditional materials."

The construction industry faces increasing pressure to adopt sustainable practices. Traditional concrete production is resource-intensive, contributing significantly to environmental degradation through the extraction of raw materials and the disposal of construction and demolition waste. As landfills reach capacity and environmental awareness grows, finding alternative materials becomes crucial.

Recycled concrete aggregates (RCA) offer a promising solution. RCA are produced by crushing existing concrete structures, transforming waste into a valuable resource for new construction projects. By using RCA, the industry can reduce its reliance on virgin materials, decrease landfill waste, and potentially lower construction costs.

However, concerns persist regarding the structural performance of concrete made with RCA. Questions about its strength, durability, and long-term behavior must be addressed to ensure the safety and reliability of buildings constructed with recycled materials.

How Strong Is Recycled Concrete, Really?

Surreal cityscape with glowing recycled concrete beam.

Researchers have investigated the effects of using RCA on the shear strength and deflection of reinforced concrete beams. The study compared the performance of beams made with varying percentages of RCA to those made with traditional natural aggregates. The results provide valuable insights into the viability of using RCA in structural applications.

The study involved testing reinforced concrete beams with different replacement percentages (PR) of natural coarse aggregates (NCA) with RCA: 0%, 20%, and 100%. The beams were designed with a longitudinal reinforcement ratio of 1.38%. The key variables examined were shear strength, deflection, crack patterns, and failure modes.

Shear Strength: Beams with 100% RCA showed a 9% reduction in shear strength compared to natural aggregate concrete (NAC) beams. Beams with 20% RCA experienced only a 3% reduction.
Deflection: The use of 100% RCA significantly increased midspan deflections, while 20% RCA had negligible effects.
Crack Patterns and Failure Mode: The replacement of NCA with RCA had limited effects on the shear cracking patterns, the development of critical shear cracks, the longitudinal steel strains, and the mode of failure.
Code Calculations: Shear strength calculations based on ACI, CSA, MC2010, and EC2 codes were generally conservative, especially for beams with recycled aggregates, ensuring that designs incorporating RCA meet safety standards.

These findings suggest that incorporating RCA affects the structural behavior of concrete beams. While a full replacement (100% RCA) reduces shear strength and increases deflections, a partial replacement (20% RCA) maintains structural integrity, making it a practical and sustainable choice for construction.

Is Recycled Concrete the Future?

The research indicates that recycled concrete aggregates can be a viable alternative to traditional materials in reinforced concrete beams, particularly when used in moderation. The study highlights that while a full replacement of natural aggregates with RCA may compromise shear strength, a partial replacement offers a promising balance between sustainability and structural performance. As the construction industry continues to seek eco-friendly solutions, understanding the properties and performance of recycled concrete is essential for creating safer and more sustainable buildings.

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Everything You Need To Know

What are recycled concrete aggregates (RCA), and how do they benefit the construction industry?

Recycled concrete aggregates (RCA) are produced by crushing existing concrete structures, transforming construction and demolition waste into a reusable material. This process offers several benefits to the construction industry. RCA reduces the reliance on virgin materials like natural coarse aggregates (NCA), decreases landfill waste, and has the potential to lower construction costs. By utilizing RCA, the industry can move towards more sustainable practices, addressing environmental concerns associated with traditional concrete production, which is resource-intensive and contributes to environmental degradation.

How does the use of recycled concrete aggregates (RCA) impact the shear strength of reinforced concrete beams compared to natural aggregate concrete (NAC)?

Research indicates that the use of RCA affects the shear strength of reinforced concrete beams. When 100% of natural coarse aggregates (NCA) are replaced with RCA, there is a 9% reduction in shear strength compared to beams made with natural aggregate concrete (NAC). However, when only 20% of NCA is replaced with RCA, the reduction in shear strength is only 3%. This demonstrates that the proportion of RCA used has a direct impact on the structural performance, with a full replacement having a more significant effect.

What are the effects of using recycled concrete aggregates (RCA) on the deflection of reinforced concrete beams?

The study revealed significant differences in deflection based on the percentage of recycled concrete aggregates (RCA) used. Beams with a 100% replacement of natural coarse aggregates (NCA) with RCA showed significantly increased midspan deflections. In contrast, beams with a 20% RCA replacement exhibited negligible effects on deflection. This suggests that while partial use of RCA has a minimal impact on deflection, full replacement requires careful consideration in structural design to account for the increased flexibility.

How do crack patterns, failure modes, and code calculations change when using recycled concrete aggregates (RCA) in reinforced concrete beams?

The replacement of natural coarse aggregates (NCA) with recycled concrete aggregates (RCA) had limited effects on the shear cracking patterns, the development of critical shear cracks, the longitudinal steel strains, and the mode of failure. Furthermore, shear strength calculations based on various codes, including ACI, CSA, MC2010, and EC2, were generally conservative, especially for beams with RCA. This ensures that designs incorporating RCA meet safety standards, as the codes provide a margin of safety that accounts for the slight reduction in shear strength observed with the use of RCA.

Based on the findings, what is the recommended approach for incorporating recycled concrete aggregates (RCA) in construction to balance sustainability and structural performance?

The research suggests that a partial replacement of natural aggregates with recycled concrete aggregates (RCA) is the most viable approach for balancing sustainability and structural performance. Specifically, using 20% RCA maintains the structural integrity of reinforced concrete beams, with only a negligible impact on shear strength and deflection. This allows the construction industry to reduce its reliance on traditional materials, decrease waste, and adopt more eco-friendly practices. While a full replacement with RCA can compromise shear strength and increase deflections, the use of RCA in moderation offers a practical and sustainable solution for constructing safer and more environmentally responsible buildings.