Sustainable building made of recycled concrete with plants.

Recycled Concrete: Is It Strong Enough for Our Buildings?

Soraya Malik in Climate & Environment August 2025 • 4 min read.

"Uncover how recycled concrete aggregate is reshaping construction, offering sustainable solutions without compromising structural integrity"

The construction industry faces a growing demand for resources, coupled with increasing pressure to reduce waste and promote sustainability. Traditional concrete production relies heavily on natural aggregates, contributing to environmental degradation and landfill accumulation. In response, recycled concrete aggregate (RCA) has emerged as a promising alternative, offering a way to reuse construction and demolition waste while conserving natural resources.

However, concerns persist regarding the structural performance of concrete made with RCA. Questions arise about its strength, durability, and suitability for various construction applications. Can recycled concrete truly match the reliability of its conventional counterpart? Addressing these concerns is crucial for widespread adoption of RCA and its integration into mainstream construction practices.

Recent research sheds light on the viability of RCA in structural applications, particularly in reinforced concrete beams. These studies investigate the impact of RCA on shear strength, deflection, and overall structural behavior, providing valuable insights for engineers and construction professionals seeking sustainable solutions.

Does Recycled Aggregate Concrete Compromise Strength?

Sustainable building made of recycled concrete with plants.

A study published in "Construction and Building Materials" (Rahal & Alrefaei, 2018) examined the shear strength of reinforced concrete beams made with RCA. The researchers tested beams with varying percentages of RCA replacement (0%, 20%, and 100%) to assess its impact on structural performance. All mixes had a target strength of 35 MPa and a consistent longitudinal reinforcement ratio of 1.38%.

The experimental results revealed some critical insights:

Shear Strength Reduction: Full replacement of natural aggregates with RCA (100% replacement) led to an average reduction in shear strength of approximately 9%. A 20% replacement resulted in a more modest reduction of about 3%.
Deflection Increase: Beams with 100% RCA exhibited considerably higher deflections compared to those made with natural aggregates, indicating a reduction in stiffness. The 20% RCA replacement had negligible effects on deflection.
Crack Patterns and Failure Modes: The study found that RCA replacement had limited effects on the shear cracking patterns, critical shear cracks, longitudinal steel strains, and failure modes of the beams.
Code Compliance: When compared to standard code calculations, the study found that code equations were generally conservative for beams with recycled aggregates.

These findings suggest that while RCA can be a viable alternative, its impact on shear strength and deflection needs careful consideration. The reduction in shear strength, though present, might be acceptable in certain applications, especially with lower replacement percentages. However, the increase in deflection, particularly at full replacement, warrants attention in structural design.

The Future of Recycled Concrete

The use of recycled concrete aggregate presents a promising avenue for sustainable construction, offering environmental benefits through waste reduction and resource conservation. While the research indicates some reduction in shear strength and increased deflections with full RCA replacement, these effects can be managed through careful mix design and structural considerations. As the industry continues to innovate and refine RCA production techniques, we can expect to see even greater adoption of this eco-friendly material, paving the way for a more sustainable and resilient built environment.

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Everything You Need To Know

What is Recycled Concrete Aggregate (RCA) and why is it important in construction?

Recycled concrete aggregate (RCA) is aggregate produced from recycled concrete, offering a sustainable alternative to traditional aggregates. Its importance lies in its potential to reduce construction waste, conserve natural resources, and lessen the environmental impact of the construction industry. The use of RCA directly addresses the growing demand for construction materials and the pressure to reduce landfill accumulation, making it a crucial component of sustainable building practices.

How does replacing natural aggregates with Recycled Concrete Aggregate (RCA) affect the shear strength of reinforced concrete beams?

Research, such as the study by Rahal & Alrefaei (2018), indicates that replacing natural aggregates with RCA can influence shear strength. Full replacement with RCA (100%) resulted in an average reduction of approximately 9% in shear strength, while a 20% replacement showed a more modest reduction of about 3%. This suggests that the percentage of RCA used directly correlates with the degree of shear strength reduction, which must be carefully considered in structural design.

What impact does the use of Recycled Concrete Aggregate (RCA) have on the deflection of reinforced concrete beams?

The study by Rahal & Alrefaei (2018) showed that beams with 100% RCA exhibited considerably higher deflections compared to those made with natural aggregates, indicating a reduction in stiffness. In contrast, the 20% RCA replacement had negligible effects on deflection. This means that the degree of RCA usage influences the beam's ability to resist deformation under load. Higher RCA percentages can increase deflection, which is an important factor in structural design to ensure the beam meets performance criteria.

Are current building codes sufficient for structures using Recycled Concrete Aggregate (RCA), and what factors need careful consideration?

According to the study by Rahal & Alrefaei (2018), standard code equations were generally conservative for beams with recycled aggregates. However, the study's findings highlight that the impact on shear strength and deflection needs careful consideration. While code compliance may be achievable, engineers must account for potential reductions in shear strength, especially with higher RCA replacement percentages, and the increased deflections that can occur, particularly at full replacement. Careful mix design, structural analysis, and adherence to specific guidelines are essential to ensure the safe and effective use of RCA in construction.

What are the long-term implications and future prospects for Recycled Concrete Aggregate (RCA) in the construction industry?

The long-term implications for Recycled Concrete Aggregate (RCA) are promising. RCA provides a sustainable pathway for construction, promoting waste reduction and resource conservation. As the construction industry continues to innovate and refine RCA production techniques, we can anticipate greater adoption of this eco-friendly material. The future of RCA likely includes advancements in mix design, improved performance characteristics, and broader acceptance within building codes. This will pave the way for a more sustainable, resilient, and environmentally responsible built environment, reducing the industry's ecological footprint.