Recycled Concrete Beam

Recycled Concrete: The Secret to Sustainable Construction?

Rhea Morgan in Climate & Environment August 2025 • 4 min read.

"Uncover how recycled aggregates are reshaping the construction industry, offering eco-friendly solutions for a greener future."

The construction industry's reliance on natural resources has surged over the past century, driven by population growth and the need to replace aging infrastructure. This demand strains landfills, increases energy consumption, and raises concerns about sustainability. Recycling construction and demolition (C&D) waste offers a promising solution by reducing the demand for virgin materials, conserving landfill space, and cutting energy consumption.

Concrete, a primary component of C&D waste, has come under scrutiny, leading to the exploration of recycled concrete aggregates (RCA) as a substitute for natural aggregates. While RCA presents a feasible alternative, its properties are generally inferior to natural coarse aggregates (NCA), sparking debates about its structural performance and long-term reliability. This article delves into a recent study that examines the effects of RCA on the shear strength of reinforced concrete beams, offering insights into the potential and limitations of this sustainable material.

The study, conducted by researchers at Kuwait University and The Hong Kong Polytechnic University, investigates the shear behavior of reinforced concrete beams made with varying percentages of RCA. By comparing the performance of beams with RCA to those with NCA, the research aims to provide a clearer understanding of RCA's impact on structural integrity and identify practical guidelines for its use in construction.

Shear Strength of Recycled Aggregate Concrete Beams Containing Stirrups

The experimental study focused on the shear behavior of reinforced concrete beams produced using RCA. Eighteen beams were tested across three series, each varying in the percentage of natural coarse aggregates replaced with RCA: 0%, 20%, and 100%. All beams had a consistent longitudinal reinforcement ratio of 1.38%. The key objective was to measure how different RCA percentages affected the beams' shear strength, cracking patterns, and deflection.

The results indicated that incorporating RCA at 20% and 100% reduced shear strength by 5% and 9% respectively, relative to beams made with natural aggregates. The use of RCA also increased midspan deflections, particularly at the 100% replacement level. However, the study found negligible effects on shear cracking patterns, critical shear cracks, longitudinal steel strains, and the mode of failure. Beams reinforced with both longitudinal and transverse reinforcement showed less sensitivity to the incorporation of recycled aggregates compared to beams with only longitudinal reinforcement.

Full use of recycled aggregates reduced shear strength by 9%, increased deflections.
A 20% use reduced shear strength by 3%, and effects on deflections were negligible.
Replacement had limited effects on crack pattern, failure mode, longitudinal strains.
Code calculations for shear strength less conservative in recycled aggregate beams.

Further analysis involved comparing the experimental shear strengths with calculations from ACI, CSA, MC2010, and EC2 codes. The calculations were conservative for the level of approximation II of the MC2010 model code but slightly unconservative for the rest of the methods checked, especially for beams with recycled aggregates. These findings suggest that current code calculations may need refinement to accurately predict the shear strength of RCA concrete beams. The results has significant implications for structural design and the broader adoption of sustainable construction practices.

Embracing Sustainable Building Materials

The research underscores the potential of RCA in construction while highlighting the need for careful consideration of its impact on structural performance. By understanding the nuances of RCA's behavior, engineers and policymakers can develop guidelines and standards that promote its safe and effective use. As the construction industry continues to seek sustainable alternatives, further research and practical implementation of RCA will be crucial in building a greener, more resilient future.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.conbuildmat.2018.10.023, Alternate LINK

Title: Shear Strength Of Recycled Aggregate Concrete Beams Containing Stirrups

Subject: General Materials Science

Journal: Construction and Building Materials

Publisher: Elsevier BV

Authors: K.N. Rahal, Y.T. Alrefaei

Published: 2018-12-01

Everything You Need To Know

What are recycled concrete aggregates (RCA), and why are they being explored in the construction industry?

Recycled concrete aggregates, or RCA, are created by processing concrete from construction and demolition waste. They are then used as a substitute for natural aggregates in new concrete mixes. The primary goal is to reduce the demand for virgin materials, conserve landfill space, and decrease energy consumption associated with traditional concrete production.

What specific tests were conducted on reinforced concrete beams to assess the impact of using RCA, and what were the main findings?

A study compared reinforced concrete beams made with varying percentages of RCA (0%, 20%, and 100%) to beams made with natural coarse aggregates (NCA). The study examined the shear strength, cracking patterns, and deflection of the beams. The results indicated that incorporating RCA at 20% and 100% reduced shear strength by 5% and 9%, respectively, relative to NCA beams. The use of RCA also increased midspan deflections, particularly at the 100% replacement level. However, the study found negligible effects on shear cracking patterns, critical shear cracks, longitudinal steel strains, and the mode of failure. Beams reinforced with both longitudinal and transverse reinforcement showed less sensitivity to the incorporation of recycled aggregates compared to beams with only longitudinal reinforcement.

How do current structural design codes account for the use of RCA in concrete, and what adjustments might be needed?

The study's findings suggest that current code calculations, such as those from ACI, CSA, MC2010, and EC2, may need refinement to accurately predict the shear strength of RCA concrete beams. The calculations were conservative for the level of approximation II of the MC2010 model code but slightly unconservative for the rest of the methods checked, especially for beams with recycled aggregates. Because calculations are slightly unconservative, it is important to verify your calculations when using RCA with another method of analysis.

In what ways does the utilization of recycled concrete aggregates contribute to environmental sustainability?

Using recycled concrete aggregates reduces the need to extract and process new natural aggregates, which helps conserve natural resources and reduces environmental disruption. Furthermore, it decreases the amount of construction and demolition waste sent to landfills, freeing up valuable space and reducing landfill-related pollution. The use of RCA can also lower energy consumption, as it typically requires less energy to process recycled aggregates compared to extracting and processing natural aggregates. These factors make RCA a more sustainable option for the construction industry.

What are the primary limitations and challenges associated with using RCA in construction, and what steps are needed to address them?

While recycled concrete aggregates present a promising avenue for sustainable construction, challenges remain. RCA generally exhibits inferior properties compared to natural aggregates, which can affect the structural performance and long-term reliability of concrete structures. Additionally, the consistency and quality of RCA can vary depending on the source and processing methods. Overcoming these limitations requires further research to improve RCA processing techniques, develop appropriate mix designs, and establish comprehensive guidelines and standards for its use in construction. Addressing these challenges is essential for the broader and more confident adoption of RCA in the construction industry.