Recycled Concrete Aggregate and Fly Ash Enhance Road Pavement Durability and Sustainability

Why It Matters

This research demonstrates a practical pathway to achieving a circular economy in construction by repurposing waste materials into durable, high-performance road infrastructure. It offers designers and engineers a viable method to balance performance demands with environmental responsibility, reducing reliance on virgin resources.

Key Finding

Concrete made with recycled aggregate and fly ash, reinforced with polypropylene fibers, performs as well as traditional concrete for roads and airfields, offering improved durability and a lower environmental footprint.

Key Findings

• Modified concrete mixtures with 10-12% fly ash replacement and at least 2 kg/m³ of polypropylene fiber achieved compressive strengths of at least 50 MPa and flexural strengths of no less than 5 MPa.
• Abrasion resistance was significantly enhanced, ranging from 0.48–0.50 g/cm².
• The environmental impact assessment showed reduced Global Warming Potential, Non-renewable Primary Energy Demand, and Abiotic Depletion Potential compared to conventional concrete.
• The modified compositions meet required performance criteria for rigid pavement applications.

Research Evidence

Aim: To investigate the feasibility of using recycled concrete aggregate (RCA) and fly ash (FA) in fiber-reinforced concrete for road and airfield applications, and to determine optimal mix designs that achieve comparable performance to conventional concrete while offering environmental benefits.

Method: Experimental research and life-cycle assessment.

Procedure: Researchers developed and tested 15 modified concrete mixtures using RCA as a full gravel replacement and FA as a partial cement substitute, incorporating polypropylene fibers and superplasticizers. Three control mixtures with natural aggregate were also tested. Workability was standardized, and key performance indicators such as compressive strength, flexural strength, and abrasion resistance were evaluated. A cradle-to-gate life-cycle assessment was conducted for the constituent materials.

Sample Size: 18 concrete mixtures (15 modified, 3 control)

Context: Civil engineering, construction materials, sustainable infrastructure.

Design Principle

Maximize resource circularity by integrating waste materials into high-performance applications without compromising structural integrity or durability.

How to Apply

When designing concrete mixes for infrastructure projects, explore the inclusion of recycled concrete aggregate and fly ash, carefully optimizing fiber content and admixtures to meet performance specifications and sustainability goals.

Limitations

The study focused on a specific range of RCA and FA percentages, polypropylene fiber content, and superplasticizer dosage. Long-term performance under varied environmental conditions and traffic loads was not assessed.

Student Guide (IB Design Technology)

Simple Explanation: You can build strong roads using old concrete and industrial byproducts like fly ash, making them last longer and be better for the environment.

Why This Matters: This research shows how to make construction more sustainable by reusing materials, which is important for reducing waste and environmental damage.

Critical Thinking: How might the variability in the properties of recycled aggregate and fly ash impact the consistency and reliability of the final concrete product in large-scale construction projects?

IA-Ready Paragraph: This research by Kryzhanovskyi et al. (2026) demonstrates that incorporating recycled concrete aggregate and fly ash into fiber-reinforced concrete can yield materials with performance characteristics comparable to conventional concrete for road applications, while simultaneously advancing sustainability goals through waste material utilization and reduced environmental impact.

Project Tips

• When researching materials, consider the environmental impact and potential for using recycled or waste components.
• Document the performance trade-offs when substituting materials and how additives can mitigate these.

How to Use in IA

• Use this study to justify the selection of sustainable materials in your design project, referencing its findings on performance and environmental benefits.

Examiner Tips

• Demonstrate an understanding of how material choices impact both performance and environmental sustainability.

Independent Variable: ["Percentage of recycled aggregate used","Percentage of fly ash used as cement substitute","Content of polypropylene fiber","Content of superplasticizer"]

Dependent Variable: ["Compressive strength","Flexural strength","Abrasion resistance","Brittleness index","Workability (slump)"]

Controlled Variables: ["Slump class (S1)","Aggregate type (full gravel replacement)","Fiber length (36 mm)","Design age for strength testing"]

Strengths

• Comprehensive experimental testing of multiple mix designs.
• Inclusion of a life-cycle assessment to quantify environmental benefits.
• Focus on practical applications in road construction.

Critical Questions

• What are the long-term durability implications of using recycled aggregate and fly ash in concrete under real-world traffic and environmental stresses?
• How does the cost-effectiveness of these sustainable mixes compare to traditional concrete over the entire life cycle of the pavement?

Extended Essay Application

• Investigate the potential for using other waste materials in concrete formulations for structural applications, assessing their performance and environmental impact.
• Develop a predictive model for concrete performance based on the proportions of recycled materials and admixtures used.

Source

Design of Recycled Aggregate Fiber-Reinforced Concrete for Road and Airfield Applications Using Polypropylene Fibers and Fly Ash · Construction Materials · 2026 · 10.3390/constrmater6010002