Performance of concrete pavements using recycled materials: A low-carbon approach

Abstract: Concrete Pavements are highly desirable for heavily trafficked highways and transport systems due to their strength and long service life; however, they are subject to early-stage failure due to concrete’s lack of tensile strength. The mechanical properties, namely compressive strength and flexural strength are crucial to the performance of a pavement. Recent research has explored the incorporation of recycled materials to enhance concrete’s mechanical properties and also reduce cracking. Plastic fibres have been found to improve these properties. In addition to plastic fibres, the use of other waste materials, such as recycled aggregates, fly ash, and slag, has also shown promise in creating low-carbon concrete by replacing traditional components and reducing the carbon footprint of concrete production. This study primarily focuses on incorporating plastic fibres, hemp, fly ash and rubber, into a standard 40 MPa concrete pavement mix design commonly used in Australia. These wastes were chosen as they are commonly available in Australia.
Each material is chosen for its ability to enhance specific properties of concrete while contributing to the circular economy by utilizing waste products and renewable resources. Plastic fibres and hemp improve tensile strength and crack resistance, addressing one of concrete's major weaknesses. Fly ash, a supplementary cementitious material, replaces a portion of Portland cement, reducing the carbon footprint of the mix while maintaining compressive strength and durability. Recycled rubber, derived from end-of-life tyres, adds flexibility and resilience, improving impact resistance and reducing the likelihood of cracking.
The results of laboratory testing showed that the mix with 0.5% plastic fibres and 10% recycled rubber achieved a 5% improvement in flexural strength compared to the control samples while meeting the requirements for compressive strength. The addition of fly ash contributed to an 18% reduction in CO2 emissions without compromising strength. Hemp fibers, at a 0.5% volume, showed moderate improvements in crack resistance, reducing early-age cracking by 20%. However, mixes with higher rubber content exhibited slight reductions in compressive strength but improved impact resistance and flexibility.