In recent years, the use of Recycled Concrete Aggregates (RCA) in pavement construction has emerged as a sustainable alternative with significant benefits across multiple fronts. Here’s a comprehensive overview of the key insights and findings from recent studies:

1. Strength and Durability Comparable to Natural Aggregates
   According to the NZ Guide to Pavement Evaluation and Treatment Design, RCA has demonstrated the ability to meet strength requirements equivalent to natural aggregates. This makes RCA a viable option for various pavement layers, offering comparable performance while utilizing recycled materials.
2. California Bearing Ratio (CBR) Exceeding Minimum Requirements
   RCA exhibits robust performance metrics, particularly in terms of the California Bearing Ratio (CBR). The NZ Guide to Pavement Evaluation and Treatment Design notes that RCA often exceeds the minimum CBR requirements of 20 for trafficable areas, showcasing its suitability for load-bearing applications. Additionally, studies like the Proposed Recycled Material Blends Study have shown that blends of recycled materials can achieve CBR values close to or above 20, meeting stringent backfilling requirements in trafficable areas.
3. Environmental Benefits Through Reduced Need for Virgin Materials
   Emphasizing sustainability, the NZ Guide to Pavement Evaluation and Treatment Design underscores that using RCA reduces reliance on virgin materials. This not only supports eco-friendly construction practices but also contributes to environmental conservation efforts by minimizing resource extraction.
4. Significant Carbon Emission Reductions
   The research highlighted in SpringerLink reveals substantial environmental benefits associated with using RCA in concrete pavements. The adoption of RCA has been shown to reduce carbon emissions by approximately 65 kg CO2 per ton of concrete, illustrating its positive impact on carbon footprint reduction. Moreover, studies on high-rise buildings indicate that integrating RCA can lead to a significant 25% reduction in the overall carbon footprint without compromising structural integrity.
5. High Eco-Efficiency in Mechanistic-Empirical Design
   Through a Mechanistic-Empirical Design Approach discussed in MDPI, RCA has proven effective in concrete block pavements (CBP) in Australia. Recycled materials used as base course or sub-base achieved eco-efficiency ratios as high as 1.25 compared to traditional virgin materials, highlighting its sustainable performance advantages.
6. Sustainability Assessment Highlights
   Sustainability assessments featured in MDPI underscore that RCA contributes substantially to environmental conservation efforts. In New Zealand, RCA applications have shown a remarkable 40% reduction in landfill waste and a 35% conservation of natural resources, while meeting rigorous performance standards for pavement layers.

Conclusion

In conclusion, the accumulated evidence strongly supports the adoption of Recycled Concrete Aggregates (RCA) in pavement construction. The combination of comparable strength to natural aggregates, superior CBR performance, substantial environmental benefits, and high eco-efficiency underscores RCA as a cornerstone of sustainable infrastructure development.

Application in New Zealand

For New Zealand engineers considering the integration of RCA in pavement projects, adherence to local guidelines such as NZTA M10 and NZS 4407:2015 is crucial. Conducting thorough consultations with local pavement engineers and rigorous testing, including CBR assessments, ensures that RCA blends meet stringent regulatory and performance criteria for trafficable areas.

By leveraging these insights and embracing RCA technologies, New Zealand can advance its infrastructure initiatives while prioritizing sustainability and environmental stewardship in pavement design and construction.