SUMMARY

Background/Objectives

The Defence and aviation sector have invested significant resources into understanding and mitigating PFAS contamination globally. While efforts have primarily focused on soil and water, secondary sources such as concrete and asphalt pose emerging challenges. These materials, previously considered highly recyclable, now risk disposal due to insufficient options for managing PFAS contamination, with even low PFAS concentrations at times jeopardising circular economy aspirations.

Currently, there are very few options for PFAS management in asphalt and concrete, and no commercially available solutions enabling the sustainable reuse of PFAS-impacted asphalt within a circular system. To address this gap, RemBind and Fulton Hogan, supported by ADE Consulting Group, conducted preliminary experiments to determine whether PFAS immobilisation and reuse in asphalt matrices were feasible from both chemical and construction material perspectives. This research led to the development of RemRAP, a specialised product designed for both remediation and circular economy applications.

RemRAP builds on the proven success of RemBind 100, a PFAS sorbent for soil remediation, by modifying its formulation and integrating additional risk mitigation measures — including a bitumen envelope and an impervious wearing course. This provides a robust “belt and braces” solution for PFAS management in recycled asphalt pavement (RAP). In collaboration with Fulton Hogan and ADE, bench-scale studies were conducted to evaluate the efficacy of RemRAP in immobilising PFAS in asphalt.

Approach/Activities

Initial work was conducted at bench scale using a batch approach to assess the feasibility of PFAS immobilisation in asphalt. Strong irreversible sorption of PFAS in these experiments demonstrated that the asphalt matrix did not interfere with the modified RemBind product’s PFAS sorption processes, allowing the trial to progress to a larger-scale bench study.

In the larger bench trial, monoliths were produced using the RemRAP product and RAP to assess efficiency in terms of chemical immobilisation through leaching methods including Multiple Extraction Procedure (MEP). Additionally, construction material assessments were undertaken to ensure the material was fit for purpose and met key airfield and road specifications.

Further testing examined the impact of hot and cold mix processes, aiming to optimise designs that prevent potential PFAS volatilisation, which, while not well understood, has been suggested could otherwise occur when heating asphalt in the presence of solvents and binders.

Results/Lessons Learned

Batch trials demonstrated over 96% reductions in PFOS and PFHxS leachability with sorbent dosages of 0.5%–2% w/w, achieving leachability below reporting limits. Monolith testing confirmed long-term stability via MEP and yielded resilient modulus values surpassing control mixes and meeting construction material specification criteria, demonstrating the material remained fit for purpose while reducing PFAS leachability to values below key reuse thresholds.

Future work will focus on field-scale trials and modelling, aiming to achieve up to 10,000-fold reductions in PFAS leachability through the technology’s three key mechanisms:

1. Sorbative properties to bind PFAS and prevent leaching.
2. An impermeable cover layer to limit water ingress.
3. A hydrophobic envelope to further restrict PFAS mobility away from particles.

This work highlights RemRAP’s potential as a viable solution for problem owners seeking to either remediate PFAS-impacted asphalt and concrete on-site or foster a circular economy for materials with low-level PFAS contamination. Further work is underway to support the application of this approach in Australia.