Environmental implications of reuse of large volumes of Recycled Concrete Material (RCM)
The reuse of demolition material in the construction industry is commonplace, with legislation and guidance listing construction and demolition waste (concrete, bricks, tiles and ceramics) as inert. This implies they can be easily reused with little environmental consequence.
The exposure of crushed Recycled Concrete Material (RCM), however, will lead to production of a highly alkaline (pH 13) leachate. Leachate produced from stockpiled or reused RCM can enter groundwater, drainage systems, or surface waters leading to compliance and environmental issues within and adjacent to sites where it is used. As pH is measured on a log scale, 1m3 of pH 13 water has the potential to raise the pH of over 100,000 m3 of water from pH 7 to pH 8 (assuming no buffering capacity). Such issues are not inevitable and are highly dependent on the site setting and reuse scenario. Some common reuses (e.g. road construction) may naturally limit the potential for high pH leachate generation, others may be appropriate with careful assessment, planning and management and some may, upon assessment, be found to be inappropriate.
There is generally a lack of guidance on how to manage and reuse RCM with respect to the potential generation and migration of high pH leachate. This is likely to be due to a combination of lack of awareness, gaps in regulatory guidance and as above that some of the most common reuse scenarios limit the generation or impact of the high pH leachate.
The United Kingdom’s Nuclear Decommissioning Authority (NDA) has identified that reuse of demolition materials will be crucial during decommissioning across its group sites. Reuse scenarios are likely to include both above and below ground use, often in large voids which extend below the water table. NDA has also recognized that stockpiling and reuse requires planning and assessment to avoid potential issues associated with generation and migration of high pH leachate. Working alongside partners NSG Environmental Ltd and KDC, AECOM has recently completed a desk-based study focusing on the management and reuse of RCM with respect to high pH leachate.
This desk study, commissioned by NDA through its Direct Research Portfolio (DRP), also considered the potential promotion of metal leaching associated with such leachate. AECOM combined information gathered from literature research, collaboration with NDA group sites and AECOM and KDC experience. This approach allowed identification of a number of practical steps which could be implemented across NDA sites when planning for, producing, stockpiling and using RCM. This included a range of steps from assessment methodologies to specifying the grade of the material. It also included advice on dealing with high pH leachate, should it be generated, whilst recognizing this is not a preferred situation.
At the conclusion of the works, AECOM also identified a number of data gaps that could be addressed by either collecting data from ongoing or future site programmes or through new modelling or research. Overall, the work should provide NDA with the tools and confidence to reuse RCM appropriately leading to both environmental and economic advantages during decommissioning of its sites.
The outcome of the work was presented to representatives from the Nuclear Industry Group for Land Quality in late 2018. Due to the level of interest received by NDA and the implications for the wider industry, a public version of the report now available on the government website below. It is anticipated that publication of this report will assist in raising awareness of the issue and highlight the need for appropriate assessment prior to reuse of RCM.