Resource recovery and low carbon transitions: The hidden impacts of substituting cement with imported ‘waste’ materials from coal and steel production

Abstract

Here we investigate the increasingly complex relationship between the resource recovery practices of the UK concrete industryandongoing low-carbontransitions takingplaceinelectricityandsteel.ReductionsinUKcoalbased electricity and primary steel production are reducing domestic availability of residues – coal ash and steel slag – that are used to replace cement in concrete; for decarbonisation purposes and to increase concrete quality. This is leading to an unusual mass-transportation of ‘wastes’ from the Global South to Global North. Focusing closely upon the mitigation pathways of concrete producers, we develop an inter-industry model of material flows, and a diversity of scenarios and sensitivity tests, to consider how resource recovery practices and carbon emissions of the three sectors may evolve. A continuation of domestic shortages in waste-derived cement substitutes appears inevitable and future international shortages possible. But even if foreign producers supplied enough cement substitutes to meet UK demand, the broader carbon implications of such trade may be far from benign. Using a revenue-based approach to allocate emissions to coal ash leads to a wide range of embodied carbon estimates – from relatively low (0.15t.CO2/t.ash) to exceeding that of traditional Portland cement (1t.CO2/t.ash). However, the carbonassociated withinternationally traded recovered resources currently stands behinda‘double-blind’systemofaccounting: emissionsdonotregisterintheconventionalterritorialaccountsof theimportingcountry andtheymaybehiddenfromitsconsumption-based accountsaswell.Theimpactsofsuch trade and related carbon accounting conventions are unclear and we emphasise the need for further investigation. To this end, our results demonstrate the importance of incorporating highly interconnected sectors and international trade into analyses of low-carbon transitions, and highlight the challenges this presents for designing appropriate policies, accounting frameworks, and interdisciplinary impact assessment methods that look beyond sectorial and national horizons.