Purpose Construction and demolition (C&D) waste recycling has been considered to be a valuable option not only for minimising C&D waste streams to landfills but also for mitigating primary mineral resource depletion. However, the potentially higher cement demand due to the larger surface of the coarse recycled aggregates challenges the environmental benefits of recycling concrete. Furthermore, it is unclear how the environmental impacts depend on concrete mixture, cement type, aggregates composition and transport distances. Methods We therefore analysed the life cycle impacts of 12 recycled concrete (RC) mixtures with two different cement types and compared it with corresponding conventional concretes (CC) for three structural applications. The RC mixtures were selected according to laws, standards and construction practice in Switzerland. We compared the environmental impacts of ready-for-use concrete on the construction site, assuming equal lifetimes for recycled and conventional concrete in a full life cycle assessment. System expansion and substitution are considered to achieve the same functionality for all systems. Results and discussion The results show clear (∼30 %) environmental benefits for all RC options at endpoint level (ecoindicator 99 and ecological scarcity). The difference is mainly due to the avoided burdens associated to reinforcing steel recycling and avoided disposal of C&D waste. Regarding global warming potential (GWP), the results are more balanced and primarily depend on the additional amount of cement needed for RC. Above 22 to 40 kg additional cement per cubic metre of concrete, RC exhibits a GWP comparable to CC. Additional transport distances above 15 km for the RC options do result in environmental impacts higher than those for CC. Conclusions In summary, the current market mixtures of recycled concrete in Switzerland show significant environmental benefits compared to conventional concrete and cause similar GWP, if additional cement and transport for RC are limited.

h i g h l i g h t sWe present a method to analyse material criticality of infrastructure transitions. Criticality is defined as the potential for, and exposure to, supply disruption. Our method is dynamic reducing the probability of lock-in to at-risk technologies. We show that supply disruption potential is reducing but exposure is increasing. a b s t r a c tDecarbonisation of existing infrastructure systems requires a dynamic roll-out of technology at an unprecedented scale. The potential disruption in supply of critical materials could endanger such a transition to low-carbon infrastructure and, by extension, compromise energy security more broadly because low carbon technologies are reliant on these materials in a way that fossil-fuelled energy infrastructure is not. Criticality is currently defined as the combination of the potential for supply disruption and the exposure of a system of interest to that disruption. We build on this definition and develop a dynamic approach to quantifying criticality, which monitors the change in criticality during the transition towards a low-carbon infrastructure goal. This allows us to assess the relative risk of different technology pathways to reach a particular goal and reduce the probability of being 'locked in' to currently attractive but potentially future-critical technologies. To demonstrate, we apply our method to criticality of the proposed UK electricity system transition, with a focus on neodymium. We anticipate that the supply disruption potential of neodymium will decrease by almost 30% by 2050; however, our results show the criticality of low carbon electricity production increases ninefold over this period, as a result of increasing exposure to neodymium-reliant technologies.

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Securing urban freshwater supplies is a major challenge for policy makers globally. This study investigated the determinants of household water conservation to identify the relative contribution of psychosocial and behavioural determinants. Using a survey of 1196 households across the UK, we found that attitudes, norms and habits play an important role in determining intention to conserve water, and that habits were the single most important predictor of water conservation intentions and self-reported water bills. Changing ingrained water conservation habits is therefore an important component of managing urban water demand.