Adding value to construction and demolition waste to achieve sustainable development

UK-China Joint Conference: Valorisation of Construction and Demolition Waste for Sustainable Infrastructure Development

A review by Dr Feja Lesniewska

In December I presented at a workshop, supported by the British Council and Newton Fund Researchers Links Programme, on the valorisation of construction and demolition and waste (CDW) for sustainable infrastructure development. The workshop’s focus on how to increase the value of CDW is timely. Globally demand for mineral based construction materials is rising, especially in developing countries. Meeting the growing demand for materials, including minerals, will places enormous strain on the environment. Not only is waste within the construction sector high, the sector also significantly contributes to climate change through greenhouse gas emissions from materials extraction, processing, manufacturing and embodied carbon in the built environment. At COP26 in Glasgow in November 2021 the first dedicated Cities, Regions and Built Environment Day was held. Topics discussed included embodied carbon emitted by the construction supply chain. Reducing CDW can decrease environmental and climate change impacts, contribute to sustainable development, and help transition to a circular economy extending the lifecycle of materials and increasing their value over time.  

The two-day workshop was held in person at both Brunel University, London and Tongji University, Shanghai with presentations linked by Zoom. The workshop aimed to give early career researchers the opportunity to present research, with a view to build up links for future collaborations. Xiangming Zhou (Brunel University London, UK) and Jianzhuang Xiao (Tongji University, China), both professors in civil engineering with research expertise in structural engineering, cement and concrete, co-organised the workshop. Overall, the workshop presentations primarily focused on how to increase demand for recycled aggregate concrete (RAC) within the construction sector by overcoming technical challenges and developing specific RAC standards. RAC come in three categories: coarse (less than 5mm), fine (0.15mm to less than 5mm) and powdered (less than 0.15 mm). Each RAC has different qualities in terms of durability, porosity, and density. Recycled aggregates take time, resources (like water), money, space, and energy to be processed. The processing itself results in by-products and waste, which subsequently need to be managed. Compared to virgin raw materials, RACs are often more expensive, making their use less attractive for the construction industry.

The workshop presentations were mainly from civil engineering researchers. Most presentations shared detailed lab-based results of how different combinations of cement and RAC ratios or other alternative materials, such as rubber (Dr Bompa, University of Surrey) performed under rigorous standardised testing. Several presenters alluded to the need for an understanding of the economic and policy context in which approaches to the valorisation of CDW are being developed, as well as the need for coherent regulation and consistent standards. The importance of context was most notable in a presentation of comparative research on the use of RAC in Southeast Asia by Professor Boksun Kim, (University of Plymouth). Professor Kim compared RAC usage ratios in Vietnam, Thailand and South Korea for non-structural purposes such as paving slabs and riverbank levelling. She argued that more specification, classification, and quality control standards could help to create market opportunities for all types of RACs. Each country in her study used different standards to set the regulated ratios of RAC’s in concrete. For example Vietnam in 2017 introduced regulations on construction and solid waste management that detailed the requirements for reuse and recycling of construction solid waste (Article 9). However, incentivising RAC use through regulations in Southeast Asia still faces significant obstacles including the availability of cheap virgin aggregates, limited recycling capacity, and the catch 22 of a lack of investment and demand.  

Several presenters highlighted China’s unique CDW situation. China’s construction industry developed rapidly due to a 57.35% increase in urbanization rate over the last three decades (2016 National Bureau of Statistics of China). According to Professor Yuanfeng Wang (Beijing Jiaotong University) between 2011-2013 China used 6.6 billion tonnes of cement which is the equivalent to the total amount used in the United States in the entire 20th century.  The construction industry in China is inefficient and wasteful resulting in high CDW rates. Professor Poon (Hong Kong Polytechnic University) claimed that 15 million tonnes of CDW was generated annually in China between 2010-2020. In a 2020 article, Li et al estimated that less than 5% of China’s CDW is recycled, claiming that most is either sent to landfill or illegally dumped in rural areas.  

China does have in place regulations to reduce CDW and promote recycling. The country began to address CDW as early as 2005 with the enactment of the ‘‘Regulations for the management of urban construction waste”. The country’s ‘‘Circular economy promotion law” promulgated in 2009 required that CDW should be comprehensively utilized or harmlessly disposed. This was followed by the “Circular Economy Development Strategies Action Plan” and more recently, “the 13th Five-Year Plan (2015–2020)”.  The 2016 ‘‘industrial specification on construction and demolition waste recycling (provisional)” regulation aimed to further stimulate the CDW recycling industry through the adoption of specification standards. China now has added more than twenty RAC specification standards to the natural concrete design code GB500010-2010. (Professor Kim, University of Plymouth) 

The workshop recognised the importance of increasing RAC and reducing CDW if China is to meet its 2060 net zero carbon target and achieve sustainable development. However, it did not explore why current regulations in China were not resulting in significant increases in RAC in construction. There was an opportunity to draw lessons from comparing the situation in China with the UK. The UK, like many countries, has unsustainable levels of CDW. Yet through fiscal and regulatory measures, the UK has significantly increased recycling of CDW. A landfill tax was introduced to encourage waste recycling in UK from 1996, with the tax rate gradually increased. At the same time, the UK applied an aggregate levy (2 lb/ton) to improve the competitive advantage of recycled aggregate. By 2015 these measures resulted in the decline of the amount of CDW disposed in landfill by 70%. In 2018 the UK recycled and secondary sources of construction aggregates supplied 28% of total demand, well ahead of the European average. However, the recycling is mainly low value backloading for road infrastructure.  It is only by reducing CDW supply that RACs value will increase. A circular, rather than a linear, economy can incentivise investment in innovations in the use of secondary materials like RAC. Yet, as evident in China, the adoption of circular economy laws and regulations is no guarantee of a move to a circular economy if demand continues to rise and supply of virgin raw materials remains cheaper than RAC alternatives. The UK has only recently incorporated circular economy concepts into policy, but existing laws and regulations can be used to advance circularity such as the Environment Act 2021 Part 3 (England and Wales) and Environmental Permitting Regulations 2016 (England and Wales). The forthcoming UK Building Safety Bill 2019 could spur innovation to ensure durability and repairability of construction products through circular design extending the lifecycle of materials, thereby leading to reduced demand.  In my own presentation I outlined the opportunities for valorising CDW within the UK by introducing the concept of the circular economy and surveying recent policy and related regulations. This was the only presentation at the workshop by a non-engineer.

I personally valued the knowledge exchange opportunity this workshop provided. I learnt a great deal about the science, testing and specification requirements for RAC and alternative materials used in construction. However, for the workshop to investigate how to increase the value of CDW to achieve sustainable development it would have benefitted from a more interdisciplinary approach by including input from economics, business studies, environmental design, architecture, law, and public policy researchers. Perhaps a next step in taking forward research on CDW, valorisation and sustainable development would be to have such an interdisciplinary workshop as part of a move to greater circularity in the minerals based construction sector.