With the race to 2050’s net zero target firmly upon us and the countdown to COP26 in November 2021, pressure is growing on the construction industry to arrive at ways to reduce their carbon footprint. Ultimately this may lead to the urgent revision of building materials and methods of construction and we examine some recent developments below.

Cement

As one of the most versatile materials on the planet and a product which is readily available and cheap, it is no wonder that, after water, concrete is the most widely used substance on earth. Unfortunately, it comes with a hefty environmental price tag considering cement is responsible for 7% of global carbon emissions. Thus, there is growing pressure on the cement industry to come up with ways to reduce their carbon footprint.

The reaction needed to form the product clinker, used to make cement, requires heat at 1,450 degrees Celsius, compromising one-third of the overall emissions, with the remaining two-thirds emitted during calcination. The Mineral Products Association (MPA) suggests that the use of alternative materials can cut cement’s carbon footprint by 12% by 2050. Two main alternatives to Portland cement (CEM1) are ground granulated blast furnace slag (GGBS), which can replace up to 85% of the cement in a concrete mix and fly ash, which can replace 30% of CEM1. Manufacturers such as Cemfree offer concrete that uses an alternative geo polymer alkali activator to CEM1, further reducing the carbon footprint of concrete. However, such concretes do not currently conform to british standards. Major concrete manufacturers, such as Cemex with their product ‘Vertua,’ are now offering ready-mixed products with varying amounts of these alternatives. But such alternatives do not come without their limitations. The supply of GGBS and fly ash could be an issue and importing these alternatives from countries further afield could shift the balance of the environmental benefits of using these alternatives in the first place.

Another possibility for the decarbonisation of concrete is to use alternative fuels to fire the kiln during cement production. The MPA has set a target of cutting emissions from cement production by 16% by 2050. MPA’s study, conducted in 2019, concluded that a combination of 70% biomass, 20% hydrogen and 10% electrical energy could be used to eliminate emissions from cement manufacturing. Currently, Hanson Concrete is trialling biomass and hydrogen at its Ribblesdale plant in Lancashire and other manufacturers are trialling hydrogen, with Cemex investing £18m in a new hydrogen system at its Rugby plant which will have the capability to run on 100% hydrogen. Again, the supply of these alternative fuels poses issues, with the Ribblesdale plant requiring 0.3 tonnes of hydrogen per hour, for example, and a road tanker is only able to carry 0.4 tonnes. To generate enough power to produce the hydrogen needed would require 60 wind turbines to supply 50% of the fuel needed at Ribblesdale.

Further, the cement industry sees carbon capture storage (CCS) as the primary solution to the problem of carbon emissions with the MPA believing that 61% of emissions from cement manufacture will be mitigated by this technology. Additionally, there is also the possibility of using the carbon dioxide captured by this process for industrial processes and fuel manufacture (carbon capture, utilisation and storage). The UK has created several low carbon clusters to experiment with CCS technology on an industrial scale, including HyNet North West which will produce, store and distribute hydrogen and also capture and store carbon. This new technology will take time to settle and to roll it out commercially to cement plants worldwide, however, there is a good case for CCS considering the challenges of cement production and the availability of alternatives.

More efficient use of materials

It may sound obvious, but one of the best ways of reducing our carbon footprint is to use less of the materials lending to large carbon emissions. A UK funded research project on decarbonising precast concrete brought together a range of partners including precast manufacturer Forterra, design for manufacture specialist Akerlof and the Ministry of Justice (MoJ) to examine the issue. The project guinea pig was the construction of Wellingborough and Glen Parva prisons. The project found that the floor loading specifications could be reduced from a slab thickness of 200mm to 160mm and a concrete mix of 50% GGBS was deemed suitable. These measures reduced the carbon content of the slabs by 30%. These changes were cost-neutral and are said to be ready to apply to a live project. The MoJ will use the lower carbon products on the next tranche of prisons.

Further, saving a building from the “wrecking ball” and opting for a refurbishment instead of a full demolition, can reduce constructions carbon footprint further. One Triton Square is said to be the new benchmark for the industry to beat in terms of its low carbon refurbishment. The initial building was designed by Arup Associates and completed in 1998. The primary goal of this project was to make it as low carbon as possible. Several strategies were used to implement the low carbon initiative including opting for small improvements in lots of areas, adding up to a large overall advantage. One of the bigger carbon reduction gains, and something rarely done, was to dismantle the façade, clean it, and put it back on. Additional space of 57% was created by adding a further three storeys and reducing the atrium. Instead of adding additional columns to strengthen the structure, the 175 original columns were strengthened. The building features all new services, with the original plant being sold where it could be reused or recycled. The refurbishment has saved 25,000 tonnes of carbon compared to that of a new build, adding up to 40,000 tonnes over the 20-year life of the building. One Triton Square is said to have set the precedent for further projects.

Modern construction methods

It is not only the materials used that the industry needs to review in order to reduce the sector’s carbon footprint, but the ways in which projects are designed can also be examined. Sustainable design is an essential part of how the industry can achieve net zero carbon in the built environment. Nature presents excellent opportunities to solve design problems such as rain gardens as part of sustainable drainage systems (SuDS). The urban heat island effect, whereby solar energy is absorbed by hard surfaces and subsequent re-radiation, causing elevated temperature in urban environments, can be combatted by introducing more soft landscaping and planting. Reducing the temperature this way not only improves the quality of environmental spaces but reduces the need for cooling solutions and thus, energy consumption. The UK Green Building Council (UKGBC) has linked the nature-based solutions programme with the climate adaptation programme and is providing several case studies to demonstrate their co-benefits. The Ignition project, Manchester, will help to build Manchester’s ability to adapt to the increasing impact of climate change by working with nature, and utilising solutions such as rain gardens, street trees, green roofs and walls. Large developers, such as the Crown estate, are looking at using nature-based solutions as part of their net zero carbon pathways.

It is clear to see that the construction industry is beginning to take steps towards a lower carbon build environment, but with many proposals still in the testing phases, the sector still has some distance to go until these modern construction methods and materials can be rolled out on the much larger scale required in order to reach the net zero target. Unfortunately, these developments are likely to continue to be gradual and incremental, as industry experience would suggest that new products and methods are often a fertile area for claims. However, a positive approach to risk allocation and sharing, can assist in managing the problems that arise from new products and methods and assist in ensuring that the path to net zero continues at an urgent pace.