Making concrete progress: sustainable building materials
The built environment will continue to expand to meet the demands of a growing global population. This will require vast quantities of new or repurposed building materials, which in turn could lead to increased carbon emissions. Unless we think differently.
Rethinking how we design and use materials, and avoiding over-specification (generally the stronger the concrete, the more cement is required), can make the construction process more efficient. And using more efficient design and delivery methods, modularization and digital rehearsals to avoid design clashes, can cut emissions.
How else can we pave the way to a sustainable future for the construction industry? Let’s have a look at four solutions from the Skanska world.
Concrete with a lower carbon footprint
At Skanska, we have already been testing and using different types of low-carbon concretes in projects around the world, either our own innovations or materials from our business partners. Data collected in Skanska and partner studies show that the use of these materials has reduced carbon emissions by up to 40-50 percent over conventional concrete. It may pose some technical limitations to usage but with the appropriate expertise and planning, it can be used in ways analogous to standard concrete. Now, let’s see some examples.
Back in 2019 in Sweden, Skanska Betong (our concrete development company) launched a collection of low-carbon mixes. In these mixes, we replace a portion of cement with either slag, a waste product from steel mills, or fly ash, produced by power plants. So far, we have developed five types of concrete for different use cases: general construction, walls, joists, garages and fast-drying concrete. These mixes reduce climate impact by up to 50 percent compared to the traditional material, while retaining their durability, strength and workability. Although it is not yet a market standard, we see a clear interest and increase in the use of this material in construction. Sales of low-carbon mixes from Skanska Betong have tripled over the last year. So far in 2022, they account for 15 percent of total concrete sales, of which 41 percent has been procured by Skanska internally*.
Less waste, more recycled concrete
The construction sector in the EU is the single largest producer of waste, accounting for 35 percent of total waste generation. To tackle the challenge of construction waste, Skanska in the Czech Republic has started producing Rebetong, concrete that uses recycled concrete and/or masonry to replace 100 percent of the aggregates. This circular approach enables new buildings to be constructed from other buildings at the end of their life cycles.
The obvious benefit is that less demolition waste is sent to landfill. It also reduces the use of natural resources for aggregates, as well as the energy required for their extraction and transport, lowering the costs of material and shipping. And because Rebetong – especially when made of recycled masonry – has better insulating properties than regular concrete, it helps lower energy consumption throughout the building life cycle. This innovation reduces the carbon footprint by more than 10 percent** compared with regular concrete. The material is suitable for a variety of common concrete and reinforced concrete building structures, such as base constructions, residential houses, base layers of roadways, sidewalks and retaining walls.
Concrete fights smog. And it’s self-cleaning
Road transport is the main anthropogenic source of nitrogen oxides (NOx) in Europe. Concentrations of this pollutant, which can damage ecosystems as well as causing and worsening respiratory problems in humans, can be higher in areas of greater road density such as large cities.
TioCem® cement has been the subject of many research projects over the years. Thanks to its unique properties, the concrete – containing titanium oxide (TiO2) – initiates a photocatalytic reaction when exposed to sunlight. This reaction reduces air pollutants including nitrogen oxides to simple, harmless compounds. Laboratory and field tests show that areas, where TioCem concrete has been used, have on average 30 percent lower nitrogen oxide concentrations***, compared with other similar sections of sidewalk.
Working with our science and business partners, we used this type of concrete for the first time on the Generation Park office development in the Polish capital Warsaw in 2018. Since then, it has been implemented in four other Skanska office developments in Poland. Local residents and users of public spaces around these city-center office complexes can now enjoy much better air quality.
Thanks to the concrete’s photocatalytic properties, it is also self-cleaning. The oxidation processes not only neutralize harmful compounds in the air, but also the dirt covering the concrete surface, such as grease, oils, dust and bird droppings. Once they've been neutralized, they are easily washed away by rain.
3D concrete printing halving carbon emissions
Cutting-edge “Printfrastructure” technology, which is due for its first test deployment by Skanska UK in late 2022, represents a major advance in construction innovation. The flexible technology is expected to simplify construction when it is used on the HS2 high-speed rail project for the first time, delivering environmental, cost and community benefits.
Printing reinforced concrete using computer-operated robots will allow our Skanska Costain STRABAG joint venture to build structures on site instead of transporting pre-cast slabs by road, assembling them and lowering them into place using large cranes. It’s estimated that the process will reduce the concrete content in some of the structures by up to 50 percent.
As a flexible mobile technology, 3D concrete printing can be used in physically restricted areas, avoiding the need for complicated and potentially expensive logistics plans. Additionally, using a computer-controlled robot allows the reinforced concrete structures to be printed with a unique strengthening internal structure.
The 3D concrete printing process also incorporates the strongest material yet tested: graphene. Microscopic strands of graphene just a few atoms thick replace traditional steel reinforcement in concrete. This provides greater construction flexibility and a shorter build time, while also reducing the quantity of concrete required – cutting waste and ensuring a smaller carbon footprint. By removing steel and simplifying the construction process, the method significantly reduces the need for delivery trucks, driving improved site safety and reducing carbon emissions even further.
Concrete steps to reducing carbon footprint
Concrete has among the highest levels of embodied carbon of all the materials used by Skanska and the broader construction industry. Using modern technologies and lower-carbon materials, we can not only reduce carbon emissions significantly, but also have a positive impact on the environment and society. We know that, together with the right partners, we can help drive construction towards a sustainable future.
To hear more about innovation in sustainable building materials, listen to the first episode of our new podcast, Shaping Sustainable Places!
* Internal data from Skanska Betong
** STRUCTURAL CONCRETE IN THE CZECH REPUBLIC 2018–2021; CONCRETE MADE OF 100% RECYCLED AGGREGATE; Bohuslav SLÁNSKÝ, Pavel ZELINKA; page 60
***Materials 2020, MDPI, Article Application of Photocatalytic Concrete Paving Blocks in Poland—Verification of Effectiveness of Nitric Oxides Reduction and Novel Test Method; Hubert Witkowski 1,2,*, Janusz Jarosławski 3 and Anna Tryfon-Bojarska 4,5; Generation Park—Field Campaign, Results of Field Campaign, page 5 – 7