Using less concrete can have multiple benefits in reducing project costs, saving time, improving safety, and shrinking a building’s environmental footprint. Here are seven ways it can be done:
Concrete is one of the major line items for many commercial construction projects, and one that usually contributes substantially to a building’s embodied carbon footprint. Research by Think tank Beyond Zero Emissions (BZE) found multiple ways to reduce the use of carbon-intensive Portland cement, including substitution with novel concrete mixes.
BZE’s Rethinking Cement report also identified tactics for reducing the use of concrete overall. According to the report, designing structures to use concrete more efficiently, utilising high-strength cement, and replacing concrete with timber could reduce overall cement consumption globally by approximately 15% within a decade.
1. Lean design
Queensland-based structural engineer Chris Morrison has been researching ways projects can use lean design principles to reduce the quantity of concrete required in construction.
The core of lean design is engineering design refinement and smart specification of materials and methods. Lean design looks to optimise the building structure and building envelope so that the least amount of materials, time and cost is used while still delivering a structurally sound, fit-for-purpose and durable project.
Techniques used to achieve this include reducing floor slab thickness, minimising large beams and other transfer structures that transfer loads back into the building’s load-bearing verticals, or removing columns through utilising post-tensioning.
“Ask your engineer, is this design as efficient as it can be? How can we make it more efficient?” Morrison says.
Dr Natasha Watson, Senior Structural Engineer, Buro Happold, has written a guide for the Institution of Structural Engineers (IStructE), Lean Design – 10 Things to Do Now. Dr Happold states it is important for engineers to communicate to the project team “the value of the time and fees spent on design development and refinement, with the potential material savings leading to cost and carbon reductions.”
The guide also stresses the value of crystal-clear briefs in terms of the immediate post-completion use for the building. Dr Watson notes that in many cases, designs are based on conventional assumptions about loads, floor plates, and other elements that result in more material use than actually required.
A study conducted by Buro Happold investigated a simple concrete frame with initial redundancy compared to a design without redundancy in the floor slabs. The design without redundancy required an estimated 12% less material, while adding strengthening during detail design only added 3% more material back in. This equates to nearly 10% savings on material costs compared to the design based on assumptions with added redundancy.
2. Choose an unconventional method
Changing the construction method can also have benefits. Using post-tensioning approaches instead of conventional formwork and reinforcing requires less concrete. As an additional benefit, it allows for larger, open floor plates as fewer support columns are needed. There is also a material saving in reducing the number of vertical elements.
Morrison notes that this has implications for the construction program, as post-tensioning requires time to be allocated after the concrete pour. On the other hand, although conventional reinforcing has increased materials cost, a typical floor can be formed and poured in a seven-day cycle.
He says there is another consideration in favour of post-tensioning: material availability. “Reinforcing steel procurement is increasingly difficult and becoming extremely expensive,” he says.
3. Go off-site
Another concrete-saving method is utilising precast concrete elements, including precast construction for walls and columns.
“This puts a project along the path of prefabrication and (off-site) modular approaches,” Morrison says. These have advantages, including making a program less vulnerable to weather and offering improved surface finish quality. Concrete pouring and curing both require the right weather conditions. Prefab, precast, and off-site modular manufacturing are generally under cover in a climate-controlled environment. The increased cost of precast should be balanced against the construction program savings.
4. Use high-strength concrete
Many precast suppliers use high-strength concrete. This type of concrete gives the fabricator better control of the prefabricated final product quality, all while requiring less material to deliver an equivalent structural strength. High-strength concrete is also suitable for architectural applications.
5. Swap concrete for other materials
Engineered timber can replace concrete in many projects and has advantages in terms of program time, safety, and environmental impact. Brock Commons at the University of British Columbia in Canada, for example, was delivered at an extremely rapid pace because of the efficiency of erecting prefabricated engineered timber components.
“The speed of construction with engineered timber is phenomenal,” Morrison says.
There’s another advantage to engineered timber—it is lighter in weight than the equivalent in structural concrete for walls and floors. Therefore, there may be a cost and materials saving in the footings and foundations required to support the building.
Recent research published by the University of Melbourne compared the use of engineered timber for the structure of a mid-rise residential project and the traditional concrete construction approach. It found the timber approach delivered a time saving of almost 50% and an overall project cost saving of 10% compared to the conventional concrete construction method.
Another methodology that is starting to get attention is the use of steel-timber hybrid floor and wall cassettes. Morrison says this approach has been proven on multiple projects in the US, Europe, UK and Canada. The use of steel in combination with engineered timbers, such as laminated veneer lumber (LVL), glue-laminated timber (GLT), and cross-laminated-timber (CLT), means the structural design can take advantage of the strength of steel to reduce the size of key structural members while still giving the project the time savings and safety benefits of timber pre-fab.
6. Stronger design collaboration
Achieving the most efficient design means ensuring the delivery pathway has sufficient collaboration at the front end. It can be facilitated by models such as early Contractor Involvement (ECI).
Morrison notes that traditional lump-sum contracting can be more challenging, as the geometry of the project is often “locked-in” at the point the client goes out to tender. BIM can help address these limitations, as the process of developing and collaborating on the BIM model can allow opportunities for refining design at the least-cost, lowest-risk stage of the project delivery.
Another approach builders can use is to have engineering designs peer-reviewed, Morrison says. This is not currently a legal requirement for most projects. However, the small outlay in consulting fees for an engineering design peer review can deliver significant cost savings in design optimisation.
It also ensures the design is “sense-checked” for buildability, safety and compliance, as well as providing an additional level of quality control. The Opal Tower investigation found, for example, that there were inadequacies in the project engineering design. Peer review may have found those issues before work commenced, reducing the level of reputational damage and costly legal fees suffered by Opal’s builder and developer.
7. Utilise technology
Morrison says that moving into 3D modelling for design rather than using 2D drawings allows the project team to more easily identify opportunities to optimise the design.
“Manufacturers have been using 3D design for decades,” he says.
It is also easier to see what can be prefabricated when using a 3D model. Morrison notes that the need for having shop drawings produced based on the architectural plans is a potential barrier to projects utilising prefab. However, with 3D modelling, this process is streamlined as the design is already digitised and more compatible with manufacturing technologies, such as CAD.
A 3D model also helps the project team fine-tune tolerances and control and track the quality of design and delivery more effectively.
“The efficiency you can achieve with some pretty simple technology makes people’s lives easier [on projects],” Morrison says. “And the end result is better quality.”