Gamechangers in sustainable construction

The built environment creates approximately 40% of CO2 emissions globally, of which 27% comes from building operations and 6% from the building construction industry, according to Architecture 2030. This also means that the construction industry has big opportunities in cutting down emissions, and precast can have a huge impact.

The need for housing, infrastructure, and construction is growing, while carbon emissions need to be cut significantly according to sustainability targets. To make the change, innovations, new technologies, and sustainable raw materials are needed. Precast is one existing technology that can contribute to making a difference. The CO2 footprint of a precast building can be even 25% smaller than that of a concrete building created with traditional methods.

“There are big opportunities in the construction industry to reduce emissions,” states Mats Jungar, CEO at Elematic. “And precast technology can significantly help. For example, with precast solutions, it could be possible to reduce the emission based on cement and steel compared to cast-in-situ. In precast, cement use is cut by one-third per m3 of concrete because of the effective compaction process in the factory and, because steel for precast is prestressed, about 10-15kg less steel per m2 of the floor slab is needed.”

The challenge is that cost is still the main driver. Adopting new technology costs, and few companies are willing to change technology without compensation.

Demand for cement replacements and lower-carbon steel

In precast manufacturing and building, logistics and raw materials such as cement and steel have a big effect on CO2 emission output. Thus, innovations to replace cement and alternatives for more CO2-free steel are sought. Some products and technologies are already on the market, for example not using coal-fired kilns in cement clinker, or using more sustainable, recyclable aggregates. Lower carbon blends like portland-limestone cement (PLC), or ternary blended cements in which by-products from other processes are used, already exist. Yet the transition is slow.

“For steel and cement, the volume is huge, and clean, long-lasting replacement material should be available all over the world. Since everyone is looking for these alternatives, demand for those kinds of materials is higher than availability is. However, based on current standards, I think you can replace cement up to 20%. That could be a good start,” Jungar says.

Mats Jungar, CEO, Elematic

Building methods matter

The carbon footprint of the construction product can be calculated only when the footprint of the production process is known. The process entails emission effects of the energy and raw materials used, and the footprint of manufactured precast elements.

There’s a growing international demand for LEED certification as a framework to help buildings and spaces meet high sustainability standards. According to the US Green Building Council’s annual list of top 10 countries for LEED certification, 5 are from developing countries, with China on top for the second year, followed by India (2nd), Brazil (4th), Mexico (7th), and Philippines making its first appearance in the Top 10 list, representing the growing interests for sustainable buildings in Southeast Asia. One factor in meeting the standards is sustainable building methods.

In the Elematic carbon footprint calculation conducted with Sweco, the results show the difference between cast-in-situ and precast building in 14-storey apartment building in China as an example.

The carbon footprint of the 14-storey apartment building is largest in model when all floors and walls are Cast-in Situ. Smallest carbon footprint is produced when walls are precast and floor slabs are made with hollow core slabs. All calculations made the assumption of the same concrete and rebar: Concrete is calculated with C30/37 (4400/5400 PSI), 10% recycled binders in cement (300 kg/m3/ 18.72 lbs/ft3). Rebar used in calculation is A615, with a density of 7850.0 kg/m3

When looking at the difference in carbon footprint between the three different options, the biggest factor making the footprint smaller is the amount of concrete in the building frame. Exterior walls, internal walls (both load-bearing and non-load-bearing), subfloors, stairs and balcony structures were taken into account in the calculation as prefabricated products.

Research: Construction methodologies and modularity are the determinants of sustainability onsite

Recent research by Wong & Loo: Sustainability implications of using precast concrete in construction: An in-depth project-level analysis spanning two decades analyzed 38 construction projects, their construction methodologies, and sustainability performance in Hong Kong from 1998 to 2022. The research examined whether the level of modularity increased in 20 years, and if modularity has had an impact on social, environmental, and economic sustainability. The research data was collected from construction companies’ projects. The information used for comparison covered the basic project details such as project number and gross floor area and the number of storeys, and facts such as total concrete volume, total prefabrication volume, total cast-in-situ volume, waste volume, total man days, accident rate, project cost, and carbon emissions were used in research evaluation.

The research concluded that construction methodologies and modularity are the determinants of sustainability on site, and that there were positive correlations between the percentage of prefabrication applied onsite and the sustainability attributes. In the research, prefabricated materials, including precast concrete, have shown a significant reduction in construction waste and operational costs. By replacing cast-in-situ concrete with precast, CO2 emissions decrease, and construction wastage is minimized. Improved safety and better building quality are also among the list of prefabricated construction benefits. Less used material and less time on site also mean savings in costs.

The Composite Sustainability Index (CSI), which combines environmental, social, and economic sustainability indices, reflects the positive correlation between construction modularity and sustainability. The higher the percentage of prefabrication, the better the overall CSI. There’s positive coefficiency between construction modularity and overall sustainability

Source: Wong & Loo, 2022. Sustainability implications of using precast concrete in construction: An in-depth project-level analysis spanning two decades. Journal of cleaner production

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