Embodied emissions – carbon accounting to save this planet

By accounting for the carbon emissions in everything we create or do, we can make progress towards saving this planet.

Read about:

• Motivation for carbon accounting
• Concrete and cement
• Steel
• Carbon-conscious material selection for pipelines

Motivation for carbon accounting

Seventy-five percent of the infrastructure that will be in place in 2050 does not exist today¹. Getting such a scale of infrastructure development right is critical to the world locking in a low-carbon growth path.

The UN Environment Program supports the development of sustainable and resilient infrastructure. This requires a clear standard to integrate low carbon and resilience criteria into infrastructure projects. Such a standard would lead to benefits for both project developers and financiers. Therefore, public sector institutions would be better able to bridge the infrastructure gap. Further, this would also improve resource efficiency, advance sustainability and improve society’s resilience against stresses.

Taking advantage of the tangible benefits of sustainable and resilient infrastructure is critical for meeting zero carbon commitments and the United Nations SDGs¹.

In the following sections I describe several issues and opportunities.

Carbon accounting in concrete and cement

Cement is a critical component of concrete. The production of cement accounts for 3% of global carbon emissions. Therefore accounting for carbon in construction works is important. Carbon dioxide is a by-product of a chemical process used in the production of clinker – a component of cement. In this reaction, limestone (CaCO₃) is converted to lime (CaO), and produces CO₂ as a by-product. Cement production also produces emissions from energy inputs².

In plain English courtesy of Bill Gates⁴: to make cement, you need calcium. To get calcium, you start with limestone—which contains calcium plus carbon and oxygen—and burn it in a furnace along with some other materials. Given the presence of carbon and oxygen, you can probably see where this is going. After burning the limestone, you end up with the thing you want—calcium for your cement—plus something you don’t want: carbon dioxide. Nobody knows of a way to make cement without going through this process. It’s a chemical reaction—limestone plus heat equals calcium oxide plus carbon dioxide—and there’s no way around it. It’s a one-to-one relationship. Make a tonne of cement, and you’ll get a tonne of carbon dioxide. (In addition, you’ll use a certain amount of energy to extract the limestone, transport it and heat the furnace.)

But – do we really need to use cement in concrete?

Researchers at the School of Engineering at Melbourne’s RMIT⁵ have done some great work. They found that an eco-friendly zero-cement concrete developed with a quaternary blended mix of nano-silica, fly-ash, slag and hydrated lime successfully addresses the mechanical and durability requirements of concrete sewage pipes. This material surpasses ASTM’s minimum strength requirement for sewage pipes. It brings about a significant improvement in withstanding an aggressive acidic environment in sewers. This is evident from the 96% reduction in mass loss due to concrete corrosion, compared to that of the Ordinary Portland Cement concrete. Moreover, the high amorphous silica content present in nano-silica, slag and fly-ash assists in totally consuming the free lime. This free lime interacts with fat, oil and grease to produce ‘fatbergs’ in sewers.

So, perhaps zero-cement concrete has a place in the infrastructure and building sector.

Carbon accounting in steel

As of 2020, steelmaking will be responsible for 7 to 9 percent of all direct fossil fuel greenhouse gas emissions³. Like, concrete, accounting for carbon in steel elements of your projects is important.

Making 1 tonne of steel produces about 1.85 tonnes of carbon dioxide. This is in addition to emissions from the energy used to manufacture the steel. By 2050, the world will be making 2.8 billion tonnes of steel every year, contributing 5 billion tonnes of carbon emissions per year.

Most emissions from making steel result from the industrial process in which coal is used as the source of carbon that removes oxygen from iron ore. This is demonstrated in the following chemical reaction, which occurs in a blast furnace:

Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g)

A group of companies in Sweden are piloting hydrogen-based direct reduced iron (DRI). DRI will be able to take away the root cause of the majority of CO₂ emissions from iron production. Together steelmaker SSAB, miner LKAB and power utility Vattenfall have built a pilot DRI plant which will start trials using “green” hydrogen gas. This will come from an electrolysis facility powered by electricity from the country’s abundant hydropower resources. In contrast to blast furnaces, the only gaseous output from hydrogen ironmaking is water³. Australia has the opportunity to do something similar – see my post Export your carbon emissions.

Carbon-conscious material selection for pipelines

In many areas of construction, there are often multiple materials which an Engineer can chose from for a specific function. This is certainly the case in pipeline material selection. This is highlighted in my own presentation to the Climate Smart Engineering: “New thinking is required for net-zero in the water industry”⁶.

Embodied carbon emissions (as CO₂-equivalent) can vary from 2 tCO₂.eq/t in concrete to nearly 4 tCO₂.eq/t in PVC (Figure 1). (Note that pressure pipes are typically not made from concrete.)

Figure 1: Embodied carbon in several pipeline materials⁶

The materials available for pipes vary in their density and strength properties. Figure 2 considers a nominal 600 mm pressure pipe rated to 16 bar. (Except that while a concrete pressure pipe is used here, it is not rated to 16 bar). For a given conveyance capacity and pressure class, wall thickness can vary significantly for different materials. Therefore, the mass per metre of pipe can be even more variable. The embodied carbon in each of the materials in the chart ranges from 0.26 to 3.7 tonnes CO2-equivalent per tonne (tCO2eq/t) of material. Figure 2 shows that from an embodied carbon perspective, GRP, PVC and reinforced concrete pipes have the least impact on global warming. That is, they have both low embodied carbon and have efficient materials strength and density properties for this type of pipeline.

Figure 2: Embodied carbon in several pipeline material options⁶

Ref 1: Egler, H-P,. Frazao, R., 2016, “Sustainable Infrastructure and Finance – How to Contribute to a Sustainable Future”, UNEP Inquiry/Global Infrastructure Basel Foundation, Inquiry Working Paper 16/09

Ref 2: “Sector by sector: where do global greenhouse gas emissions come from?“, viewed 25/04/2021

Ref 3: “Europe leads the way in the ‘greening’ of steel output”, www.ft.com, retrieved 20/11/2020.

Ref 4: Gates, B., 2021, “How to Avoid a Climate Disaster: The Solutions We Have and the Breakthroughs We Need”, Penguin, 1st Edition

Ref 5: Roychand, R., et al, 2021, “Development of zero cement composite for the protection of concrete sewage pipes from corrosion and fatbergs”, Resources, Conservation and Recycling, Volume 164.

Ref 6: van Winden, M., Window, A., 2021, “New thinking is required for net-zero in the water industry”, Engineers Australia Climate Smart Engineering conference. Download a copy of the paper.