Overview: CO2 counting and rating

To fully decarbonise Portland cement production, will push its energy need from at least 1.35 MWh (currently) to anything up to approaching 8 MWh per tonne.** Hence, as stated by the UNFCCC, for the foreseeable future a high level of Portland cement substitution is likely the only realistic way forward to decarbonise cement production (and hence the embodied carbon in concrete)...

Is awareness growing of the importance of reducing embodied carbon? In many leading OECD countries, yes. The approach can also incorporate regulatory (legislative) measures.

So, first: what does "embodied carbon" mean? It means the “CO2 emissions associated with energy consumption and chemical processes during the extraction, manufacture, transportation, assembly, replacement and deconstruction of construction materials or products" (PDF).

And how are legislators responding? In the EU there is no unifying legal measure requiring low embodied carbon in concrete, despite that since 1989 the EU's over-arching Construction Products Directive (CPD - here) required the protection of the environment – even if the EU waited till 2011 to expressly incorporate the term "greenhouse gasses" into the CPD's successor, Regulation EU 305/2011 (here)! Hence, it is down to EU Member States, of which for example the Netherlands has formed its "Betonakkoord" statutory body (here) to drive down the embodied carbon in concrete. In the U.S. at Federal level and in the U.K., as of 2022 there are no such equivalent measures that pertain to concrete – although in the UK attempts have been made to pass the Carbon Emissions Bill (here), while in U.S. there is state-level law such as California's SB596 (effective Sep. 2021, here). Further, both the U.S. Federal Government (PDF 16.05.23, earlier draft March 2022 version here) and the U.K. Government (here) have passed measures that cover procurement – requiring low carbon commitments in certain procurement applications.

But how is the construction sector itself responding? In several ways, including CO2 counting and CO2-ratings. Cutting the embodied CO2 means that component CO2 measurements must be understood. To do this, look-up data has been developed and also a number of assessment toolkits have been developed. The EPD Registry (here) is a limited searchable online database and by no means represents the totality. One of the most sophisticated is that published by the UK's Institute of Civil Engineering (PDF here). There are several others too including for example, the Netherlands' National Environmental Database (here).

Counting the CO2 costs. Let's take buildings as an example. A framework published by the WBCSD in 2020 has the stated aim of enabling opportunities for stakeholders to, "identify the best emissions-reduction strategies for all parts of the value chain". While the WBCSD framework is deliberately not prescriptive in its form and structure, it introduces a very important metric, expressed as the carbon intensity of the project, as a kgCO2/m2 measure (kilograms CO2 per square meter of floor space), and is, "applicable by all the companies across the life-cycle of buildings" (PDF):

The framework uses the building life-cycle standards defined in the EEA+UK by EN15978:2011, categorising the spectrum of the CO2 emissions from "cradle to grave".

The total amount of CO2 is added up and divided by the area of the project. This is the embodied CO2 of the project.

As "product stage and manufacturing" components, EMC Volcanics can be tallied into categories A1-A3 as "cradle-to-gate" (i.e., ex works) embodied CO2 emissions.

Real prospect of net negative concretes for 95% of the ready mix market's needs. Although not part of the calculations that follow, nonetheless there's also the ability of volcanics (comprising silicates) to naturally capture CO2 and sequester it independently of the usual calcium oxide routes. This effect will occur during the concrete's useful life and also at its end-of-life stage — especially if the volcanic material is crushed to a particle size of less than 100µm before distribution into soil systems (Nature Geoscience, 2022, PDF). Our Climate Perspectives webpage (here) provides further insight for the enhanced CCS delivered by volcanic materials — and how this positively correlates with an increase in substitution levels.

But how might any sense of comparison be visualized? The simple way to do this is to use a visual rating, similar to labels stuck on EU appliances—but in concrete's case, here we use the colour-bands developed by the UK's Institute of Civil Engineering ("I.C.E"), which is now gaining prominence per its Low Carbon Concrete Route-map, the full version published in April 2022 (full version PDF here).

So below, we "rate" a cubic meter of different concretes to see how they compare in categories A1-A3 in the diagram above — but first we take a look at the underlying context...

Concise summary:

These are now exciting times! There is now a positive requirement to seek CO2 mitigation at the earliest stage of construction in most OECD countries, whether by legal measures or voluntary project specifications. No matter the driver, the most fundamental components are environmental product declarations (EPDs). Further below is a table showing examples of measures to introduce CO2 assessments using lifecycle analysis from the report here.

EPDs. ISO 14025 (here) establishes the principles and specifies the procedures needed to develop EPDs. These "Type III" declarations are the most rigorous since they have detailed rules and must be verified by a third party. Since 2001, the EEA+UK has a system of EPDs, flowing from the EU's integrated product Policy (here). Like ISO 14025, these EPDs are a third-party Type III procedure, with the full body of metrics going beyond CO2 metrics, and per EN 15804+A2, incorporating later lifecycle stages beyond A1-A3. However, for EN 15804+A2 compliance, because "cements" are "intermediate" products (i.e. "physically integrated with other products during installation so they cannot be physically separated from them at end of life", plus other factors), an EPD is to be declared only across LCA categories A1 to A3 in the diagram above and—for the purposes here—only CO2 is considered. The U.S. follows essentially the same A1-A3 LCA boundaries for cements.

Making EPDs count. Deriving a mechanism to standardise EPDs is only half the picture. There must also be compliance pressure. For example, in the EEA there is building standard EN15978:2011 and its progeny (e.g. EN 17472:2022) that categorize the various stages across the lifecycle of buildings in the same manner as ISO 14025 (here). This allows for a standardised approach to assess the CO2 impact across a spectrum of discrete areas. Therefore, understanding how the CO2 "price" stacks-up across the various stages of a building's lifecycle-costs, has never been so important and relevant in the industry...

Our ratings below can serve A1-A3 above and will be in the range of < 30kg CO2 per tonne of EMC Volcanics (see diagram below)!

Read more: For general insight, please see the PDF here. For a more detailed insight of the product category rules per EN 15804+A2, please see the PDF here. For U.S. LCA system boundaries, hence covering the LCA requirements for US Federal GSA compliance, see, cement: here; slag cement, here; and concrete: here.

Explaining the Concrete ratings above:

For the reasons stated below, the strength-class chosen for the diagrams above is C25/30. At that strength class, we calculate the CEM I mix at 220 kg CO2 per cu•m. The Construction Material Pyramid (here) rates the lesser stength-class C20/25 at 229 kg CO2. Hence, given the considerations that follow below, we believe the diagrams above serve as a good faith estimates.

The format and the colour-bandings are as suggested by the UK's Institute of Civil Engineering (ICE):

Total cement dose for both ratings is 275 kg of cement per cubic metre of concrete.

The only difference between the two tables are the proportions within the "total cement".

In private correspondence with the UK's Mineral Products Association, classes C20/25 through to C30/37 (respective cylinder/cube compressive strengths) account for ~90-95% of the UK's ready-mix concrete market.

Per EN 206 (Table F1), C25/30 and C30/37 concretes both carry a "minimum cement" need of 280kg per cu•m concrete. C20/25 concrete mixes carry a minimum cement requirement of 260kg per cu•m concrete (PDF here).

275kg/cu•m concrete is the average between those three EN 206 classes.

Total cement at 275kg/cu•m concrete is nevertheless a low cement dosage. Hence, the tables represent a good approximation of the most CO2-favourable rating that can be given to concrete made from purely CEM I cement for 90-95% of the UK ready-mix market.

For CO2, we use the cement industry's own figures then adjusted on account that CEM I is 95% clinker. The starting point is the GNR figure of 842 kg CO2/metric tonne (T) clinker (PDF here), to yield 800kg/T CEM I. For EMC Volcanics, there are no CO2 emissions.

To keep this assimilation simple, and focused solely on the process emissions of making the cement component, we do not account for aggregates in any concrete mix, which in any event carry a relatively negligible carbon footprint according to ICE figures. According to the ICE, the total embodied CO2-equivalent (incl. all GHGs) for aggregates stands at 5.2kg CO2/T of aggregate (PDF here). This same figure probably serves as a good approximation for mining the raw materials needed for EMC Volcanics (which prior to processing are aggregates), but is excluded for negligibility and simplicity here.

For the same reason, we do not include the embodied carbon for shipping raw materials. This is because the comparison focuses only on process emissions. Also, we do not have the corresponding data for individual cement plant operations. This said, in EMC Volcanics case, assuming dry bulk transport from a source in the Aegean to (say) FOB London, then the CO2 measure would compute as ~20kg/T EMC Volcanics, using the 2010 figure of 4g CO2 per kg•tonne across all classes of dry-bulk carriers (PDF here).

For energy calculations, we used the industry's preferred measurement 1350 kWh/T for CEM I (rather than 1,550 kWh/T per I.C.E. figures) and 122 kWh/T for EMC Volcanics.

We do not include the embodied carbon profile of CEM I according to the ICE. The ICE's figure stands at 950kg CO2/T CEM I — rather than the 800kg CO2/T we have used for the sample tables above. Using this higher ICE figure instead, the CO2 rating for CEM I concrete (total cement 275kg/cu•m) increases from 220kg to 261kg/cu•m (Band D). The CO2 rating for EMC Volcanics concrete increases from 66kg to 77kg/cu•m (Band A+).

We do not use the energy profile of CEM I according to the ICE. The ICE's figure stands at 1530 kWh per tonne CEM I — rather than the 1350 kWh figure we have used for the sample tables above. Using this higher ICE figure instead, the energy profile for CEM I concrete (total cement 275kg/cu•m) increases from 372 kWh to 422 kWh per cu•m. The energy profile for EMC Volcanics component remains unchanged, however the overall figure would increase from 135 kWh to 150 kWh per cu•m concrete.

As independent results have shown, by increasing the concrete's total cement dose to 350kg/cu•m, at 70% replacement, EMC Volcanics hit 51.9 MPa in just 7-days (see here). Assuming 100% CEM I concrete could make the same strength at the same 350kg/cu•m cement dose, then using the same background figures used per the tables above:

The CO2 rating for EMC Volcanics concrete would increase from 66kg to 88kg/cu•m (Band A+), with the energy profile increasing from 135 kWh to 174 kWh per cu•m.

The CO2 rating for CEM I concrete would increase from 220kg to 280kg/cu•m (Band "Special"), with the energy profile increasing from 372 kWh to 472 kWh per cu•m.

To fully decarbonise Portland cement (OPC) production, will push its energy need from about 1.5 MWh (currently) to anything up to approaching 8 MWh per tonne.**

>> Click image to view the PDF...

The EU’s "Renovation Wave" needs low embodied-CO2 (see chart above)

Embodied CO2. Until recently, embodied CO2 in buildings has been addressed on the EU level only with voluntary measures. Cities, regions and countries in Europe have also put in place various provisions in the form of certification systems, regulations, standards, and guidelines. Studies suggest that the number of measures addressing embodied CO2 have more than doubled over the last five years (here). However, comprehensive EU-level policy, targeting the whole-life CO2 footprint of buildings (including both embodied and operational CO2), still remains largely missing.

Low embodied CO2 is important not just in new structures. The major CO2-producing aspect of buildings is the energy used to maintain and use them (heating, lighting etc.) during their useful life. To combat this, existing energy systems need to be updated. This is the "Renovation Wave".

The policy landscape is set to change. In the 2020 Renovation Wave strategy, the European Commission has adopted the principle of “lifecycle thinking and circularity” to make buildings “less carbon-intensive over their full life-cycle” (here). The ongoing review provides a significant opportunity for the EU to begin consistently integrating whole-life CO2 in its policy framework. This requires building-level policies to be well-coordinated and aligned with policy actions upstream on raw materials and construction products, as well as at the end-of-life.

The objective. To at least double the rate of annual energy-renovation over the next 30 years, in order to set the entire building stock on a net zero emissions pathway. However, energy efficiency renovations do not simply contribute to reducing operational CO2 emissions; they also increase embodied CO2 by adding new materials and systems into the building. Without accounting for the cumulation of all embodied and operational CO2 attributable to buildings over their entire life, there is a risk of exceeding the remaining carbon budget.

The EU’s buildings sector will only be able to keep on the 2˚C global warming scenario track if the embodied emissions produced by the renovations do not exceed around 125kg CO2 per sq•m...

>> Click image to view the PDF...

** Notes on OPC's energy needs for Green-H2 / CCS:

i.e., to meet the "green" H2 and carbon capture need, on the basis that "1kg of H2 contains 33.33 kWh of usable energy" (here).

In the following analysis we distinguish between Portland cement's calcination as "Phase 1" and sintering as "Phase 2" :

The difference between using hydrogen over a fossil fuel as a combustible is that energy has to be expended to make the hydrogen, which is not required for coal or natural gas. Recall, OPC's calorific requirement and that Phase 2 requires coal or methane to induce sintering. This means CO2 is always produced in Phase 1 (calcination), even if H2 is used as the combustion fuelstock, and will always be an output in Phase 2 (sintering). According to a leading Swedish study, in a "net zero" setting, the Phase 1 energy overhead is 1,500 KWh per tonne (PDF here). This means if green hydrogen was used, 42 kg hydrogen is required for that phase (assuming 100% efficiency in the combustion process).

In the context of those two dynamics, the energy costs of producing 1kg of green H2 is at least 50 kWh per kg H2 (here). A 2019 U.K. Government report rejected hydrogen as a fuel stock for Phase 2 (PDF here). Hence, the stated 8MWh total computes as:

1,500 kWh for the thermals of the OPC processes as they currently stand;

PLUS 2,100 kWh to produce H2 for combustion fuel (for Phase 1) ;

PLUS up to 5,500 kWh for a CO2 capture system (for Phases 1 & 2) — itself also using "green" H2.

All figures stated as on a per-tonne of Portland cement (CEM I) basis.

All told, on the one hand although an energy need of 8,000 kWh/t Portland cement may prove to be an over-estimate, nonetheless the first two above bullet-points, already stand at about 3,500 kWh/t alone, when:

whereas at present the estimate for both Phase 1 and Phase 2 is in the order of 1,350 Kwh / tonne CEM I (OPC), the energy for a "clean" system using a fluidised bed for Phase 1 alone stands at 1,400 kWh / tonne. Therefore, the first bullet-point above is likely an under-estimation in the "net zero" regime per the Swedish study referenced above;

it is clear that "there is no final consensus about the rate of calcination of limestone particles. The huge number of rate equations presented differs considerably and it is obvious that limestone quality and impurities affect the rate, as do heating rate and gaseous environment" (PDF here); and

over 20% of hydrogen is lost from the electrolyser during its production: "for 57,980 kg of hydrogen produced, 11,960kg of hydrogen is lost to the atmosphere because of system conditioning – a loss of 21%" (PDF here) . Even at 100% combustion efficiency this pushes the second bullet point to about 2,500 kWh...

In the above context:

The current energy consumption unit for CO2 removal systems, the "Specific primary energy consumption per unit of CO2 avoided" (SPECCA), sees an average value of ~1,250 kWh/tonne CO2 captured via CCS for gas-fired powerplants, where there is a lot spent energy also carrying the potential to be "re-cycled" for CO2-capture purposes (PDF here).

The EU's own Horizon 2020 CLEANKER project—dedicated to providing a small capacity demo-plant—has at its stated aim the goal of enabling CO2 removal at the SPECCA energy-cost of ~550 kWh/t CO2 (here).

Against these ambitions, the thermal and electricity needs expressed as MWh for all DAC approaches range from ~2MWh/T for low temperature "solid DAC" to ~5.5 MWh for "liquid DAC". See, Hanna, R, Abdulla, A et al., Emergency deployment of direct air capture as a response to the climate crisis (2021) Nat Commun 12, 368 (PDF here). All treatments assume a slew of efficiencies that are unproven and yet to be realised, including capture rates and solvent recycling efficiencies over time and upon scaled use (PDF here).

Indeed, more recently per Qiu, Y., Lamers, P. et al. (2022), Environmental trade-offs of direct air capture technologies in climate change mitigation toward 2100. Nat Commun 13, 3635 (PDF here): "Several DACCS technologies can offset GHG emissions and aid with long-term climate change mitigation efforts, but their net sequestration efficiencies and holistic environmental performance are interdependent with the energy system in which they operate. Merely shifting to low-carbon energy sources for plant operation could lead to environmental trade-offs. These findings are in-line with other. We find that solvent-based DACCS generally has lower impacts than sorbent based DACCS in five out of eight impact categories studied herein. This is contrary to the conclusions of another study, which states sorbent-based DACCS has lower environmental impacts for the impact categories considered therein ...These differences appear to be linked to the study’s optimistic electricity (180 kWh/t CO2) and heat (2.6 GJ/t CO2) consumption assumptions for sorbent-based DACCS. These are less than half of those reported by several other studies and the ones used herein (470–700 kWh/t CO2 for electricity and 5.4–5.8 GJ/t CO2 for heat)."

The International Energy Agency (IEA) total for liquid-DAC stands at ~2KWh per T CO2, but excludes the energy needs for H2 for liquid DAC. See, esp., CCUS in Clean Energy Transitions, IEA, 2020 (PDF here): "Solid-DAC could operate solely on electricity, which could come from renewable power sources. On the other hand, Liquid-DAC will most likely always need a source of heat such as natural gas in order to achieve the high operating temperature needed in the calciner (around 900°C), unless a new way of providing a low-carbon source of heat (which does not currently exist) becomes commercially available. If gas were used to provide the heat (as it is the case nowadays), the associated CO2 emissions would also need to be captured and stored along with the CO2 captured directly from the air to maximise carbon removal."

Therefore, adding-in a modest 20% energy overhead for inefficiencies, it's hard to see how the energy totals can be realistically kept to less than ~4.5 MWh/tonne as the sum total across all three domains — even if thermal recycling from clinker plants can lower the nascent energy need of capture systems.

At 4.5 MWh/t, that would still be over three-times the current energy need...

>> Click image for 2020 academic paper...

Overview: CO2 counting and rating

Concise summary:

EMC Volcanics' LCA Cradle-to-Gate (A1-A3) tally per tonne:

Explaining the Concrete ratings above:

EMC Volcanics' LCA Cradle-to-Gate (A1-A3) tally per tonne:

The EU’s "Renovation Wave" needs low embodied-CO2 (see chart above)

** Notes on OPC's energy needs for Green-H2 / CCS:

How about visiting our resources page?

Overview: CO2 counting and rating

Concise summary:

EMC Volcanics' LCA Cradle-to-Gate (A1-A3) tally per tonne:

Explaining the Concrete ratings above:

EMC Volcanics' LCA Cradle-to-Gate (A1-A3) tally per tonne:

The EU’s "Renovation Wave" needs low embodied-CO2 (see chart above)

** Notes on OPC's energy needs for Green-H2 / CCS:

How about visiting our resources page?

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