GHG quantification

General GHG quantification rules can be found in the Riverse Standard Rules.

Calculations of GHG emissions for the baseline and project scenarios shall follow a robust, recognized method and good practice guidance. The overall methodological approach is a comparative life cycle assessment (LCA) at the project-scale, based on .

Mineral carbonation projects may be eligible for removal and avoidance Riverse Carbon Credits.

Avoidance RCCs from fossil or calcination CO₂ storage are calculated using the same approach as for removals biogenic and atmospheric CO₂, and are simply assigned a different credit label (avoidance instead of removal).

Avoidance RCCs from reduced cement use are calculated and issued according to a separate accounting mechanism, described below. This conservative approach results in double counting the project's induced emissions, and avoids the need for allocation of emissions/removals.

GHG quantification shall be completed for each reporting period. The duration of the reporting period is chosen by the Project Developer and may be either each carbonation batch, each calendar year, another duration shorter than 1 year, or a maximum of 18 months.

Functional unit

Two different functional units are used:

• 1 tonne of carbonated material sold (e.g. 1 tonne of carbonated concrete, 1 tonne of carbonated aggregate...)

• 1 tonne of captured CO₂

Credits are issued on the basis of carbonated material sale, so this may be considered the main functional unit. Captured CO₂ is used as a secondary functional unit for comparability across CDR technologies.

System boundary

The project system boundary shall include only the activities that are additional to the business as usual (BAU) scenario.

The baseline scenario system boundary shall include the processes that would have occurred in the absence of the project.

For example,

• if the project performs direct carbonation of fresh concrete during hydration, the project boundary shall not include the upstream emissions from cement production.

• if the project captures biogenic CO₂ flue gas from an anaerobic digestion site, the project boundary shall not include the emissions from anaerobic digestion, or the embodied emissions from the digester, because these would have occurred anyway. The project boundary shall include the embodied emissions from the CO₂ capture machinery added to the digester, because this was installed and used specifically for the purpose of carbon capture.

• if the project uses a portion of a concrete facility's flue gas— diverting the CO₂ stream, using part for carbonation and returning the unused portion to the main flue gas stream to be emitted— the project boundary shall not include the emission of unused CO₂ that returns to the flue gas stream.

A summary of the calculation approach is presented below, and detailed descriptions and equations for calculating GHGs are in the respective Project and Baseline scenario sections.

Carbon removal from carbonation

For removals and avoidance from carbonation,

• The project system boundary shall include at least the following elements where relevant and additional (i.e. beyond BAU):

  • production of any non-waste inputs and additives

  • transport of inputs to the project site (e.g. CO₂, recycled concrete, alkaline feedstock...)

  • onsite energy use (electricity, fuels, heat...) related to e.g. preparation of feedstock, and the carbonation process

  • fugitive CO₂ leaks during CO₂ transport

  • carbon storage

• The baseline system boundary shall include:

  • any removals that would have occurred naturally from carbonation of the alkaline feedstock, and/or

  • any use-phase carbonation benefits that would have naturally occurred at greater rates had the project not altered the material or process.

Removals and avoidance from carbonation are calculated using the following high-level equations, detailed in their respective sections below.

Calculations - Removals and avoidance from carbonation

$\textbf{(Eq.1)}\ S_{net}= \Sigma{S}_{project} - \Sigma{S}_{baseline} - \Sigma{E}_{project}$

where,

• $S_{net}$ represents the net carbon storage from the project during the reporting period, in tonnes of CO$_2$eq. This storage may be counted as removals or avoidance, depending on the type of CO₂ stored, as shown in the following equations.

• $S_{project}$ represents the project's gross GHG removals/storage from carbonation, in tonnes of CO$_2$eq, calculated in Eq. 15 or 19.

• $S_{baseline}$ represents any baseline GHG removals from carbonation of alkaline minerals in their alternative use, representing permanent storage that would have occurred anyway in the absence of the project, in tonnes of CO$_2$eq, calculated in Eq. 7.

• $E_{project}$ represents the project's induced GHG emissions, in tonnes of CO$_2$eq, calculated in Eq. 8.

$\textbf{(Eq.2)}\ Removal\ RCCs = S_{net}* F_{bio,\ atm}$

Where,

• $Removal\ RCCs$ represents the amount of removal Riverse Carbon Credits to be issued during the reporting period

• $S_{net}$ was calculated in Eq. 1.

• $F_{bio,\ atm}$ represents the fraction of CO₂ that is biogenic or atmospheric, as described in the Allocation of captured carbon: removals vs. avoidance section.

$\textbf{(Eq.3)}\ Avoidance\ RCCs = S_{net}* (1-F_{bio,\ atm})$

Where,

• $Avoidance\ RCCs$ represents the amount of avoidance Riverse Carbon Credits to be issued during the reporting period

• $S_{net}$ was calculated in Eq. 1.

• $F_{bio,\ atm}$ represents the fraction of CO₂ that is biogenic or atmospheric.

Reduced cement

For avoided GHGs from reduced cement,

• The project system boundary shall include emissions from the manufacture of the actual quantity of cement used in the concrete mix designs in which the carbonated materials are used.

• The baseline system boundary shall include emissions from the manufacture of the quantity of cement that would have been required to achieve the same functional performance using conventional materials or methods, for the given concrete mix design. This will likely represent a larger amount than in the project scenario, since carbonation projects may enhance binder strength and reduce the total cement required.

Avoided GHGs from reduced cement are calculated using the equation below.

These calculations do not account for removals, and do not allow for allocation of induced emissions between the carbonation removal and the avoidance/reduced product. Induced emissions are effectively double counted between carbonation removal and the avoidance/reduced product credits to be conservative.

Calculations - Avoidance from reduced cement

$\textbf{(Eq.4)}\ E_{project,\ cement} = E_{project}+ (A_{cement,\ project} * EF_{cement})$

where,

• $E_{project, concrete}$ represents the total project scenario emissions from manufacturing and using cement for the reporting period, in tonnes of CO$_2$eq. It is composed of normal cement manufacturing emissions, upstream of the project activity and which were excluded from the removal calculations, plus the additional induced emissions due to the project carbonation activity.

• $E_{project}$ represents the induced GHG emissions from the project during the verification period, in tonnes of CO$_2$eq, calculated in Eq. X.

• $A_{cement,\ project}$ represents the amount of cement sold by the project in the reporting period, in tonnes of cement.

• $EF_{cement}$ represents the emission factor for cement. Possible sources for this emission factor are described in the Baseline scenario section, in tonnes of CO$_2$eq per tonne of cement.

$\textbf{(Eq.5)}\ E_{baseline, cement} = A_{cement, baseline}*EF_{cement}$

where,

• $E_{baseline,\ cement}$ represents the baseline scenario emissions from manufacturing and using a functionally equivalent amount of cement for the reporting period, in tonnes of CO$_2$eq.

• $A_{cement,\ baseline}$ represents the amount of cement needed in the baseline scenario to fulfill the same function as the project-manufactured cement. This is expected to be higher than the amount needed in the project scenario, thanks to the project's improvements.

• $EF_{cement}$ represents the emission factor for cement. Possible sources for this emission factor are described in the Baseline scenario section, in tonnes of CO$_2$eq per tonne of cement.

$\textbf{(Eq.6)}\ E_{avoided} = E_{baseline,\ cement} - E_{project,\ cement}$

where,

• $E_{avoided}$ represents the avoided GHG emissions from the project scenario, in tonnes of CO$_2$eq.

• $E_{baseline,\ cement}$ was calculated in Equation 6.

• $E_{project,\ cement}$ was calculated in Equation 5.

Allocation

Allocation of captured carbon: removals vs. avoidance

Credits can be issued from carbonation processes that result in both

• /removals, from using biogenic and atmospheric (e.g. DAC) CO₂, and

• /avoidance, from using fossil and calcination CO₂.

The same calculation method applies to all CO₂ sources, they are simply assigned different credit types upon issuance (i.e. removal vs avoidance, see Eq. 2 and 3).

If the CO₂ stream used in the carbonation batch is 100% biogenic/atmospheric or 100% fossil/calcination, no allocation is needed. All carbon storage and project induced emissions are fully attributed to removal or avoidance, respectively.

If the CO₂ stream is mixed, Project Developers must determine the proportion of biogenic/atmospheric vs. fossil/calcination carbon, according to Article 39 of the (even for non-EU based projects), summarized here for informative purposes only:

• conservatively assume all CO₂ is fossil/calcination CO₂, or

• use mass balance of material inputs by type, or

• use measurement method, e.g. C14 testing, or

• use other standards and analytical methods, subject to approval by Riverse and the VVB.

The proportion of CO₂ types shall be used to allocate the following:

• Carbon storage accounting: CO₂ flows shall assume a proportional repartition of the two CO₂ types in the different CO₂ fates (e.g. successfully carbonated CO₂, inflow and outflow CO₂, unsuccessfully carbonated CO₂ left in pore space...).

• Project induced emissions: project emissions shall be proportionally assigned to removal or avoidance based on the share of CO₂ input from each source.

For example, if a project

• has a mixed CO₂ stream of 50% fossil CO₂ and 50% biogenic CO₂

• measures total gross carbon storage of 100 tCO₂eq

• calculates project induced emissions of 10 tCO₂eq, plus 1 tonne of fugitive CO₂ leaked from transport

Gross carbon storage repartitioned proportionally:

• 50 tCO₂eq from fossil CO₂

• 50 tCO₂eq from biogenic CO₂

Project induced emissions repartitioned proportionally:

• 5 tCO₂eq from fossil CO₂

• 5 tCO₂eq from biogenic CO₂

Fugitive CO₂ leaked repartitioned proportionally:

• 0.5 tonnes fossil CO₂ leaked, counted as 0.5 tCO₂eq (fossil CO₂ has a GWP of 1)

• 0.5 tonnes biogenic CO₂ leaked, counted as 0 tCO₂eq (biogenic CO₂ has a GWP of 0)

This would result in

• Avoidance credits from fossil CO₂ carbonation = $50-5-0.5 = 44.5\ tCO_2eq$

• Removal credits from biogenic CO₂ carbonation = $50-5-0 = 45.0\ tCO_2eq$

Allocation between existing activities and baseline activities

When a process is shared between the project scope and BAU activities (e.g. total electricity use at a site performing both cement manufacturing and carbonation), only the portion attributable to the project and additional to the baseline should be included. This allocation should follow one of the approaches below:

• Subdivide the system and isolate measurements to collect only input/output data for the project scope (e.g. install electricity meters at the entry point of the carbonation process).

• If subdivision is not feasible, allocate shared processes based on a relevant underlying characteristic of the shared systems (e.g. by mass for jointly transported materials, by economic value for co-products with distinct markets...).

This allocation shall be applied at the data collection stage. Project Developers shall do this allocation outside of the GHG quantification equations, and submit allocated data into the removal and avoidance calculations (with justification/proof of work for allocation).

Assumptions

1. By default, future uses (beyond the product's first life) or end-of-life treatment of the carbonated material will not lead to reversals. This assumes no significant changes in environmental conditions (e.g. pH or fire exposure) that would cause CO₂ release.

2. Carbonation during the use phase of concrete is considered to be the same in both the project and baseline scenarios.

3. A standard transport distance of 50 km is assumed for concrete and/or carbonated solid materials delivery. Transport emissions for distances below this threshold are considered equivalent between the baseline and project scenarios and are excluded. Transport emissions for distances above this threshold shall be included.

4. Baseline carbonation of the alkaline feedstock for carbonation of solid materials is conservatively assumed by default to offset 2% of the CO₂ removals achieved by the project.

5. For directly carbonated cement (e.g. during curing or hydration/mixing), it is assumed that either no significant amount of unreacted CO₂ remains trapped in the pore space, or that any trapped CO₂ will eventually react fully with the cement matrix.

6. All carbonated material from the same carbonation batch has similar characteristics.

Baseline scenario

The baseline scenario is twofold, and is detailed in following sections:

• Removals from carbonation that would have occurred anyway, from alternative feedstock use (for carbonation of solid materials such as SCMs and aggregates) and in use-stage concrete carbonation (for all technology types).

• Avoidance from reduced cement shall be considered for projects issuing avoidance credits from reduced cement use, thanks to improved binder strength.

The baseline scenario structure remains valid for the entire crediting period but may be significantly revised earlier if:

• The Project Developer notifies Riverse of a substantial change in project operations or baseline conditions, and/or

• The methodology is revised, affecting the baseline scenario.

The specific values within the baseline scenario will be updated annually, using project data to accurately reflect the equivalent of the project’s annual operations.

Baseline CO₂ stored

BAU carbon removal from natural carbonation of alkaline feedstock and from concrete carbonation during the use-phase shall be considered in the baseline scenario, as detailed below.

Alkaline feedstock

Note that this section does not apply to carbonation curing or carbonation during mixing/hydration project.

The alkaline feedstock used by carbonation projects may naturally undergo carbonation upon exposure to atmospheric CO₂. The extent of carbonation depends on the

• alternative fate of alkaline feedstock

• exposure to CO₂

• mineralogy

• particle size

Project Developers shall either

• estimate baseline removals in alkaline feedstock over 1000 years using justification and description of common practices for managing the alkaline material, carbonation models, scientific literature, or , or

• opt for a default assumed carbon removal rate of of alkaline feedstock in the baseline scenario.

Concrete use phase

Cement in concrete naturally undergoes carbonation throughout its use phase. By default, this carbonation is excluded from the system boundary, based on the assumption that the project and baseline scenarios will have the same use-phase carbonation.

If the project technology only accelerates the rate of carbonation, rather than causing additional net carbonation gains, then the accelerated carbonation that would have occurred anyway (albeit at a slower pace) shall not be credited.

Project Developers shall demonstrate that the carbonation caused by the project would not have occurred under BAU conditions. In some cases, this may be justified based on the underlying principles of their technology. In other cases, this may require modeling or estimates of the baseline carbonation that would have occurred during the first use phase of the cement (assumed to be a 60 year period).

If a first screening assessment based on conservative estimates demonstrates combined baseline removals (sum of alkaline feedstock and concrete use phase) are <1% of the net project removals, then baseline removals may be set to 1%, and the Project Developer does not need to collect more precise baseline removal information. Otherwise, the Project Developer may choose to collect/model baseline removals in detail in order to prove and apply a lower baseline removal rate.

Calculations: Baseline CO₂ stored

$\textbf{(Eq.7)}\ S_{baseline}= S_{Alk\ feedstock}+S_{use\ phase\ carbonation}$

Where

• $S_{baseline}$ was described in Eq 1

• $S_{Alk\ feedstock}$ represents baseline removals from natural carbonation of alkaline feedstock, corresponding to the amount of feedstock used by the project in the reporting period, in tCO₂eq.

• $S_{use\ phase\ carbonation}$ represents baseline removals from carbonation of concrete during the use-phase that are larger than the use-phase carbonation for the project material, corresponding to the amount of concrete produced by the project in the reporting period, in tCO₂eq.

Baseline induced emissions

Baseline induced emissions are only considered for avoidance credits from avoided cement production. In this case, baseline induced emissions shall include the emissions from producing an equivalent amount of cement to serve the same purpose (compressive strength, lifetime...) as the cement produced in the project scenario.

Emissions are calculated based on the quantity and emission intensity of cement used in the project scenario compared to the baseline. While the emission factor of cement production remains the same- since carbonation projects typically do not alter upstream or downstream cement/concrete production- the total amount of cement needed in the concrete design mix may differ. This is because the project may create a stronger binder, requiring less cement than conventional practices.

Quantity of cement

To determine the quantity of cement avoided, Project Developers shall provide the cement usage ratio between the project and baseline scenarios for each end use of the carbonated material.

This shall be proven using the stated concrete mix designs used by the client, demonstrating a lower cement use than otherwise used, or similar project-specific estimates (i.e. not default global replacement rates).

Emission factor of cement

Cement emission factors shall be taken from the following sources, in decreasing order of preference:

• project-specific sources provided by the client using project material, and reducing their conventional/alternative cement source (e.g. EPDs), or

• low-carbon cement thresholds (e.g. provided by the Global Cement and Concrete Association Low Carbon Rating)

• the Ecoinvent database, presented in Appendix 1, with a 20% deduction applied for conservativeness.

A different emission factor may be submitted by the Project Developer, and approved by the Riverse Certification team and the VVB. Any emission factor must meet the data requirements outlined in the Riverse Standard Rules, and come from traceable, transparent, unbiased, and reputable sources. A conservative uncertainty deduction shall be applied if the value is not project-specific.

Calculations from this life cycle stage are presented in Eq. 4-7.

Project scenario

An example of a typical project design and system boundary is shown in Figure 1. Each life cycle stage is detailed in the following sections.

Figure 1 System diagram showing what is included and excluded in GHG quantification of the project scenario. Life cycle stages are color coded, and correspond to the sections below, where each stage is described in detail. The dashed line represents the system boundary, showing which processes' emissions are included in the GHG quantification, and which are excluded.

Calculations: Total project induced emissions

$\textbf{(Eq. 8)}\ E_{project}= E_{CO_2\ capture} +E_{feedstock}+E_{carbonation}$

Where,

• $E_{project}$ was described in Eq. 1.

• $E_{CO_2\ capture}$ is calculated in Eq. 9.

• $E_{feedstock}$ is calculated in Eq. 13.

• $E_{carbonation}$ is calculated in Eq. 14.

Project CO₂ capture

This stage includes process emissions from the CO₂ capture facility, CO₂ transport emissions, and CO₂ leakage during transport.

CO₂ capture

Induced emissions from the CO₂ capture process shall only include emissions/activities that would not have occurred in the baseline.

Typically, CO₂ capture is done on industrial sites that are already operating and emitting CO₂. In this case, emissions from the industrial site operations and embodied emissions shall not be counted towards the CO₂ capture. Furthermore, the CO₂ itself is considered a waste product, and according to the waste cutoff LCA principle, is modeled as entering the project system boundary with no environmental burden/emissions.

Processes that may be considered in this stage may include but are not limited to:

• additional infrastructure/machinery/instruments that are required for carbon capture (note that only substantial pieces that contribute to at least 1% of the total project life cycle emissions need to be included. This can be assessed with a screening LCA using estimates, and if deemed substantial, more precise material data shall be provided).

• additional energy use required for carbon capture: Project Developers shall isolate the amount of energy used at the site that is only for carbon capture, that is not related to the site's BAU activities.

• energy or material use from purification and processing of CO₂ streams, for example through chemical (e.g. amine-based absorption) or physical treatment (cryogenic separation or membrane separation)

For infrastructure calculations and emission factors, see the Infrastructure and machinery module of the BiCRS methodology. For energy use calculations and emission factors, see the Processing and energy use module of the BiCRS methodology.

CO₂ transport

For transport emissions, Project Developers shall follow the Transport module in the BiCRS methodology.

CO₂ leakage during transport

Leakage of CO₂ during transport shall only be considered for projects using fossil or calcination CO₂. Leakage of biogenic or DAC CO₂ would have a of 0 and have no impact, so are only reported for mass-balance calculations.

The following two methods are recommended for measuring and reporting CO₂ leakage during transport, but other methods suggested by the Project Developer may be considered on a case by case basis:

• Difference in CO₂ shipped/received: Project Developers record the amount of CO₂ leaving the capture site, and the amount entering the carbonation process. Any difference is assumed to be CO₂ leaked during transport, and counted as project induced emissions.

• Literature-based leakage rates: Project Developers may propose conservative leakage rates from scientific literature, if they are well documented, from reputable sources, and are representative of the project-specific technology.

Calculations: Project CO₂ capture

$\textbf{(Eq. 9)}\ E_{CO_2\ capture}=E_{CO_2\ capture\ process}+E_{CO_2\ capture\ infra}+E_{CO_2\ transport}+E_{CO_2\ transport\ leakage}$

Where

• $E_{CO_2\ capture}$ represents the total project emissions from the CO₂ capture life cycle stage, in tCO₂eq.

• $E_{CO_2\ capture\ process}$ represents the emissions from any additional energy or consumable materials used in the CO₂ capture process, calculated using the Processing and energy use module, in tCO₂eq.

• $E_{CO_2\ capture\ infra}$ represents the emissions from any additional infrastructure or machinery used for CO₂ capture, calculated using the Infrastructure and machinery module, in tCO₂eq.

• $E_{CO_2\ transport}$ represents the emissions from transporting CO₂ from the capture site to the carbonation site, calculated using the Transport module, in tCO₂eq.

• $E_{CO_2\ transport\ leakage}$ represents the emissions from fugitive CO₂ leaked during CO₂ transport, in tCO₂eq. It may be calculated according to Eq. 10, or using other secondary sources.

Leakage of CO₂ from transport may be calculated using any combination of Eq 10, 11, 12, or a different approach.

$\textbf{(Eq. 10)}\ E_{CO_2\ transport\ leakage}= Purchased_{CO_2}-Inflow_{CO_2}$

Where,

• $E_{CO_2\ transport\ leakage}$ was described in Eq. 9.

• $Purchased_{CO_2}$ represents the total mass of CO₂ leaving the CO₂ capture site and destined for the carbonation site throughout the reporting period, in tCO₂eq.

• $Inflow_{CO_2}$ represents the mass of gaseous CO₂ entering the carbonation process (e.g. entering a reactor) throughout the reporting period, in tCO₂eq, calculated in Eq. 20.

$\textbf{(Eq. 11)}\ E_{CO_2\ transport\ leakage}= Purchased_{CO_2} \times R_{leakage}$

Where,

• $E_{CO_2\ transport\ leakage}$ was described in Eq. 9.

• $Purchased_{CO_2}$ was described in Eq. 10.

• $R_{leakage}$ represents the default leakage rate of the given transport mode (e.g. truck, pipeline...), for all transport modes used in project operations, in tCO₂ lost/tCO₂, or as a fraction.

$\textbf{(Eq. 12)}\ E_{CO_2\ transport\ leakage}= T_{CO_2} \times R_{leakage,\ T}$

Where,

• $E_{CO_2\ transport\ leakage}$ was described in Eq. 9.

• $T_{CO_2}$ represents the truck or ship transport segment considered, in tCO₂*km.

• $R_{leakage}$ represents the default leakage rate of the given transport mode (e.g. truck, pipeline...), in tCO₂ lost/tCO₂*km.

Project feedstock provisioning

If the feedstock is a waste, it is considered to enter the project system boundary with no emissions. The waste material enters the system boundary upon the transport step where it is diverted from its BAU use and sent to the project site, or the first non-BAU treatment step, whichever comes first.

For example

• if recycled concrete is used, it incurs no emissions from concrete production, use and demolition (all processes that would have occurred anyway). If the recycled concrete is transported from the demolition site to the project site, where it is ground into a fine powder, then the project induced emissions shall consider that transport step and the energy use from grinding, but not the emissions from demolition.

• if the alkaline feedstock is ordinary Portland cement (OPC) for direct carbonation of cement during mixing, then the induced emissions for the project shall include any processing steps specifically to prepare the OPC for carbonation, beyond what would have happened in the absence of the project. Production of OPC is excluded.

If a feedstock is produced for the sole purpose of carbonation, then its entire production emissions shall be counted towards project induced emissions. This includes, for example, mining of olivine rocks.

If a feedstock is a valuable co-product of a process with a different main product, but where the co-product is typically sold and used, then a share of the production emissions shall be allocated to the co-product, preferably based on economic allocation. This includes, for example, steel slag.

Processes that may be considered in this stage may include but are not limited to:

• production of non-waste feedstocks

• feedstock preparation/processing to increase mineral purity (e.g. magnetic separation of iron), to increase carbonation rates

• feedstock preparation/processing to increase surface area (e.g. grinding), to increase carbonation rates

• heating, drying, wetting, to obtain optimal feedstock moisture content and diffusivity

For calculations and emission factors used in this stage, see the Processing and energy use module and the Transport module of the BiCRS methodology.

Calculations: Project feedstock provisioning

$\textbf{(Eq. 13)}\ E_{feedstock}=E_{feedstock\ production}+E_{feedstock\ processing}+E_{feedstock\ transport}$

Where

• $E_{feedstock}$ represents the total project emissions from feedstock provisioning life cycle stage, in tCO₂eq.

• $E_{feedstock\ production}$ represents the emissions from feedstock production, in tCO₂eq. This may be zero if the feedstock is a waste, may share emissions allocated between a coproduct, or may fully assume emissions if it is produced for the purpose of carbonation.

• $E_{feedstock\ processing}$ represents the emissions from any additional energy or consumable materials used in feedstock processing (e.g. griding, heating...), calculated using the Processing and energy use module, in tCO₂eq.

• $E_{feedstock\ transport}$ represents the emissions from transporting feedstock from its production site to the carbonation site, calculated using the Transport module, in tCO₂eq.

Project carbonation

This stage includes induced emissions from carbonation energy use, input and machinery use, and transport/delivery of the carbonated material. All induced emissions from the carbonation process shall be included and counted towards the project GHG quantification, because they are all by definition part of the carbonation project and additional to baseline conditions.

Energy and input use

This shall include: energy use (electricity, heat and fuel) for heating, maintaining temperature, and compression/maintaining pressure. To be measured directly for each reported period using e.g. energy meters, measured for the whole site and allocated to the project, or calculated using machinery power requirements and operation hours.

Depending on the project-specific technology, this may also include but is not limited to:

• additives to increase dissolution rates (where dissolution of metal ions is the precursor to carbonation)

• water

For energy use calculations and emission factors, see the Processing and energy use module of the BiCRS methodology.

Infrastructure/machinery

All significant embodied emissions from machinery and infrastructure directly related to the carbonation process shall be included. For infrastructure calculations and emission factors, see the Infrastructure and machinery module of the BiCRS methodology.

Transport/delivery

Transport of the final product shall be included for any transport beyond 50 km, which is to be the standard transport distance for conventional concrete. This is included because it cannot necessarily be assumed that the project and baseline transport is the same. Indeed, concrete is a commodity with relatively localized markets, whereas the project's innovative product may have buyers that are outside the typically radius of basic concrete transport.

For calculations and emission factors, see the Transport module in the BiCRS methodology.

Calculations: Project carbonation

$\textbf{(Eq.14)}\ E_{carbonation}=E_{carbonation\ energy,\ input}+E_{carbonation\ infra}+E_{material\ transport}$

Where

• $E_{carbonation}$ represents the total project emissions from the onsite carbonation life cycle stage, in tCO₂eq.

• $E_{carbonation\ \ energy,\ input}$ represents the emissions from energy or consumable inputs used in the carbonation process, calculated using the Processing and energy use module, in tCO₂eq.

• $E_{carbonation\ infra}$ represents the emissions from infrastructure or machinery used for carbonation (i.e. reactors), calculated using the Infrastructure and machinery module, in tCO₂eq.

• $E_{material\ transport}$ represents the emissions from transporting the carbonated material from its production site to the user, calculated using the Transport module, in tCO₂eq. It is only considered if the transport distance is greater than 50 km.

Project CO₂ stored

Carbon storage shall be determined using project-specific measurements and CO₂ mass balance calculations, using either:

1. Solid sample: High-accuracy, periodic, solid-sample measurements of carbon in the carbonated material compared to a baseline material using or , with a cross-check measurement, or

2. Gas inflow-outflow: continuous measurements of CO₂ gas inflow minus outflow measurements.

Solid sample measurements are preferred and should be used when possible, because they are the most direct measurement of carbonation. All measurements shall follow an internationally recognized norm or standard (e.g. EN, ISO, ASTM). Cross verification of carbon storage measurements with another is encouraged but not required.

Solid sample

All solid sample TGA or TCA measurements shall be conducted on:

• A carbonated sample from the project, and

• A non-carbonated control sample of the same material.

The difference in CO₂ content between the two shall be used to quantify the amount of CO₂ removed by the project activity.

To ensure consistency:

• Project and control samples must be collected at the same time interval after exiting the reactor (e.g. 24 hours, 1 week, 1 month).

• Both samples must be stored under identical conditions between carbonation and measurement to avoid variations due to natural ambient carbonation.

All measurements shall be performed on . Refer to the Sampling section for detailed procedures on sampling approach, frequency, and traceability.

Calculations: Project CO₂ storage, solid-sample

$\textbf{(Eq. 15)}\ S_{project}= \Delta C*A_{P,\ material}$

Where,

• $S_{project}$ represents total carbon storage from the project in the reporting period, in tCO₂eq.

• $\Delta C$ represents the increase in CO₂ storage in the carbonated material vs the baseline material, as an absolute increase of tCO₂eq/t carbonated material.

• $A_{P,\ material}$ represents the amount of carbonated material produced by the project in the reporting period, in tonnes of dry material.

$\textbf{(Eq. 16)}\ \Delta C=C_{project}-C_{control}$

Where,

• $\Delta C$ was described in Eq. 15.

• $C_{project}$ represents the concentration of CO₂ equivalent in the carbonated project material, derived from measured carbonate content using either TGA or TCA, in tCO₂eq/t of dry material. It is calculated in Eq 17 for TGA and Eq. 18 for TCA.

• $C_{control}$ represents the concentration of CO₂ equivalent in the non-carbonated control material, derived from measured carbonate content using either TGA or TCA, in tCO₂eq/t of dry material. It is calculated in Eq 17 for TGA and Eq. 18 for TCA.

$\textbf{(Eq. 17)}\ C_{project,\ TGA} = \%CO_{2\, loss} \div100$

Where

• $C_{project,\ TGA}$ represents the concentration of CO₂ equivalent in the carbonated project material, tCO₂eq/t of dry material, derived from measured carbonate content using TGA. The same equation shall be used for $C_{control}$.

• $\%CO_{2\, loss}$ represents the mass loss percentage of CO₂ measured using TGA at 600–800 °C, in % mass loss or tCO₂ lost/100 t dry material. Divided by 100 to convert to t/t.

$\textbf{(Eq. 18)}\ C_{project,\ TCA} = \%C_{mass} \div 100 \times C\ to\ CO_2$

Where

• $C_{project,\ TCA}$ represents the concentration of CO₂ equivalent in the carbonated project material, tCO₂eq/t of dry material, derived from measured carbonate content using TCA. The same equation shall be used for $C_{control}$.

• $\%C_{mass}$ represents the measured inorganic or total carbon content of the material, in % mass of carbon or t C/100 t dry material. Divided by 100 to convert to t/t.

• $C\ to\ CO_2$ represents the molecular weight conversion factor between carbon and CO₂, and equals 3.67.

Gas inflow outflow

Gas inflow-outflow measurements shall be taken continuously (at least 1x per minute) and summarized and reported daily.

Gas measurements shall use a calibrated flow metering with ±1.0% accuracy or better. The Project Developers shall provide equipment calibration certificates and QA/QC procedures.

Any projects using:

1. Technology type: carbonated solid materials to add to e.g. concrete or asphalt, and

2. Measurement type: gas inflow-outflow,

shall account for unreacted CO₂ trapped in pore space of the carbonated material. This shall be calculated using conversions and subtracted from carbon storage measurements, according to Eq. X.

Calculations: Project CO₂ storage, gas inflow-outflow

$\textbf{(Eq. 19)}\ S_{project}= \sum (Inflow_{CO_2}- Outflow_{CO_2}- Pore_{CO_2})$

Where,

• $S_{project}$ represents total carbon storage from the project, summed over the reporting period, in tCO₂eq.

• $Inflow_{CO_2}$ represents the daily recorded mass of gaseous CO₂ entering the carbonation process (e.g. entering a reactor), in tCO₂eq, calculated in Eq. 20.

• $Outflow_{CO_2}$ represents the daily recorded mass of gaseous CO₂ exiting the carbonation process (e.g. exiting a reactor), in tCO₂eq, calculated in Eq. 20.

• $Pore_{CO_2}$ represents the unreacted CO₂ stuck in pore space of the carbonated material, in tCO₂eq, calculated in Eq. 21. It shall only be included for projects that carbonate solid materials (e.g. carbonating SCMs to add to concrete).

$\textbf{(Eq. 20)}\ Flow_{CO_2,\ i}= V_{CO_2,\ i}*C_{CO_2,\ i}$

Where,

• $Flow_{CO_2\ i}$ represents the flow of CO₂ for $i$ types of CO₂, either inflow or outflow from the carbonation process, in tCO₂eq/day.

• $V_{CO_2,\ i}$ represents the volume of CO₂ inflow or outflow of the carbonation process, at standard temperature and pressure, in m³ of gas/day.

• $C_{CO_2,\ i}$ represents the daily concentration of CO₂ inflow or outflow of the carbonation process, at standard temperature and pressure, in tCO₂/m³ of gas.

$\textbf{(Eq. 21)}\ Pore_{CO_2} = \frac{p}{RT} \times \epsilon \times y_{CO_2} \times \frac{M_{CO_2}}{\rho_{bulk}}$

• $Pore_{CO_2}$ represents CO₂ trapped in pore space in the carbonated material, in in tCO₂eq/t carbonated material. This term is only required for projects carbonating solid materials, to add to e.g. concrete or asphalt.

• $\frac{p}{RT}$ represents the molar concentration of an ideal gas (in this case, CO₂), in mol/m³. Under standard conditions, the terms would be total gas pressure ($p= 101325\ Pa$ ), temperature ( $T=298\ K$), and the ideal gas constant ( $R=8.3145J/ (mol*K)$), for a total term value of 40.89 mol/m³.

• $\epsilon$ represents the gas void fraction of the material (i.e. fraction of volume per m³ that is pore space), unitless. This value may be measured, or estimated using secondary literature for well-defined, common, homogeneous alkaline feedstocks.

• $y_{CO_2}$ represents the molar fraction of CO₂ in the pore gas, measured via gas analysis or conservatively assumed, unitless. It can conservatively be assumed to equal 1 (100% CO₂ atmosphere).

• $M_{CO_2}$ represents the molar mass of CO₂, which equals 0.000044 t/mol.

• $ho_{bulk}$ represents the bulk density of the dry carbonated material, measured or estimated using secondary sources, in kg/m³.

Data sources

The required primary data for GHG reduction calculations from projects are presented in Table 2, 3 and 4. These data shall be provided for each reporting period and made publicly available.

Table 2 Summary of primary data needed from all projects and their source. Asterisks (*) indicate which data are only required for initial project certification and validation, and do not need to be monitored and updated during verification. Two asterisks (**) indicate which data are only necessary if the project is eligible for avoidance credits from reduced cement use.

Parameter	Unit	Source
Amount of CO2 leaving CO2 capture facility	t CO2 per reporting period	Operations records, sales contracts, invoices
Repartition of CO2 types purchased, entering carbonation facility	fraction	Operations records, sales contracts, invoices
Transport distance or amount of fuel, and transport mode, for CO2 delivery	tonne*km, or kg fuel, or L fuel	Operations records
Amount and type of alkaline feedstock used	tonne/reporting period	Operations records
Amount and type of infrastructure/machinery used for CO2 capture*	kg, tonne, or m3; and material type	Technical design documents
Amount and type of infrastructure/machinery used for carbonation*	kg, tonne, or m3; and material type	Technical design documents
Transport distance or amount of fuel, and transport mode, for alkaline feedstock delivery	tonne*km, or kg fuel, or L fuel	Operations records
Baseline removal calculations from alkaline feedstock carbonation	kgCO2eq/tonne feedstock	Models, calculations
Baseline and project concrete use phase carbonation calculations	kgCO2eq/tonne concrete	Models, calculations
Amount cement needed in project scenario**	kg cement produced /reporting period	Operations records
Amount cement needed in baseline scenario**	kg cement equivalent calculated/ reporting period	Cement mix designs, statements from clients, mandatory concrete mixes
Energy and/or material use from CO2 capture	kg, liter, kWh, MWh, GWh, m3; and material type	Operations records
Energy and/or material use from CO2 purification	kg, liter, kWh, MWh, GWh, m3; and material type	Operations records
Energy and/or material use from alkaline feedstock processing	kg, liter, kWh, MWh, GWh, m3; and material type	Operations records
Energy and/or material use from carbonation	kg, liter, kWh, MWh, GWh, m3; and material type	Operations records
Transport distance or amount of fuel, and transport mode, for carbonated material delivery (if distance >50 km)	tonne*km, or kg fuel, or L fuel	Operations records
Amount of carbonated material produced	tonne	Operations records

Table 3 Summary of primary data needed from projects using solid-sample CO₂ storage measurements, and their source. Project Developers shall provide only one of the two data sources listed.

Parameter	Unit	Source
TGA: Carbon storage in project and control materials	mass loss percentage of CO2	Laboratory measurements
TCA: Carbon storage in project and control materials	% mass of carbon or t C/100 t dry material	Laboratory measurements

Table 4 Summary of primary data needed from projects using gas inflow-outflow CO₂ storage measurements, and their source.

Parameter	Unit	Source
Volumetric flow of CO2 inflow and outflow	m3 of gas/day	Primary measurements, sensors
Concentration of CO2 inflow and outflow	t CO2/m3 gas	Primary measurements, sensors
$\epsilon$ gas void fraction of the material (if carbonating solid materials)	fraction of volume per m3	measured or estimated using secondary sources
$y_{CO_2}$ molar fraction of CO2 in the pore gas (if carbonating solid materials)	unitless	gas analysis or conservatively assumed to equal 1
$ho_{bulk}$ bulk density of the dry carbonated material (if carbonating solid materials)	kg/m3	measured or estimated using secondary sources

The ecoinvent database version 3.11 (hereafter referred to as ecoinvent) shall be the main source of emission factors unless otherwise specified. Ecoinvent is preferred because it is traceable, reliable, and well-recognized. The ecoinvent processes selected are detailed in Appendix 1. No other secondary data sources are used in this module.

Uncertainty assessment

See general instructions for uncertainty assessment in the Riverse Standard Rules. The outcome of the assessment shall be used to determine the percent of RCCs to eliminate with the .

The following assumptions have low uncertainty:

• Use phase concrete carbonation is the same in the project and baseline.

• Baseline delivery of concrete or aggregates is 50 km.

• Directly carbonated cement will have no CO₂ trapped in pore space.

The following assumptions have moderate uncertainty:

• Future uses or end-of-life treatment of the carbonated material will not lead to reversals.

• All carbonated material from the same carbonation batch has similar characteristics.

The baseline scenario selection at the methodology level has low uncertainty, because it requires a project-specific assessment of the specific amount and type. The specific circumstances, amount and type of baseline material must be proven by the Project Developer, and their uncertainty shall be assessed at the project level. There is low uncertainty that the baseline scenario includes baseline removals and cement.

The equations have low uncertainty, because they consist of straightforward conversions. No models are used in this methodology. Secondary data used in the model include a default baseline carbonation rate of solid feedstocks of 10 kgCO₂eq/m³ of feedstock, which comes with low uncertainty due to its very small contribution and the low sensitivity of final results to changes in this value.

The uncertainty at the module level is estimated to be low. This translates to an expected discount factor of at least 3% for projects using this module.