Process Emissions in Building Materials: What Renewables ...

A cement plant installs solar panels on every available rooftop and signs a power purchase agreement for 100% renewable electricity. Their Scope 2 drops dramatically. Their total emissions barely move.

That's the fundamental problem with process emissions in building materials. When you heat limestone to 1,500 degrees Celsius, the calcium carbonate decomposes into calcium oxide and CO2. That chemical reaction - calcination - accounts for 55% of cement's total emissions according to Cement Industry Federation data. No amount of renewable energy changes the chemistry. The CO2 comes from the rock itself, not the fuel.

And cement is just the start. Steel production using blast furnaces requires metallurgical coal as a chemical reductant, not just a heat source. Aluminium smelting involves carbon anode consumption that releases CO2 as a byproduct of the electrolytic process. These are process emissions - greenhouse gases released from industrial chemical reactions, distinct from the combustion emissions that come from burning fuel for energy.

For Australian building materials manufacturers reporting under both NGER and AASB S2, this distinction isn't academic. It changes how you calculate, what methods you're required to use, what decarbonisation pathways are actually credible, and what your Safeguard Mechanism compliance strategy looks like for the next decade.

Why Process Emissions Are a Different Reporting Problem

The NGER Measurement Determination treats process emissions and combustion emissions as fundamentally different calculation exercises. Division 4.2 of the Determination contains specific methods for cement clinker production, lime production, and the use of carbonates to produce products other than cement or lime - which is how iron and steel production gets covered when limestone or dolomite is used as a flux.

For cement clinker, Division 4.2.1 provides three methods with increasing accuracy requirements. Method 1 uses default emission factors applied to clinker production tonnage. Method 2 requires facility-specific data on the calcium oxide content of clinker. Method 3 - the most granular - requires sampling and analysis of raw materials to determine actual carbonate content, plus the fraction of calcination achieved (Fcal) and the fraction of calcination for cement kiln dust (Fckd).

The parameters Fcal and Fckd must be estimated in accordance with industry practice and be consistent with the NGER Measurement Determination's principles of transparency, comparability, accuracy, and completeness. That sounds straightforward. In practice, it means your production team needs to feed quality-controlled data about clinker tonnage, raw material composition, and kiln dust losses into your emissions calculations - not just energy consumption figures.

For integrated metalworks producing both steel and coke, the Determination requires a carbon mass balance approach. You're tracking carbon inputs (coal, coke, limestone, dolomite, scrap, electrodes) and carbon outputs (steel, slag, coke oven gas, blast furnace gas, basic oxygen furnace gas) across the entire facility. Miss an input or output stream and your numbers are wrong in a way that's hard to detect without a full reconciliation.

This is categorically different from combustion emissions reporting, where you multiply litres of fuel by an NGA emission factor and you're done. Process emissions need production data - tonnes of clinker, tonnes of crude steel, tonnes of aluminium - linked to material-specific factors that reflect the actual chemistry happening at your facility.

The Numbers That Matter: How Big Is This Problem?

Process emissions from Australia's building materials sector aren't marginal. They're the main event.

Australia produces roughly 5.2 million tonnes of clinker per year, with specific CO2 emissions of 791 kg per tonne of clinker - about 4% below the global average of 824 kg per tonne. That's approximately 4.1 million tonnes of CO2 just from cement production. Around 60% of that is process emissions from calcination. The remaining 40% is split between kiln fuel combustion (roughly 26%) and electricity (12%). Even if you fully decarbonised the energy inputs, you'd still have more than half the emissions left.

Steel tells a similar story, though the split depends on the production route. Blast furnace steelmaking (BF-BOF) emits around 2.0-2.3 tonnes of CO2 per tonne of crude steel - and a significant portion is process emissions from the use of metallurgical coal as a reductant. Australia produced 5.5 million tonnes of crude steel in recent years, with 74% coming from blast furnaces. Electric arc furnace (EAF) production, which uses scrap steel and electricity, produces roughly 0.4-0.7 tonnes of CO2 per tonne - and most of those are Scope 2 from grid electricity, which actually can be addressed with renewables.

That BF-BOF vs EAF distinction matters enormously for reporting. If you're a steel producer using blast furnaces, your process emissions are locked in until you fundamentally change your production technology. If you're running EAFs, renewable energy actually works. Australia's EAF share grew from 17% in 2010 to 26% in 2020, but that still leaves three-quarters of domestic steel production tied to blast furnace chemistry.

Infrastructure Australia's 2024 projections put upfront embodied carbon from our buildings and infrastructure pipeline at 37 to 64 million tonnes of CO2-e per year over the next five years. A 23% reduction is achievable by 2026-27 through known decarbonisation strategies. But that still leaves tens of millions of tonnes that can't be touched without technology shifts that are years away from commercial scale.

Safeguard Mechanism: 4.9% Decline With Nowhere to Hide

All 219 facilities covered by the Safeguard Mechanism face declining baselines of 4.9% per year until 2030. For building materials facilities, that maths is brutal.

Consider a cement plant with a baseline of 500,000 tonnes CO2-e. A 4.9% annual decline means that baseline drops to roughly 475,500 in year one, 452,200 in year two, and keeps falling. If 60% of your emissions are from calcination - from the chemistry itself - and you can't commercially eliminate those process emissions yet, you're going to exceed your baseline. Every year. By more.

The government recognised this. Hard-to-abate facilities can apply for Trade-Exposed Baseline Adjusted (TEBA) status, which provides a reduced decline rate for three years. And the government committed $400 million to support industries like steel, cement, and aluminium with technology development. But the reduced decline rate doesn't mean zero decline. You still need to demonstrate progress.

In FY2024 - the first year under reformed settings - 147 out of 219 covered facilities exceeded their baseline, up from just 18% the year before. The aggregate position flipped from 31.7 million tonnes of headroom to a net exceedance. ACCUs are trading around $30-35 per tonne in early 2026, with the cost containment measure capping at $82.68. For a facility 50,000 tonnes over baseline, that's $1.5 million to $4.1 million in compliance costs depending on ACCU pricing - and those costs only grow as baselines tighten.

We wrote about the broader Safeguard Mechanism changes in a separate post. For building materials specifically, the 2026-27 review is the one to watch. The government's Carbon Leakage Review has already recommended a carbon border adjustment for cement and clinker imports as a priority, with steel and aluminium potentially following. If implemented, that would change the competitive dynamics for domestic producers significantly.

The Scope 3 Cascade: Your Process Emissions Are Someone Else's Purchased Goods

Here's where this gets complicated for the broader construction industry. When a builder buys 10,000 cubic metres of concrete for a project, the process emissions from cement production - the calcination CO2 - become the builder's Scope 3 Category 1 emissions under the GHG Protocol. The steel reinforcement carries blast furnace process emissions. The aluminium window frames carry smelting process emissions.

Under AASB S2, construction companies in Group 2 (reporting from July 2026) and Group 3 (from July 2027) will need to disclose Scope 3 emissions from their second reporting period. For a construction company, Category 1 - purchased goods and services - is almost certainly where the bulk of Scope 3 sits. And the quality of that number depends entirely on how well building materials manufacturers report their own process emissions.

This creates a data supply chain. The cement producer measures clinker tonnage and calcination fractions under NGER Division 4.2. That data feeds into an Environmental Product Declaration (EPD) for their concrete. The builder uses that EPD to calculate their Scope 3 Category 1. The builder's auditor, under ASSA 5010, wants to see where the EPD number came from. If the EPD is a generic industry average rather than a product-specific declaration, the Scope 3 number could be off by 30-40%.

We've seen this data quality challenge firsthand. Many builders default to spend-based estimates for materials - dollars spent on concrete multiplied by an economic emission factor. That gives you a number, but it's a bad number. A spend-based estimate can't distinguish between high-performance concrete with 60% ground granulated blast furnace slag (lower carbon) and standard Portland cement concrete (higher carbon). The difference in embodied carbon can be 40% or more, but the price difference might be minimal.

EPDs: The Data Source That's Getting Better (Slowly)

Environmental Product Declarations are the mechanism that's supposed to solve the data quality problem. An EPD is a standardised, third-party-verified document that reports the environmental impacts of a product across its lifecycle stages (typically A1-A3 for cradle-to-gate). EPD Australasia is the regional programme operator, running under the International EPD System.

The good news: EPD availability in Australia is improving. Major steel and concrete producers now publish product-specific EPDs. Some concrete producers offer bespoke EPDs for individual mixes - meaning you can get an emission factor for the exact 32 MPa mix delivered to your site, reflecting the actual cement content, supplementary cementitious materials, and aggregate source.

The less good news: coverage is patchy. Smaller producers often don't have EPDs at all. Asphalt EPDs are harder to find than concrete or steel EPDs. And even when EPDs exist, they vary in age, system boundary, and methodology in ways that make direct comparison tricky. An EPD from 2021 might use different allocation rules than one published last month. The underlying emission factors may have changed.

For construction companies trying to calculate Scope 3, this means you'll end up with a patchwork: product-specific EPDs for some materials, industry-average EPDs for others, and spend-based estimates for whatever's left. That's reality. Pretending otherwise doesn't help anyone prepare for assurance.

The Australian Government's Environmentally Sustainable Procurement Policy, effective from July 2024, requires environmental consideration for construction procurements above $7.5 million - with EPDs serving as credible evidence. That procurement pressure is probably going to do more to drive EPD adoption than any reporting standard.

AASB S2 Scenario Analysis: Modelling Technology Transitions You Don't Control

AASB S2 requires entities to use scenario analysis to assess climate-related risks and opportunities. For building materials manufacturers, this means modelling decarbonisation pathways for emissions you can't eliminate with today's commercial technology.

The credible pathways exist on paper. For cement: supplementary cementitious materials to reduce clinker ratio, alternative fuels for kiln energy, and carbon capture and storage for the calcination CO2. For steel: hydrogen direct reduced iron (H-DRI) to replace blast furnace coke as the reductant, then electric arc furnace steelmaking powered by renewables. For aluminium: inert anode technology to eliminate carbon anode consumption.

But none of these are trivially deployable today at commercial scale in Australia. Carbon capture on cement kilns is being piloted globally but isn't operating at scale domestically. Green hydrogen for steel requires both cheap renewable electricity and electrolyser capacity that's still being built. Inert anodes for aluminium remain in development.

Under AASB S2, your scenario analysis needs to credibly model when these technologies become commercially viable for your operations, what the capital expenditure looks like, how your emissions trajectory changes under different adoption timelines, and what happens to your Safeguard Mechanism compliance position in the interim. That's not a one-off exercise. It needs updating as technology matures and policy settings change - particularly after the 2026-27 Safeguard Mechanism review.

We're honest about this: scenario analysis for hard-to-abate sectors is one of the areas where most organisations still need specialist support. The modelling requires assumptions about technology readiness levels, capital costs, and policy trajectories that go beyond what any software can generate automatically. What software can do is give you the baseline emissions data - broken down by process vs combustion, by product line, by facility - that makes those scenarios grounded in reality rather than aspiration.

The Data Collection Problem Nobody Talks About

For building materials manufacturers, the data challenge for process emissions is different from anything an office-based company faces.

You need production data at the facility level: tonnes of clinker produced, tonnes of cement kiln dust, tonnes of crude steel, tonnes of aluminium. You need material input data: tonnes of limestone consumed, coal composition, carbonate content of raw materials. For NGER Method 3 reporting on cement, you need actual sampling and analysis results for raw material carbonate content. For steel production carbon mass balance, you need carbon content measurements for every significant input and output stream.

This data exists in operational systems - kiln control systems, production databases, quality management systems, weighbridge records, lab information management systems. But it rarely exists in the format your sustainability team needs for emissions calculations. The production manager tracks clinker tonnes because it drives revenue. The quality lab tracks calcium oxide content because it affects product specification. Neither is tracking those numbers specifically for NGER Division 4.2 compliance.

The result is a manual data collection exercise that typically takes 400-600 hours per reporting cycle for a complex facility, according to industry estimates. And that's before you reconcile production data with energy data with purchased materials data to make sure nothing's been double-counted or missed.

For construction companies on the buying side, the data problem is different but equally painful. You need to match every material purchase - concrete, steel, asphalt, aluminium - to the right emission factor. Not a generic factor for "concrete" but the specific factor for the product you actually bought, from the plant that actually produced it, with the mix design that was actually delivered. Your procurement system tracks dollar value. Your project management system tracks cubic metres or tonnes. Neither system was built to store emission factors or link purchase orders to EPDs.

Carbonly's material library is built for exactly this kind of matching. It combines NGA emission factors, EPD data from EPD Australasia, and an AI-powered factor lookup that learns from the materials your organisation actually purchases. When you upload a delivery docket for 32 MPa concrete, the system matches it against the most specific emission factor available - product-specific EPD first, then industry-average EPD, then NGA default. You can see exactly which factor was applied and why, which matters when your auditor asks.

Where NGA Factors Meet Industry-Specific Factors

The NGA Factors 2025 workbook, published by DCCEEW, provides default emission factors for industrial processes including cement, lime, and steel production. These are the baseline Method 1 factors that any NGER reporter can use.

But NGA default factors are national averages. They don't reflect the efficiency of your specific kiln, the clinker-to-cement ratio of your product mix, the proportion of supplementary cementitious materials you use, or the scrap ratio in your EAF. A facility that's invested heavily in reducing clinker content - substituting fly ash, slag, or calcined clay - will have lower actual process emissions per tonne of product than the NGA default suggests.

That's why NGER provides higher-tier methods. Method 2 and Method 3 for cement require facility-specific data that should yield a more accurate (and often lower) emission factor. For steel, the carbon mass balance approach is inherently facility-specific. Using the higher-tier method costs more in sampling and analysis, but it can make a material difference to your reported emissions - and therefore to your Safeguard Mechanism position.

There's a technical wrinkle worth flagging. NGER uses AR5 Global Warming Potential values from the IPCC, while AASB S2 references AR6 (the latest IPCC assessment). For CO2, this doesn't matter - GWP is 1 in both. But for methane and nitrous oxide, the values differ. If your process emissions include CH4 (which some industrial processes do), you'll need to reconcile the two. The AASB granted jurisdictional relief in December 2025 allowing NGER reporters to use AR5 GWPs for AASB S2 disclosures covering NGER-reported portions, so you don't have to recalculate everything. But you do need to document which GWP values you've used and where the relief applies.

What Actually Reduces Process Emissions (And What Doesn't)

Since process emissions can't be eliminated by switching energy sources, the decarbonisation options are fundamentally different. It's worth being specific about what works and what's marketing.

What works now for cement: Reducing the clinker-to-cement ratio by substituting supplementary cementitious materials - ground granulated blast furnace slag, fly ash, calcined clay. This directly reduces the amount of calcination per tonne of cement. The Infrastructure Australia report identifies this as a cost-effective near-term strategy. Some producers have achieved 40% reductions in embodied carbon per tonne of concrete through aggressive SCM use.

What works now for steel: Increasing the share of electric arc furnace production using scrap steel, powered by renewables. EAF steel has roughly one-fifth to one-third the emissions of BF-BOF steel. Australia's EAF share is growing but remains well below the US (71%) and EU (42%).

What's coming but isn't commercially deployed in Australia: Carbon capture on cement kilns. Hydrogen direct reduced iron for steel. Inert anodes for aluminium. Alternative binders that don't require limestone calcination. These are real technologies with pilot plants operating globally, but they're not options you can put in your FY2027 emissions reduction plan and have your auditor accept.

What doesn't work: Buying offsets to cover process emissions and calling it a decarbonisation strategy. Offsets address your compliance obligation under the Safeguard Mechanism, but they don't reduce your actual process emissions. Under AASB S2, you need to disclose gross emissions before any offsets - and your transition plan needs to describe the actual operational changes you're making, not just the credits you're buying.

Pulling It Together: What to Do First

If you're a building materials manufacturer, start by separating your process emissions from your combustion emissions in your NGER reporting. That sounds obvious, but we've seen facilities where everything gets lumped together and the Division 4.2 calculations are an afterthought. Your process emissions are the ones you can't buy your way out of with PPAs and renewable electricity. They need a separate decarbonisation strategy, a separate line in your scenario analysis, and separate data pipelines from your production systems.

If you're a construction company buying these materials, start building your Scope 3 data infrastructure now. Request EPDs from your top five material suppliers by volume. Where product-specific EPDs exist, use them. Where they don't, use industry averages from EPD Australasia - but flag those as lower-quality data in your disclosures. Don't default to spend-based estimates for your biggest material categories just because it's easier.

Both sides of this equation need better data flowing between manufacturers and buyers. That's the fundamental infrastructure gap, and it's the one we're focused on closing.

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