A lower carbon result is not automatically a better engineering result if the improvement is purchased by shifting burden into durability, toxicity, energy, other emissions or lifecycle cost.
Decarbonisation targets are useful because they create focus. They can also create tunnel vision.
When one metric becomes strategically dominant, teams begin to optimise around it. Materials with lower embodied carbon are preferred. Fuels with lower lifecycle emissions are promoted. Alternative processes are ranked by greenhouse-gas reduction. These are legitimate decisions.
But engineering systems remain multi-objective even when leadership attention is not.
A material that lowers global-warming potential may require energy-intensive curing. A fuel additive that reduces one pollutant can increase another. A recycled concrete mix may reduce virgin material demand but lose strength unless the composition is balanced. A gas-separation membrane can improve selectivity while sacrificing permeability.
The strategic risk is not decarbonisation itself. It is burden shifting: solving the metric that receives executive attention while degrading another outcome that matters to the system.
The Strategic Context
The supplied research contains several strong examples.
Kurad and colleagues studied concrete incorporating recycled concrete aggregate and high volumes of fly ash. Their findings did not support a simplistic "more recycled content is better" rule. The strongest combined environmental and strength performance emerged from the interaction between fly ash and recycled aggregate. The study reported that the strength-to-global-warming-potential relationship depended more on the FA-RCA incorporation ratio than on either material considered independently.
That is a systems result. The design variable was the combination.
Passuello and colleagues evaluated geopolymer binders using conventional and waste-derived activators. Their work is even more explicit about burden shifting. Waste-derived rice-husk-ash activators could lower impacts substantially in several lifecycle categories and reduce global-warming potential relative to the Portland-cement comparator. Yet the same formulations could have higher impacts in other categories. Thermal curing and commercial sodium silicate production were also significant contributors.
Ashok and colleagues examined Calophyllum inophyllum biodiesel with titanium-dioxide nanoparticles and the antioxidant BHT. The additives moved multiple outcomes in different directions. The tested TiO2 formulation improved brake thermal efficiency and reduced some emissions, while BHT achieved stronger NOx reduction but increased hydrocarbon and carbon-monoxide emissions under the reported conditions.
Jusoh and colleagues provide a smaller but equally useful example. Surface modification of zeolite particles changed both interface quality and CO2/CH4 separation performance. A formulation that increased selectivity could involve a modest loss in permeability, while another improved both metrics. The result depended on how the material system was configured.
None of these papers says decarbonisation is misguided.
They show why engineering decisions require an objective function broader than one environmental number.
What Leaders Commonly Misread
The first error is treating carbon as a complete proxy for sustainability.
Carbon is material, measurable and increasingly important. It does not represent every environmental or engineering consequence.
The second error is comparing materials or technologies per kilogram rather than per unit of useful function.
If one low-carbon material requires greater thickness, shorter replacement intervals or more intensive curing, a mass-based comparison can mislead.
The third error is assuming environmental improvement and technical performance are independent.
They are often coupled. A binder formulation changes strength and lifecycle impact simultaneously. An additive changes combustion efficiency and pollutant formation together. Surface chemistry changes both adhesion and transport properties.
The fourth error is allowing different teams to optimise different metrics without a common decision hierarchy.
Sustainability may minimise carbon. Engineering may maximise strength. Operations may minimise downtime. Procurement may minimise purchase price. Safety may minimise hazardous exposure.
If no one integrates those objectives, the organisation does not have an optimum. It has competing local optima.
Reframing the Issue
The correct unit of analysis is the functional system.
For a material, that means the quantity and process needed to deliver the required strength, durability, thermal behaviour, acoustic behaviour or service life.
For a fuel, it means useful energy and the associated performance, emissions, storage and equipment consequences.
For a membrane, it means separation performance under the required operating conditions, not one isolated material property.
For a capital project, it means the delivered enterprise outcome across the asset lifecycle.
This changes the question from:
"Which option has the lowest carbon footprint?"
To:
"Which option delivers the required function with the best defensible balance of lifecycle carbon, environmental impact, technical performance, cost and risk?"
Carbon Per Unit of Function
The concrete and geopolymer studies demonstrate why functional normalisation matters.
A binder with lower emissions per kilogram may not be superior if it requires more material to provide the same structural performance. Conversely, a higher-strength formulation may justify a higher impact per kilogram if less material is needed for the same function.
This is why metrics such as environmental impact per unit of compressive strength can be useful, although they still do not capture durability or service life by themselves.
Executives do not need to prescribe the exact functional unit. They should insist that engineering teams choose one that represents the real decision.
Possible functional units include:
- tonne-kilometres transported;
- square metres of floor over a defined service life;
- cubic metres of water treated to a required quality;
- megawatt-hours delivered at a required reliability;
- structural capacity over a defined design life;
- kilograms of product manufactured within specification.
The discipline prevents superficial comparisons.
Burden Shifting Across Environmental Categories
The geopolymer study provides a direct warning.
A formulation can reduce global-warming potential and still perform worse in other lifecycle categories. That does not automatically disqualify it. It means the decision requires weighting and judgement.
The organisation should ask:
- Which impacts are material in this context?
- Are any close to regulatory, ecological or community thresholds?
- Is one impact reversible while another is persistent?
- Does the alternative move burden to a different geography or life-cycle stage?
- Are data quality and uncertainty similar across categories?
The objective is not to create a mathematically perfect sustainability score. It is to prevent an improvement claim from hiding a material deterioration elsewhere.
Burden Shifting Across Performance Metrics
The biodiesel-additive study shows the same problem inside an engine.
BHT produced a stronger reduction in NOx under the reported conditions, but HC and CO increased. TiO2 improved brake thermal efficiency and some combustion outcomes but also altered the emissions profile.
If regulation or public-health priorities make NOx the dominant constraint, one trade-off could be acceptable. If local air quality, carbon, fuel efficiency and equipment durability all matter, another choice could follow.
The governing principle is:
Trade-offs are not failures of optimisation. Hidden trade-offs are failures of governance.
Leadership should make the hierarchy explicit.
Interfaces Can Create or Destroy the Benefit
The composite-membrane study adds an important engineering dimension. Performance depended on the interface between inorganic zeolite and polymer.
This matters because sustainability programs often focus on substituting one component for another. But substitution can alter the behaviour of the complete system.
A recycled aggregate changes the concrete matrix. A new fuel changes combustion. A lower-carbon resin changes adhesion or curing. A lightweight component changes vibration, wear or thermal performance.
The interface is where unintended consequences often appear.
A mature decarbonisation program therefore requires system validation, not merely component qualification.
Engineering Margin Matters More Than a Bare Pass
A low-carbon alternative should not be considered equivalent simply because its average laboratory result crosses the minimum requirement.
Industrial systems experience variation. Raw-material chemistry changes, batches differ, temperatures move, operators make adjustments and equipment drifts. A formulation sitting just above the minimum threshold may therefore require tighter quality control, more rejects or more conservative design than the reference material. Those consequences can consume both economic and environmental gains.
Leaders should ask engineering teams to show performance margin, not just compliance. The relevant question is how far the expected operating distribution sits from a failure or non-conformance threshold.
This also changes how uncertainty should be treated. If two alternatives have similar average carbon performance but one has much wider uncertainty around durability or production quality, the apparently greener choice may create greater lifecycle risk. A pilot program, narrower application or staged adoption may then be more valuable than immediate full-scale substitution.
Decarbonisation decisions should therefore combine mean performance, variability and reversibility. This is particularly important when the new material or process is difficult to remove once embedded in a long-life asset.
Decision Framework
ERANORTH recommends an eight-part Multi-Objective Engineering Gate.
1. Define the required function
Specify the performance that cannot be compromised without redesigning the product or service.
2. Establish non-negotiable thresholds
Safety, regulatory compliance, minimum strength, service life, quality and critical environmental limits belong here.
3. Select the material environmental metrics
Include carbon, but add other impacts that could plausibly change the decision. Do not measure everything simply because a database allows it.
4. Normalise by function
Compare alternatives on an equivalent service basis, including quantity, lifetime and replacement where relevant.
5. Map cross-metric interactions
Identify where improving one variable changes another. Use experimental evidence rather than assumptions where consequences are material.
6. Test interfaces and process requirements
Include curing, mixing, compatibility, additives, energy, equipment changes, maintenance and quality-control burden.
7. Evaluate uncertainty and reversibility
A small environmental advantage based on weak data may not justify a hard-to-reverse technology commitment.
8. Make the trade-off explicit
Decision papers should state what becomes better, what becomes worse and why the trade is acceptable.
If nothing appears to worsen, the analysis may simply be incomplete.
Portfolio Governance for Decarbonisation
Engineering trade-offs become portfolio trade-offs when many projects compete for capital.
One project may deliver large carbon reduction at modest cost but little strategic capability. Another may deliver smaller immediate reduction while building infrastructure needed for deeper future transition. A third may reduce operational carbon while increasing embodied impact.
Portfolio leaders should therefore avoid ranking projects solely by tonnes of CO2 avoided.
Useful additional criteria can include:
- cost per unit of functional improvement;
- reversibility;
- technology maturity;
- regulatory exposure;
- resilience;
- dependency creation;
- capability development;
- lifecycle burden shifting;
- future option value.
This produces a more balanced decarbonisation portfolio.
From Strategy to Execution
Immediate action: require major engineering sustainability proposals to include a concise burden-shifting statement: which metrics improve, which could deteriorate, and how the trade-off was evaluated.
Medium-term capability building: integrate lifecycle assessment, materials engineering, operations, safety, procurement and finance earlier in design. Build functional-unit and service-life thinking into specifications.
Long-term strategic positioning: shift from carbon-only project pipelines toward multi-objective design standards that make low-carbon performance part of normal engineering quality rather than a separate initiative.
Related article: Circular Materials Must Pass the Same Performance Gates as Virgin Materials
Related article: Relative Efficiency Can Still Be Unsustainable: The Executive Case for Environmental Budgets
Signals to Monitor
Watch for carbon reductions accompanied by shorter service life; rising chemical, water or curing-energy requirements; increased toxicity or waste intensity; lower purchase price but higher maintenance burden; recycled-content increases with narrowing performance margin; regulatory metrics improving while local pollution worsens; technical teams unable to explain the functional unit behind an environmental comparison; and investment rankings that change dramatically when durability or replacement is included.
A useful governance signal is the number of projects described as "low carbon" without a documented statement of the other material impacts considered.
Questions for the Leadership Team
- What function are we comparing, and are all alternatives truly equivalent on that basis?
- Which environmental impacts other than carbon could materially change the decision?
- What performance metric worsens as our preferred environmental metric improves?
- Have we included durability, service life, maintenance and replacement in the comparison?
- Which interfaces or process changes could erode the laboratory advantage at industrial scale?
- What trade-off are we consciously accepting, and why is it acceptable?
- Are we building a portfolio that optimises enterprise value or merely maximises reported tonnes of carbon avoided?
Closing Perspective
Decarbonisation becomes stronger, not weaker, when it is subjected to full engineering discipline.
A credible low-carbon solution should survive questions about function, durability, safety, other environmental burdens, process requirements, cost and uncertainty. If it cannot, the answer is not to abandon the objective. It is to redesign the solution.
The mature organisation does not ask whether carbon matters.
It asks how to reduce carbon without losing sight of the rest of the system.
Source basis: This article is an original ERANORTH synthesis principally informed by Kurad et al. (2017), Effect of incorporation of high volume of recycled concrete aggregates and fly ash on the strength and global warming potential of concrete; Passuello et al. (2017), Evaluation of the potential improvement in the environmental footprint of geopolymers using waste-derived activators; Ashok et al. (2017), Experimental studies on the effect of metal oxide and antioxidant additives with Calophyllum Inophyllum Methyl ester in compression ignition engine; and Jusoh et al. (2017), Fabrication of silanated zeolite T/6FDA-durene composite membranes for CO2/CH4 separation, all published in Journal of Cleaner Production, volume 166.
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