Replacing clinker with supplementary cementitious materials (SCMs) is the most accessible near-term strategy for reducing cement's CBAM liability. South Africa has abundant SCM resources.
Since calcination emissions cannot be eliminated without carbon capture technology, the most accessible near-term strategy for reducing cement's CBAM liability is clinker substitution — replacing a portion of the clinker in cement with supplementary cementitious materials (SCMs) that have lower or zero embedded emissions.
Supplementary cementitious materials are materials that can partially replace clinker in cement production while maintaining or improving cement performance. The most common SCMs are:
| SCM | Source | Embedded Emissions | Availability in SA |
|---|---|---|---|
| Fly ash (Class F) | Coal power station by-product | ~0.01 tCO₂/t | Abundant (Eskom) |
| Ground granulated blast furnace slag (GGBS) | Steel plant by-product | ~0.05 tCO₂/t | Available (AMSA) |
| Calcined clay | Clay deposits | ~0.2 tCO₂/t | Abundant |
| Silica fume | Ferrosilicon production by-product | ~0.01 tCO₂/t | Limited |
The clinker-to-cement ratio (k-value) is the key metric for measuring clinker substitution. A lower k-value means more SCM and less clinker per tonne of cement.
Current SA average: k-value ~0.70 (70% clinker, 30% SCM/gypsum) Best practice: k-value ~0.55–0.60 (40–45% SCM) Maximum (for standard cement grades): k-value ~0.50
CBAM impact of reducing k-value from 0.70 to 0.55:
At 500,000 tonnes of EU cement exports, this represents a saving of €5.9 million/year.
South Africa has a significant advantage in SCM availability:
Fly ash: Eskom's coal-fired power stations produce approximately 6 million tonnes of fly ash per year. Currently, only a fraction of this is used in cement production — the rest goes to ash dams. Increasing fly ash utilisation in cement is both an environmental benefit and a CBAM mitigation strategy.
GGBS: ArcelorMittal South Africa's blast furnaces at Vanderbijlpark produce granulated blast furnace slag that can be ground into GGBS. Proximity to SA cement plants makes this a viable SCM source.
Increasing SCM content requires careful attention to:
Most SA cement producers have the technical capability to increase SCM content, but may need to invest in additional grinding capacity and quality control systems.
Use the CBAM Calculator [blocked] to model the CBAM impact of different clinker substitution rates.