What share of clinker does the IPCC assume in slag cement, fly ash (pozzolan) cement and portland cement?
The Intergovernmental Panel on Climate Change (IPCC) table, built on US standards, gives clinker shares of 95 to 97% for portland, 28 to 70% for portland slag, 28 to 81% for portland pozzolan and under 29% for slag cement. With no data it says use 75% for a mix, 95% for all portland.
Table 2.2 in plain words
- Portland cement: 95 to 97 percent clinker, with a note that some US states allow 3 percent ground granulated blast furnace slag. A second portland row, for the latest standards that allow up to 5 percent ground limestone, shows 90 to 92 percent.
- Slag-modified portland, slag under 25 percent: more than 70 to 93 percent clinker.
- Portland blast furnace slag, slag 25 to 70 percent: 28 to 70 percent.
- Portland pozzolan, pozzolan 15 to 40 percent: 28 to 79 or 81 percent.
- Pozzolan-modified portland, pozzolan under 15 percent: 28 to 93 or 95 percent.
- Slag cement, slag over 70 percent: under 28 or 29 percent. The table notes it can use lime (CaO) instead of clinker.
The two Tier 1 defaults
If output cannot be split by type and blended or masonry cements are likely, the guide says an overall clinker fraction of 75 percent is acceptable within good practice. If the output is essentially all portland cement, use 95 percent.
The guide also says the clinker fraction varies widely even within one blended type, and asks that assumptions be documented.
How a product mix moves it
The table's own example: a country making 50 percent portland and 50 percent blended cement, where the blend is 70 percent portland and 30 percent additives, has a clinker share of 80.8 percent. Check: 0.50 x 95 + 0.50 x (0.70 x 95) = 47.5 + 33.25 = 80.75.
Use it for Indian grades with care
The table is based on US standards (ASTM, the American standards body, C-150 and C-595). My reading: Indian Portland pozzolana cement (PPC) and Portland slag cement (PSC) clinker shares should come from your supplier's actual consumption records. The page on PPC against ordinary Portland cement (OPC) covers the Indian standards.
A grinding unit with a two grade mix, using the guide's own factor
- 40,000 tonnes of portland at 95% clinker = 38,000 tonnes of clinker
- 60,000 tonnes of portland pozzolan at 70% clinker = 42,000 tonnes
- Clinker: 38,000 + 42,000 = 80,000 tonnes
- CO2 at the IPCC Tier 1 clinker factor: 80,000 x 0.52 = 41,600 tonnes
Tonnes and the 70% share are example numbers, inside the table's 28 to 79 percent range. Use the unit's clinker stock and production records. A grinding unit that buys clinker carries this CO2 at the clinker maker, as described on the grinding page.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records, so kiln fuel and mill power are on file for each month. Clinker chemistry and cement type records stay with your plant laboratory and production log.
- PPC against OPC carbon footprint
- Grinding unit CO2 per tonne
- OPC and PPC from one clinker, Carbon Border Adjustment Mechanism (CBAM) split
- Free calculators
Last reviewed 2026-11-05. Figures are from the 2006 IPCC Guidelines. Check whether your buyer or reporting scheme asks for a different edition of the IPCC guidance, and use your own plant measurements where you have them.