I don't disagree with your logic Giga and you make some very...

I don't disagree with your logic Giga and you make some very valid points.

I agree, looks at SCM's from a waste perspective is obviously cheaper, albeit my understanding is the flyash (primarily pond ash) comes with additional costs to remedy prior to utilisation & at some point the source of these materials will be switched off. That said, there is heaps of flyash laying around, so that won't be a major issue. A key factor for consideration, is how much flyash and/or slag can you use as a binder before the integrity of the concrete is compromised. I would assume no more than 10-20% and from what I've read, you can got to 40-50% metakaolin and the concretes properties actually improve, not diminish and you achieve correlating % reduction in the carbon emissions - in a simple way.

You are also spot on, with the fact that economics will always rule and ultimately the actual cost of a HRM metakaolin product and logistics combined, need to be at a level that makes it a feasible proposition, supported by the carbon emission reduction tail winds.

And, yes (new) technologies that can improve the enery & emission profiles of heating limestone are in train and will play a major part in aiding the cement industry to meet is net zero ambitions.

If ADN or ZEO can deliver a low cost HRM close to the primary cement players and near domestic concrete consumption, then, maybe just maybe metakaolin will play a role in Australian cement mix strategy towards net zero - noting, this is already happening in Europe.