You can't really replace clinker, you want to be using the SCM...

You can't really replace clinker, you want to be using the SCM (flyash,slag ect) in the concrete process not in clinker production.

Also clinker is was less expensive that quoted in your post ( its limestone, clay and alot of power basically )

the best way to reduce co2 if you really want to is at the clinker production stage but considering currently you will have to convince indonesia/china/vietnam ect to stop burning old tires ( where do you think your used tires go that get picked up by tirecycle ect??) and other WORSE fuels it aint gunna happen.

Best course of action is to do nothing until nuclear and a little bit of innovation come along to power these furnaces with little to no emission.