There’s tonnes of good content on this in the UK market. Here’s a good starting point for you, where you’ll find a section on this topic, and references to more good resources:
https://www.concretecentre.com/Publications-Software/Publications/Specifying-Sustainable-Concrete.aspx
@martintorres, I would agree that cement content is important, but it’s a bit of both matters, isn’t it? You want to limit cement content and include cement replacements. In cases where we’ve specified cement replacements, contractors worried about strength gain (and overestimating the impact of the cement replacement on strength gain delays) will just massively increase the total cement content, counterproductively. So you want to spec cement replacement and limit total cement content.