Lafarge are introducing ECOPact concrete to North America, with EC reductions up to 100%. From what I can glean these reductions are achived through cement substitution, recycling aggregates, and offsetting. Based on this information the ECOPact Max formulation uses alkali activated materials, which is huge if true - AFAIK net-zero activators are possible, but financially not yet viable, this may be a side benefit of an ammonia based hydrogen economy.
More information is here:
@matt.dalkie can you provide any information?