Cemex has an alkali activated alumina silicate net zero mix. They say that they get the thermodynamics down to 30% and use offsets, not RECs, for the rest of the way. There is definitely some concern about the alumina and silicate carbon from the NGO side. Sorry, I don’t have better specifics. Also, for cement kilns across the board, air toxics are as big of a concern as carbon. A sizable variety of hazardous waste without much legitimate fuel value gets dumped into unregulated cement kilns. This generates some big tipping fees. Perhaps some of the newer CO2 injection processes at kilns will work better without a lot of different toxic contaminants. Also, as the rest of the EPD or LCA is ignored besides GHGs, kilns are also big ozone and smog generators.