This was a while ago now but I did say that they should not include infrastructure like garden beds and paths in their calculations because they don't get "used up" and because they are usually recycled items anyway I would argue they have a minimal carbon footprint.
IMO if your concrete blocks were purchased new then I guess they have some minimal carbon penalty but if they were recycled/saved from landfill then I would say absolutely none, zilch, nada, not a single molecule of carbon dept still needs to be paid for their use.
