how is this carbon negative? since lime is used for the mixture, doesn't it mean the carbon was removed earlier during production and released? so essentially any carbon absorbed was the carbon released during production.
The carbon released from the limestone. If your concrete kiln, say, burns huge amounts of fossil fuels to convert your limestone to line, that doesn't get reabsorbed.
Hemp is a plant which consumes CO2 from the atmosphere. Using it as part of a structure keeps it sequestered within that structure.
That’s the same as every other fibrous cement product, though. Is this different apart from using hemp for the purposes of marketing to a certain crowd?
It has other advantages compared to fibrous cement, like being a very good moisutre buffer, having a time shift of 10…12 hours, CO2 absorption as it cures etc. It can use natural hydraulic lime or pozzolanic binders.