Low-carbon calcined clay-based binders for sustainable hempcrete

The building sector is responsible for approximately 40% of total anthropogenic greenhouse gas emissions and 37% of global energy consumption. Hempcrete, fabricated from industrial hemp, can offer a tremendous potential to alleviate the carbon emissions and energy usage from buildings and construction based on its carbon capture and storage capability and low thermal conductivity. However, conventional lime-based binders for hempcrete are carbon intensive. This study investigates three low carbon binder alternatives for hempcrete: HL-Ref (100% hydrated lime), HL–CC (50% hydrated lime, 50% calcined clay), HL–CC–LS (50% hydrated lime, 50% calcined clay and limestone), Geo-CC [geopolymer binder with 70% calcined clay and 30% granulated ground blast furnace slag (GGBFS)]. Compressive strength, bulk density, sound absorption coefficient, thermal conductivity, surface bond strength and crystalline phases of hempcrete were assessed and a multicriteria analysis was carried out to compare the hempcrete performance between different mix designs. Results showed that the Geo-CC hempcrete using the calcined clay/GGBFS geopolymer binder achieved the best performance in terms of compressive strength, surface bonding capacity and thermal conductivity. The performance of HL–CC–LS hempcrete also achieved outstanding properties which could not be achieved by using only calcined clay (HL–CC), highlighting the beneficial synergy between limestone and calcined clay in a lime-based system. The HL–CC–LS hempcrete achieved the best acoustic performance with the highest sound absorption coefficient.