Mechanical properties and durability of hemp-lime concretes

• The effect of binder type on mechanical strength and durability is investigated.
• At the hemp interface, the commercial binder has abundant hydrates while lime:pozzolan binders are mainly carbonated.
• Binder hydraulicity contributes to strength development but has a lesser effect at 1 year when other factors also contribute.
• Hemp concretes made with lime:pozzolan binders are more sensitive to freeze:thaw action than more hydraulic binders.
• Short-term salt exposure resulted in the precipitation of salt layers but did not impact compressive strength at 1 year.

Hemp-lime concrete is a sustainable and carbon negative construction material. This paper investigates the effect of binder type on mechanical strength and durability (resistance to freeze–thaw, salt exposure and biodeterioration). It compares hemp-lime concretes made with a hydrated lime and pozzolan binder to those including hydraulic lime and cement.SEM analysis revealed abundant hydrates at the hemp interface of the strongly hydraulic commercial binder while the lime:pozzolan binders were mostly carbonated. Increasing binder hydraulicity enhances early strength development however, all concretes achieved similar compressive strengths at 1 year irrespective of the binder type. The concretes with lime:pozzolan binders are more sensitive to freeze:thaw action than those with more hydraulic binders. Salt exposure resulted in the precipitation of salt layers in the concrete however, this did not have a detrimental impact on the compressive strength of the concrete at 1 year. The results evidenced that hemp concrete is resistant to biodeterioration (7 month exposure). Finally, the addition of water retainer improved the early strength development and freeze:thaw resistance of the concrete with lime–pozzolan binder.