The natural lime cement has a 50% CO₂ reduction compared to Portland cement. It also has higher durability and chemical stability, especially near the sea. However, the hardening of lime concrete is very slow (up to 3 months) and the maximum compressive strength is around 6N/mm² much lower than reinforced concrete. Furthermore, it is a corrosive material and therefore cannot be reinforced with conventional steel bars.
The 14 dwellings project in Sant Ferran is a very light building which transmits a load lower than 0.8 N/mm². It’s also expected to use the rocks from the excavation as structural aggregate which prevents any kind of reinforcement. In addition, local regulations “Ordenances de Policia i Bon Govern del Consell de Formentera “ force to stop the works from May to September in order to avoid causing inconvenience to tourism, so the 90 day period hardening is guaranteed.
The final lime dosing will depend on the quality of the extracted rock.
A test of NHL-5 lime concrete has been carried out with recycled aggregate to characterize its strength and analyze the effect of gypsum sulphates.