Benefits of an increased use of lime in construction

• Lime is a low-carbon alternative to cement. Lime is produced at a lower temperature compared to Portland cement,[1] and sequesters a larger portion of CO₂ during setting (68%-80%[2]). The UK Built Environment accounts for 42% of greenhouse gas emissions, and cement production alone contributes 6-8%.[3] Despite efforts to reduce such emissions, those related to cement production increased by 1.5% annually in 2015-2021[4], while a 3% annual decline is needed by 2030[5]. Increased cement import has also reduced the UK’s resilience to global market changes.[6] To meet the 2050 net zero target, the construction industry must increase recyclability and lower its embodied carbon using low-carbon and low-energy materials.

• Lime in construction is already fully regulated and has a long history of use in construction so aspects such as the long-term behaviour of this binder are well known. Because of this, lime can immediately replace cement in applications where high strength is not necessary such as in any 2-3-storey buildings (e.g., normal dwelling houses)[7] where this material has already proved to be successful (e.g., Victorian houses).
• In target applications (e.g., bedding mortars for new dwelling houses, renders and plasters), lime already partially replaces cement (~20%), but there is scope to increase this further.[8]
• Lime mortars are porous. Because of this are easy to dry and, in turn, have high frost resistance. Furthermore, because of this have a high permeability to vapour and water leading to a higher breathability.
• Lime mortars have a low elastic module and therefore can accommodate moves without the need for movement joints like in modern townhouses.
• Lime mortars are easier to remove from bricks aiding recyclability and reducing construction waste[9]. In a world where new constructions are built with a shelf life of a few decades (e.g., modern car parks have a ‘shelf life’ of about 30 years), the idea of durability (considered as having a long life) can have a limited meaning. However, lime mortars – being weaker than cement-based mortars – allow for an easy removal from construction elements such as bricks and blocks and this allows for an easier reuse of the elements.
• When made with carbonate sand, lime mortars have the potential to be fully recyclable (i.e., reprocessed to obtain a product with the same value as the original one, if not higher).
• Lime mortars’ ‘spontaneous’ self-healing[10] properties (i.e., cracks are healed by the continuous process of dissolution and re-carbonation of the mortars) allow for reduced maintenance costs (hence, improved durability).
• bactericide properties[11] (i.e., bacteria do not find an appropriate environment where to proliferate thanks to the high pH of the mortars that often contain calcium hydroxide) improving users’ health, when lime is used for plasters in interiors.
• Lime plasters do not emit VOCs
• Lime has already proved that can be successfully mixed with other binders such as cement but also gypsum, organic additives, etc.
• Recent trials using hydrogen fuel in lime kilns suggest it may become a net-zero product[12].

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