Global Warming Potential Comparison of Lime and Cement-Based Masonry Repair Mortars

Lime has been used in masonry mortars for millennia, and many old buildings remain standing today with purely lime technology, despite its low compressive strength compared with cement. Modern approaches tend towards stronger and more durable materials to minimise repair cycles and labour costs, but this comes at the detriment of traditional buildings. Cement-based mortars used to repair historical masonry has accelerated the decay of old buildings, which had previously been in reasonable condition for decades. This has seen the conservation industry return to consider lime technologies as a more compatible solution for solid masonry buildings. Life cycle analysis is used to assess environmental impacts of materials across various categories throughout the different stages of their interaction with humans and the wider environment. Despite an increasing number of life cycle analyses investigating mortars, few studies compare the impacts of cement-based and lime-based mortars, and those that do rarely consider the implications for heritage repair and maintenance. This paper uses life cycle analysis to estimate global warming potential associated with a repair intervention, taking historical sandstone ashlar masonry as a case study, and considering iterative replacement cycles under two different repair methods. Global warming potential per unit area (m²) over 100 years for cement-based mortar is found to be between 43 and 348% greater than scenarios using lime-based mortars. Sensitivity analysis finds the choice of functional unit to greatly impact outputs, such that when comparing mortars, that with highest emission intensity can change. Careful selection is needed of the most relevant functional unit for a specific case.