Global warming potential comparison of lime and cement-based masonry repair mortars

Abstract

Lime has been used in masonry mortars for millennia, and many old buildings remain stand-ing today with purely lime technology, despite its low compressive strength compared with ce-ment. Modern approaches tend towards stronger and more durable materials to minimise repair cycles and labour costs, but 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 con-sider lime technologies as a more compatible solution for solid masonry buildings. Life cycle analysis is used to assess environmental impacts of materials across various cate-gories throughout the different stages of their interaction with humans and the wider environ-ment. 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. Life cycle analysis is used to estimate global warming potential associated with a repair in-tervention 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 – 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.