Environmental performance of three innovative calcium carbonate-based consolidants used in the field of built cultural heritage

In this study, the environmental performance of three newly developed materials for the conservation of built Cultural Heritage is preliminary evaluated by means of life cycle assessment (LCA). Although LCA has been adopted since many years in many fields, including the construction industry, still it is barely used the field of the Cultural Heritage conservation. Therefore, this paper aims to put a step forward to a wider use of the method for a more sustainable conservation of built heritage.

Cradle-to-gate approach was applied, which includes activities beginning with production of constituent and ancillary materials and concluding with the manufacturing of the product and its packaging. The functional unit was the production of 1 kg of the consolidant stored in a canister and ready to use. Ecoinvent database was used for the life cycle inventory of chemicals. This database was also taken into account to evaluate impacts related with energy (electricity) needs during manufacturing of the consolidants and production of polyethylene canisters (packaging material). The IMPACT 2002+ method was used to select the impact categories.

The consolidants under investigation are calcium acetoacetate and two calcium alkoxides (calcium ethoxide and calcium isopropoxide). In the case of calcium acetoacetate consolidant, the highest environmental impact is related to the use of acetone dicarboxylic acid as raw material. Manufacturing process of the final product is not an energy-demanding process; hence, it is regarded as relatively clean from the environmental point of view. In the case of calcium ethoxide and calcium isopropoxide nanosuspensions, the innovative materials just recently developed for conservation purpose, manufacturing has been performed and optimized at a kg/lab scale; therefore, the results must be considered provisional. The two calcium alkoxides nanosuspensions show a relatively high environmental footprint that reflect the high consumption of ancillary materials, i.e. solid CO₂ used to cool down the reaction and liquid ammonia as catalyst, currently released in the atmosphere.

The environmental footprint of calcium acetoacetate is relatively low showing that 1 kg of the consolidant is associated to 0.32 kg of CO₂ equivalent emissions. In the case of two calcium alkoxides nanosuspensions, the global warming impact amounts to 198 kg (calcium ethoxide, 1 kg) and 132 kg (calcium isopropoxide, 1 kg) of CO₂ equivalent emissions. Given the planned optimization of the industrial production currently under investigation, the environmental footprint of the two calcium alkoxides nanosuspensions is expected to reduce between 60 and 85%.