## 3 State of the Art
### LCA and EPD Standards  
ISO/TC 59/SC 17, at an international level, and CEN/TC 350, for Europe, describe a methodology for the environmental assessment of construction assets based on LCA. The methodology for the environmental assessment of buildings is defined in the international standard ISO 21931-1:2022 [15] and in the European standard EN 15978:2011 [16]. A revised version of the standard for buildings (EN 15978:2025) will be available in December 2025 if the CEN Formal Vote is approved in October. For civil engineering works (CEWs), the relevant standards are ISO 21931-2:2019 [17] and EN 17472:2022 [18]. The assessment at building or infrastructure level according to these standards requires data from their constituents, i.e., construction products and materials.  
The main sources of environmental data for these constituents are EPDs, a tool to communicate standardized LCA results calculated according to the international standards EN ISO 14025 [19], which defines the criteria and requirements for EPDs, and EN ISO 14040 [20] and EN ISO 14044 [21], which defines the requirements for the LCA. These standards are applicable to any product and can also be used for services. EPDs require horizontal rules for each product grouping, called PCR (product category rules), defined as a group of products that can fulfill equivalent functions. To avoid confusion between the terms used in ISO 14025 and in the new CPR, this article uses the terminology proposed in Aragon & Alberti [9]. Therefore, the term _EPD category_ is used in place of _product category_, but maintaining the abbreviation PCR. EN ISO 14025 is currently under revision and the DIS ballot concluded on 26 June 2025, with a positive result. The definition of _product category_ remains.  
For construction products and materials, the PCRs are defined in ISO 21930:2017, at a global scale, or EN 15804:2012+A2:2019, for Europe. One of the improvements of EN 15804+A2, compared to its previous version, was the alignment with the international standard in terms of modules, impact categories, and other relevant LCA criteria.  
CEN and ISO standards use impact categories and other indicators to describe the environmental performance of buildings and infrastructures presented with a modular approach. The modules have been expanded into the latest version of CEN/TC 350 standards and are listed below:  
* Non-physical processes before the construction (A0): Studies, tests, acquisition, etc.
* Product stage (A1-A3): Raw material extraction and sourcing, transport to the factory and manufacturing.
* Construction process stage (A4-A5): Transportation to the site and incorporation (e.g., installation) of the product into the built asset.
* Use stage (B1-B8): Use-related processes and maintenance, repair, replacement or refurbishment activities. It also includes operational energy and water consumption.
* End-of-life stage (C1-C4): It includes the removal or the product and deconstruction processes, the processing for reutilization or recycling, disposal and all the related transports.  
Benefits and loads beyond the built asset LCA boundaries (D1-D2): It includes the net flows from reuse, recycling and recovery as well as the exported utilities (e.g., energy or potable water).  
Modules A0, B8, D1 and D2 were not included in ISO 21930 or EN 15804+A2, as these standards were published before the new modules were incorporated into the life cycle stages. However, they should be incorporated into the new versions of these standards and will be needed for the environmental assessment of buildings according to the future standard EN 15978:2025. The standard also subdivides some existing modules (see Section 4.2), e.g., B6 can be structured into B6.1, for the energy consumption of regulated building integrated systems, B6.2 for the energy consumption of unregulated building integrated systems, and B6.3 for user-related energy consumption.