Life Cycle Boundary 

 In the context of construction materials, LCA quantifies the embodied carbon across all lifecycle stages, from raw materials extraction (the "cradle") to final disposal and recycling (the "grave"). The International Organization for Standardization (ISO-14040, 2006) has outlined several steps for conducting LCA, including aim and scope definition, inventory analysis, impact assessment, and interpretation.

The first step should define the system boundaries according to the life cycle phase that is of particular interest. The system boundaries for the research are based on the modular approach, where the environmental impact for each module in the building life cycle is calculated separately based on the amount of embodied carbon. Currently, various tools for embodied carbon quantification have utilized the above mentioned modular approach for the evaluation of carbon performance of buildings and infrastructures. There are also various international standards available while conducting the carbon assessment and certification, specifying the requirements and system boundaries to ensure the results are consistent and accurate.

The above figure illustrates the complete life cycle of a construction product. Throughout the life cycle of construction activity, the carbon footprint embodied in each construction material varies significantly under different conditions. 

Jiang et al. (2018) observed that the majority of studies conducted in the field of life cycle assessment tend to focus on the overall life cycle of buildings, as the operational phase typically accounts for the highest proportion of carbon emissions. However, it is considered crucial to acknowledge the significant environmental impact resulting from CO2 emissions during material production and site construction processes. 

Zhang et al. (2015) suggested that while emissions during the operational stage contribute to approximately 82% to 86% of the total emissions, controlling carbon emissions during the cradle-to-site life cycle stages is also essential for mitigating environmental pressures. This viewpoint aligns with the findings of Jiang et al., who emphasized that the cradle-to-site life cycle represents a substantial portion of the construction industry, with the construction phase characterized by high energy and material consumption.

Moreover, Ramesh et al. (2010) highlighted that on-site construction methods constitute a significant source of carbon emissions, primarily attributed to the extensive fuel utilization of heavy equipment for transportation and the energy consumed during manufacturing processes. Thus, it is imperative to explore the potential for carbon reduction facilitated by innovative construction technologies, particularly during the cradle-to-site stages, through the implementation of partial LCA analysis from cradle-to-site.