**4. Discussion of results**

The management of the end-of-life of a building involves a series of processes and activities as well as diverse carbon-intensive waste materials. However, only limited studies have focused on combining the various stages of demolished waste materials, carbon emission reduction along with treatment strategies. This study aimed to develop an integrated analytical framework based on the LCA model to assess the impact of the life cycle stages of demolished waste materials on carbon emission in order to provide guidance for carbon emission reduction and raw materials conservation.

**Figure 4.** *Analysis of treatment options.*

The results from the breakdown of the life cycle stages (demolition, transportation, processing and disposal) indicated that the processing or treatment stage generated the largest amount of carbon emission (81%) during end-of-life. On the other hand, the transportation of demolished waste material contributed the least (1%) to the total life cycle of carbon emission. The insignificant impact of the transportation stage on end-of-life carbon emissions has also been highlighted by previous studies. Coelho and de Brito [41, 42] assessed the carbon emission embodied in construction and demolition waste materials and suggested that the overall transportation distance should be always reduced because of the related energy consumption and carbon emissions.

As presented in the results section, carbon emission reduction can be achieved through the substitution effects of reusing recycled waste materials. While some past studies have indicated that the recycling of construction and demolition waste has environmental benefits due to the potential to replace virgin materials, the environmental performance of some demolished waste materials has been ignored. For example, a study to evaluate embodied carbon, [17] only considered the recycling of steel and aluminium. Similarly, a study to develop a model to evaluate the cradle-to-grave environmental impacts of a building in Italy, [43] only considered the recycling of steel and aggregate. The current study, however, considered at least four major waste materials. The analysis of the results revealed that steel has a significant impact on demolished waste life cycle carbon emission reduction. Despite representing only 10% of the total mass of generated waste materials, the result analysis indicates that steel has a carbon emission reduction potential of more than 90% of the case building. This result indicates that the recovery and the subsequent processing of metal should be given priority in terms of material potential to reduce carbon emissions during end-of-life.

Furthermore, by investigating the two waste treatment strategies (recycling and landfill) currently viable to the supermarket, this study revealed that landfilling generated the largest amount of carbon and the largest contributor to life cycle carbon emission during the end-of-life phase. In contrast, the analysis of the results emphasises that overall recycling building waste can lead to significant environmental benefits rather than adverse environmental impacts, particularly for materials with a high-value recyclable potential such as steel, aluminium and timber. This is due to the carbon emission reduction potential associated with material recovery. For instance, the results indicate that recycling instead of landfilling could achieve an overall 7% environmental benefit. The significant impact of recycling demolished waste materials has also been highlighted by previous studies. In a study to develop a model to evaluate the cradle-to-grave environmental impacts of a building in Italy, [43] stated that recycling steel and aggregate can lead to environmental gain. Similar findings were reported by [12, 41, 42], who found that recycling demolished waste materials could provide environmental benefits because of the potential to substitute raw materials. Conversely, [10] pointed out that the carbon emission associated with demolished waste materials can be considered lost if landfilled, since virgin materials would be required to replace them. Therefore, careful consideration should be given to the treatment strategies of demolished waste materials.
