**3.2 Carbon emission reduction potential of waste materials replacement**

The total carbon emission reduction that can be achieved through replacement was 797,147.34 kgCO2eq. Steel accounted for the majority of the environmental benefits and was much higher than other materials in the case building even though it represents only 10% of the total waste materials (see **Figure 3**). Aluminium was the second largest contributor, followed by timber and concrete. As illustrated in **Figure 3**, the environmental benefit of concrete contributes to as low as 0.16%, although it accounts for nearly 80% of the weight of all generated waste. This is because the value of the environmental benefit of concrete in terms of carbon emission reduction potential is much smaller than that of steel and aluminium. For example, the environmental benefit of recovering one kg of aluminium (in the roof) for reuse can contribute to 17.43 kg CO2eq of carbon emission reduction, while this value is only 0.000989 for

recovering one kg of concrete. 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.

### **3.3 Carbon emission of treatment options**

As noted in Section 2.3.4, two waste treatment options (recycling and landfill) were considered to explore the best waste treatment strategy. The net environmental impacts or benefits due to recycling were also accounted for. **Figure 4** shows the contribution of each waste material to the two treatment options' carbon emissions. In all, 2,364,839.37 kg of waste was generated from the demolition of the case building. Out of this total, 83% were recycled accounting for 595,330.41 kgCO2eq of the overall carbon emissions, whereas landfilling waste contributed 150,945.83 kgCO2eq. Recycling the waste materials, however, has huge environmental gains as indicated in **Figure 4**. The result reveals that recycling contributes a net environmental benefit of up to 201,816.93 kgCO2eq when the environmental gain is combined with the carbon emission. This suggests that the most significant end-of-life management option is recycling compared with landfilling demolished waste. Additionally, by comparing the two end-of-life management options, recycling contributed to a potential reduction of approximately 7% in overall carbon emissions.
