**2.1 Case study**

This research employed a case to conduct detailed calculations of carbon emission during the end-of-life. A case study is recognised to be appropriate in investigating complex research particularly, where there is a lack of data available to understand the effect of demolished building waste and the treatment strategies on carbon emissions [10]. The selected case study was a current UK supermarket building. The case building was a single-storey with an average area of 2500 m<sup>2</sup> . Autodesk® Revit® BIM software was used to provide the data on demolition waste generation. Design drawings were obtained and validated with a site survey. The case building simulation is shown in **Figure 1**. The height of the front elevation was 7.02 m while the back was 5.10 m.

**Figure 1.** *The simulated model of the case building.*


**Table 1.**

*Inventory of main waste materials in the case building.*

The structural form determines the main materials. The main materials in the case building are displayed in **Table 1** along with the quantities. The waste materials were derived from two categories. The waste materials in category **A** are considered waste with a high recyclable value. Category **B**, on the other hand, is considered waste with a very low recyclable value and is therefore landfilled. This is because large-scale demolition is usually carried out using mechanised techniques. Consequently, the generated demolished waste is in small volumes, difficult to sort and is generally generated in a mixed form [32].

#### **2.2 Carbon emission factors of the main waste materials and end-of-life stages**

The life cycle of demolished waste materials involved various stages and a series of processes (see Section 2.3.3 for a full explanation). Carbon emission factors (CEFs) are vitally important as they affect the accuracy of the life cycle calculation results. CEFs can be derived from numerous sources. More localised CEFs enhance the accuracy of the assessment results [33]. Consequently, the choice CEFs was based on the principle of regional priority. CEFs of the main waste materials are listed in **Table 2**.

#### **2.3 Life cycle assessment**

The life cycle of waste materials involves various processes and activities. In this study, the assessment used is consistent with the four ISO standards for LCA: definition of scope and goal; life cycle inventory (LCI) which quantifies the inputs; inventory analysis (LCIA) which converts the inputs to emissions; and interpretation of results.

Based on the above breakdowns, the LCA estimation model was developed to evaluate the life cycle carbon emission of demolished waste materials. To generate


*a Environmental Product Declaration (EPD).b Royal Institute of Chartered Surveyors (RICS) [34]c The Institute of Structural Engineers (IStructE) [35]<sup>d</sup> The Department for Business, Energy and Industrial Strategy (BEIS) [36].*

#### **Table 2.**

*Waste materials and carbon emission factors.*

data for the estimation, BIM was used, while data from other sources were used to complement the estimation.

### *2.3.1 Scope, goal and system boundaries definitions*

This LCA examines the carbon emissions of demolished building waste materials under two end-of-life treatment strategies (see Section 2.3.4). Data was taken from a UK supermarket building. As noted above, an assessment framework that incorporates BIM with an LCA was used to provide data on demolition waste generation. The assessment framework comprises various elements as illustrated in **Figure 2**. The scope and goal phase covers all activities and resources involved in the process of demolished waste from generation to final disposal.

#### **Figure 2.**

*Framework of carbon emission assessment of demolished waste [7].*

In LCA, functional units are used to ensure like-to-like comparisons. In this study, the functional unit of demolished waste considers two variables – materials weight (kg) and carbon emission (kgCO2eq). In order to scale up the results to any weight of demolished waste material, the functional unit will consider 1 kg of waste materials. The functional unit is therefore kgCO2eq of per 1 kg demolished waste.

#### *2.3.2 Life cycle inventory*

The main type of life cycle inventory (LCI) and data used was the process LCI (primary and secondary environmental data). The process LCI was used to systematically quantify the physical inputs and outputs of the waste materials within the process LCA system boundary. The process LCI of each component and activity was derived using the breakdown approach, which gives carbon emissions per kg of waste material generated. The LCA quantification formulas were developed to estimate the life cycle carbon emission during the end-of-life (see **Figure 2**). As stated earlier, the LCA was integrated with BIM to provide data imported into the calculation of end-oflife carbon emissions. During these end-of-life activities and processes, records of energy consumption by machines were sought through multiple data sources including EPDs from manufacturers/suppliers and site surveys. To complement the robustness of these data, additional carbon emission factors for each phase and activity were gathered from other literature. Where data was not available from EPD and recognised eco-data source the mean value of the other literature searches was used.

#### *2.3.3 Life cycle impact assessment of demolished building material*

As noted in Section 2.1.2, the life cycle impact assessment (LCIA) approach employed in this study was the process-based LCA inventories (where the physical flow of all aspects of building materials can be identified and traced) to establish the carbon emission embodied in building demolished waste. As an LCA technique, the processbased has the strength to reveal carbon emissions from the specific demolition process and activity, along with its accuracy and detailed processes [17, 37, 38]. The rationale of this method is straightforward and clear, carbon emissions from individual activities can be estimated and analysed separately [17]. This method is frequently adopted in the

#### *Life Cycle Assessment of Buildings: An End-of-Life Perspective DOI: http://dx.doi.org/10.5772/intechopen.110402*

quantification of carbon emissions of construction processes [17, 39, 40]. Finally, the results of the LCIA were then analysed and the conclusions were drawn.

Meanwhile, there are four stages of the life cycle the waste materials and a series of activities are involved. The analysis of these activities is fundamental to identifying carbon emission factors (CEFs). The first stage covers all the processes in the demolition of the building at the end of its useful life. During the demolition, several machines can be used and energy/fuel consumed through the use of these machines or equipment as well as related emissions serve as a source of CEF. Carbon emissions at this phase also include the projected operating time for machines or equipment used in carrying out the demolition of the building multiplied by the average electric power used and/or fuel per unit of time and the related carbon intensity per litre of fuel used. The second stage covers the transportation of the demolished waste materials to treatment plants, recycling plants or landfill sites. CEFs are also derived from the environmental impacts associated with these activities. The third stage covers all the processes in the waste treatment plant, while the fourth and final stage covers the processes associated with the final disposal of demolished building materials.

The conceptual LCA framework focuses on the demolished building materials for which waste treatment is expected, and therefore, the environmental impacts were calculated. However, two aspects of carbon emission are associated with recycling waste materials - the adverse environmental effects and the environmental benefits [7]. The net environmental impact is equal to the difference between the impacts due to the recycling process that replaces the production of virgin materials and the impacts due to the production of the avoided virgin material. The net benefits associated with material replacement and energy consumption, or carbon emission is the difference between the input and output of the secondary material.

Using life cycle inventories, the process LCA for the use of machine/equipment can be defined by Eq. (1) as:

$$\text{EC}\_{\text{equip}} = \sum \text{EQ} i \* \text{EQ} \text{Fi} \* \text{EQ} \text{EC} i \tag{1}$$

Where:

ECequip refers to carbon emission associated with plant or equipment used in dismantling or demolishing a building at the end-of-life (kgCO2eq); EQi refers to the number of hours plant/equipment <sup>i</sup> is used for the dismantling or demolition process (hour); EQFi refers to the type of fuel used by the demolition plant/equipment <sup>i</sup> (kWh or litre per hour); and EQECi refers to carbon intensity per unit consumption of fuel <sup>i</sup> (kgCO2eq per litre).

Carbon emission is also calculated for waste generation during the demolition of the building. It is assumed that waste from the demolished building during the end-of-life of the case building is equal to the mass of material in the constructed building excluding the waste factor and has the same building component category breakdown. Consequently, the process LCA of building demolition can be represented by Eq. (2) as:

$$\text{EC}\_{\text{struct}} = \sum \text{Si} \ast \text{SCEF} \,\text{i} \tag{2}$$

Where:

ECstruct refers to carbon emission associated with the demolished building; Si refers to the quantity of material <sup>i</sup> resulting from the demolished structure or building (m<sup>2</sup> , m<sup>3</sup> or kg); and SCEFi denotes the carbon emission coefficient per unit of material <sup>i</sup> (kgCO2eq per kg, m<sup>3</sup> or m<sup>2</sup> ).

Using life cycle inventories, the process LCA for transporting demolished materials can be defined by Eq. (3) as:

$$\text{ECCrans} = \sum \text{TDi} \ast \text{TL} \dot{\ast} \ast \text{TF} i \ast \text{TCEF} i \tag{3}$$

Where:

TDi denotes the total distance covered for material <sup>i</sup> (km); TLi refers to the number of loads of trucks for the transportation of material <sup>i</sup> (No.); TFi represents the fuel used per load of truck (litre per km); and TECFi refers to the carbon emission coefficient per fuel unit used <sup>i</sup> (kgCO2eq per litre).

In this study, two waste treatment approaches - recycling and landfilling were assumed. As noted above, recycling demolished waste materials has both adverse environmental impacts and environmental benefits. Therefore, the environmental benefits of substituting virgin materials with recycled (secondary) materials are subtracted. Subsequently, the process LCA for recycling demolition waste can be defined by Eq. (4) as:

$$\text{EC}\_{\text{rec}} = \sum \text{EC}\_{\text{rec}-\text{q}} i - \text{EC}\_{\text{rec}-(-\text{ben})} i \tag{4}$$

Where:

ECrec is the carbon emission from the recycling plant (kgCO2eq.); ECrec-qe is the emission resulting from machine operation during recycling (kgCO2eq); and ECrec- (�ben) is the carbon emission reduction through the replacement of raw materials (kgCO2eq).

Accordingly, using life cycle inventories, the process LCA for the total carbon emissions of the demolished waste over the life cycle for recycling and landfill treatment options can be represented by Eq. (5) and (6) respectively.

$$\text{EC}\_{\text{TOTALRECT}} = \sum \text{EC}\_{\text{de}} + \text{EC}\_{\text{tp}} + \text{EC}\_{\text{pr}} \tag{5}$$

$$\text{EC}\_{\text{TOTALAN}} = \sum \text{EC}\_{\text{de}} + \text{EC}\_{\text{tp}} + \text{EC}\_{\text{dp}} \tag{6}$$

Where:

ECTOTALREC and ECTOTALLAN refer to the total carbon emission of the life cycle of building demolition waste for recycling and landfilling respectively (kgCO2eq); ECde is the carbon emission at the demolition phase (kgCO2eq); ECtp is the carbon emission during transportation phase (kgCO2eq); and ECpr refers to the carbon emission during recycling (kg CO2eq.), while ECdp is the carbon emission during disposal.

Results analysis is a key aspect of a life cycle assessment study. Therefore, through the scenario analysis, the stage of the end-of-life with greater carbon emission can be identified. Also, the type of waste material and treatment strategy with the largest carbon emission potential can be identified. Hence, low-carbon waste materials can be proposed to manage the end-of-life carbon emission and associated substantial amounts of building waste. Accordingly, the process LCA for the comparison waste can be defined by Eq. (7) as:

$$\mathbf{P}\_{\rm eol} = \mathbf{B}\_{\rm eol} / \sum \mathbf{B}\_{\rm eol} \tag{7}$$

Where:

Peol is the proportion of carbon emission from a stage of demolition waste life cycle, treatment strategy and type of waste material the case building (%).

Beol is the total carbon emission from the case building (kgCO2eq).

## *2.3.4 End-of-life scenarios and assumptions*

In this study, two waste treatment options were considered. Based on the recovery rates of the UK from localised literature and other sources, the percentage of each material was determined. **Table 3** shows the assumed end-of-life treatment options for the waste materials along with the percentages A heavy-duty diesel truck (17 tonnes load) was assumed as a transportation mode for the demolished waste materials [34, 35]. In addition, a maximum distance of 50 km by road for both treatment options was assumed.
