**2.1 Circularity of building materials**

Building components should be selected with their potentialities of circularity by following the 3Rs (reduce, reuse, recycle) hierarchy of circular economy [15]. An extensively clean life cycle strategy of circulating building materials in society, excluding contaminants and adulteration, is required to reduce the consumption of primary

### **Figure 2.**

*Model framework to assess circularity of the building materials [16].*

### **Figure 3.**

*Representation of processes, material flows, transport and system boundary of the thermal insulation material case study.*

resources [18]. Tazi [16] used a replicable methodology to locate, extract, construct and assess the end-of-life (EOL) and circularity of the building material (**Figure 2**).

He also created a model map flow, based on a material flow analysis (MFA) and a STAN (State-of-the-art platform) software run for uncertainty assessment, which can thus be used by decision-makers in cities in order to yield an outlook of material stock and flows which were contained in French residential buildings over a time period extending from 1919 until late 2013 [16] (**Figure 3**).

Wiprachtiger M. et al. [19] suggested the sustainable circular system design (SCSD) method in three structured phases to provide an extensive assessment of material flow, impact and circular economy strategies. One-third of the 60 metals studied by Eurostate (2011) [20], showed a global end-of-life recycling rate of 25% or more. Taking a closer look at various ferrous and non-ferrous metals reveals that even for metals that already have high recycling rates, it was found that significant value has been already lost [6].

### **2.2 Evaluation of circular economy of building materials**

From a circular economy perspective, the major criteria to consider in the selection of construction materials for all types of buildings should include local availability, embodied energy, recyclability potential, recycled content, renewability potential, potential to reduce construction waste, life span and durability, and maintenance needs [11]. According to Potting et al. [21], the circular economy (CE) principle is based on the assessment of 10 circularity strategies which are refuse, rethink, reduce, re-use, repair, refurbish, re-manufacture, repurpose, recycle, and recover.

**Recyclability-** Generally, recyclability means converting waste materials into new products, materials or ingredients [22]. Recyclability is one of the prime strategies to establish the design of a circular economy through a closed loop [20]. From the analysis by [22, 23], the thermal recycling process was identified as one of the best processes and the mechanical recycling process was found as the least energy-consuming process.

**Reusability-** The concept of reusing materials is one of the most sustainable and established methods to reduce the waste and use of primary resources [24]. Reusing *Circular Economy in Buildings DOI: http://dx.doi.org/10.5772/intechopen.107098*

contraction materials can reduce not only the building materials but also the overall cost of the project [24].

**Toxicity-** Toxicity of the material is defined as the behavior to release sufficient harmful chemicals or ingredients during the production or end of life which can directly or indirectly impact the environment negatively [25]. Incinerated wastes, slags, dust, sludges and other hazardous products are considered toxic waste [22].

**Assembly and disassembly-** Assembly refers to the installation or construction of individual parts and disassembly refers to the detachment of individual parts of building fabric including wall cladding, non-structural wall panels, flooring, kitchens and internal finishes [26]. Disconnecting of different materials may take place at any time in the whole life cycle of the building, including renovation or the end of the building's life.

**Wastage-** The number of materials that cannot be used or recycled or reused in the construction process is counted as wastages. Analyzing the construction and demolition waste, Noor et al. [26] have identified the major construction wastes which are plastic, wood, steel, surplus mortar, surplus concrete, broken bricks, green waste and excavated soil.

**Finishing-** Finishing refers to the additional layer of materials over the real materials which is generally used to enhance the durability and esthetic aspects of the materials.

From the analysis of [2], the highest reusability ratio was found in the buildings with the structural components largely made of steel structure. Other building structural components like timber structure have 0.65 reusabilities and 0.35 recyclability, and concrete structure has 0.42 reusability and 0.58 recyclability (**Figure 4**). The concrete structures are difficult and unsuitable to reuse as it has the least reusability of 0.42 [26]. By comparing the recyclability and reusability quality of different materials, designers will have a clear understanding of the building materials which can increase the circularity of the building materials.

The whole life performance of the buildings and required adjustment opportunities can be analyzed with a BIM-based whole life performance estimator (BWPE) model which also leads to an efficient material recovery system for the circular economy [2]. Akanbi et al. [2] prepared a table to establish the recyclability, reusability, toxicity, finishing and connection typology of the building materials for the building structure, floor, roof, frame, wall, doors, windows and ceiling systems (**Table 1**).

End-of-life scenarios can demonstrate the possibility of reusing or recycling existing building materials which help to select the materials in line with circular economy strategies. But due to the lack of sufficient research on the end-of-life treatment of each building material, it is not possible to decide on the end-of-life scenarios of all the materials of the building precisely. Tazi [16] investigated end-of-life treatment on some of the building materials which are listed in **Table 2**.

Based on the design science approach of Hever et al. [31], the Circularity Assessment Tool (CAT2022) was prepared by Tokazhanov et al. [32]. The circular economy in the construction industry was the focal point of this assessment tool which was a process and practitioner-based assessment tool. The third-party assessment was also involved to include the responses from the construction industry at different positions and levels. This proposed tool can also complement the existing certification method circular economy by providing specific and required information.

However, the 3DR method can be different due to the local recycling and reuse regulations and facilities. Northern European countries can recover almost 80%

### **Figure 4.**

*Salvage performance of materials (a) concrete (b) steel (c) timber [2].*

