## 3 Results
### Circularity Assessment Frameworks
#### 3.2.1 Models for Circular Materials and Products  
Several metrics and assessment models have been developed to evaluate individual aspects of the circularity of products relying on the calculation of certain aspects of their composing materials circularity. These models/indicators often target companies to support the decision-making regarding the circularity versus economic viability of the productsthey design and manufacture. However, they can also apply to construction and building products. Some of these models are discussed below:  
1. The Circularity Calculator. Tha circularity calculater was developed by IDEAL and CO Explore BV [50]. The calculator uses the bill of materials of a product to compare the impacts of different circularity scenarios (e.g., reuse, refurbishment, remanufacture, and recycling) and consequently choose the best design options and business models relying on experimental trade-offs between circularity and value capture. The calculator provides four quantitative key performance indicators (KPIs): circularity indicator, value capture indicator, recycled content indicator, and reuse index, which help companies to determine the economic viability of potential design ideas for products [51].
2. Material Circularity Indicator (MCI). MCI was developed by the Ellen McArthur Foundation (EMF) and Granta Design [13] to assess the ability of material flows of a product or company to be restorative. The calculation of the MCI for a product relies on a detailed bill of materials and three types of inputs: * Amount of virgin, recycled, or reused content V; * Mass of unrecoverable waste W; * Product utility factor X.  
The indicator is developed to assess the circularity of single products. However, it can be utilized at a company scale by using the sum of the material circularity of its products after normalization.  
The MCI can be utilized to access the material circularity of construction and building products. However, other indicators should be used to assess the overall circularity of a building, taking into consideration its complexity, including design aspects and hierarchical composition of systems, components, and materials.
3. The Material Reutilization Score (MRS). MRS was proposed by the Environmental Protection Encouragement Agency through the Cradle-to-Cradle certification scheme to address the recycling value of materials. A material reutilization score is estimated based on the end-of-life strategy considering the performance of input materials and reutilization options. MRS is calculated using two variables: the intrinsic recyclability (\(IR\)) and the recycled content (\(RC\)), according to the following formula: \[MRS=(2\cdot IR+RC)/3\] (2)
4. Longevity and resource duration. Longevity is a value-based performance indicator that relies on the length of time a resource is used in a product system, which can be measured in time units [52, 53]. The idea is that the higher the material retention, the slower the loop and consequently, the higher the contribution to a circular economy [53]. According to the authors, the indicator can be measured using three parameters that are the three drivers for longevity: 1. the initial lifetime, 2. lifetime after refurbishment, 3. lifetime after recycling. These parameters fell short in considering the number of times a resource can be utilized, which is essential to measure resource efficiency and eventually close the loop. Moreover, the indicators do not address the complexities of refurbishment and recycling processes and assume that a resource is refurbished, recycled, and reused through a similar product which is not always the case [52]. Still, the longevity indicator provides a simple tool companies can use to determine the value chain of a product.