## 2 State-of-Art Review
### The Effect of Varying RFA Incorporation Ratio on Environmental Impact of Concrete
#### 2.3.2 Life Cycle Assessment of RFA in Concrete  
A life cycle assessment (LCA) is an agreed methodology to identify and quantify the EI and energy consumption paving the way for making improvements to the environmental sustainability of the process or product understudy [93; 94]. An LCA can be classified into 4 stages: (1) the system  
Figure 12: Influence of increasing the RFA content on chloride penetration resistance. boundary. A system boundary of a concrete product could be Cradle-to-Gate, which means including all processes and emissions until the production of its different constituents or Cradle-to-Grave which includes the \"Use\" and \"End-of-Life\" phases as per Table 2 [95]. In most of the references reviewed in this paper, a cradle-to-gate boundary was selected on the strict condition that the CDW are allocated the avoidance of landfill from their previous life cycle. (2) System Inventory. In this stage, the data required for the definition of the EI of the products and processes involved in the predefined scope are acquired either first hand from the site or through EI declarations or databases such as Ecoinvent and ELCD [96]. (3) The third stage it to multiply the inventory data by the functional unit specified and determine the impact using environmental indicators [1]. Mostly, the following eight midpoint environmental categories are considered: Abiotic Depletion Potential ADP, Acidification Potential AP, Eutrophication Potential EP, Global Warming Potential GWP, Photochemical Ozone CPOCP, and consumption of primary energy, renewable (PE-RE) and non-renewable (PE-NRe). The former six categories are quantified using the CML baseline method, while the Cumulative Energy Demand method for the last two [97]. (4) The final stage is to analyse the concluded data and communicate it with the stakeholders. [PERSON] and [PERSON] [98] found that the EI (ADP, GWP, ODP, AP, EP and POCP) decrease between 6% and 8% and between 19% and 23%, when 30% and 100% of fine NA are replaced with RFA, respectively. According to these studies [99; 100], impacts from NAC and RAC can be similar when the additional cement content of RAC is below 10%. However, these may not be a sustainable strategy because the EI of cement is significantly higher than that of the aggregates [101]. [PERSON] et al. [2] carried out a calculation of the EI of NA (Scenario i) and RA in the manufacture of concrete using, for the latter, a recycling fixed (Scenario ii) and mobile plant (Scenario iii) and concluded that the use of RA in the production of concrete is more favourable than the use of NA only in terms of land use and respiratory inorganic-impact categories, resulting mainly from the exploitation of the quarry. This study also concluded, however, that coarse RA can present a better EI than coarse NA if fine RFA were also used in concrete production instead of being sent to a landfill. Additionally, they also reported that advantage of RFA in terms of EI are mainly dependent on transportation distances. The summary of the literature findings of the EI of RFA concrete compared to NA concrete could be seen in Table 3.