# Carbon Dioxide Uptake by Cement-Based Materials: A Spanish Case Study
## 6 Results and Discussion
### Carbon Dioxide Uptake by the Spanish Cements  
The amount of carbon dioxide that can be absorbed during the service life (Figure 9) of a product manufactured with cement is calculated with a fixed conservative value using the simplified methodology. This value could either be 15% or 20% [27] of the CO\({}_{2}\) emissions owing to the process of calcination that is a long way from the maximum theoretical value of carbon dioxide that can be absorbed (around 490 kg of CO\({}_{2}\) per tonne in the case of a cement without addition, CEM I).  
The Spanish domestic data for CO\({}_{2}\) emissions have been used to directly apply the simplified methodology to estimate CO\({}_{2}\) absorption (Figure 10). Such emissions have fallen from 2005 to 2015 as a consequence of the drop in clinker production (Figure 11).  
Figure 10: Absolute CO\({}_{2}\) emissions (tons) evolution from 2005 to 2015 for the Spanish clinker production: process emissions (bars in blue); fuel emissions (bars in orange).  
Figure 9: Circular economy in the cement production sector.  
Figure 12 evidences the decrease of the carbon dioxide combustion emissions intensity from 336 kg\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\) in 2005 to 308 kg\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\) in 2015. In addition, the carbon dioxide process emissions intensity from 529 kg\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\) in 2005 to 522 kg\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\) in 2015.  
The taxonomy report [29] proposes a limit value for clinker production of 766 kg\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\). This value is lower than the reported for the Spanish clinkers shown in Figure 12. Such report also suggests threshold values for other parameters (clinker/cement ratio \(<\) 0.65; kg\({}_{\text{CO2}}\)/t\({}_{\text{cement}}\)\(<\) 498, and kWh/t\({}_{\text{cement}}\)\(<\) 85). This proposal was presented with very strict limits on CO\({}_{2}\) emissions and energy demand in cement production. Therefore, it will be very difficult to meet in many cases, particularly in CEM I production [28].  
All in all, if a factor of 0.20 is applied to the CO\({}_{2}\) calcination emissions Equation (1) (which is what is proposed in the IVL simplified methodology [26]), given that, CO\({}_{2}\) absorption in Spanish cement manufacturing plants attributed to the service life period has been estimated at 27,358.481 tons of CO\({}_{2}\) in the period from 2005 to 2015 (Figure 13). In a similar way, the CO\({}_{2}\) absorption estimation during the end-of-life and secondary use was calculated by using Equation (2), and the results are also given in Figure 13.  
Figure 11: Clinker production (tons): grey clinker (bars in blue); white clinker (bars in orange).  
Figure 12: CO\({}_{2}\) global emissions intensity (t\({}_{\text{CO2}}\)/t\({}_{\text{clinker}}\)). Evolution from 2005 to 2015 of the Spanish clinker production.  
The CO2 total amount for the end-of-life and secondary use between 2005 and 2015 is estimated at 3,932,272 tons of CO2. Summing up, it can be said that the total amount of carbon dioxide uptake of the Spanish cement industry from 2005 to 2015 is 31,290,753 tons of CO2 (Figure 13).  
Figure 13 shows the carbon dioxide uptake by the cement-based materials produced with the Spanish cement manufactured between 2005 and 2015 considering the IVL simplified methodology [26]. (Only the CO2 emitted as a result of the decarbonation process is taken into account, i.e., emissions due to fuel are not considered).  
Climate models have been improved since the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (AR4). The ability of climate models to simulate temperature increase has enhanced in many significant aspects, though not all. Given that, the climate models evaluated by Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (AR5) do not take into account the net carbon dioxide emissions of the cement industry [30]. Therefore, all the models can be improved by adding this parameter.