# Carbon Dioxide Uptake by Cement-Based Materials: A Spanish Case Study
## 1 Introduction  
According to The Intergovernmental Panel on Climate Change (IPCC) [1; 2], from 1750 until 2011, the CO\({}_{2}\) emissions coming from the use of fossil fuels and cement production released an average of about 375 GtC year\({}^{-1}\) (from 345 to 405). Between 2002 and 2011, the average emission of fossil fuels and cement production stood at 8.3 GtC year\({}^{-1}\) (from 7.6 to 9.0), showing an annual growth of 3.2%, which is greater than what was recorded in the 1990s, which was 1%. In 2011 alone, the fossil fuel emissions amounted to 9.5 GtC year\({}^{-1}\) (from 8.7 to 10.3) [2]. Figure 1 shows the anthropogenic world emissions of greenhouse gases (GHG) by economic sectors. It must be pointed out that the anthropogenic emissionsof greenhouse gases (GHG) have almost doubled in the past 50 years (Figure 2). In that same period, CO\({}_{2}\) emissions in the cement sector have increased fourfold.  
The economic sectors that most affect the direct world emissions of greenhouse gases (GHG) are the electricity and heat production (25%), industry (21%), and transport (14%). All of them represent 60% of the global direct GHG emissions (Figure 1). In particular, the effect of the electricity, heat production, and transport (39%) could be reduced by means of technological improvements (better thermal insulations, usage of the hydrogen power, fuel cells, electrical engines, and so on). Therefore, a lower contribution of these economic sectors would be expected in the near future. With regard to the industrial sector, such reduction of emissions of greenhouse gases (GHG) is a sensitive matter.  
On the other hand, indirect emissions of greenhouse gases (GHG) are mainly due to buildings (12%) and industry (11%). Considering together direct and indirect emissions of both economic sectors, the impact of buildings (18.4%) and industry (32%) became of great significance.  
Figure 2 shows the evolution of the world emissions of greenhouse gases (GHG) from 1970 to 2010 by economic sectors. In the last decade (2000-2010), the increase in emissions attributed to industry  
Figure 1: World emissions of greenhouse-effect gases (GHG) by economic sectors [2]. Definition of AFOLU: Agriculture, Forestry and Other Land Use.  
Figure 2: World emissions of greenhouse gases (GHG) by sectors, in gigatons of CO\({}_{2}\) equivalent annually [2].  
(+45%) and energy (+36%) was higher than three quarters (+81%). These data suggest the need to implement technological measures to reduce the mentioned emissions.  
In order to register the contribution of the European countries to the EU record of emissions, the Union's registers guarantee exact accounting of all the emission rights allocated as a result of the European Union Emissions Trading System (EU ETS). The register keeps a record of the ownership of the emission rights that appear in the electronic accounts in the same way that a bank keeps a record of customers and their respective funds.  
The European Union Transactions Log (EUTL) automatically checks, records, and authorizes all the operations between union account records. This guarantees that all the transfers comply with the EU ETS standards. The EUTL is the successor to the Community Independent Transaction Log (CITL), which performed the same function before the union register was introduced.  
The data contained in the union records include the 31 countries that take part in the European Union Emissions Trading System (EU ETS), which is merely an online database that stores the accounts of holders of fixed installations. According to the data, the Portuguese industry subject to emission rights emitted 4.6 million tons of carbon dioxide in 2015 (total absolute gross CO2 emissions without biomass emissions), which is 31.25% less than in 2005 (6.7 million tons of carbon dioxide).