Carbon Dioxide Uptake by Mortars and Concretes Made with Portuguese Cements

Abstract

As the cement industry continues to address its role in the climate crisis, Portugal’s cement industry has started to calculate its net CO2 emissions to become an entirely carbon neutral sector. These emissions are calculated by simply subtracting the total CO2 uptake due to mortar and concrete carbonation from the total CO2 that is emitted during the calcination process (clinker production). However, the procedures given in the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas (GHG) Inventories to report GHG emissions do not contain any element that would grant this calculation method the status of an internationally recognized procedure. Therefore, some climate models are not accurate because they do not account for the carbon dioxide uptake due to concrete and mortar carbonation, as is evidenced in this paper. Climate models have improved since the IPCC’s Fourth Assessment Report (AR4), but they can further improve by implementing carbon dioxide uptake by cement-based materials. In the present paper, a quick and easy method of evaluating net CO2 emissions is utilized (simplified method) along with an advanced method. Portuguese net CO2 emissions of the cement produced from 2005 to 2015 were calculated while taking carbon dioxide uptake during the service-life and end-of-life and secondary usage stages into account. Following the simplified method, 8.7 million tons of carbon dioxide were found to be uptake by mortars and concretes made with Portuguese cement over the ten-year period, in which 37.8 million tons were released due to the calcination process. In addition, an advanced method has been used to estimate the carbon dioxide uptake, which provided only slightly higher results than that of the simplified method (9.1 million tons).

Properties of concrete with binary binder system of calcined dolomite powder and rice husk ash

“…Cement is the most widely used construction material worldwide. Nevertheless, the cement industry faces environmental and energy challenges, including the following: 1) Generation of between 5% and 10% of the world's total anthropogenic CO 2 emissions [ 1 , 2 ]; the production of cement releases 0.73 to 0.99 t CO 2 /t cement depending on the clinker-per-cement ratio, manufacturing process, and fuel type [ 3 , 4 ]; 2) Waste material from the cement industry reaches up to 20%, including cement kiln dust production from 54 to 200 kg/t of produced cement clinker [ 5 , 6 ]; 3) Production of one t of cement requires the extraction of about 1.5 t of raw material from the earth's surface [ 7 ]; 4) Clinker is made by a dry or wet manufacturing process at a temperature around 1400–1600 °C [ 8 ] where the dry process requires 3.35 MJ/kg of clinker and the wet process requires 5.4 MJ/kg of clinker [ 9 ]. Consequently, it is necessary to seek environmentally friendly materials as alternatives to cement to reduce the adverse environmental impact, minimise raw material waste, and reduce energy requirements.…”

Performance of GGBS Cement Concrete under Natural Carbonation and Accelerated Carbonation Exposure

“…e process of Portland cement production is energy intensive, releasing a huge amount of CO 2 [1,2], both of which are likely to have a significant impact on the environment. According to Sanjuan et al (2020), Sanjuan et al (2019), and Mo and Panesar [3][4][5], the production of cement was responsible for about 7.4%, 6.7%, and 5% of the global CO 2 emission, respectively. On the other side, some studies have been conducted to find the carbonation uptake in order to verify a better carbonation emission balance.…”

“…On the other side, some studies have been conducted to find the carbonation uptake in order to verify a better carbonation emission balance. Given that, the calcium oxide in cementitious materials is not stable over time, and the hydration products gradually reabsorb atmospheric carbon dioxide as a result of carbonation process [3,6,7]. For instance, 8.7 million tons of carbon dioxide were found to be up taken by mortars and concretes made with Portuguese cement over a ten-year period, in which 37.8 million tons were released due to the calcination process [3].…”

“…Given that, the calcium oxide in cementitious materials is not stable over time, and the hydration products gradually reabsorb atmospheric carbon dioxide as a result of carbonation process [3,6,7]. For instance, 8.7 million tons of carbon dioxide were found to be up taken by mortars and concretes made with Portuguese cement over a ten-year period, in which 37.8 million tons were released due to the calcination process [3]. Sanjuan et al further reported that 31 million tons of carbon dioxide were found to be up taken by mortars and concretes made with the Spanish cement industry from 2005 to 2017 [8].…”

“…Supplementary cementitious materials (SCMs) are progressively being used in the construction industry to reduce the OPC content. Use of SCMs improves concrete durability and has environmental and economic advantages [3,5,7,9]. However, it is critical to understand the long-term performance and durability of these materials in order to maximize the service life of the structure.…”