Study of two concrete mix-design strategies to reach carbon mitigation objectives

Abstract

The building and construction sector is a major CO2 producer and climate change perspectives urged to reduce CO2 emissions. The impact of concrete buildings on environment is mainly due to clinker, which is the main material used all over the world to produce cement and which releases a bit less than 1 ton of CO2 per ton of clinker produced. In this study, we first evaluate if the medium term CO2 emission reduction objectives for the cement industry are realistic according to our current scientific and technologic knowledge. We consider two environmental strategies. The first one is the substitution of clinker by mineral additions in cement in order to reduce the environmental cost of the material for a given volume of material; the second one is the reduction of the concrete volume needed for a given construction process by enhancing the concrete performances. The impact on CO2 emissions of a combination of these options is also roughly evaluated. We show that medium term objectives can be reached although long term objectives will need further research developments. We moreover present here a first step towards mix-design methods associating environmental costs and performance requirements which could allow for a better balance between societal demand in terms of environment and technical building requirements. 2009 Elsevier Ltd. All rights reserved. The industrial sector is responsible for approximately 25% of global carbon dioxide (CO2) emissions among which CO2 emissions from cement plants represent no less than 5% of total anthropogenic emissions [1,2] despite the efforts of the cement industry to reduce emissions. Recent studies on the Life Cycle Assessment (LCA) for concrete structures show that 85% of the CO2 emissions are related to cement production [3]. Moreover, LCA for cement shows that 95% of the CO2 is produced during the fabrication of the cement, compared to emissions during the transport of raw materials and finished products [4]. It seems therefore obvious that the necessary effort in the building and construction sector in term of CO2 reduction has to be made on the type and amount of cement used in concrete, at least as a first step. The cement industry has been encouraged to keep on improving its production processes to reduce its CO2 emissions due to the Kyoto protocol goals. The so-called Kyoto protocol was signed in 1997 with the aim of reducing the developed country’s greenhouse gas emissions by 5.2% from the 1990 level by 2008–2012. To enforce the implementation of the Kyoto targets, the European Union