A method for allocation according to the economic behaviour in the EU-ETS for by-products used in cement industry

The most efficient way to reduce the environmental impact of cement production is to replace Portland cement with alternative cementitious materials. These are most often industrial waste such as blast-furnace slags (GBFS) and coal combustion fly ashes (FA). However, a recent European directive no longer considers these products as waste but as by-products. Therefore, the impact of their production has to be considered. Within this new framework, this study develops an evaluation method of their environmental impacts. This paper presents pre-existing methods and underlines their limits. Through our evaluation of these methods, it has become clear that the allocation procedure is necessary; however, results depend highly on the chosen allocation procedure. This study presents a new allocation method, based on the fact that both cement and the alternative materials, GBFS and FA, are produced by energy-intensive industries (cement iron and coal) which are all subjected to the European Union Greenhouse Gas Emission Trading System. In this carbon trading system, it is economically beneficial for industries to reduce their environmental impact, like for when, by example, by-products from one industry are used as alternative 'green' material by another industry. Our allocation coefficient is calculated so that the economic gains and losses are the same for all of the industries involved in these exchanges and provides the overall environmental benefit of the exchanges. The discussion shows that whilst this method has much in common with other allocation methods, it is more accurate as it allocates the environmental costs fairly over the industries involved and is more robust because of its constant value. One of its limits is that it cannot be used for life cycle inventories; however, we test the possibility of choosing a coefficient from one impact category and applying it to all the others. Lastly, the technical term of the equation this paper presents could be employed for consequential life cycle assessment, to calculate the most environmental uses by-products could be put to.