Development and evaluation concept for CO2-reduced concretes

Technical and ecological performance

Concrete construction is considered to be both CO2 and resource-intensive. This is essentially attributable in terms of the raw materials to the cement clinker, from whose production worldwide more than 5 % of the anthropogenic greenhouse gas emissions result [1]. Therefore strategies are primarily being pursued for the design of concretes with a reduced CO2 load that partly or completely replace the clinker con- tent in the cement or the cement content in the concrete by inert or reactive additions (fly ash, limestone meal, etc.). These have already given rise to a number of approaches that are available to the user for a low-CO2 concrete design. [2, 3] Nevertheless it is currently not possible, or only possible to a very limited extent, to use concretes with a reduced CO2 load in practice. This is essentially attributable to three points: I) Concretes with a reduced CO2 load have a considerably reduced cement content, which lies below the limit value prescribed in the European regulations for ensuring sufficient durability. Therefore the descriptive proof of the performance anchored there is not possible. II) The performance (e.g. the durability) is changed by replacing the clinker with alternative materials. For the special application, therefore, the necessary cement content of the concrete must be determined, taking into consideration the required per- formance. III) Due to the substitution of cement, the water/cement ratio increases although the water content is the same. Therefore it is necessary to reduce the water content and to use the remaining water efficiently for the formation of consistency. There is a lack of simple, practically oriented concepts here. Hence, a comprehensive and objective evaluation concept is necessary that can determine the largest possible clinker substitution with respect to the required performance in the respective application and the associated CO2 load of a concrete. The principles for this evalua- tion concept are being developed in a collaborative research project conducted by the Building Materials Institutes at three universities in Lower Saxony – Braunschweig, Hanover and Clausthal. Within the scope of the investigations a design concept for concretes with a reduced CO2 load was also created in order to estimate the performance of the concretes even during the design process. The main goal is to develop CO2-reduced normal concretes that are suitable for everyday use in a wide range of applications and whose mix- ture concept is usable worldwide, because a significant reduction of the CO2 load in concrete construction is possible only with large-scale use. Niche products with either very low CO2 loads or special concretes whose usage quantities are only minimal in comparison can have very little effect on the climate change.

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