GREEN CONCRETE - Institut für Massivbau

GREEN CONCRETE
Tilo Proske, Carl-Alexander Graubner
There is great potential for the reduction of the environmental impact and the consumption
of scarce resources in the field of concrete construction especially in the production of raw
materials, concrete technology and structures (see Fig. 1). Investigations on the topic of
environmental optimisation of concrete are being carried out at the “Institut für Massivbau”
in support of research activities in the field of Sustainable Concrete Structures.
Fig. 1: Opportunities for ecological optimisation in concrete construction
The major environmental impact of concrete comes from the CO 2 -emissions during cement
production as a result of the calcination and grinding process including the deacidification
of the calcium carbonate. Therefore reduction of the cement-clinker content has positive
effects on the environmental life cycle assessment of the concrete and can be achieved by
the optimisation of the mixture design (higher packing density, use of high reactive
binder). Furthermore, substitution of the cement by secondary raw materials is an additional
opportunity.
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For the practical application of green concretes, questions must be answered regarding the
workability, the strength development and the durability. At the “Institut für Massivbau“ -
different concretes with reduced cement content were developed. A compressive strength
of 10 N/mm² at an age of 24 h and 35 N/mm² after 28 days was targeted. Starting with a
cement content of 270 kg/m³ (type CEM I, minimum value according to DIN 1045-2:2001-
07 for some exposure conditions), the cement content was reduced below 100 kg/m³. The
powder content of approximately 400 kg/m³ was kept constant by the addition of fly ash
und limestone powder.
TC = 25°C
Fig. 2: Compressive strength of cement reduced concretes
It was noted, that even concretes with cement content lower than 150 kg/m³ were able to
meet the defined strength requirements (see Fig. 2). However, a significant reduction in the
water content, as well as addition of reactive powders like fly ash and silica fume or a
higher cement strength class was necessary to achieve this. Additionally, a higher demand
of superplasticizer was required. The optimisation of the clinker volume in the mixture
composition has led to a reduction of 55 % in environmental impact compared with the
standard concrete mixture. Further research work will include high performances binders
and durability aspects.
Keywords
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Green Concrete, cement reduced concrete, fly ash, sustainability, environment, CO 2
http://www.darmstadt-concrete.de/2008/greenconcrete.html