Concrete is the world's most important building material today – and will remain so. With special additives, construction chemicals improve its properties and reduce the amount of CO2.
More than 10 billion tonnes of concrete are produced and used worldwide every year – making it the most important building material of our time. Concrete has always been developed further and its original formula of cement, water and an aggregate of sand and gravel has changed. Today, the original three ingredients are supplemented by intelligent concrete admixtures.
These liquid or powder additives change the properties of concrete. They can, for example, delay or accelerate the hardening time of fresh concrete and improve workability, but also increase the resistance, durability, and strength of hardened concrete. This makes them indispensable aids, especially in the production of ready-mixed concrete or precast concrete; or they enable new compositions of concrete that provide a significant CO2 reduction.
With concrete admixtures: reduce CO2-intensive ingredients
Positive effects
Optimising concretes and cement-bound building materials by concrete admixtures can help to reduce the proportions of water, clinker and binder. This results in concretes with identical durability but a significantly lower CO2-content, especially by reducing the cement clinker.
Concrete admixtures can be used to make concrete more sustainable. One focus lies on the component cement, the precursor of which, cement clinker, must be produced with enormous energy input. To achieve the reactivity of the cement clinker, a large amount of CO2 continues to be expelled from the basic raw materials (including limestone) during the burning process (calcination process).
To increase efficiency and sustainability, additional raw materials are added to the clinker, resulting in a so-called clinker-reduced cement – with significantly lower CO2 emissions as outcome.
However: concrete with clinker-reduced cement is more difficult to process and more difficult to maintain in consistency over a certain time. This is where concrete admixtures come into play. Highly effective superplasticisers can optimise workability, concrete rheology, workability time and consistency maintenance – making concrete applications more sustainable.
In numbers
In 2021, a total of around 29 million tonnes of cement were consumed in Germany. This quantity can be further divided into different cement classifications, depending on the composition. The so-called Portland cement, which has the highest proportion of cement clinker and causes around 700 kg of CO2 emissions per tonne in its production, falls into the CEM I class. The average of all cement types is significantly lower, namely 583 kg of CO2.. If it were now possible to replace the total of 7.5 million tonnes of CEM I produced in Germany in 2021 with cement types with average emissions, this would correspond to a reduction of 877,500 tonnes of CO2 per year. This approach can be transferred to numerous other cement qualities, which means that the overall potential is significantly higher.
Conclusion
For example, a new generation of clinker-reduced cements to produce practical, robust concretes can help to significantly reduce CO2 emissions – made possible by the use of modern concrete admixtures.
Sources
Broschüre VDZ Zementindustrie im Überblick 2022/2023
With concrete admixtures: producing building components more sustainably
Positive effects
In the production of components in precast concrete plants, various improvements in terms of sustainability and resource conservation can also be brought about with the help of concrete admixtures. Up to now, cements with a particularly high clinker content have often been used to achieve a high early strength of the components. Thanks to concrete admixtures for accelerated early strength, the same or even better results are achieved, so that less clinker-rich and thus significantly CO2-reduced cements can be used.
In addition, in many cases, heaters and heated formwork are used in precast factories to achieve the minimum strength of the precast concrete element required for demoulding as quickly as possible. If accelerating concrete admixtures are used instead, normal ambient temperatures are often sufficient for strength development and heating energy can be saved.
In numbers
In a calculation example for early strength reduction, a clinker reduction of 50 to 70 kg/m3 can be achieved by concrete admixtures in precast plants, in special cases even up to 150 kg. The result is a CO2-reduction in concrete of 40 to 55 kg/m3, in specific cases over 100 kg. Transferred to the precast concrete industry, which produces 5 million m3 annually, a reduction of up to 275,000 tonnes of CO2 is possible.
Another example quantifies the effect of eliminating the heating of the plant or formwork by heating oil. Assuming emissions of 2.6 kg of CO2 due to the combustion of 1 litre of heating oil and 10 litres of oil per m3 of concrete for precast production, this results in a savings potential of 26 kg of CO2 /m3 .
Conclusion
Concrete admixtures achieve tangible sustainability effects in the production of precast concrete elements – whether through clinker-reduced concretes or the elimination of heating energy in the production process.
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Martin Ludescher
Director Government Affairs
Phone: +32 2 / 5 48 06 - 92
E-mail: martin.ludescher[at]vci.de
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