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Climate-kind concrete - A key building block for the future
Sep 15, 2020
Sustainably effective concepts are becoming increasingly in demand worldwide as a means to mitigate climate change. In the field of construction, too, there are important contributions that can be made to securing the future of mankind. The world’s population is still growing inexorably, with living space already at a premium. Climate-kind concrete can go a long way to significantly improving the carbon footprint of the entire industry. And MC too is in the vanguard of related research.
Climate change is a reality and the measures needed to arrest its progress are undisputed: First and fore most it is about cutting CO2 emissions. In particular, there is a huge onus on industry to effectively reduce its output of this, the number one greenhouse gas. Much has happened in this regard within the construction sector in recent years under the heading of "sustainable building" – and there is still plenty of scope for exponential progress. Construction today relies heavily on concrete. And one of its main constituents is cement. Depending on which data sources you read, global cement production accounts for between five and eight percent of the world’s CO2 emissions. Currently, around one tonne of the greenhouse gas is released per tonne of cement. This CO2 balance results from the technically unavoidable deacidification of the limestone, the burning (calcination) of the cement clinker, and the power used by the grinding process.
The world needs concrete
Of course, our modern world is unthinkable without concrete, because the need for buildings and infrastructure is ongoing, and concrete structures are durable. As a material, concrete offers many advantages: It is malleable, structurally stable and inexpensive, so there is really no alternative to it as a general-use building material.
Intensive efforts are therefore being made worldwide to further reduce the carbon footprint of concrete. Using secondary fuels for the rotary kiln is one major improvement in this respect. And now another can be achieved by reducing the clinker content in the cement, for instance by using granulated blast furnace slag and limestone powder. However, new compositions such as this bring with them new challenges.
The company Holcim is able to supply a concrete mix that can significantly reduce its carbon footprint as a construction material. At the end of April, Holcim Beton und Betonwaren GmbH delivered its first climate-neutral concrete in the form of Holcim EcoPact Zero, in which MC concrete admixtures are a key ingredient. Holcim EcoPact is suitable for all components in building construction, from foundations and exterior and interior walls to stairways, roofs and ceilings. For the construction of the new Rheinauen NABU nature conservation centre in Bingen (Rhineland-Palatinate), Holcim truck mixers delivered around 280 cubic meters of the construction material to the site adjacent to the river Rhine. Optimised composition means the CO2 balance of Holcim EcoPact is significantly reduced.
Recycling in concrete production
Holcim is not the only company for which environmental and climate protection is playing an ever-increasing role in its decision-making. In almost all ready-mixed concrete and precast concrete plants in Germany, residual concrete and residual water are recovered, processed and reused. Legislators are also demanding the use of recycled aggregates, helping to drive a trend that will undoubtedly gain further traction in the coming decades. Ultimately, the availability of primary raw materials such as gravel and sand is finite, and the amount of fly ash in Germany, for example, is also steadily declining with the abandonment of coal-based electricity generation. The concrete industry is acutely aware of these changes in the economic and environmental landscape and is seeking out alternative raw materials for concrete production. Plasticisers that also function with these new materials are thus destined to become increasingly important.
MC-PowerFlow evo for technological challenges in concrete development
MC-Bauchemie has launched MC-PowerFlow evo, a new generation of superplasticisers that enable the technological challenges associated with this kind of eco-friendly concrete to be overcome. These are synthetic flow enhancers manufactured in MC’s own production facilities on the basis of a patented process derived from our proven PCE polymer technology. Categorised as high-performance superplasticisers, they are ideally suited to the production of ready-mixed concrete and precast elements, free-flowing and self-compacting concretes, and also to combination with clinker-optimised cements. They exert a liquefying effect that ensures fast and cost-efficient concrete production. And because they can also be combined with alternative starting materials such as clinker-optimised binders, recycled material and water, or lower-quality raw materials, they also contribute to environmental and climate protection.
Cement-free concrete based on geopolymers
Geopolymers are a viable alternative to cement. They contain blast furnace slag, fly ash and other latent hydraulic and pozzolanic substances as binding agents. Like normal concrete, polymer concrete also contains aggregates. The binder is activated by certain additives. Previously it was not possible to install such concretes in large quantities due to the short reaction time involved in this process. Together with WAGNERS, Australia, MC-Bauchemie has developed concrete admixtures which ensure that the required processing properties are maintained – representing a true milestone in concrete technology!
Earth Friendly Concrete a proven success
The resultant “Earth Friendly Concrete” (EFC) was successfully used in the construction of Brisbane West Wellenkamp Australia (BWWA) Airport. Development of this geopolymer concrete to mature applicability took 10 years to complete. During the last four years of this phase, WAGNERS worked closely with MC-Bauchemie on the development of superplasticisers to create the application properties required for efficient EFC installation. Conventional concrete admixtures are completely ineffective in such binder systems, so that a completely new admixture technology had to be developed. The geopolymer concrete offers a number of significant technical advantages: It is fully resistant to sulphates and highly resistant to acids, has minimal shrinkage and low thermal expansion. Any sulphate exposure actually has an additional strengthening effect on this geopolymer concrete, serving to further increase its resistance and resilience. It is therefore ideal for use in structures subject to aggressive chemical attack, such as sewage treatment plants or chemical production facilities, plus – of course – infrastructure projects. After extensive testing to verify suitability and durability, EFC was used to construct BWWA's taxiways, turning nodes and hangar aprons over an area of more than 50,000 m2. The concrete was produced near the construction site in a mobile mixing plant and installed using a conventional slip form paving machine. The pavement structure is impressive both technically and due to the fact that using EFC meant the avoidance of 6,600 tonnes of CO2 emissions. MC's expertise and concrete admixture technology was a major driver in the development of this innovative material.
World’s first cement-free backfill grout for tunnel construction
A unique geopolymer-based technology, jointly patented by MC and PORR GmbH in Germany, has already been used in the Stuttgart 21 megaproject. The consortium ATCOST21 responsible for constructing the railway tunnel for this project approached MC and together we developed a special geopolymer for use in anhydrite-containing rock formations: the new backfill grout MC-Montan Grout AA 03. Its unique selling proposition is that it combines the advantages of a single-component (1C) grout with those of a two-component (2C) grout through the flexible use of an activator. The grout also contains complex phosphates which influence the solution equilibrium of the anhydrite in such a way that swelling is inhibited. It thus ensures optimum tunnel tube bedding properties together with exceptional sulphate resistance.
Bright future for geopolymers
Geopolymers offer many advantages and are already in use in various applications. They are more thermostable than conventional concrete due to the fact that the water bound in the latter gives rise to steam pressure in the event of a fire, with cracking and spalling an inevitable result. Geopolymers are more resistant to chemicals because they do not contain lime, which dissolves on contact with acids and other aggressive substances. After just one day, geopolymers develop similar compressive strengths to high-strength concrete. They can be quickly stripped from their form setup and are suitable for the mass production of prefabricated parts. They are particularly ideal for (steel-reinforced) concrete components likely to be exposed to aggressive acid or sulphate attack, such as sewage treatment plants, sewerage pipes or components in sulphate-containing (ground) water. By making use of secondary raw materials such as granulated blast furnace slag or fly ash, they also significantly reduce the burden on the environment.