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Thursday, 18 July 2019
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Raw materials & technologies, Technologies

Controlling the rheology of modern concrete

Monday, 23 September 2013

Understanding the rheology of cementitious systems and how to control the workability by the use of chemical admixtures is the key to innovations in concrete technology.

<emphasize>Concrete has evolved into high-performance material</emphasize>

<emphasize>Source: Stefan Körber - Fotolia.com</emphasize>

Concrete has evolved into high-performance material

Source: Stefan Körber - Fotolia.com

During the last three decades concrete has emerged from a rather simple mass construction material based on only the three components cement, water, and aggregates towards a high performance material, which can be adjusted for high performance applications and according to ultimate user specifications. The reason for the rapid evolvement was the increasing awareness about how the rheology of concrete can be improved without negatively affecting the mechanical properties of concrete. Hence, mineral additions and in particular chemical admixtures have been the most influential factors for the technological boost since approximately the 1980s.

The incorporation of superplasticizers into concrete mixture compositions eventually facilitated concrete engineers to improve the workability properties without need to increase the water-cement-ratio (w/c) and furthermore to significantly reduce the w/c without loss of workability. This finally resulted in concrete with higher performance and specified properties. Fillers are basically used to improve the particle packing of cementitious systems, but they can also be used beneficially to support the rheology, since they modify the water demand and may interact with superplasticizers as well. Finally, supplementary admixtures like polysaccharides have become more popular in the field of mortar, plaster, and grout technology. They can have a variety of rheological effects on cementitious systems, which can be used to individually adjust their performance.

Catalyst for invention of mortar and concrete innovations

The possibility to control the rheology and the significantly widened range of consistencies that can be adjusted opened up the gates for modern concrete and any type of high performance concrete. Therefore, without doubt, it can be concluded that the capability to control the rheology of concrete systems can be considered as the catalyst for the invention of the many recent mortar and concrete innovations such as polymer modified cementitious composites (PCC) self-compacting concrete (SCC), high-performance concrete (HPC), ultra-high performance concrete (UHPC) or engineered cementitious composites (ECC).

Therefore, understanding the rheology of cementitious systems and how to control the workability by the use of chemical admixtures is the key to innovations in concrete technology. However, the other side of the coin of versatility is that sophisticated cementitious systems have become more sensitive. Hence, concrete mixture composition with admixtures demands for a high level of expertise and often there is lack of awareness about the mode of operation of rheology modifying admixtures among concrete technologists. In his paper at the European Coatings Conference "Façade coatings and plasters”, Wolfram Schmidt, BAM Federal Institute for Materials Research and Testing, gives a comprehensive overview about rheology modifying constituents such as superplasticizers, stabilising agents, and mineral fillers, and how they can be used depending upon the application in the most favourable way.

 

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