Rheological investigations on the workabilityof self compacting concrete

The rheology of mineral building materials

Production process optimization, greater ease of concrete installation and the durability improvement of concrete structures are just some of the benefits derived from the use of Self Compacting Concrete (SCC). SCC is the result of a technological advancement that is in continual progress and whose potential for optimization with respet to the process of industrialization in the construction industry is far from being complete. This was also made possible by the substitution of conventional admixtures based on naphtalene-sulphonates with new admixture developments based on polyacrylates. The result is a concrete featuring special workability characteristics during the casting stage and prominent elasto-mechanical properties during its service life. Workability is a term addressing several properties of concrete, such as stability, a low tendency to segregation, and last but not least, a well developed flowability. This article describes new developments on rheological characterization that allow for an optimization of the mix design and the performance of SCC property control by highlighting the results of comparative tests between standardized slump flow test runs on concrete workability and rheological test runs based on system deformation capacity and the way movement occurs if an external force is applied. Rheological tests were performed using a viscosimeter that better describes concrete flow behaviour. Conventionally, the characterization in the plastic stage is achieved by means of single point measurements as in slump flow testing, in some cases density and air content are measured. On the other hand, the rheometry describes rheological behaviour with the help of a shear rate/stress gradient and by evaluating parameters such as plastic viscosity and yield stress. In this paper, the test run results were obtained by performing comparative tests on SCC while changing the quantity and type of admixture. Also, it has been demonstrated that rheology is an appropriate tool to identify an adequate mix design.

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