Improved microstructure by optimized water requirements

In everyday construction practice concrete is often produced applying water amounts in excess of what intrinsically is needed for appropriate workability and complete hydration. This is especially true for high slump and self-compacting concretes (SCC). For an increased robustness of concrete to water overdose the building chemistry sector supplies viscosity modifying admixtures (VMA), which would not have been needed when the amount of mixing water was optimized beforehand. Therefore, in this research the spread-flow test has been analyzed in more detail. In this way new measures are derived which contribute to a deeper understanding of wet granular mixtures at the onset of flowing. The deformation coefficient which is derived by the spreadflow test was confirmed to correlate with the product of Blaine surface and intrinsic density of the individual powders when the mixture is flowing only under its own weight. Similarly, correlations with equal accuracy have been found with a computed specific surface based on measured particle size distributions instead of the Blaine surface. Using simple flow experiments it was furthermore possible to derive an overall factor for assessing the nonspherical shape of the powder particles. A good correlation of this computation algorithm was derived compared to the standard Blaine method. Finally, a constant water layer thickness around the powder particles was derived for all powders at the onset of flowing. This implies the possibility to predict flow behavior of mortar and concrete mixtures only based on the knowledge of their granular characteristics. This water layer thickness is of different nature and size as the well-known ITZ.