Mixing concrete is a complex procedure and can be subdivided into two parts. Within the first, the so-called distributive mixing, the attitudes of mix particles are changed. At second, the so-called dispersive mixing.
In comparison to normal concrete UHPC can be described as a 6-7material system consisting of cement, additives and additions, water, super fine aggregates, minerals, polymers and of course fibers. Use of undensified or pozzolanic materials in special cases makes mixing procedure more complex. Due to the concrete composition the packing density of UHPC is essentially higher than for NC. Therefore, mixing parameters such as particle size, distribution and shape, differences in density as well as their surface roughness is of main importance. A “usual mixing” which is common for normal concrete seems not reasonable for UHPC concerning high energy and time requirements
The UHPC components are to be blended so that a homogeneous mixture is produced. The duration of mixing is to be chosen to produce sufficient blending of the materials. If insufficient mixing energy is used, the properties expected from the composition chosen cannot be achieved. The necessary duration of mixing depends particularly on the type of mixer as well as the composition of the concrete. Due to the low water content with respect to the content of fines (<0.125 mm) and the high dosage of admixtures, the production ultra-high strength concrete UHPC requires more mixing energy to homogenize the concrete components