Evaluation of mixing time and speed on the rheological properties of self-consolidating concrete

Due to the composition, the production of self-consolidating concrete (SCC) requires more mixing energy to uniform and homogenize the concrete components. This limits the rate of concrete production in comparison with the convectional concrete and therefore is an important financial factor. So mixing energy (mixing time and power) is one of the main factors in concrete production and before large production, the appropriate mixing time and speed should be determined for each mixture. In this study, according to objectives and considering that mixing time and speed are two main factors in content of mixing energy and according to guidelines and regulations, two SCC mix designs (powder type and VMA type) were mixed in three mixing times (3, 8 and 11 minutes) and each of them in two mixing speeds (20 and 40 RPM) and their effect on rheological properties was evaluated. The results showed that in each series of mixtures by increasing the mixing time up to a certain level that is called stabilization time (the shortest mixing time) and in this study is 8 minutes, the workability of concrete increases and after that by mixing up to 11 minutes it decreases 6 percent. Static yield stress in the 8 minutes mixing has minimum amount too and by mixing up to 11 minutes it increases 42 percent. This increment reaches to 62 percent for Dynamic yield stress, so the rheology tests also confirm these results.