Development of a modified concrete rheometer to measure the rheological behavior of conventional and self-consolidating concretes

The modified concrete rheometer (MCR) apparatus developed in this study is based on existing concrete rheometers, the main differences being the gap size and measurement method, and thus the interpretation of the results. The gap between the inner cylinder wall and the tip of the vane was set to 6.4 times the diameter of the largest coarse aggregate in order to reduce interaction between the aggregate and the wall and the friction force from the wall. The MCR apparatus was used to measure yield torque directly at different low rotational speeds (above 0.003 rev/s). A study of the yield torque and viscosity of 37 fresh concrete mixtures was also made, with a particular focus on self-compacting concrete or self-consolidating concrete (SCC), and the results were compared with those obtained using other workability tests. The test results showed that the MCR can differentiate between conventional concrete (CC), powder-type SCC and SCC with viscosity-modifying agents (VMA). The rheological behavior of powder-type SCC was found to be influenced by the composition of Class F fly ash and ground granulated blast-furnace slag (GGBFS), and this type of concrete exhibited a wider range of viscosity and yield torque values. Despite the lower powder content and larger water to binder ratio (w/b), the viscosity of VMA-type SCC was shown to be slightly lower than that of powder-type SCC, and the values were clustered together within a certain range; thus, the workability of SCC containing VMA is more easily controlled. In addition, the MCR apparatus can also be applied to CC of differing viscosity and yield torque, thus making this apparatus suitable for determination of the workability of all kinds of fresh concrete. (C) 2010 Elsevier Ltd. All rights reserved.