Computer Controlled Workability Test For Fresh Cement And Concrete
equipment manufacture, process control, control equipment
Fresh cement and concrete pastes behave as Bingham fluids, that is to say that they do not flow until a characteristic Yield Stress has been exceeded. After this yield stress, they flow in a linear manner, with the shear stress being proportional to the shear rate. The level of the yield stress and the degree of proportionality between yield stress and shear rate (ie the plastic viscosity) are functions of processing parameters such as water content, sand to cement ratio and the amount and type of aggregate present.
If these parameters could be measured for each batch of fresh concrete, a pattern could be established of which batches were acceptable and which caused problems. We have considerably improved the original design of the machine by adding state-of-the art automation in order to eliminate some operator variables of earlier versions, and have built in full guarding to protect the operator.
The sample, of about 20 to 30 litres, is contained in a steel bucket. An impeller (of which there are several geometries) is rotated in the mix at a series of controlled speeds, and the torque required to mix at each speed is displayed on a pressure gauge and recorded electronically. A planetary drive is available to avoid problems due to cavitation. A purpose-written computer programme analyses the data and determines the characteristic Yield Stress intercept and the Slope of the torque vs speed graph.
The CTPT3 is supplied with a separate PC system. A Site version with an embedded computer and industrial display is available too. The machine may be programmed to run a "standard" test with ramped speed, or may be run at constant speed or at a series of constant speeds. The instrument is extremely useful in formulation development, quality control, troubleshooting, and for research applications.
, equipment manufacture
, materials testing
, process control
, Process control equipment