Instrument takes a sample of fresh concrete or cement and stirs it over a controlled range of speeds, measuring as the speed changes the torque needed to maintain stirring at that speed
A rugged instrument for testing the flow properties or rheology of fresh cement and concrete is offered by Celsum Technologies.
The instrument, the Controlled Two-Point Tester (CTPT), takes a sample of the fresh concrete or cement in a bucket-like container and stirs it with an agitator over a controlled range of speeds, measuring as the speed changes the torque needed to maintain stirring at that speed.
A computer then processes the data, plots the speed-torque graph and calculates both the slope of the resulting line and the intercept.
The two points, the slope of the graph, and the intercept, give the two characteristic parameters for the material's flow behaviour since, broadly, fresh cement and concretes behave as Bingham Fluids.
These only start to flow (during useful experimental timescales) after a certain yield stress has been overcome, and flow in a linear or Newtonian manner after this; indeed, the slope of the graph is a measure of the specimen's viscosity.
Experimental work has shown that these two parameters are good indicators of the water content and of the composition ratio of the mix, providing a valuable quality control test both on-site and in development and teaching departments.
Roy Carter, Celsum's managing director, said: "The CTPT is a complementary technique to the conventional slump test.
"CTPT gives more scientific engineering information, and the data can give allow quality problems and batch-to-batch changes to be readily identified".
The CTPT is supplied with a helical impeller which mounts centrally in the sample, and with a plantary gear and two H-impellers for materials with a tendency to cavitate.
The machine is electrically driven and is fitted with double-interlocked safety guards and a control panel sealed to IP65 standards.
The impeller speed may be controlled over the range 5-120rpm, and torques up to 30Nm measured and logged on the computer system.
The CTPT computer-controlled two-point workability tester also has applications in testing materials other than fresh cement and concrete, especially non-homogeneous fluids which cannot be tested with normal laboratory instruments.
The CTPT complements Celsum Technologies's other materials testing instruments.
which include the Eta 2100 and BFR 2100 capillary extrusion rheometer, the MXR2 extensional rheometer, the T2SR time and temperature scanning rheometer, Cest combined extrudare swell and temperature, and also complements Celsum's range of process control instrumentation.
