Fresh cement and concrete pastes have been shown to 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. In the 1970s, Dr G H Tattersall, working at the Centre for Cement and Concrete at the University of Sheffield, designed a rugged machine which would establish the two characteristic parameters. We have considerably improved 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 CTPT is available in a Laboratory version, with separate PC system. A Site version with an embedded computer and industrial display is planned. 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.

Key features of the CTPT2:

Robust, welded-frame construction
State-of-the art servomotor drive
Contactless independent torque sensor
Electrically interlocked guards
Automatic control of speed of rotation
Impellers may be fitted centrally or via planetary gear
Sample container mounted on wheels to ease loading & improve safety
Stainless steel impellers available as an option
Suitable for R & D, troubleshooting and QA/QC
Impeller speeds <0.01 rpm to 120 rpm
Torque to 30 Nm
Torque measured electronically
Speed profile may be ramped or stepped,
      constant or manually varied
Working parts may be cleaned with hose
Powered from single phase 230V 50Hz.
    110/120V 60Hz available also
Computer system logs data and analyses rapidly
CTPVT Version allows Vane Test too.

We are always happy to quote for special modifications to suit your needs

CTPT2 Two Point Workability Test

To show different types of flow behaviour that have been observed for different materials. Cement based materials tend to be Bingham Fluids.

Plot of CTPT2 raw data for a sand and cement mortar, showing the preprogrammed "staircase" speed profile and the resultant torque.

Effects on the Flow Curve of the addition of Water and Superplasticiser

© 2003 - 2009 Celsum Technologies Limited
Page last updated 15th June 2009
Specifications subject to change without notice
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