The CTPVT, developed by Celsum Technologies, carries out the vane test to allow the yield or slump characteristics of the materials to be accurately determined
Celsum Technologies has designed and built a new instrument for testing fresh cements and concretes, developed from its CTPT two point workability test instrument.
The first instrument is being shipped to a research institute in Australia to study and develop shotcrete compositions sprayed to stabilise tunnel walls in goldmines.
The CTPT is basically an instrumented but robust stirrer that measures the torque required to stir the mix at a series of controlled speeds.
Since most concretes conform to a flow pattern known as a Bingham fluid, where the material will not start to flow until a certain yield stress has been exceeded and, after this, flows in a linear manner, where torque increases linearly with speed, the flow characteristics of the sample may be described by two points, namely the yield stress value and the slope of the line after the yield stress has been exceeded.
Experimental work has shown that these two points are sensitive to the sand-to-cement ratio, the water and aggregate content, and the proportions of additives such as superplasticisers.
The instrument is fully computer controlled, and may be run in manual, ramp or staircase speed control modes.
The maximum torque is 30Nm, and the maximum speed of the impeller is 120rpm.
The CTPVT is a modified version that allows the vane test to be carried out.
Designed originally for soil testing, the vane test involves inserting a cruciform, or cross-shaped, probe into the sample, then rotating the probe at a slow, controlled speed, typically 0.1 revolutions per second (6rpm).
As the probe is rotated, the torque generated is monitored.
The torque builds to a maximum until the yield stress is overcome, when the sample slips and rotates around the boundary of the cross-shaped profile, thus giving an accurate and directly measured value for the yield stress.
Celsum Technologies's managing director, Roy Carter, said, "The CTPVT has involved solving some tricky technical problems.
"We have modified the drive so that we can use a highly accurate, state-of-the-art, servo-drive system, and are directly measuring torque using a contact-free strain-gauge based torque transducer.
"The CTPVT is about 500mm higher that the CTPT, as we needed to arrange for the Vane probes to be inserted carefully without disturbing the structure of the sample.
"We have accomplished this using a telescopic, splined-shaft arrangement.
QAdditionally, we have incorporated many safety features to ensure that the machine can be used without harming the operator.
"Since the CTPVT and CTPT use large samples (typically 20 to 30litres), they can be used to test samples that are not homogeneous, such as concrete with large aggregate particles, that cannot be tested using the usual laboratory techniques.
"We think that these instruments will have applications to other difficult-to-measure materials, as well as to fresh cements and concretes".
Celsum Technologies designs and manufactures a range of special test instruments for materials testing, and distributes a wide range of sensors measuring load, pressure, acceleration, as well as instrumentation for data-logging, serial connectivity, strain gauge conditioning and process control
