The following Application Note addresses the testing of concrete using the C-Therm TCkit™. The document highlights the use of bulk thermal conductivity testing on porous samples with the TPS method.
Researchers, engineers, and students in the field of concretes, cement, geopolymers, and similar materials need to tune their products’ thermal properties to the application in question, to optimize energy efficiency and control thermal strain. Too low thermal conductivity can result in a large temperature gradient between opposite ends of the material in the application, resulting in thermal strain and cracking. On the other hand, very high thermal conductivity can make it difficult to control the internal temperature.
To maximize efficiency in construction, a variety of lightweight concretes have been developed to decrease the weight of walls and foundations without losing much strength. However, these lightweight concretes often are more porous than their standard analogs, resulting in changes to the effective thermal conductivity. To counteract these changes and ensure the new lightweight formulations will still pass heat-transfer requirements, additives are often added to tune the thermal properties.
This document highlights the TCkit’s performance capabilities in testing concrete samples.
In testing the thermal conductivity of concrete, two similar pieces should be obtained and the TCkit’s TPS Flex sensor is sandwiched between the two pieces, as shown above. Note that the effect of contact resistance is addressed within the method and procedure outlined in the ISO standard for TPS testing. The TCkit does not, however, have the Wheatstone bridge circuitry specified in the ISO standard as it relies on a standard Keithley Source Measure Unit for its data acquisition. Should researchers wish to achieve the higher sensitivity outlined in the ISO standard, they would be advised to consider C-Therm Trident thermal conductivity instrument. .
Between each test, there is a waiting period of approximately 5-10 minutes in allowing the sample and sensor to return to equilibrium.
As concrete is typically heterogeneous, it is recommended to test the sample in multiple locations establishing a composite average thermal conductivity as illustrated in the Figure above. The results match well with the expected value for concrete and demonstrate the effectiveness of applying the TCkit in testing concretes, cement, asphalt and other similar materials.
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 International Standards Organization (ISO). 2015. ISO 22007-2: Plastics — Determination of thermal
conductivity and thermal diffusivity — Part 2: Transient plane heat source (hot disc) method.