Measuring the Thermal Conductivity of Building Materials
Energy demands continue to rise as a result of increasing population and urbanization. Maintaining a comfortable indoor temperature accounts for a significant portion of energy use worldwide, and innovative new insulative and efficient materials for building structures are at the forefront of energy conservation.
Cement and concrete play major roles in the construction industry and researchers are seeking ways of creating better materials that provide high levels of insulation without sacrificing structural strength. Thermal conductivity is critical in the development of these materials as lower thermal conductivity values correlate to better insulative systems. With Trident, testing thermal conductivity of concrete is easy, as sample sizes do not need to be adjusted and can be tested in a matter of seconds. Both MTPS and TPS transient sensor can be used, depending on the objectives of the testing.
Thermal Conductivity Testing of Aerogel Concrete with MTPS
Thermal Conductivity Testing of Concrete with TPS
Thermally Insulated Concrete
The main benefit of the TCi to our testing lab is its ease of use and short test times. It allows us to get accurate results as quickly as possible and with excellent repeatability. Our test times are only a fraction of what they are using steady state methods. Equally important, the service level has exceeded our expectations.”
Dr. Ernest Wolff, CEO, PMIC Lab (Sector: Contract Lab)
Chemical Retreating for Gel-Typed Aerogel and Insulation Performance of Cement Containing Aerogel
This case highlights research into more insulative building materials by mixing aerogels with cement for better thermal performance. Aerogel is an extremely insulative material with a stated value of less than 0.03 W/mK in pure form.
Thermal conductivity results of the mixed samples tested with the TCi are shown in the graph below. Increasing weight % of aerogel content directly related to a reduction in thermal conductivity of the cured cement composite. Treating of 2.0 weight % aerogel saw a thermal conductivity decrease of over 75%.
Thermal Conductivity Testing of Lightweight Concrete with Transient Plane Source Method
The thermal conductivity of a light-weight concrete was measured utilizing the C-Therm Transient Plane Source (TPS) FLEX sensor.
The flexible, 13mm Kapton-based sensor was placed between a sliced lightweight concrete cylinder.
Referencing ISO standard documents and an approximation of the thermal conductivity, the power applied was chosen to be 0.5W and the measured test time to be 40s. Experiments were carried out in 10 trial segments.
Following ten measurements with removal of the sensor between tests, the thermal conductivity of the lightweight concrete was determined to be 0.52 W/mK with a reproducibility better than 5%.
Figure 1. illustrates the reproducibility results, with the average thermal conductivity of the 10 trials represented by the solid line. Above and below the average line are +/- 5% error lines. The observed variation between tests can be partially attributed to the sample’s inhomogeneity.
The precision was also examined via an additional 10 measurements without the removal of the sensor between measurements. A 3 minute wait time between measurements ensured the heat completely dissipated prior to the next measurement. The precision was determined to have a better than 2% relative standard deviation.