Building Materials

Three instruments to measure thermal conductivity, from left to right: heat flow meter, laser flash analysis, and C-Therm’s Thermal Conductivity Instrument with the MTPS sensor

The following is an excerpt from the paper Building materials thermal conductivity measurement and correlation with heat flow meter, laser flash analysis, and TCi. The thermal conductivities of various building materials such as wood floor, wall materials, plywood, and high density fiber (HDF) were measured using a heat flow meter (HFM), laser flash analysis (LFA) and C-Therm’s Thermal Conductivity Instrument (TCi) using the Modified Transient Plane Source (MTPS) method.

“This experiment was conducted to measure the correlation in the thermal conductivities measured using TCi <employing the MTPS method>, as well as HFM (KS L 9016) and LFA (KS L 1604) that are included in the existing KS standard.

An examination of the correlation by measuring the thermal conductivity of various materials using HFM and TCi revealed a high coefficient of correlation (R²) of more than 0.9. Accordingly, the thermal conductivity measured using TCi can be accepted with confidence, as the thermal conductivity measured using HFM and TCi showed a high correlation for wood flooring, wall materials, and plywood with an increased mass percentage of reformed graphite and HDF.

The thermal conductivity measured using LFA and TCi for the epoxy adhesive with an increased mass percentage of reformed graphite showed a high coefficient of correlation (R²) of 0.978. Accordingly, the thermal conductivity measured using TCi for the epoxy adhesive with an increased mass percentage of reformed graphite can be accepted with confidence. However, the thermal conductivity measured using LFA and TCi for the HDF with an increased mass percentage of reformed graphite showed a very low coefficient of correlation (R²) of 0.504 because the thermal conductivity in the LFA experiment did not increase consistently. Based on this result, the value obtained by using LFA cannot be accepted with confidence since it is not suitable for measuring the thermal conductivity of consistent materials such as HDF. Contrary to the existing method, TCi can conveniently measure thermal conductivity by using various sample shapes. The device is expected to find wide application and use in various areas due to its small size that allows convenient measuring of thermal conductivity even in places of spatial restrictions.”

See the article here: https://ctherm.com/resources/tech-library/building-materials-thermal-conductivity-measurement-and-correlation-with-heat-flow-meter-laser-flash-analysis-and-tci/

Abstract from original publication: Foam concrete refers to a type of low-density concrete that is commonly known to have favorable insulation and thermal performance due to its intentionally increased porosity. However, foam concrete is known to generally have a very low physico-mechanical and durability performance mainly due to its high porosity and the con- nectivity of the pores that can allow the entrance of unfavorable substances into the concrete medium. As a result, most often, foam concrete is considered inapplicable to major load bearing structural elements. To counter this tendency, this study adopted the use of basalt fibers with silica fume to increase the structural integrity of foam concrete. In that respect, 18 mixes with varying content of foaming agent, basalt fiber and silica fume have been prepared. Apparent porosity, water absorption, compressive, flexural and splitting tensile strength, sorp- tivity, ultrasonic pulse velocity (UPV), drying shrinkage, freeze–thaw, thermal conductivity, and thermal resis- tance tests were performed to evaluate the physico-mechanical, durability, and insulation properties of the produced foam concretes. Based on the results, a highly durable foam concrete with a maximum compressive, flexural and splitting tensile strength of ~ 46, 6.9 and 3.07 MPa, respectively, has been developed. Furthermore, it is observed that the inclusion of silica fume can significantly influence the pore network and enhance fiber- paste matrix. The effect of basalt fiber, however, is found to be more dependent on the use of silica fume, potentially due to its low integration with cementitious paste. The results of this study are significant and point out to the great potential for producing a highly durable and lightweight insulating foam concrete through the use of basalt fiber and silica fume. [1]

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%.

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.