Abstract
Recent standardization developments within the European Union relating to masonry and block systems now allow calculation of thermal performance to be undertaken based on the block configuration and reliable values of the material thermal conductivity. In general, to attain the optimum thermal resistance of a block a minimum amount of material is used such that the webs and faces bounding the air spaces are usually of the order of 6—8 mm. However, the current standard measurement methods are not suitable or precise enough for direct measurement on thin specimens cut from blocks. As a result the masonry industry requested that CEN TC89 investigate and recommend candidate alternative methods suitable for standardization.
A working group was established and following consideration of the issues involved, including, in particular, the thermal conductivity range, simplicity, small size, and short operating times, two methods were proposed for further investigation. The first was the steady-state guarded heat flow meter and the second the transient hot strip in both its linear and disc configurations. In order to verify their applicability both methods were used in an initial inter-comparison involving a total of nine organizations. Measurements were made at or close to room temperature on uniform thin test specimens fabricated from a batch of one typical masonry material.
This article contains details of the distinctive features and suitability of each method for the task, the participants, the material and test criteria, and includes a summary and discussion of the results that includes unexpected effects due to anisotropy in the particular material. Overall, the results were very promising such that a further series of intercomparison measurements is now underway on some typical materials within the total conductivity range for masonry type products.
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