Hygric properties of porous building materials: Analysis of measurement repeatability and reproducibility

Abstract

Material properties are crucial input parameters for the analysis of heat, air and moisture transfer phenomena in built environment. However, many round robin tests reveal that the measurements on material properties – especially hygric properties – have poor reproducibility. Thus the measurement and data analysis methods should be questioned, and the currently available databases for material properties are not perfectly reliable.In this paper we aim at analyzing the material errors, repeatability errors, between-lab errors and reproducibility errors involved in the determination of hygric properties of porous building materials. The same materials as those used in the EC HAMSTAD project – autoclaved aerated concrete, calcium silicate board and ceramic brick – are chosen as target materials in our tests to facilitate error analysis. Static gravimetric tests, cup tests, capillary absorption tests, vacuum saturation tests and pressure plate tests have been repeated three times under repeatability conditions. Then the experimental results are analyzed in combination with the EC HAMSTAD report to calculate various errors. Results show that different materials have different heterogeneity errors, which can hardly be avoided. Moreover, in general these tests have excellent repeatability, indicating that under proper control the tests themselves are trustworthy. However, the large between-lab errors and the subsequent poor reproducibility demonstrate that in different labs the experimental procedures, condition controls, as well as data processing methods can deviate significantly. As a result, stricter and more detailed instructions are needed to improve the reproducibility of the tests for determining the hygric properties of porous building materials.