A note on the difficulties of measuring the thermal conductivity of concrete

It has been observed that partially saturated concrete takes several hours to reach a steady state when the hot-plate method is used to measure thermal conductivity; theoretically, the time should be far less than one hour. This indicates that moisture movement always takes place. Consideration of the thermal gradients and the measurement times for the hot-wire transient method indicates that moisture movement should affect the measurements. This has been observed experimentally. Other methods are considered, and it is shown that little improvement can be expected from increasing the size of conductivity probes. The intrinsic difficulties of all methods are discussed.