The use of a thermal dual - Probe for the moisture measurement of building fabrics: The testing of the technique via comparisons with measurements from an x-ray system

The measurement of moisture in building fabrics has been of interest for many years due to the potentially devastating consequences of moisture problems within buildings. A range of potential techniques are available with which to measure the moisture content of building fabrics in-situ and this paper focuses on one particular technique, the 'thermal dual-probe'. Note that this method is distinct from the single probe technique. Essentially, a short pulse of electrical energy is applied to a wire within the 'heating' needle. A separate 'temperature sensor' needle, which incorporates a thermocouple (for example), records the resulting maximum temperature rise in the material at a certain distance from the heating needle from which the moisture content can be deduced. This approach offers the potential for some significant advantages over existing techniques. Whilst the technique has been successfully applied to soil measurements, a reliable and appropriate dual-probe system for in-situ measurements in building fabrics has not previously been established. This study (funded by the UK Government's Engineering and Physical Sciences Research Council) has, for the first time, successfully optimised the technique for this particular application via extensive Finite Element modelling and experimental work. Previous work by the authors has compared moisture measurements taken using the thermal dual- probe with those obtained from gravimetric analyses. Close agreement between the two techniques was achieved. This current work extends the development of the thermal dual-probe via comparisons with moisture distribution measurements made using an X-ray absorption system. This paper details the experimental work and the results obtained. Encouraging agreement between the two methods was achieved. This work is significant as it opens up the possibility of using this technique reliably in the field for an application such as monitoring the drying out of a structure post-flood.