A `pad' sensor for measuring the moisture content of building materials

Abstract

A range of techniques are available to measure the moisture content of building fabrics. Indeed a thermal dual-probe has been successfully developed by the authors for measuring the moisture content of building fabrics in situ. However, the dual-probe technique has limitations due to the fact that two, small diameter, parallel holes must be drilled for inserting the dual-probe into the material to be measured. It is difficult to drill such holes accurately in many building envelops and thus, such a dual-probe may be most useful for relatively `soft' materials, such as aerated concrete. This paper describes the `proof of concept' of an innovation that surmounts this problem via the development of a `pad' sensor. Instead of the `traditional' dual-probe approach, the heater and temperature sensor are fixed to the surface of a thermally insulated block. The most important benefit of the pad sensor approach is that no holes are required to be drilled in the material of interest. The moisture content of the building envelops can be measured simply by placing the pad sensor against the wall surface. Extensive finite element modelling was carried out to design the pad sensor and a prototype built. Initial experimental work was then carried out to test the pad sensor — the measured moisture content obtained from the pad sensor was compared with the results of a series of gravimetric analyses. Encouraging agreement between the two methods was obtained. Practical application: A thermal dual-probe has been successfully developed by the authors for measuring the moisture content of building fabrics in situ. However, the dual-probe technique has limitations due to the fact that two, small diameter, parallel holes must be drilled for inserting the dual-probe into the material to be measured. This paper describes an innovation that surmounts this problem via the development of a `pad' sensor. The moisture content of the building envelopes can be accurately measured simply by placing the pad sensor against the wall surface. The pad sensor offers a non-destructive method to measure the moisture content and thus is potentially attractive for applications where this issue is of importance e.g. monitoring the moisture content of historical buildings.