Moisture monitor

An x-ray moisture-detection system is to provide the construction industry with information to develop materials that can withstand the UK’s changing climate.

The testing unit, at Glasgow’s Heriot-Watt University, allows users to monitor moisture uptake and movement within buildings. This should allow firms to create structures that are relatively immune to moisture damage, protecting inhabitants from related health problems such as mould allergies.

‘Climate change is a very important issue,’ said Heriot-Watt’s Prof Graham Galbraith. ‘The construction industry needs to know how this will affect building materials and the changes they might need to make.’

The unit includes a climate-controlled chamber containing an X-ray source and X-ray detection system. This allows researchers to subject the sample to a variety of temperatures and humidity levels. After an X-ray is fired through the sample a sub-millimetre resolution image of the material is produced.

Analysis of the X-ray’s spectra can provide scientists not only with details of moisture levels, but also tell them whether the moisture exists as a vapour or as free liquid in the brick’s pores, and how it is being transferred from one state to another.The team is working on allowing the machine to simulate climate gradients at different areas within the chamber. This would replicate how bricks are affected by the difference in climate between the inside and outside of a house, and map moisture transfer between the two.

Researchers aim to help Historic Scotland deal with the problems caused by delamination erosion of sandstone. Wetter summers and increased humidity mean that the amount of water absorbed by porous sandstone used to build many of Scotland’s older buildings has increased.

Although climate change has made frosts less common, when they do occur the absorbed moisture freezes and expands. This makes the sandstone split and shed, creating thousands of pounds’ worth of damage.

The device will also be used to investigate how historic buildings dry out after floods, to find the best way of minimising damage to the buildings’ materials.Other applications will include examining the water content of drying concrete to determine optimum setting times; testing the effectiveness of water-repellent substances and their success at penetrating brick; and testing wood for knots.

‘The machine is large enough to to place samples as large as a brick in the chamber, allowing you to test things such as a brick and mortar joint,’ said Chris Sanders, principal consultant at the Building Research Establishment, Scotland. ‘Alternative gamma ray devices can only take 10mm samples and have no climate control.’

The university, and partners at the University of Strathclyde, are now working on moving items in the chamber to form a 3D image.