Introduction

The use of masonry has been an accepted method for the construction of buildings, bridges and walls for a very long time. This is because it has proved to be a successful method in producing both very strong and attractive structures. A consequence of this great strength, however, is that many masonry buildings in use today are centuries old and beginning to show their age, becoming in desperate need of repair. Many of these buildings will be an important part of a town or city providing an attractive central figure or maybe a place of frequent use by locals and tourists. It is therefore important to maintain the safety of users by investigating how stable the structure is and identify areas that will need repair before the possibility of collapse. An example of the extreme consequence of not conducting investigations is given when the bell-tower of Pavia collapsed in 1989, killing 4 people.

So what techniques are available? There are three categories: the destructive, the slightly destructive and the non-destructive techniques (NDT). Destructive techniques including coring and slightly destructive techniques (such as the flat-jack test) are unpopular methods to gauge the characteristics of masonry as they leave visible scars, tarnishing the structure's beauty. NDT, however, offers an insight into the internal structure enabling initial identification of problems and allows a method of analysing the success of repairs while avoiding any damage to the masonry.

 

Currently the field of ND radar evaluation of structures is under continued development. So far radar tests have been able to provide qualitative data about a structure, but have fallen short when actual quantitative results are needed, i.e. radar can detect a defect in a structure but cannot give any exact information about its size. The field of radar is also restricted to experts in analysis of the data and no set guidelines exist over elucidation of the results, allowing for inconsistency in interpretation.