2D image-based crack monitoring: an affordable, sufficient and non-invasive technique for the democratization of preventive conservation of listed buildings.

In order to democratize the preventive conservation of most listed buildings, we need to have an affordable tool that allows controlling their main vital signs. Complex and costly control installations, such as large digital data collection campaigns or 3D laser scanning, are not always possible. Methods for analogue data collection, such as comparators and callipers, are much more affordable and discreet but require the use of auxiliary lifting platforms for both installation and reading and control, hence resulting too invasive. In this paper we study techniques for digital indoor monitoring of cracks of listed masonry buildings. 2D image-based crack monitoring technique was found to be sufficient, affordable, traceable, and respectful with the use of the building. To verify its effectiveness, we performed laboratory tests and implement it in a real case study, a church in Zaragoza, Spain, currently undergoing a reparation process. The obtained results show that the proposed 2D image-based inspection technique provides measurements closer to the comparator, used as a reference, than the calliper, with a mean difference of 0.15 mm with respect to the reference, and a standard deviation of 0.17 mm, and its use can be up to 56% cheaper than the comparator. Therefore, the technique is easily generalizable to different heritage buildings. [ABSTRACT FROM AUTHOR]