METHODOLOGICAL PROPOSAL OF IMAGE PROCESSING WITH FREE SOFTWARE TO EVALUATE THE ROUGHNESS OF MASONRY PIECES

Resumo

Masonry is widely used in a large number of constructions around the world. However, these register
severe damages in seismic areas. An important parameter to guarantee adequate structural behavior is the adhesion
between the piece and the mortar, which has two origins: a) chemical, b) mechanical. The latter is related to the
fineness of the mortar components and the roughness of the piece. Under this consideration, a proposal is presented
to calculate the roughness of the faces of a concrete masonry block made with cement and fine sand, using
photographs taken with a 24 megapixels camera capacity and processed with three free software applications. The
procedure has four steps: a) calibration of the camera and taking of photographs, b) three-dimensional
reconstruction of the piece using the Visual SFM software, c) obtaining the points of both faces with the Meshlab
software from the three-dimensional model, d) construction of a point cloud using the CloudCompare software,
where it is possible to visualize the crests and valleys of the faces, and therefore it is possible to measure the
average roughness. For the piece under study, 25 images were taken and processed for each face, the average
values of roughness were 0.06 mm and 0.23 mm for the smooth and rough faces, respectively; the references show
values of 0.08 and 0.32 mm measured in red clay brick. For the lightweight concrete block and the same order,
there are references of 0.45 and 0.77 mm. In the case of concrete, average values of 0.3 mm on smooth surfaces
and between 0.3 -1.0 mm on standard surfaces are reported. The proposed methodology, in the experimental phase,
provides values of roughness in the range defined in other investigations of similar materials with two additional
advantages: it does not require special equipment, and the computer applications are free software. This tool can
be used to evaluate the influence of the roughness of masonry faces on the resistance to lateral loads generated by
earthquakes.