Author
HENDRICKX, R.; BRUYNINCKX, K.; SCHUEREMANS, L.; KERCKHOFS, G.;VERSTRYNGE, E.; WEVERS, M.; VAN BALEN, K.
Katholieke Universiteit Leuven, Civil engineering

Abstract
The nature of the failure mechanism of masonry under compression depends on the properties of the brick and mortar. It is well-known that the ratio of stiffness of both materials has an important effect. Furthermore the pattern of crack development and propagation and the occurrence of local compaction of soft mortars have been the subject of some study, but remained difficult to observe. This study aims at the visualisation of these phenomena by using a hydraulic press inside a microfocus X-ray setup, so that the deformation under imposed stress steps can be registered. Tests were performed on brick-mortar-brick cylinders of 29×48 mm² (dxh).
This technique visualises the spatial distribution of propagating cracks. If mortar strength is higher than brick strength (cement mortar), failure starts as splitting cracks in the joint. If on the other hand mortar strength is comparatively low (lime hydrate mortars), it is rather the brick which shows splitting cracks, however at that point the mortar may already be severely damaged. The doublets with lime-cement mortar present an intermediate case, which seems to behave most like a homogeneous material.

Key words
Failure mechanism, masonry, X-ray, computed tomography (CT), doublets