Deformation of the brick-mortar interface in compression and the use of ESPI

For masonry loaded in compression, the interaction between brick and mortar is of main interest. Tests showed that the deformation-properties of the mortar itself could be measured with ESPI. With the usual measuring techniques this turns out to be difficult as only small gauge lengths are applicable. This paper discusses the ESPI measuring technique and shows some of the effects of joint imperfections on the behaviour of masonry loaded in compression. Precise quantitative information about the deformation of brick and mortar separately was obtained. It may be concluded that the load is mainly transmitted through the central 60 to 70 mm of the specimen. ESPI measurements under various stages of testing confirm the linear behaviour of the specimen up to 80% of failure load. The bottom load platen of the used moving seating arrangement had too much freedom of movement in relation to the bending stiffness of the specimen around the weak axes and caused unintended deformations. Lateral deformation could be measured quite simply with ESPI but only provided a general idea of the behaviour of the specimen.