Electronic speckle interferometry for the deformation measurement in masonry testing

The principles of ESPI (electronic speckle pattern interferometry) are summarised and the use of optical interferometric methods is discussed in comparison with common measuring techniques for measuring the deformation parameters of solid masonry units under mechanical tests. The brick-mortar interaction under certain states of stress has also been studied, owing to the influence of mortar strength and deformability on the brick masonry behaviour under compression and shear. The difficulties related to the use of classical measurement devices, such as strain gauges or displacement transducers on masonry, are highlighted. The experimental results obtained show the effectiveness of the ESPI technique in the case of low-stiffness materials and small specimens. The quantitative evaluation by ESPI measurements of the deformability characteristics of solid softmud bricks is also proposed.