The confinement of mortar in masonry under compression: Experimental data and micro-mechanical analysis

Abstract The present paper deals with the behavior of several types of mortar in masonry under compression. The quantification of the response of mortar to triaxial confinement afforded by the masonry units in the composite subjected to compressive stresses is paramount in the determination of the peak stress of wallettes and pillars under compression. This behavior is greatly affected by the behavior of the mortar micro-structure and is manifested by the constrained lateral expansion of the mortar in the joint. A series of experimental results is presented, carried out on different assemblages of masonry composites (couplets and wallettes) with different types of masonry units and mortar, ranging in type from pure lime to cement based mortars. These experiments are subsequently simulated numerically using micro-mechanical techniques accounting for the shifting behavior of the Poisson's ratio of the mortar for varying levels of applied compression. Masonry is treated in a micro-mechanical framework as a composite material composed of two macroscopically distinct material phases: units and mortar. The experiments and their simulation provide insight into the complexities of masonry under compression that need to be accounted for in numerical analysis, including a discussion on the progression of damage in each material phase. The results and their analysis are further enriched through a comparative parametric study. A clear difference emerges between the assigned and the apparent Poisson's ratio for the material components.