Evaluation of test procedures and correlations for the mechanical characterisation of brick masonry and its constituents

This paper describes an experimental campaign for the mechanical characterisation of brick masonry and its constituents (i.e. lime mortar and solid clay bricks). It explores the use of different tests to characterise specific properties: dynamic and static tests are used to characterise Young’s modulus of constituents, while flexural and splitting tests are used to characterise their tensile strength. To understand why these tests provide different results, the validity of assumptions adopted in the mechanical interpretation of tests are queried using full-field displacement data from 3D Digital Image Correlation (DIC). Young’s modulus, compressive, shear and tensile strength of masonry samples are also determined. The whole dataset is then analysed to investigate possible relationships and correlations between mechanical parameters. One of the contributions of this paper is a new procedure to define the static Young’s modulus of masonry constituents during standard flexural tests. The new procedure evaluates how the Young’s modulus estimation varies with maximum principal strain levels in the sample; it highlights how this parameter reduces with increasing strain levels, even at small strain magnitudes. This nonlinearity is not accounted for by the existing empirical relationships between static and dynamic Young’s moduli for bricks and mortar and leads to noteworthy differences between these parameters. It is also concluded that tensile strength is better estimated by flexural tests, for which mechanical interpretations are consistent with the measurements. Finally, it is concluded that the expressions to estimate masonry compressive strength and Young’s modulus from constituent properties yield reasonable approximations, while masonry parameters relating to bond strength (masonry tensile and shear strength) cannot be reliably correlated to constituent properties. Accurate estimation of masonry Young’s moduli requires constituent properties characterised using on-sample measurements at consistent strain levels. • Static Young’s modulus of masonry constituents is determined in flexural tests. • Flexural test yields more reliable tensile strength values than splitting test. • Masonry tensile and shear strength show poor correlation with constituent properties. • Specimen heterogeneities can determine inaccurate static/dynamic modulus ratios. • Strain levels need to be considered in masonry Young's modulus determination.