Experimental investigation of in-plane shear and compressive behaviour of dry-stacked interlocking concrete masonry

Dry-stacked interlocking masonry (DSIM), also known as mortarless masonry, is an alternative construction technique that replaces conventional mortar joints with integrated interlocking shear keys. This system offers significant advantages, including faster construction times and improved cost efficiency. Nevertheless, a notable gap exists in the literature regarding the quantitative assessment of the in-plane shear strength of mortarless masonry systems, particularly with respect to the effects of grouting and reinforcement. Therefore, an experimental program was conducted involving fifteen DSIM assemblages, each measuring 1.20 m × 1.20 m, constructed using mortarless units called Sparlock, with various grouting conditions and vertical and horizontal reinforcement ratios. The assemblages were tested under diagonal compression loading to evaluate their in-plane shear performance in terms of shear strength, modulus of rigidity, and ductility. Additionally, six DSIM prisms were tested under uniaxial compression to evaluate the compressive behaviour of both grouted and ungrouted configurations. The experimentally obtained shear strength values in addition to DSIM walls from literature were further compared with the predicted values derived from existing design standards developed for conventional masonry construction to assess their applicability to dry-stacked interlocking systems. The experimental results showed that DSIM assemblages lacking horizontal reinforcement experienced premature failure, characterized by brittle sliding along the dry joints. In contrast, the horizontally reinforced specimens exhibited a more ductile response, characterized by progressive crack development and enhanced deformation capacity prior to failure. This could be attributed to the layout of the blocks, which is stack-patterned and not staggered. The increase in vertical reinforcement within fully grouted specimens led to a 78 % enhancement in shear strength compared to partially grouted assemblages. Similarly, increasing the horizontal reinforcement ratio in partially grouted assemblages resulted in a 33 % improvement. The shear strength predictions obtained from conventional masonry design equations showed poor correlation with the experimental results, primarily due to the fundamentally different shear-resisting mechanisms present in the DSIM systems. To address this limitation, an equation was proposed to calculate the shear strength for different DSIM systems. The findings of this study contribute to the quantification and potential codification of the shear behaviour of DSIM systems. • Horizontal reinforcement enhanced ductility and prevented sliding, while vertical bars greatly increased shear strength. • Higher vertical and closer horizontal reinforcement increased shear strength by up to 78 % and 33 %, respectively. • Design code equations underestimate DSIM shear strength due to its distinct resistance from mortared masonry. • The proposed equation accounts for block and material properties, axial stress, and reinforcement ratios.