Experimental investigation of the influence of head joints and grouting conditions on the shear strength of concrete block masonry

The nonlinear composite nature of masonry has limited theoretical understanding of material shear strength – especially with concrete block, where minimal experimentation has rendered the influences of two important variables (head joints, presence of grout) unknown. The effects of these variables were investigated experimentally on non-precompressed triplet specimens. Head joints did not influence shear strength statistically significantly: the proportion of grouted cores linearly increased shear strength. The provisions in the Canadian standard lacked accuracy when predicting partially grouted specimen strengths (overestimating up to 135%). Units from tested triplet specimens were also found to have similar compressive strengths to undisturbed units. •Head joints in concrete masonry do not influence shear strength statistically when no precompression is applied.•The proportion of cores grouted in partially grouted concrete masonry linearly increases its shear strength.•The compressive strength of hollow concrete masonry units from tested triplet specimens is similar to that of fresh units.•Standard triplet specimens are recommended instead of ones with head joints to enable careful specimen handling.