Reliable unit strength correlations to predict the compressive strength of grouted concrete masonry

Compressive strength of grouted concrete masonry is an important parameter to design reinforced/grouted concrete masonry walls. The design standards stipulate two methods to determine the compressive strength of masonry (1) using tabulated unit strength and mortar type, and (2) testing representative masonry prisms. The compressive strength prediction of grouted concrete masonry is influenced by compressive strength values of hollow blocks, mortar and grout, and their geometries. Therefore, a multi-level approach was employed in this study to improve the existing unit strength correlations of the standards for more reliable prediction of compressive strengths of grouted concrete masonry. The existing methods to determine the compressive strength of grouted masonry were critically appraised and a database of compression tests of grouted concrete masonry prisms/wallettes was developed. This database was then used to evaluate the correlations between the compressive strengths of block, mortar, grout and masonry. The applicability of existing unit strength correlations from the design standards and literature were assessed and their relevancy and limitations are highlighted. Subsequently, updated sets of unit strength correlations are proposed in this study, through statistical reliability analyses of the predictions against the experimental results included in the database. The proposed unit strength correlations were classified according to the mortar type/strengths (≤ 10 MPa and > 10 MPa). It has been shown that the new correlations are more structurally reliable than the existing unit strength correlations through comparing the 95th percentile error values.