Tests on direct tensile characteristics of expanded clay lightweight aggregate concrete

The tensile characteristics of lightweight aggregate concrete under direct tension were examined with a view to enhancing the utilisation of artificially expanded clay granules as secondary aggregates. Ready-mixed concrete specimens were classified into two groups: all-lightweight concrete (ALWC) and sand-lightweight concrete (SLWC). The test parameters considered for each group were the maximum aggregate size (4–19 mm) and the lateral depth of specimens with a rectangular section (100–500 mm). The complete stress–crack mouth opening displacement (CMOD) response was measured under direct tension. The results show that the slope of the ascending branch of the stress–CMOD curve is slightly smaller for SLWC specimens than for ALWC specimens. The displacement at peak stress tends to increase with the lateral depth of the specimen, whereas the tensile strength of the concrete decreases, revealing the size effect phenomenon. However, the tensile strength of concrete and the softening slope at the descending branch of the stress–CMOD curve are marginally affected by the specimen's lateral depth and maximum aggregate size, owing to the reduced aggregate interlocking capacity across the crack. Gopalaratnam and Shah's model was modified to evaluate the stress–CMOD responses of the lightweight aggregate concretes, and the suggested and existing models were compared with the test results.