On the direct experimental measurement of mortar fracture toughness by a compression-to-tensile load transformer (CTLT)

The tensile or Mode I fracture toughness is one of the most important strength parameters of mortar which is usually measured experimentally in the laboratory. Several widely accepted indirect methods have been used for toughness measurement but they estimate it and do not provide the real and precise fracture toughness of mortar. In this paper, the direct tensile fracture toughness of mortar is determined through a compression to tensile load transferring device (called Compression-to-Tensile Load Transformer (CTLT)) in the laboratory. This sophisticated device is developed to use a specially prepared Bond Shaped Sample (BSS) containing edge cracks. These samples are carefully prepared and subjected to the direct tensile loading by the special loading device. The direct fracture toughness results are verified by performing the Notched Brazilian Disc (NBD) tests (the standard indirect tests). The effect of crack length and crack overlapping on the stress concentration at the crack tip is analyzed numerically using finite element method. However, comparison of these results can provide a good basis for the validity of the direct toughness result. The experimentally observed fracture propagation pattern is also in good accordance with those obtained by the standard finite element method.