Effect of particle structure on mode I fracture process in concrete

Mode I fracture of concrete is normally regarded at the macro-level, and the effect of micro-structure is reduced to the use of several empirical constants in the fracture law. A key parameter is the softening diagram in tension. In a series of numerical analyses with a simple beam lattice model, the effect of material structure both on the pre-peak and softening regimes of the stress-deformation diagram in uniaxial tension has been established. The simulations are in good agreement with experimental observations that show the propagation of a large ‘crack-like’ feature in the steep part of the softening curve and substantial crack face bridging in the tail of the diagram. The simulations indicate that the density of stiff particles, which ranged between 35% and 83% in the analyses, has a significant effect on pre-peak micro-cracking. This part of the tensile stress-strain behaviour is usually ignored in macroscopic fracture models, but here it is shown that the material composition may have a significant effect in the pre-peak regime, but also on the peak stress. Furthermore the model analyses give output in terms of crack length distributions during the entire fracture process, which may be falsified in new experiments.