Monte Carlo simulations of mesoscale fracture of concrete with random aggregates and pores: a size effect study

•Size effect of concrete studied by realistic mesoscale models and Monte Carlo simulations.•Key meso-control parameters (aggregate fraction and porosity) considered.•Weibull size effect laws of strength obtained considering the key parameters.•Equations relating strength and the key parameters obtained.•Both aggregate fraction and porosity play significant role. Size effect in concrete under tension is studied by Monte Carlo simulations of mesoscale finite element models containing random inclusions (aggregates and pores) with prescribed volume fractions, shapes and size distributions (called meso-structure controls). For a given size and a set of controls, a number of realisations with different spatial distribution of inclusions are simulated to produce statistical data for macroscopic load/stress–strain curves. The complex meso-crack initiation and propagation is captured by pre-inserted cohesive interface elements. The effects of specimen size and meso-structure controls on macroscopic strength and toughness are analysed, and empirical size-effect laws for their dependences are proposed by data regression. It is also shown that the mesoscale porosity affects both strength and toughness and should not be ignored in size effect studies of concrete.