A micromechanical investigation for the effects of pore size and its distribution on geopolymer foam concrete under uniaxial compression

•The enriched DEM model can describe well the fracture behaviour of foam concrete.•Pore-size and porosity of foam concrete strongly affect its fracture resistance.•The fracture process is triggered by a transition state of mortar bonds. This study investigates the influences of pore-structure and mortar properties on the fracture behaviour of geopolymer foamed concrete. The discrete element method (DEM) is utilised to explicitly describe the internal pore-structure, while the mortar phase is modelled at the micro/meso-scale using a cohesive-frictional model. Numerical tests are conducted on numerous DEM foam concrete specimens with various porosities and pore-size distributions. The numerical results show that the pore-size can have a profound effect on the material’s fracture resistance. A decrease in pore size results in higher compressive strength and this influence is more significant for foam concrete with lower porosity. However, the elastic modulus seems to be less sensitive to the pore size variation. Further looking at the fracture process of the foam concrete at the micro-scale shows a gradual transition contact bonds from compressive to tensile modes, which is triggered by the breakage of contact bonds persisting as the loading continues. The study also demonstrates that the pore size distribution mainly affects the empirical power exponent of Balshin’s equation of compressive strength-porosity relationship, while the mortar properties have a profound influence on the strength of the material at zero porosity.