Fracture behavior and brittleness of bacterial self-compacting concrete with varying maximum aggregate sizes from three-point bending tests

Bacterial concrete, as a novel type of bio-mediated cementitious material, can serve as a sustainable and environmentally friendly alternative to conventional concrete. Despite growing research efforts on bacterial concrete, the literature has primarily focused on mechanical features, durability, and calcite precipitation, while the fracture behavior of such concretes in the presence of bacteria has not been systematically addressed, in particular, the combined effect of bacteria concentration and maximum aggregate size (MAS), as two main factors affecting the quality of the interfacial transition zone (ITZ) and the crack propagation mechanism. Therefore, this work focused on the simultaneous effect of using Bacillus pasteurii (BP) (concentrations of 0, 10 5 cells ml , 10 7 cells ml ) and MAS (sizes of 9.5, 12.7, and 19) mm on the fracture parameters of bacterial self-compacting concrete. Here, three-point bending was applied to 135 notched beam specimens using the Work of Fracture Method (WFM) according to RILEM TC 50-FMC and the Size Effect Method (SEM) per RILEM TC 89-FMT. Moreover, mechanical features, including compressive strength, splitting tensile strength, and modulus of elasticity, were evaluated using 81 specimens. It was found that increasing bacterial concentration and MAS improved in several fracture parameters, including initial fracture energy (G f ), total fracture energy (G F ), characteristic length (L ch ), fracture toughness (K IC ), effective fracture process zone length (C f ), and the brittleness number. Specifically, increasing the bacterial concentration from 0 to 10 7 cells ml at MAS of 19 mm resulted in increases of 21.08% and 22.6% in total f racture energy (G F ) and initial fracture energy (G f ), respectively. Furthermore, a strong correlation was observed between G F from WFM and G f from SEM, expressed as G F ≈ 2.44 G f (SEM).