The study included a detailed examination of the crack resistance of heavy concrete and foam concrete that were not subjected to autoclave curing. An important aspect of this study was the use of polypropylene fiber as a reinforcing material, which made it possible to identify differences in the characteristics between reinforced and unreinforced samples. The purpose of the work was to evaluate the mechanical properties of the materials under study, as well as their behavior during destruction. For this purpose, the criteria of fracture mechanics were used, which made it possible to establish not only the strength and deformation characteristics, but also the force and energy indicators of crack resistance. The experimental results showed that the addition of polypropylene fiber significantly improves the strength characteristics of both heavy concrete and foam concrete. This improvement was especially noticeable in the case of foam concrete, which, due to reinforcement, demonstrated increased crack resistance. This is due to the fact that polypropylene fiber promotes a more uniform distribution of stress in the material, which in turn reduces the likelihood of cracking and improves resistance to destruction. In addition, the study confirmed that the use of polypropylene fiber not only increases strength, but also improves the durability of concrete, making them more suitable for use in construction, especially in conditions where materials are subject to significant mechanical loads and adverse environmental factors.