Modeling of the compliant structure of concrete matrix

The purpose of the study is to develop and verify a mathematical model of the cement-sand matrix (CSM) of concrete with an auxetic returnably-concave structure structure to enhance the energy-absorbing properties of construction materials used in special facilities (SF) of the Civil Defense of the Russian Federation. The work is based on the analysis of the physical and mechanical characteristics of composite materials modified with voids of various geometries, taking into account the requirements for protective structures operating under elevated dynamic loads of technogenic nature. Methods include mathematical modeling using the finite element method to create a verified model of the cement-sand matrix of concrete with compressive strength classes B30 and B60. Verification was performed by comparing the modeling results with data from real tests on a press, specifying boundary conditions, physical and mechanical properties of materials, and loading parameters. For the auxetic structure, returnably-concave structure cells with a concavity angle of 60° and an edge length of 15 mm were used, modeled for cubes of various sizes (scaling and overlapping of cells). The results demonstrate uniform stress distribution in the auxetic structure of the CSM without the "hoop" effect characteristic of standard concrete, with a reduction in compressive strength (down to 8.7 MPa for B30 and 17.4 MPa for B60) while increasing deformability up to 10 times. Stress-strain diagrams confirm increased compliance, and consequently, energy absorption. The practical significance lies in the application of the model for designing energy-absorbing protective structures of SF, enhancing their protection.