It is shown that during operation reinforced concrete structures are very often susceptible to cracking, which leads to a deterioration in the quality and expected life of them. The traditional methods of restoration and strengthening of structures are methods of building up, impregnating the structure of concrete with polymer and other materials, applying monolithic coatings or gluing metal polymer and other elements. Known repair methods are characterized by high complexity of execution, high cost, etc. It is shown that there is a pressing economic incentive for the development of concrete capable of self-repairing and repairing damage. Recently, tendencies toward the creation of new materials that are capable of actively interacting with external factors have been outlined towards world practice; such materials have received the name “intellectual”. The use of «intelligent» materials allows you to monitor and predict the state of various structures and structures, at the required time and even in hard-to-reach areas, significantly increase the resource of engineering systems and their reliability. It has been shown that to date, various chemical methods have been developed for creating self-healing concrete. One of the breakthrough technologies in the field of obtaining effective materials and structures based on them are biotechnologies based on the use of microorganisms. Many researchers have studied the use of calcite produced by bacteria to increase the life of concrete-based structures and restore buildings by eliminating cracks, increasing the strength of concrete, reducing permeability, and reducing water absorption. The article provides an overview of the work of foreign specialists in these areas.
Reinforced concrete as one of the main materials for a wide class of building structures for civil, industrial and transport purposes has a number of specific properties: physical nonlinearity, anisotropy, and crack formation. The behavior of reinforced concrete in the elastoplastic stage before its destruction is more characterized by deformation of concrete. It is shown that the physical nonlinearity of concrete is due to plastic deformations, which are characteristic of various types of stress state. For a triaxial stress state, the system of equations in the mechanics of a deformable solid, it includes two groups of formulas that combine nine equations that include 15 unknowns (three displacements, six strain components, and six stress components). In order for the system to be closed, it is necessary to supplement it with six equations. Such equations are the basic physical relationships that relate the six stress components to the six strain components. The use of linear relationships between stresses and strains introduces the greatest error in the assessment of the stress-strain state (NDS) of structures made of materials with the properties of nonlinearly deformable bodies. In this regard, the more correctly the physical law defining the correlation reflects the material, according to which the material resists various types of deformations, the less error will be allowed in the assessment of the NDS of structures. The article proposes a new approach to the construction of basic physical relationships based on an invariant solution to the problems of mechanics of a deformable solid for concrete in a plane stress state. The correspondence of the proposed dependences to the real stress and deformable state of the material is shown.
The paper considers the modification of the generally accepted formulation of the finite elements method by applying in the calculation I.Mileykovski’s refined technical theory of shells that takes into account the deformations of the transverse shear along the thickness of the model. When applying this solution path, it is possible to calculate thick and thin shells (plates) with equal efficiency, taking into account the complex strained state of an anisotropic material. It illustrates the inclusion in the computational algorithm of variable parameters of the elasticity of concrete, allowing more accurate evaluation of the stress-strain state in the finite element under complex (combined) loads. The presence of reinforcement in the material is modeled by dividing the structure into layers and sequentially reduction the elastic characteristics of the material based on the volume ratio of the components. The advantage of the algorithm is the ease of its integration with the conventional finite elements method. All transformations in this case consist in the modification of expressions for determining the elastic characteristics of the construction, calculating the gradient and stiffness matrices, while the sequence of further calculations does not change. This enables to use the proposed algorithm, including as a plug-in software module, expanding the capabilities of existing computing programs. The article demonstrates the application of the method in modeling a reinforced concrete slab made with the use of multi-component high-strength concrete of a heavy class having a prismatic strength under uniaxial compression of more than 110 MPa.
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