Improvement of Strength and Strain Characteristics of Lightweight Fiber Concrete by Electromagnetic Activation in a Vortex Layer Apparatus

Analysis of the Current State of Research on Bio-Healing Concrete (Bioconcrete)

The relatively small tensile strength of concrete makes this material particularly vulnerable to cracking. However, the reality is that it is not always possible and practically useful to conduct studies on high-quality sealing cracks due to their inaccessibility or small opening width. Despite the fact that currently there are many technologies for creating self-healing cement composites, one of the most popular is the technology for creating a biologically active self-healing mechanism for concrete. It is based on the process of carbonate ion production by cellular respiration or urease enzymes by bacteria, which results in the precipitation of calcium carbonate in concrete. This technology is environmentally friendly and promising from a scientific and practical point of view. This research focuses on the technology of creating autonomous self-healing concrete using a biological crack-healing mechanism. The research methodology consisted of four main stages, including an analysis of the already conducted global studies, ecological and economic analysis, the prospects and advantages of further studies, as well as a discussion and the conclusions. A total of 257 works from about 10 global databases were analyzed. An overview of the physical, mechanical and operational properties of bioconcrete and their changes is presented, depending on the type of active bacteria and the method of their introduction into the concrete mixture. An analysis of the influence of the automatic addition of various types of bacteria on various properties of self-healing bioconcrete is carried out, and an assessment of the influence of the method of adding bacteria to concrete on the process of crack healing is also given. A comparative analysis of various techniques for creating self-healing bioconcrete was performed from the point of view of technical progress, scientific potential, the methods of application of this technology, and their resulting advantages, considered as the factor impacting on strength and life cycle. The main conditions for a quantitative assessment of the sustainability and the possibility of the industrial implementation of the technology of self-healing bioconcrete are identified and presented. Various techniques aimed at improving the recovery process of such materials are considered. An assessment of the influence of the strength of cement mortar after adding bacteria to it is also given. Images obtained using electron microscopy methods are analyzed in relation to the life cycle of bacteria in mineral deposits of microbiological origin. Current gaps and future research prospects are discussed.

Prediction of Mechanical Properties of Highly Functional Lightweight Fiber-Reinforced Concrete Based on Deep Neural Network and Ensemble Regression Trees Methods

Currently, one of the topical areas of application of artificial intelligence methods in industrial production is neural networks, which allow for predicting the performance properties of products and structures that depend on the characteristics of the initial components and process parameters. The purpose of the study was to develop and train a neural network and an ensemble model to predict the mechanical properties of lightweight fiber-reinforced concrete using the accumulated empirical database and data from construction industry enterprises, and to improve production processes in the construction industry. The study applied deep learning and an ensemble of regression trees. The empirical base is the result of testing a series of experimental compositions of fiber-reinforced concrete. The predicted properties are cubic compressive strength, prismatic compressive strength, flexural tensile strength, and axial tensile strength. The quantitative picture of the accuracy of the applied methods for strength characteristics varies for the deep neural network method from 0.15 to 0.73 (MAE), from 0.17 to 0.89 (RMSE), and from 0.98% to 6.62% (MAPE), and for the ensemble of regression trees, from 0.11 to 0.62 (MAE), from 0.15 to 0.80 (RMSE), and from 1.30% to 3.4% (MAPE). Both methods have shown high efficiency in relation to such a hard-to-predict material as concrete, which is so heterogeneous in structure and depends on many factors. The value of the developed models lies in the possibility of obtaining additional useful information in the process of preparing highly functional lightweight fiber-reinforced concrete without additional experiments.

Numerical Simulation of the Bearing Capacity of Variotropic Short Concrete Beams Reinforced with Polymer Composite Reinforcing Bars

One of the disadvantages of reinforced concrete is the large weight of structures due to the steel reinforcement. A way to overcome this issue and develop new types of reinforcing elements is by using polymer composite reinforcement, which can successfully compensate for the shortcomings of steel reinforcement. Additionally, a promising direction is the creation of variotropic (transversely isotropic) building elements. The purpose of this work was to numerically analyze improved short bending concrete elements with a variotropic structure reinforced with polymer composite rods and to determine the prospects for the further extension of the results obtained for long-span structures. Numerical models of beams of a transversally isotropic structure with various types of reinforcement have been developed in a spatially and physically nonlinear formulation in ANSYS software considering cracking and crashing. It is shown that, in combination with a stronger layer of the compressed zone of the beam, carbon composite reinforcement has advantages and provides a greater bearing capacity than glass or basalt composite. It has been proven that the use of the integral characteristics of concrete and the deflections of the elements are greater than those when using the differential characteristics of concrete along the height of the section (up to 5%). The zones of the initiation and propagation of cracks for different polymer composite reinforcements are determined. An assessment of the bearing capacity of the beam is given. A significant (up to 146%) increase in the forces in the reinforcing bars and a decrease in tensile stresses (up to 210–230%) were established during the physically non-linear operation of the concrete material. The effect of a clear redistribution of stresses is in favor of elements with a variotropic cross section in height.

Influence of Recipe Factors on the Structure and Properties of Non-Autoclaved Aerated Concrete of Increased Strength

At present, the load-bearing enclosing structures of buildings and structures are designed and built considering the increasing requirements for energy efficiency and energy saving of such structures. This is due to the need for a thrifty attitude to the energy consumed and the need to strive for the greening of construction and increase the energy efficiency of buildings and structures. In this regard, one of the most effective and proven building materials is cellular concrete. The purpose of this study was to study the influence of some prescription factors on the structure formation and properties of non-autoclaved aerated concrete with improved characteristics. Standard test methods were used, as well as SEM analysis of the structure of aerated concrete. Non-autoclaved aerated concrete with the replacement of part of the cement with microsilica in an amount from 4% to 16% MS showed higher strength characteristics compared to aerated concrete, where part of the cement was replaced by the addition of granulated blast-furnace slag and a complex additive. The maximum value of compressive strength was recorded for aerated concrete with 16% MS addition. The largest increase in the coefficients of constructive quality was observed in compositions of aerated concrete with the addition of silica fume from 11% to 46% compared with the control composition. The addition of microsilica makes it possible to achieve an improvement in the thermal conductivity characteristics of non-autoclaved aerated concrete (up to 10%). Replacing part of the cement with slag and complex additives does not have a significant effect on thermal conductivity. The obtained dependencies were confirmed by the analysis of the structure formation of the studied aerated concrete at the micro level. An improvement in the microstructure of aerated concrete with the addition of microsilica in comparison with samples of the control composition has been proven.

Theoretical and Experimental Substantiation of the Efficiency of Combined-Reinforced Glass Fiber Polymer Composite Concrete Elements in Bending

An essential problem of current construction engineering is the search for ways to obtain lightweight building structures with improved characteristics. The relevant way is the use of polymer composite reinforcement and concrete with high classes and prime characteristics. The purpose of this work is the theoretical and experimental substantiation of the effectiveness of combined-reinforced glass fiber polymer composite concrete (GFPCC) bending elements, and new recipe, technological and design solutions. We theoretically and experimentally substantiated the effectiveness of GFPCC bending elements from the point of view of three aspects: prescription, technological and constructive. An improvement in the structure and characteristics of glass fiber-reinforced concrete and GFPCC bending elements of a new type has been proven: the compressive strength of glass fiber-reinforced concrete has been increased up to 20%, and the efficiency of GFPCC bending elements is comparable to the concrete bending elements with steel reinforcement of class A1000 and higher. An improvement in the performance of the design due to the synergistic effect of fiber reinforcement of bending elements in combination with polymer composite reinforcement with rods was revealed. The synergistic effect with optimal recipe and technological parameters is due to the combined effect of dispersed fiber, which strengthens concrete at the micro level, and polymer composite reinforcement, which significantly increases the bearing capacity of the element at the macro level. Analytical dependences of the type of functions of the characteristics of bent concrete structures on the arguments—the parameters of the combined reinforcement with fiber and polymer composite reinforcement—are proposed. The synergistic effect of such a development is described, a new controlled significant coefficient of synergistic efficiency of combined reinforcement is proposed. From an economic point of view, the cost of the developed elements has been reduced and is economically more profitable (up to 300%).

A Study on the Cement Gel Formation Process during the Creation of Nanomodified High-Performance Concrete Based on Nanosilica

One of the most science-intensive and developing areas is nano-modified concrete. Its characteristics of high-strength, high density, and improved structure, which is not only important at the stage of monitoring their performance, but also at the manufacturing stage, characterize high-performance concrete. The aim of this study is to obtain new theoretical knowledge and experimental-applied dependencies arising from the “composition–microstructure–properties” ratio of high-strength concretes with a nano-modifying additive of the most effective type. The methods of laser granulometry and electron microscopy are applied. The existing concepts from the point of view of theory and practice about the processes of cement gel formation during the creation of nano-modified high-strength concretes with nano-modifying additives are developed. The most rational mode of the nano-modification of high-strength concretes is substantiated as follows: microsilica ground to nanosilica within 12 h. A complex nano-modifier containing nanosilica, superplasticizer, hyperplasticizer, and sodium sulfate was developed. The most effective combination of the four considered factors are: the content of nanosilica is 4% by weight of cement; the content of the superplasticizer additive is 1.4% by weight of cement; the content of the hyperplasticizer additive is 3% by weight of cement; and the water–cement ratio—0.33. The maximum difference of the strength characteristics in comparison with other combinations ranged from 45% to 57%.

Modeling and Experimental Verification of the Performance of Polymer Composite Reinforcing Bars of Different Types in Concrete of Different Density

Currently, there is a scientific and practical deficit in new methods of integrated technological and design solutions based on improving the properties of concrete as the primary material that perceives compressive loads, and its joint work with various types of reinforcing rods. A new system using an integrated engineering approach to the design of building structures is proposed, which involves minimizing their cost and weight through numerical simulations and an experimental verification of the operation of reinforcing bars made of various materials in concrete of various densities. The control of the bearing capacity of reinforced building structures on the example of compressed elements is proposed to be carried out using the developed recipe-technological methods at the manufacturing stage. The economic and environmental efficiency of nano modification with the help of production waste and the use of lightweight dispersion-reinforced concrete to obtain such structures was revealed. The most effective concrete formulations showed strength gains ranging from 10% to 34%. Ultimately, this led to an increase in the bearing capacity of the elements up to 30%. The application of such an integrated lean approach will allow saving up to 20% of resources during construction.

Mathematical Modeling and Experimental Substantiation of the Gas Release Process in the Production of Non-Autoclaved Aerated Concrete

The widespread use of aerated concrete in construction has led to the emergence of many types and compositions. However, additional research should fill theoretical gaps in the phenomenon of gas release during the formation of the structure of aerated concrete. Based on theoretical analysis and experimental studies, the article proposes a mathematical model of the swelling process based on the physicochemical laws of convection and molecular diffusion of hydrogen from a mixture and the conditions of swelling, precipitation, and stabilization of the mixture. An improved method for the manufacture of aerated concrete is proposed, which consists of introducing cement pre-hydrated for 20–30 min into the composition of the aerated concrete mixture and providing improved gas-holding capacity and increased swelling of the mixture, reducing the average density of aerated concrete up to 29% and improving heat-shielding properties up to 31%. At the same time, the small dynamics of a decrease in the strength properties of aerated concrete were observed, which is confirmed by an increased structural quality factor (CSQ) of up to 13%. As a result, aerated concrete has been obtained that meets the requirements of environmental friendliness and has improved mechanical and physical characteristics. Economic efficiency is to reduce the cost of production of aerated concrete and construction in general by about 15%.