The development of new and improvement of existing technologies based on the use of waste products from various industries or recyclable materials is a current trend in the construction industry. Including in the composition of binders and concrete by-products of industry, reducing the proportion of Portland cement, it is crucial to maintain and improve the resulting products’ mechanical characteristics and life cycle. The main aim of the study was to investigate the influence of biochar additive on the microstructure and properties of the concrete and obtain the composition with improved characteristics due to nanomodification of rice straw recycled biochar. An environmentally friendly technology for concrete manufacture was obtained, using agricultural waste, rice straw, as its components, developing a composition of concrete nanomodified with processed rice straw biochar, identifying the dependences of concrete properties on their nanomodification with processed rice straw coal. It has been established that the most effective dosage is the addition of rice straw biochar in the amount of 6% by weight of cement. The improvement in the properties of concrete was expressed in the increase in its physical and mechanical characteristics and changes in deformability according to the results of the analysis of the stress-strain diagrams. The increase in strength characteristics ranged from 17% to 25%. The modulus of elasticity increased to 14%. The deformation characteristics decreased from 12% to 24%. Introducing a finely dispersed additive of rice straw biochar modified by the electromagnetic method leads to a decrease in cement consumption by up to 10%.

The article develops methods and methodology for experimental studies of centrifuged and vibro-centrifuged concrete products of annular cross-section. They assess the real variatropy of the structure and confirm the correctness of the accepted research. An original technique for experimental studies of the variatropy of the cross-sections of vibrated, centrifuged and vibro-centrifuged concretes is proposed to determine their integral (common) and differential (differing in layers) strength and strain characteristics and deformation diagrams. It has been proved that with vibro-centrifugation it becomes possible to obtain concretes with improved structure and higher characteristics compared with centrifugation and vibration techniques. Experimental studies of the differential characteristics of centrifuged and vibro-centrifuged concretes under compression and tension revealed that the outer layer of concrete had the best characteristics after centrifugation and vibro-centrifugation, and the inner layer had the worst ones. The three-layer model of the variatropic structure for centrifuged and vibro-centrifuged concrete has been experimentally confirmed. The concrete of the outer layers had the highest strength and modulus of elasticity and the least deformability; the concrete of the inner layers had the lowest strength and modulus of elasticity and the highest deformability; and the concrete of the middle layers had average characteristics. The deformation diagrams of centrifuged and vibro-centrifuged concretes were also differentiated by layers, confirming the variatropy of the structure of such concretes. The deformation diagrams for the outer concrete layer demonstrated the highest strength; the diagrams for the inner concrete layer showed the lowest strength; and the diagrams for the middle concrete layer corresponded to mean characteristics.

Alkalization technology and its application to obtain high-performance concrete compositions is an urgent scientific problem that opens opportunities for improving building structures. The article is devoted to the new technology of manufacturing reinforced concrete structures with low energy consumption, resource, and labor intensity based on the improved variatropic configuration of vibro-centrifuged concrete using activated water with high pH. The synergistic effect of the joint use of the proposed novel solutions has been theoretically and experimentally proved. Thus, growth in physical and mechanical characteristics of up to 15–20% was obtained, the structure and its operational ability were improved (the effectiveness of structural improvement, expressed as a percentage, reached values over 70%, concerning control samples). A positive effect on the properties of vibro-centrifuged concrete over the entire thickness of the annular section has been revealed. A method for controlling the integral characteristics of concrete has been obtained. The possibility of regulating the variatropic structure and controlling the differential characteristics of vibro-centrifuged concrete has been established. An assessment of the constructive quality and variatropic efficiency of vibro-centrifuged concrete was carried out, and new calculated dependencies were proposed, expressed in the form of relative coefficients.

The development of perspective concrete mixes capable of resisting the action of external loads is an important scientific problem in the modern construction industry. This article presents a study of the influence of steel, basalt, and polypropylene fiber materials on concrete’s strength and deformation characteristics. A combination of various types of dispersed reinforcement is considered, and by methods of mathematical planning of the experiment, regression dependences of the strength and deformation characteristics on the combination of fibers and their volume fraction are obtained. It was shown that the increase in compressive strength was 35% in fiber-reinforced concretes made using a combination of steel and basalt fiber with a volume concentration of steel fiber of 2% and basalt fiber of 2%; tensile strength in bending increased by 79%, ultimate deformations during axial compression decreased by 52%, ultimate deformation under axial tension decreased by 39%, and elastic modulus increased by 33%. Similar results were obtained for other combinations of dispersed reinforcement. The studies carried out made it possible to determine the most effective combinations of fibers of various types of fibers with each other and their optimal volume concentration.

One main global problem is the accumulation of a large amount of agricultural waste. This problem causes environmental pollution and requires an immediate comprehensive solution. The purpose of this study was scientific substantiation and experimental testing, at the micro- and macro levels, of the joint influence of electromagnetic activation of cement paste and nano-modification by rice straw biochar on the strength and strain properties of concrete. In addition to standard methods, the methods of electromagnetic activation, scanning electron microscopy, and energy dispersive spectrometry were used. The results of the joint influence of electro-magnetic activation and nano-modification by rice straw biochar on the strength and strain characteristics of concrete were experimentally verified and confirmed by microstructure analysis. Electromagnetic treatment of the cement paste increased the compressive strength, axial compressive strength, tensile strength in bending, and axial tensile strength of concrete. The best performance was demonstrated by electromagnetically-activated concrete containing 5 wt.% rice straw biochar. Strength characteristics increased from 23% to 28% depending on the type of strength, ultimate tensile strains decreased by 14%, and ultimate compressive strains by 8% in comparison with the control concrete composition. Replacing part of the cement with 10 wt.% and 15 wt.% rice straw biochar led to a strong drop in strength characteristics from 14 to 34% and an increase in strain characteristics from 9 to 21%. Scanning electron microscopy showed a denser and more uniform structure of electromagnetically activated samples.

The application of the agricultural waste of cashew nut shells (CNSs) from the Ivory Coast is proposed for the production of activated carbon (AC) used in