Monolithic Concrete Structures Research Articles

Study on the Shear Performance of the Interface between Post-Cast Epoxy Resin Concrete and Ordinary Concrete

The interface of fresh-aged concrete represents a critical vulnerability within monolithic assembled monolithic concrete structures. In this paper, the shear performance of the interface between post-cast epoxy resin concrete and standard concrete is studied using experimental methods and finite element analysis. The objective is to furnish empirical data that support the broader adoption of epoxy resin concrete in assembled structures. A direct shear experiment of 19 Z-shaped samples and a computation of 20 finite element models were completed. The results from both experimental and computational analyses provided insights into several factors influencing the shear performance at the interface. These factors include the pre-cast part of concrete strength, the friction coefficient of the interface, the longitudinal reinforcement ratio at the interface, the compressive strength of concrete in the post-cast part, and confining stress. The findings indicate that utilizing epoxy resin concrete for post-cast material, roughing the interface, and setting keyways can enhance the shear performance of the interface so that it equals or even exceeds the cast-in situ sample. Optimal shear results are obtained when the compressive strength of the post-cast epoxy resin concrete closely matches that of the pre-cast conventional cement. Moreover, increasing the depth of the keyways rather than their width is more effective in improving the shear capacity of the sample. It is recommended that the depth of the keyway should be at least 30 mm, and its width should be no less than three times the depth. As the longitudinal reinforcement ratio at the interface increases, there is an enhancement in shear capacity coupled with a reduction in deformative performance. It is advisable to maintain this ratio below 1.0% to balance the strength and ductility effectively.

CARBON FOOTPRINT OF A CONCRETE TRANSPORT STRUCTURE - A DEEP TUNNEL

The research object of this scientific work is the massive concrete structures of underground low-deep transport tunnels, reinforced with steel and non-metallic composite reinforcement. Circular-section tunnels with the frame nominal diameters of 5, 10 and 15 m are considered. The subject of the research study is the assessment of the averaged carbon footprint in both types of the constructive solution throughout their entire life cycle. The presented research is due to the need to implement the European Climate Law (the European Green Agreement. At the same time the Paris Agreement (2016) recommends to stop producing and using carbon steel in construction by 2030. The ecological impact of both types of transport tunnels is expressed in the form of carbon footprint, as the equivalent of carbon dioxide emissions, which is calculated separately for each stage of their existence in accordance with the current European Codes, including the recommendations of the proprietary methodology. To determine the required sizes of the tunnels concrete frames and their reinforcement, the numerical routine (B3) experiment was carried out in PLAXIS software complex in accordance with the current regulations. Averaged according to three different diameters and generalized carbon dioxide emissions during the life cycle of the reference structure (type 1) and proposed one (type 2) of the underground transport tunnel with the length of 1 m.p. were, respectively, 15.97 t СО2 eq and 11.551 t СО2 eq, i.e. decreased by almost 1.4 times. The conducted research made it possible to analyze the carbon dioxide emissions into the atmosphere, to systematize the existing factors and impact factors of the specified building on the environment, and to determine the ways of their reduction. The possibility and expediency of using basalt-plastic reinforcement instead of steel in monolithic concrete structures, incl. transport tunnels, according to the criterion of reducing greenhouse gas emissions are proved. Keywords: carbon footprint, carbon dioxide emissions, underground transport tunnel, monolithic heavy concrete, steel and non-metallic composite reinforcement, construction life cycle, stage, information group (module).

ANALYSIS OF THE COMBINATION OF METHODS OF FASTENING THE JUNCTION POINT OF A HORIZONTAL TUNNEL WITH A VERTICAL SHAFT IN CONDITIONS OF DENSE URBAN DEVELOPMENT

Purpose. The problem of compares the long-term behavior of a tunnel-well taking into account the rigid and flexible couplings in the projected structures in Ukraine with 3d digital modeling using the three-dimensional finite element method. A refined geotechnical model has also been developed, taking into account the nature of the piezometric starting conditions and the proposed piezometric conditions for assessing the long-term condition as well as a summary of the properties and dimensions of the tunnel and the shaft. Methodology. Analysis of structural connections based on the experience of building shallow subways in dense urban development on the example of construction projects in China and Mexico. Search for the optimal combination of implemented methods to achieve the optimal result. Problems of a choice of a mode with 3d digital modeling using the three-dimensional finite element method based on two assumptions; the first assumption considers the rigid connection as a monolithic concrete structure between the shaft wall and the tunnel body, and the second assumption considers a material with elastic behavior between the two structures, which in turn leads to a flexible connection. The main parameters that must be clarified and corrected by the designer of the system during commissioning are determined. Next, the soft soil model was used to perform the analyzes with end elements for compressible layers. Findings. Simulation in the application, the Plaxis software environment obtained graphs of transients for the most important operating parameters, such as the geometry of the tunnel and the indicated lining, the flotation pool, three-dimensional clusters. Originality. Scientific interest in advancing technologies used in combination. Development of an algorithm for the optimal selection of the parameters of flexibility and durability in specific conditions, to save time and simplify the calculation forms. Practical value. The analysis of the obtained results is carried out, the main focus was on the relative loads and stress concentrations in the connecting elements, namely the stresses that occur in the transverse direction of the joint. Also in articles were determined some of the advantages and disadvantages of the different connection alternatives are discussed in order to neutralize the impact of the case in the future.

Multi-layer casting of self-consolidating concrete: Influence of mortar rheology and casting parameters on the inter-layer bond strength

Inter-layer bond strength is a critical factor to achieve structurally sound monolithic concrete structures. This paper discusses the effects of the cementitious paste volume (CP%vol), structural build-up of mortar (Athixm), and their interactions with casting parameters (i.e., free fall height (HFF), and delay time) on the residual bond strength of multi-layer self-consolidating concrete. It is found that the residual bond strength can be improved by increasing the CP%vol and HFF, or by reducing the delay time and Athixm. Out of the factors investigated, Athixm has the largest effect on both the residual bond strength and the critical delay time.

LABORATORY AND PRODUCTION TESTS OF A HYDROPHOBIC ADDITIVE FROM THE GROUP «RAMSINKS-2M» FOR CONCRETE USED FOR THE MANUFACTURE OF STATION BLOCKS AND BLOCKS OF TRANSPLANTING TUNNELS WITH HIGH WATERPROOFING

In the work, conducting experimental works and experiments on the choice of optimal ratios of PTCs 1-100 and hydrophobic material «Ramsinks-2MU», studying hydrophobicity of mixtures, recipes-solutions, research of technological properties of mixtures. Experimentally proved that the brand of concrete is not permeable reached by W12, which can not be obtained by sealing concrete. The results of laboratory tests of concrete with the addition of «Ramsinks-2m» are given. To increase the waterproofing of concrete antiltration barriers, underground structures of buildings and structures, reservoirs, etc. It is proposed to achieve high waterproofing of concrete by adding to its composition of the hydrophobic additive «Ramsinks-2MU». The use of new hydrophobic materials such as "Ramsinks-2MU" for the manufacture of concrete on the construction of the subway in Kyiv - is an exhaust direction in metrobudination. Reliable waterproofing of outflows and openings can be achieved by applying a water-retailing additive "Ramsinks-2MU" and its modifications. Technological simplificence in the introduction of the latest material is achieved by direct use of hydro-insulating works by introducing it in the appropriate ratio in traditional solutions. A method for selecting a percentage of a hydrophobic additive with cement for different classes of concrete and for specific mining-geological conditions has been developed. This technique makes it possible for the latest technologies to determine the qualitative characteristics of the hydrophobic additive offered. The use of this additive in the manufacture of concrete and solutions contributes to an increase in the elasticity of the mixture, prevents the uneven concentration of fillers, as well as prevents mixing of the mixture and increases resistance to aggressive factors. The high waterproofing of products with the additive is achieved with the corresponding concrete composition by fine schedules of hydrophobic particles. By reducing the negative impact of moisture on the design, their durability increases. Laboratory test tests showed that the introduction of a hydrophobic additive "Ramsinks-2M" significantly affects the strength of the cement stone in the hydrophobic mixtures "Ramsinks-2MU". The proposed hydrophobic materials have qualitative advantages over other similar materials, as well as cost-beneficial. They can be used when the seams of tunnel processing and stations, as well as waterproofing of monolithic concrete structures in the subway.

The Curing of Concrete Samples with Water - Experimental Verification of the Concrete Properties

The process of producing a monolithic concrete structure on site is constructed out under different climatic conditions, which can often be unsuitable for setting and hardening of concrete. The necessary conditions for setting and hardening of concrete are ensured by various ways of its curing. In practice, concrete curing is carried out in most cases by water spraying. It is used mostly in reinforced concrete ceiling slabs, which are further discussed in the work. A common procedure is to cure the upper surface of reinforced concrete ceiling slabs. This work therefore deals with the effect of curing of a reinforced concrete slab, on its strength properties. Long-term curing would yield higher values of compressive strength, but it is also necessary to consider how effective it is. As a pilot research in this work is investigating the properties of concrete cubes in various curing. It further develops theoretical possibilities for continuing research.

Ecologically safe construction of monolithic concrete structures

The construction of monolithic concrete vaulted structures technology is proposed. The technology involves in the factory conditions to produce a design based on pneumatic formwork. That allows all processes associated with environmental pollution to be transferred to factory conditions. At the construction site, environmental and human impacts are minimized.

Carbon emission modeling and analysis of building materialization process

The environmental properties of building assembly and recycled concrete are becoming highly related to the theme of the construction industry developments. Therefore, in order to account for the reduction effect of greenhouse gas arising from the combination of such two techniques, the building materialization process is divided into fabrication stage, transport stage, and site operation stage, and the calculation model for the assembled monolithic recycled concrete structures, ordinary assembled monolithic concrete structures, and cast-in-place concrete structures is established. Analyses and comparisons on the cases in Chongqing can be conducted owing to the model. The research results show that from the perspective of the entire materialization process, OAMCS can save 25.94% of carbon emissions compared to CCS per cubic meter of components, while AMRCS can further save 8.5% of carbon emissions compared to OAMCS per cubic meter of components, which can provide basic data for emission reduction and facilitate integration of the two techniques.

Information technology in the study of the quality of concrete work

The article presents the results of using information technologies in the study of changes of concrete characteristics at different hardening conditions. The use of the developed temperature measurement complexes made it possible to control the conditions of hardening of monolithic concrete structures directly under production conditions. The results by means of using regression analysis are obtained, regression models of the dependence of the compressive strength of concrete on time and hardening temperature are determined. A significant decrease in compressive strength and resistance to air penetration of concrete samples during their storage under conditions of significant temperature fluctuations has been established.

Spar concrete monolithic design for offshore wind turbines

Significant research efforts are now being directed at floating offshore wind turbines. The main challenge posed by floating wind turbines is the high construction and installation costs of the substructure, which make it too expensive for commercial exploitation in the current energy market. With the aim of achieving a cost-effective floating platform for offshore wind turbines, a new concept of a monolithic floating spar buoy is hereby presented. The monolithic concrete structure includes both the tower and the floater, built as a continuous single piece. This new concept offers a significant cost reduction during the construction phase and also while in operation, because the platform becomes almost free of maintenance during its lifetime. The main dimensions and the hydrostatic and hydrodynamic properties are presented, including a basic structural assessment of the platform to ensure its structural integrity. The construction and installation processes are presented, taking into account the special requirements of the monolithic design. Finally, a cost comparison between a steel and an equivalent concrete platform design has been performed, showing a material cost reduction larger than 60% in the case of the concrete design.

Ultra-lightweight concrete: Conceptual design and performance evaluation

The present study presents a methodology to design ultra-lightweight concrete that could be potentially applied in monolithic concrete structures, performing as both load bearing element and thermal insulator. A particle grading model is employed to secure a densely packed matrix, composed of a binder and lightweight aggregates produced from recycled glass.The developed ultra-lightweight concrete, with a dry density of about 650–700kg/m3, shows excellent thermal properties, with a thermal conductivity of about 0.12W/(mK); and moderate mechanical properties, with a 28-day compressive strength of about 10–12N/mm2. Furthermore, the developed concrete exhibits excellent resistance against water penetration.

Reduction of the Thermal Gradient in Concrete Mixture in Dry and Hot Climates Using Phase Change Materials

Dynamic development of construction industry and related with it implementation of more and more modern design, forces the use of more advanced concreting technology. Tight, short construction deadlines force the contractors often to conduct works, regardless of weather conditions.The development of materials technology, implementation of new products, measurement techniques and methods of registration “data” information makes regardless of still useful, traditional tools for rising concrete structure, there must be sought and developed new methods for reduction of adverse events inside the concrete elements, but also allowing faster construction rising.Ageing of concrete is a result of cement hydration, which is an exothermic process. Approximately a full hydration of 1kg of standard Portland cement causes emission of approximately 400kJ of heat. The ambient temperature and emition of hydration heat of fresh concrete mix and encountered difficulties in transmitting heat to the outside of the element initiates the formation of thermal gradient in the concrete structure. As time goes by, as a result of hydration process progress, the hardening concrete acquires mechanical characteristics (it increases its strength). If the resulting stress, caused by the temperature gradient, exceed at any given time the strength of the forming “concrete structure”, it is followed by its destruction, and result in emerging fractures and cracks in the constructed element [1].From the above it can be concluded that the proper thermal care becomes one of the primary factors determining a solid monolithic concrete structure, hence the idea of application of PCM (Phase Change Materials) for the care of the inner concrete mix when ageing in hot and dry climates.

Indoor radon problem in energy efficient multi-storey buildings.

Modern energy-efficient architectural solutions and building construction technologies such as monolithic concrete structures in combination with effective insulation reduce air permeability of building envelope. As a result, air exchange rate is significantly reduced and conditions for increased radon accumulation in indoor air are created. Based on radon survey in Ekaterinburg, Russia, remarkable increase in indoor radon concentration level in energy-efficient multi-storey buildings was found in comparison with similar buildings constructed before the-energy-saving era. To investigate the problem of indoor radon in energy-efficient multi-storey buildings, the measurements of radon concentration have been performed in seven modern buildings using radon monitoring method. Values of air exchange rate and other parameters of indoor climate in energy-efficient buildings have been estimated.

Shoring/Reshoring Operations for Multistory Buildings

An analytical procedure to determine the loads on the shoring system and supporting slabs during construction of multistory concrete buildings is presented. The procedure assumes a 2-dimensional slab beam-column frame similar to the equivlent frame concept described in the ACI Building Code. There have been several efforts to determine construction-load distribution; however, most analytical methods, though regarded as sufficiently practical for everyday application, have employed single-bay idealizations for multistory sructures. This is a definite limitation to the proper representation of a multibay continuous monolithic concrete structure, which the equvalent frame model overcomes. Several construction cases are investigated to determine the effect of various parameters on the construction load distribution using the equivalent frame model.

Provision of strength and watertightness in the contact joint of monoliths of built-up reinforced-concrete elements

1. The use of earlier methods (application of cement paste, denting, furring, etc.) either is not practical or requires more expensive operations (wire brushing, notching, sandlbasting) and is not economically profitable for the types of built-up elements being constructed at the Saratov and Lower-Kama hydroelectric stations as concrete monoliths. 2. With the sole purpose of providing safety of contact it is recommended that the surfaces of the built-up elements be cast in new types of light removable forms — meshwork forms with burlap surfaces, or metal-plastic forms. The use also of open removable meshwork forms is permissble. 3. Careful maintenance after the concrete surface is produced will guarantee good waterightness and rupture strength without any subsequent mechanical operations. Its rupture strength will nearly equal that of monolithic concrete and the shear strength will be 60–80% of the corresponding monolith strength. 4. The conclusions and recommendations to be carried out for built-up elements should be applied also to the erection of monolithic concrete structures. The proposed methods for securing a dependable union of the blocks in inter-block joints seem to us to be the most effective and least labor-consuming in comparison with presently universally used notches, sandblasting and others.