Concrete Structures Research Articles

A novel approach to assess internal pore structure and quantify tortuosity of clogged pervious concrete through image analysis techniques

ABSTRACT The major objective of this research was to develop an innovative approach to characterise the pore structure of pervious concrete (PC) mixtures and quantify tortuosity in pre- and post-clogged conditions through 2D and 3D image analysis. Four different types of PC mixtures were prepared and subjected to computed tomography (CT) scanning to retrieve morphological information covering over 1900 images, followed by tortuosity quantification of each of 200 interconnected pore paths using vascular modelling toolkit (VMTK). The porosity of PC obtained from laboratory-based tests was 10–25% lower than image analyses. Further, along the depth of PC, a significant decrease in the number of pores in the top 60–80 mm was observed due to clogging, which revealed that maintenance be adopted only in the top 80 mm. Control and clogged PC with smaller sized aggregates and lower w/c ratio were more tortuous compared to higher w/c ratio while opposite for larger sized aggregates, ascribed to the occurrence of shorter interconnected pore paths comprising larger pore diameter, remarking that permeability will depend on both tortuosity and path diameter. CT scanning was used in predicting tortuosity and pore interconnectivity of PC through VMTK approach extensively used in medical science and seldom used in engineering.

Assessing progressive collapse regions of reinforced concrete frame structures using Graph Convolutional Networks

In the progressive collapse, the structural topology changed dynamically as failures propagate. Representing reinforced concrete (RC) frames with graph data leverages the topology of beam–column joints and structural components, enabling graph neural networks (GNNs) to predict the failure propagation. Graph convolutional networks (GCNs), a specific type of GNN, offer superior computational efficiency for graph data to traditional GNNs. However, three challenges must be addressed for GCNs to rapidly assess collapse regions: (1) insufficient data, (2) lack of graph representations for structural collapse, and (3) absence of tailored GCN architectures. To address these gaps, this study focused on RC frames with the following initiatives: (1) an efficient and accurate method for generating progressive collapse data was developed; (2) joint-based representation and component-based representation were established, accompanied by a method for converting RC frames into these representations; (3) two GCN architectures were designed to identify failure paths and predicting collapse regions. The performance of the GCN models using various convolutional layer configurations was evaluated on the two graph representations, and the CGR-based model using SAGEConv layers exhibited the best performance with an accuracy and F1 score of 0.9839 and 0.8853, respectively. The proposed method exhibited over a 99 % improvement in calculation efficiency and approximately a 75 % reduction in memory usage compared with traditional FEM. Moreover, it captured the contribution of each component to progressive collapse resistance with better accuracy than previous approaches. Finally, this method was employed to predict the internal and external collapse regions of a real-world structure by incorporating a physics engine-based approach from prior studies.

ПРОЦЕСНО-ОРІЄНТОВАНИЙ ПІДХІД ДО ОБЛІКУ ВИТРАТ Й КАЛЬКУЛЮВАННЯ СОБІВАРТОСТІ ПРОДУКЦІЇ ПІДПРИЄМСТВ З ВИРОБНИЦТВА ЗБІРНИХ ЗАЛІЗОБЕТОННИХ КОНСТРУКЦІЙ

Costs are one of the most important economic categories, and production costs are the main indicator of construction materials industry enterprises activity. In today's difficult business conditions for Ukrainian enterprises, taking into account the specifics of the production process of companies producing prefabricated reinforced concrete structures, constant monitoring of production costs helps to maintain the profitability and competitiveness of these business entities. Therefore, the development of management tools and cost accounting using a process-oriented approach for enterprises producing building materials allows taking into account all the features of production processes influencing the size and behavior of costs. The purpose of the article is to reveal and improve the features of cost accounting and costing of products according to production processes at enterprises producing precast reinforced concrete structures. The article analyzes the main directions of classification of production processes at enterprises of the production of prefabricated reinforced concrete structures and its influence on the organization of accounting. The directions for grouping costs in production processes are detailed and attention is focused on its impact on accounting and control of the costs. This will affect the quality of management decisions and the main performance indicators of the enterprises under study. In the process of research, the main foreign methods of accounting for costs and calculating the cost of products in production processes, which are possible for use at enterprises of the production of precast reinforced concrete structures, were determined. It was found that the ABC-costing method is the most acceptable from the point of view of the technological process of manufacturing products of the studied enterprises. Its combination with the regulatory method of cost accounting and product costing will provide significant opportunities for strategic planning of production costs, will contribute to the accuracy of product costing, and will improve the process of management decision-making.

Assessment of the Influence of Features of Crack Formation in Reinforced Concrete Products on their Fire Resistance

The paper considers possible scenarios of cracking during heating and their impact on fire resistance using the example of a bending reinforced concrete structure (beam). It is shown that if the calculated critical temperature of reinforcement is less than the critical temperature of concrete (this indicates a significant load on the structure), then cracks in the tensile zone of concrete are formed after reaching the second stage of the stress-strain state. The concrete of the protective layer does not have time to degrade, the depth of the crack remains constant, and the fire resistance limit is calculated taking into account that the thickness of the protective layer of concrete is reduced by the depth of the crack opening. If the calculated critical temperature of the reinforcement is greater than the critical temperature of the concrete (this indicates a slight load on the structure), then cracks are formed as a result of the degradation of the surface layer of concrete. Their depth should constantly increase with the progression of the concrete layer heating to the critical temperature. In this case, the calculation of the fire resistance limit can be performed without taking into account the formation of cracks. Based on the considered assumptions, a methodology for assessing the impact of cracks on the fire resistance limit of bending reinforced concrete structures is proposed, which consists in analyzing the possibility of open cracks (which is facilitated by heating) and estimating their depth. At the next stage, the heating time of the concrete layer to the crack opening depth τΔ1 and the temperature in the crack after this time are estimated. Next, the time until the critical temperature of the reinforcement τΔ2 is estimated when the concrete layer is heated from the bottom of the crack to the reinforcement. The fire resistance limit is defined as the sum of τΔ1 and τΔ2. The results of the calculations according to the proposed methodology showed that the presence of open cracks in bending reinforced concrete structures can almost halve the fire resistance limit.

Systematic review of the use of phase change material (PCM) in concrete and the fire performance of PCM in concrete

ABSTRACT The Mechanical properties of concrete significantly deteriorate when exposed to fire, with explosive spalling posing a major threat to structural integrity. This highlights the need for effective insulation systems to protect concrete structures in fire conditions. However, current insulation solutions are typically installed externally, requiring additional labour and materials. This review explores the potential of incorporating Phase Change Materials (PCMs) directly into concrete as an embedded insulation system. As a latent heat storage material, PCM offers promising fire-resistant properties, reducing the need for external insulation while improving the fire performance of concrete. This paper presents a bibliometric analysis and a systematic review of recent publications on the use of PCMs in concrete and their fire performance applications. One thousand two hundred and four publications retrieved from Scopus© and Web of Science databases were passed through the PRISMA flowchart to obtain a database of recent literature on the study area. The current trend of research shows a shift towards inorganic PCMs in concrete. There is a significant lack of studies on using inorganic and eutectic PCM in concrete for fire applications and existing studies show inorganic PCM can be a viable solution. Commercial availability and lack of synthesised encapsulated PCM were found to be barriers to research.

Justification of the Efficiency of Application of Plaster for Fire Protection of Concrete Structures

The problem of using concrete for building structures is to ensure their stability and durability during operation within wide limits. Therefore, the object of research was the change in the properties of concrete during a fire and its protection when applying a heat-insulating layer of plaster, which is able to inhibit the temperature when the flame affects the coating. It has been proven that in the process of thermal action on fire-resistant plaster, the process of thermal insulation of concrete consists in the application of materials with low thermal conductivity as part of the plaster on the surface of the material. Similarly, under the influence of the burner flame, a temperature was created on the surface of the sample under the influence of the burner flame with a temperature of more than 800°С for 1800 s, the temperature on the surface of the concrete under the plaster coating did not exceed 120°С, which indicates the formation of a curtain for temperature. In this regard, experimental studies were conducted and it was established that the presence of aluminosilicate microspheres in the plaster leads to the formation of a thermally protective layer on the surface of concrete resistant to mechanical vibrations. According to experimental data, the coefficient of thermal conductivity and thermal conductivity of the plaster was calculated, which is 6.22·10–7 m2/s and 0.142 W/(m∙K), respectively, due to the addition of aluminosilicate microspheres. Thus, there are reasons to assert the possibility of targeted regulation of concrete fire protection processes by using fire-resistant plaster capable of forming a protective layer on the surface of the material, which slows down the rate of heat transfer.

Image-based assessment of seismic damage in RC exterior beam-column joints

Seismic damage to reinforced concrete (RC) beam-column joints in reinforced concrete (RC) structures significantly impacts their stability and safety after an earthquake. Cracks caused by earthquakes weaken these joints, reducing their ductility, strength, and stiffness. Therefore, a systematic method for assessing damage in RC beam-column joints is crucial. This study introduces a new method that uses image analysis, along with ranking algorithms and machine learning, to assess seismic damage in RC exterior beam-column joints. The study identified three key indicators of severe damage in joints: drift ratio, strength, and stiffness. The method uses image analysis to extract features from preprocessed, binary images of cracks. These features capture both the texture and geometry of the cracks. The chosen features, including crack area, aspect ratio, and distribution of line widths, along with structural parameters like geometry and bond index, were selected using F-test and MRMR algorithms. Seismic damage assessments were conducted on 115 images from 37 specimens using four machine learning models (Regression Trees, Support Vector Machine, Gaussian Process Regression, and Gradient Boosting). The study achieved a high R-squared value of 0.80, indicating strong accuracy, for assessing seismic damage based on drift ratio using the image-based method. This demonstrates that image analysis techniques can effectively link surface crack patterns to quantifiable image features, leading to a more precise assessment of seismic damage.

Corrosion Assessment in Reinforced Concrete Structures by Means of Embedded Sensors and Multivariate Analysis—Part 2: Implementation

The economic cost of repairing corrosion-affected reinforced concrete structures (RCSs) means that reliable and accurate assessment and early detection methods must be sought after. Conventional techniques, such as visual inspections, or measuring either cover layer resistivity or the corrosion potential, are methods that require accessibility and involve personnel having to travel to take in situ measurements. Monitoring by embedded sensors is a much more efficient approach that allows early detection by remote sensing. This work presents the implementation of a new measurement protocol regarding the existing monitoring system called INESSCOM (Integrated Sensor Network for Smart Corrosion Monitoring). Along with the corrosion intensity measurement in embedded sensors, it also proposes monitoring the double layer capacity of the sensors’ responses. It aims to determine, along with the rebars’ corrosion rate, the triggering agent of the corrosion process. This study was carried out using three reinforced concrete scaled columns that were exposed to different environments. The results demonstrate with this new protocol that the remote INESSCOM monitoring system can establish the corrosion rate and identify the precursor agent of corrosion (carbonation or chlorides), even when the recorded corrosion rates are similar.

Compensating for Concrete Shrinkage with High-Calcium Fly Ash

Shrinkage of concrete during hardening is a serious problem in attempts to maintain the integrity of concrete structures. One of the methods of combating shrinkage is compensating for it using an expansive agent. The purpose of this work is to develop and study an expanding agent to concrete, including high-calcium fly ash and calcium nitrate as an expansion activator. The content of Ca(NO3)2 can be used to regulate the degree of expansion of the additive itself during hydration and, accordingly, to control shrinkage, thus obtaining shrinkage-free or expanding concrete. Shrinkage–expansion deformations of concrete can also be regulated by the amount of expanding additive replacing part of the cement. With the Ca(NO3)2 content of fly ash being 10% or more, concrete experiences expansion in the initial stages of hardening. The transition of deformation through 0 to the shrinkage region occurs depending on the composition and content of the additive after 8–15 days of hardening. It has been established that replacing cement with pure fly ash with a curing period of 90 days or more has virtually no effect on the strength of concrete, either in bending or in compression. The use of an expanding additive containing 5–15% Ca(NO3)2 reduces the strength of concrete by an average of 9%, despite the fact that calcium nitrate is a hardening accelerator.

Influence of randomly placed resonant aggregates on the attenuation properties of metaconcrete: A numerical study

Concrete is a key material for many structural components in engineering, but its acoustic performance remains under discussion. Hence, the potential of the so-called metaconcrete has gained attention in research, mainly due to its capability to control vibrations and sound transmission when resonant aggregates are embedded in the concrete. These resonant aggregates are designed to have resonant frequencies regarding frequency bands of interest, so the interaction with the incident sound waves is attenuated within those frequencies. While available research has focused on the characterization of metaconcrete with a periodic arrangement of resonant aggregates, there is a gap regarding how their random allocation affects the characterization of metaconcrete. This study focuses on the numerical analysis of metaconcrete and the influence of randomly placed resonant aggregates on its attenuation properties. The numerical approach concentrates on the aggregate's material composition, location and volume fraction within the concrete to identify configurations that exhibit great wave attenuation. The results have shown that the attenuation effect is substantially advantageous when using a multi-frequency configuration for aggregates within the metaconcrete. Additionally, the random embedding of resonant aggregates offers a practical solution for their application in concrete structures.

Factors Influencing Measurement of Dynamic Elastic Modulus from Disk-Shaped Concrete Specimen

The decrease in dynamic elastic modulus is a primary indicator of quantitative damage in concrete. To quantitatively assess depth-by-depth damage within a concrete structure, cylindrical specimens obtained through coring can be cut into disk specimens to measure the dynamic elastic modulus of concrete at each depth. To minimize external damage during coring, it is essential to extract cylinders with the smallest possible diameter. In addition, for higher resolution in depth-based damage assessment, creating disk specimens with the smallest possible thickness is necessary. However, there is no information available in the literature on experimental limitation of smallest possible diameter and thickness for dynamic elastic modulus of disk-shaped specimens. This study evaluated whether the dynamic modulus measured from various sizes of concrete disk specimens provided sufficient reliability compared to reference values obtained from cylinders. Moreover, the study examined how the presence of coarse aggregate and variation in the water–cement ratio significantly influenced the dynamic modulus measurement. In addition, test results from impulse excitation technique (IET) and impact resonance (IR) were compared to find a more reliable test method for dynamic elastic modulus of disk specimen. The experimental findings revealed that as the thickness-to-radius ratio of the disk specimens decreased, measured data variation increased. Mortar specimens without coarse aggregates showed less variability compared to concrete specimens, and the variation in dynamic modulus measured by IR was lower than that measured by IET.

Experimental study on damage of steel fiber reinforced concrete- and wood-filled GFRP tubes under axial compression

In order to reduce the self-weight of concrete structures and improve its corrosion resistance, it is an effective way to fill GFRP tubes with wood columns instead of part of concrete. However, concrete structures are prone to cracks, which will reduce the bearing capacity of the structure and affect the safety and applicability of the structure. Incorporating the steel fibers (SF) in concrete seems to be an excellent solution to limit crack propagation and improve the ductility of concrete structures. Based on the premise, in this paper, a new type of structure composite material of steel fiber reinforced concrete- and wood-filled GFRP tubes was developed. The mechanical properties, damage evolution process and crack fractal characteristics of steel fiber reinforced concrete- and wood-filled GFRP tubes under axial compression with different SF volume fractions (0 %, 1 %, 1.5 % and 2 %) were studied by acoustic emission (AE) technology. The finite element method (FEM) was established to simulate the test work and expand the analysis. The results showed that the bearing capacity and ductility of the specimens increased first and then decrease with the increase of SF content, and the specimens with 1.5 % volume fraction of SF showed the best mechanical properties. According to the characteristics of AE ringing counts, the damage process of the specimen was described by three marker events, which were concrete cracking, wood cracking and GFRP tube fracture. The incorporation of SF increased the intensity of AE signal and the proportion of shear cracks, and reduced the damage scale. The fractal dimension of concrete surface cracks had a good correlation with the degree of local damage and the complexity of crack propagation. The damage evolution model based on AE cumulative events and stress obeyed the two-parameter Weibull distribution. The incorporation of SF reduced the degree of damage, and the parameter m had a negative correlation with brittleness. In addition, the damage process of the specimens revealed by the FEM matched well with the experimental results. Additionally, the incorporation of SF made the stress distribution of each part of the specimen more uniform and avoided the phenomenon of stress concentration.

Comparative study of different programs for sound insulation calculations

Engineering programs for calculating sound insulation in wooden buildings are a shortage, especially when it comes to wooden structures. There are some possibilities today to calculate field values using commercial programs following ISO 12354. However, detailed calculations for each construction part are sometimes crucial to optimize correctly, specifically for CLT or wood beam structures since they are far more complex than traditional concrete structures. Now, some programs are available on the market to calculate sound insulation for CLT structures. StoraEnso offers "Calculatis" online for free, and Marshall Day Acoustics provides "Insul 10". In short, the company Sonusoft will release a software called "Acoulatis". These three programs have slightly different approaches, and their capability to calculate various wall and floor structures differs. Nevertheless, the different programs are all limited to walls or floors construction parts, e.g. the outcome is Rw and Ln,w including spectrum adaptation terms, e.g. junctions are not included. In this paper, a comparison is made using the three different programs, including comparisons to measured values when available.

Physical and numerical tests on adjustable–height structures of high–speed railway transition section

The disparity in stiffness and differential settlement between the subgrade and rigid structures can lead to track irregularities within transition sections, resulting in significant train vibrations and impacts. This study proposes an adjustable–height subgrade structure for transition sections by introducing a raft slab to divide the subgrade into upper and lower parts. When settlement occurs in the subgrade, the raft slab can be elevated using height–adjustment techniques to compensate for the settlement. To this end, large–scale physical model tests are conducted under train loading to verify the design's rationality and to elucidate the influence of settlement magnitude and train speed on the stress and deformation of the slab. The experimental results indicate that the maximum principal stress and maximum shear stress of the slab generally increase with settlement magnitude and train speed, and the area near the abutment end is the most unfavorable position for the deformation of the slab. However, it is still lower than the design compressive strength of the C40 concrete structure. Thus, the designed adjustable–height structure meets the load–bearing requirements under train loading. Additionally, a numerical simulation model of the adjustable–height structure is developed to investigate the recovery capabilities and stress distribution of the settled raft slab. The results indicated that whether the lifting operation employed linear load or equal load methods, the raft slab primarily endured compressive stress, and there is stress concentration at the lifting points. For the same lifting displacement, the linear load method proved to be more reasonable than the equal load method. These findings have significant practical and theoretical implications for ensuring the safe and smooth operation of high–speed railways, effectively addressing the post–construction settlement deformation control challenges in ballastless track transition sections.

Eccentric compression behaviors of iron tailings and recycled aggregate concrete-filled steel tube columns

This paper presents a sustainable method for using iron ore tailings (IOTs) sand and recycled coarse aggregate (RCA) in concrete and concrete-filled steel tube (CFT) columns. The study first examines the impact of RCA replacement ratios (0 %, 50 %, 100 %) on concrete's mechanical properties, finding that both compressive and tensile strengths decrease with higher RCA content due to the negative effects of old interfacial transition zones and adhered cement in RCA. Then, twelve iron tailing and recycled aggregate concrete-filled steel tube (ITRAC-CFT) columns were tested under eccentric compression to assess the effects of varying RCA replacement ratios, eccentricity ratios (0.3, 0.5), and slenderness ratios (12.12, 19.05). Results indicate that RCA ratios have minimal impact on failure modes, ultimate bearing capacity, and stiffness, although ductility increases with higher RCA content. As slenderness ratios increase, the ultimate bearing capacity decreases by 5.3 % and 6.8 % for eccentricities of 0.3 and 0.5, respectively. The study further validates these findings through the finite element method (FEM), showing strong agreement between experimental and predicted results, average value, standard deviation, and coefficient of variation of Nu/NFE were 1.02 %, 0.04, and 3.92 %, respectively. Finally, a comparison with existing design codes (EC4, AISC 360, and GB 50396) reveals that AISC 360 provides the most accurate predictions of the ultimate bearing capacity of ITRAC-CFT columns. The research concludes that the comprehensive use of IOTs sand and RCA in CFT structural concrete is a highly viable and eco-friendly solution, offering potential benefits for sustainable construction practices.

Analysis of dynamic response and impact resistance of corrugated plate-reinforced concrete under simulated rockfall

In this study, corrugated plate material is used as the internal mold for the reinforced concrete structure, proposing a combined shelter structure designed to protect against rockfall hazards in mountainous areas. The research focuses on the impact of low-velocity rockfall (below 150 km/h) directly hitting both the reinforced concrete structure and the corrugated plate and reinforced concrete combined shelter structure. The accuracy of the numerical simulation results is validated through comparative analysis with indoor model experiments. Further investigation reveals the impact resistance and failure characteristics of RC (Reinforced Concrete) structures, CPRC(D) (Corrugated plate double-layer reinforced concrete composite structure) structures and CPRC(S)（Corrugated plate single-layer reinforced concrete composite structure）, with the residual resistance index (RRI) introduced for the quantitative analysis of the residual load-bearing capacity of the protective structures post-impact. The results indicate that the shape of impact craters and the maximum impact force obtained through numerical simulations closely match the experimental findings, demonstrating the validity of the simulation parameters. Under the same impact energy, the maximum peak stress at various points in the CPRC structure is reduced by more than 50 % compared to the RC structure. Damage to the RC structure under rockfall impact is primarily characterized by central penetration failure and extensive development of diagonal cracks. In contrast, the CPRC structure effectively suppresses penetration, dent deformation, and crack propagation, significantly reducing the volume of concrete damage and the proportion of rebar damage, with the residual resistance index consistently remaining above 0.27.The corrugated plate and reinforced concrete combined structure outperforms the reinforced concrete structure in several impact resistance factors, including maximum impact force, effective stress extremes, structural damage, and penetration depth. Additionally, after reinforcement with corrugated plates, the CPRC structure maintains a high level of impact resistance in most scenarios, even when the lower layer of rebar is eliminated, providing a theoretical basis and preliminary feasibility proof for the lightweight modification of the structure.

Features of construction at low temperatures

The present paper considers the features of construction at low temperatures and introduces the previous studies on improving the reliability of metal and reinforced concrete structures. Low temperatures adversely affect penetration of the edges of metal products during welding. Notably, design engineers consider the results of investigations and calculations, and incorporate steel products made of lowalloy, stainless steels, and nickel alloys. These materials demonstrate high viscosity, good weldability, retain strength in the process of manufacturing structures and their operation. The paper analyzes the construction works in winter conditions and considers installation as one of the main technological processes in construction. In addition, the paper lists the restrictions for welding and concreting, as well as indicates the conditions for structures to be installed using bolts or manual arc welding. Manufacturing plants are known to treat metal products and structures with protective coatings prior to transportation to the construction site. These technological operations are aimed at protecting metal from corrosion and at retaining heat within buildings. All winter concreting techniques are indicated to be implemented on the construction site at temperatures below 5°C. Gaining the required strength of the cement needs more time in cold temperatures than at a temperature of +20°C. The method of artificial heating, presented in the paper, is intended to create durable concrete and reinforced concrete products and structures.

Experimental study on the flexural behavior of reinforced concrete beam strengthened with novel prefabricated HSSM-UHPC thin plate

Ultra-high performance concrete (UHPC) has been used to strengthen reinforced concrete (RC) structures recently. Although UHPC has high compressive strength, the tensile strength is still low and, the high curing condition on site requirements of UHPC may hinder the further application in complex condition. In this study, a novel prefabricated UHPC thin plate, which is reinforced with high-strength steel wire strand meshes (HSSM), is proposed for rapidly strengthening RC beams. In order to understand the flexural performance of RC beams strengthened with the prefabricated HSSM-UHPC thin plate, four-point bending tests were conducted on three beams including one unstrengthened RC control beam (CB), one cast-in-place HSSM-UHPC strengthened beam (SUB) and one prefabricated HSSM-UHPC strengthened beam (PSUB). The failure modes of the beams were investigated and, the crack development process of the test beams was detailly observed by digital image correlation (DIC). Experiment results showed that compared with CB, the cracking, peak load of SUB and PSUB increased by 25.30%, 28.5% and 19.8%, 26.4%, respectively. However, the deflection ductility of the strengthened beams slightly decreased. Finally, calculation model and theoretical equation for predicting the cracking as well as peak flexural capacity of HSSM-UHPC plate strengthened beams were proposed. Comparison between theoretical and test results showed that the proposed model can accurately predict the cracking and peak capacity of the strengthened beams, and can be used for strengthening design.

External crosslinking of biopolymers on concrete for crack sealing under high pressure and increased durability applications

The durability of concrete structures is compromised by the presence of cracks, which can lead to further deterioration if left untreated. To prevent this, it is crucial to close the cracks and restore impermeability. This paper proposes an economical and practical solution: the application of biopolymers as an external treatment layer on horizontal concrete surfaces to seal cracks. The study explores the crosslinking of calcium alginates and gelatin at various concentrations. Several properties are investigated, including water permeability, freeze-thaw resistance, overall visual degradation, resistance to chloride intrusion, and adhesive strength of the repair layer. The findings indicate that repair layers utilizing calcium alginate demonstrate promising results for external crack sealing applications. These layers effectively restore impermeability, exhibit resistance against chloride intrusion, improve freeze-thawing resistance, while showing an acceptable adhesive strength to the horizontal concrete substrate. This suggests a viable solution for enhancing the durability of concrete structures.

Study on the self-vibration characteristics of non-circular arches with cracks based on the transfer matrix method

As the span of reinforced concrete arch bridges continues to increase, so does the difficulty of construction. The structure is at risk of cracking. Most of the bridges under construction are non-circular arches, and there are few studies on such arches. The current study tried to investigate the self-vibration characteristics of non-circular arches with existing cracks. A computational approach proposed in the original non-circular arch is substituted with multiple infinitesimal arch segments having different radii of curvature, enabling the determination of natural frequencies and mode shapes of the non-circular arches with cracks. Furthermore, a finite element model (FEM) of the reinforced concrete structure with existing cracks is developed to assess the effects of various factors, including axial location, crack depth, and positions within the same cross-section. The results demonstrate the feasibility of the computational method using multiple infinitesimal arc segments with varied radii of curvature, yielding a maximum error of only 1.58 %, which satisfies engineering application standards. An increase in crack depth leads to a reduction in the natural frequencies of specific modes of the structure, while the effect on others is insignificant. For cracks situated at the top or bottom plates within the same cross-section, the impact differs based on the local deformation being convex or concave. If the deformation is convex, the top plate cracks exhibit a higher rate of change in natural frequencies compared to the bottom plate cracks; conversely, with concave deformation, the bottom plate cracks have a greater influence than the top plate cracks.