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This study evaluates the potential use of discarded plasterboard paper as fibers from buildings to reinforce concrete. Various concentrations of wastepaper fibers (0.5%, 1%, 1.5%, 2%, and 2.5% by weight of the binder) were investigated in this research. To mitigate the water absorption effect of the paper fibers, metakaolin was employed as a partial cement replacement. The results demonstrate that the inclusion of the wastepaper fiber enhances the mechanical and durability performance of the concrete. The optimal fiber proportion was identified as 1%, leading to a 29% increase in the compressive strength, a 38% increase in the splitting tensile strength, a 12% decrease in the water absorption, and a 23% decrease in the drying shrinkage with respect to the concrete containing 20% metakaolin. However, exceeding this optimal fiber content results in decreased mechanical and durability properties due to the fiber agglomeration and non-uniform fiber distribution within the concrete matrix. Based on the microstructural analysis, the improved performance of the concrete is ascribed to decreased porosity, more refined pore structure, and reduced propagation of microcracks within the concrete matrix in the presence of wastepaper fiber. According to the results, concrete containing 20% metakaolin and 1% wastepaper fiber exhibits durability and mechanical properties comparable to those of the traditional concrete. This finding highlights the significant promise of reducing dependency on conventional cement and incorporating suitable recycled materials, such as discarded plasterboard, and secondary by-products like metakaolin. Such a strategy encourages the preservation of resources, reduction in carbon dioxide emissions, and a decrease in the ecological footprint resulting from concrete production. [ABSTRACT FROM AUTHOR]

Waste valorisation as secondary or alternative raw materials in several sectors products and processes has been an important way to implement a more sustainable and circular way to manage the efficient use of natural resources. This action contributes not only to save natural resources but also to prevent sending large amounts of wastes, some of them dangerous, to landfill disposal, creating a major environmental, economic and social impact. To promote circular economy, this work attempts to demonstrate the environmental gains in a competitive way, by bringing together in an industrial symbiosis action, two large producing sectors (the pulp and paper industry and concrete construction sector), which are also able to consume significant amounts of resources and to generate large amounts of wastes. A sustainability evaluation based on a life cycle and circular approach is presented and discussed using a simple case study performed at real industrial scale. The lime ash waste from the pulp and paper industry is used to replace 100% of the natural filler used in precast concrete production and the impacts and benefits from the technical, environmental, economic and social level were assessed. It was demonstrated that this simple action causes positive impacts in the evaluated dimensions of sustainability without causing any changes in production time and causes no degradation on relevant concrete properties. [ABSTRACT FROM AUTHOR]

This Special Issue covers the latest research on fatigue, performance, and damage assessments of concrete. Concrete fatigue is known as a phenomenon characterized by the repetition of loads. The fatigue-based performance of concrete may be affected by a combination of diverse loads, mechanical strength properties, and environmental changes. These factors eventually lead to poor concrete performance. In this Special Issue, nine papers were accepted, divided into three subgroups: two papers on fatigue, two papers on performance, and five papers on damage assessment. Unlike articles published in past Special Issues, our Special Issue contains papers that address concrete performance in concrete pavement applications. In particular, six of the articles contained in this issue concentrate on pavement performance and damage assessments, especially in terms of the Pavement Condition Index. Together with a brief introduction, the keywords, research significance and potential impacts of each article are summarized in this Editorial. [ABSTRACT FROM AUTHOR]

The grid plays a prominent role in architecture, aiding in space organization and influencing all aspects of planning, ranging from urban design to intricate building details. This paper posits that the grid receives heightened emphasis in Brutalism, particularly in constructivist Brutalism, where materials and construction are intentionally exposed. A question arises regarding the grid's characteristics—despite its subtle appearance, the grid can sometimes be deceptive, ambiguous, and manipulative. The paper analyzes the merits and drawbacks of employing the grid in architecture, shedding light on its contributions to both structural and perceptual comprehensibility, as well as its role in increasing usefulness. To illustrate the application and perception of the grid, the paper examines two primary planning levels: urban planning and building design. The case studies focus on examples from New York City housing developments, specifically those constructed between the 1950s and the 1970s, and projects by architect I. M. Pei, which offer valuable insights into practical implementation. The paper concludes that while the grid can establish order, it may also engender an "uncanny" feeling. [ABSTRACT FROM AUTHOR]

Large-span, post-tensioned (PT) beams play a crucial role in maximizing the benefits of post-tensioning techniques. Bonded and unbonded systems are prevalent, with the latter being more widespread in the United States. While bonded systems are advantageous for creating long spans when multiple tendons are grouped in ducts, limited studies in the literature exist on their demolition. With a case study, this paper addresses the unique challenge of demolishing large-span-bonded, post-tensioned beams that occurs due to a building's functional change. Emphasizing insights for engineers, it explores the use of cutting and dismantling methods, thereby considering the presence of prestressed cables. The demolition process is distinctive due to the presence of numerous prestressed cables along the beams, necessitating a specialized and cautious cutting approach. This is accomplished through the use of a drilling technique that selectively distresses the tendons, ensuring they are not all affected simultaneously. An intriguing observation discussed in this paper pertains to the occurrence of horizontal cracks accompanied by loud sounds following the drilling process, thereby offering insights from the design perspective of PT systems. This paper details an innovative method for safely demolishing large-span, bonded PT beams using ground-penetrating radar and computer models to navigate structural complexities and ensure nearby structures' safety. [ABSTRACT FROM AUTHOR]

To accurately quantify the time-varying pattern of concrete's compressive strength, selecting an appropriate curve model is of paramount importance. Currently, widely adopted models such as polynomial, hyperbolic, and exponential models all possess limitations, particularly in terms of low fitting accuracy during the ultra-early-age stage. This paper innovatively introduces a mathematical model that utilizes a combined curve approach. This model boasts a simplified structure with only two fitting parameters. Compared to traditional models, when utilizing three or more sets of experimental data on compressive strength across different ages, the new model is capable of yielding more precise strength predictions. Due to its minimal reliance on experimental data, the new model exhibits high practicality and convenience in real-world applications. To validate its superiority, a detailed comparison between the new model and existing models was conducted based on several sets of experimental data. The results demonstrate that the new model has significant advantages in terms of mean fitting error and standard deviation, making its predictions the most reliable. For most cases, the standard deviation of the new model is reduced by approximately 30% to 80% compared to the second-best model, underscoring its exceptional stability and consistency. Additionally, the predicted long-term compressive strength values of the new model are closer to the design strength grade of the concrete. This model can also be successfully applied to predict the tensile strength of concrete during its ultra-early age. It has been demonstrated that the combined model proposed in this paper shows promising application prospects in evaluating the time-varying behavior of concrete strength. [ABSTRACT FROM AUTHOR]

The research on and application of electric fields to promote the rapid infiltration of ions into cement concrete have been widely explored. Still, there are few studies on the migration of sulfate ions using electric fields. In this paper, a new test method is designed using the principle of electric fields, that is, to accelerate the attack of sulfate into concrete under the action of the electric field, to test the resistance of concrete to sulfate attack. By testing different water–cement ratios, different pulse frequencies, different ages, and different soaking environments, the influence of the electric field on the sulfate resistance of concrete was analyzed. The results show that the compressive strength of concrete in a sulfate attack environment is smaller than that of conventional attack and water immersion environment when the water–cement ratio is 0.3, 0.4, and 0.5 under the action of the electric field and increases with the increase of water in the water–cement ratio. Compared with a 14 day test, the compressive strength of concrete in a sulfate attack environment decreased by 1.9%, 8.6%, and 2.9%, respectively, at 28 days, which was faster than that of conventional attack and water immersion. The compressive strength of the concrete in the sulfate attack environment during the full immersion test and the semi-immersion test is smaller than that of the conventional attack and water immersion, and the semi-immersion test method is more obvious than the full immersion test method. The microscopic morphology of the test group, the water group, and the solution group were compared. From the microscopic morphology comparison, it can be seen that the electric field accelerates the diffusion of sulfate ions into the cement concrete and accelerates the reaction of sulfate ions with the relevant components in the cement concrete. Given the demand for concrete to resist sulfate attack under the action of the electric field, developing new and efficient protective materials is an important research direction. At present, the market lacks protective materials specifically for such an attack environment. This paper provides the theoretical basis and technical support for improving the effectiveness of concrete surface protection technology and engineering practices. [ABSTRACT FROM AUTHOR]

Sensitivity analysis of influencing factors on frost resistance is carried out in this paper, and a two-stage neural network model based on grey theory and Back Propagation Neural Networks (BPNNs) is established for the sake of predicting the frost resistance of active-admixture recycled concrete quickly and accurately. Firstly, the influence degree of cement, water, sand, natural aggregate, recycled aggregate, mineral powder, fly ash, fiber and air-entraining agent on the frost resistance of active-admixture recycled-aggregate concrete was analyzed based on the grey system theory, and the primary and secondary relationships of various factors were effectively distinguished. Then, the input layer of the model was determined as cement, water, sand, recycled aggregate and air-entraining agent, and the output layer was the relative dynamic elastic modulus. A total of 120 datasets were collected from the experimental data of another author, and the relative dynamic elastic modulus was predicted using the two-stage BPNN prediction model proposed in this paper and compared with the BPNN prediction results. The results show that the proposed two-stage BPNN model, after removing less-sensitive parameters from the input layer, has better prediction accuracy and shorter run time than the BPNN model. [ABSTRACT FROM AUTHOR]

Composite fibers are an essential component of modern concrete structures, providing enhanced mechanical properties and durability. There are different types of fibers commonly used in concrete such as steel, glass, carbon, polypropylene fibers, etc. Composite fibers include a combination of two or more of these fibers. Composite fibers are discussed in detail, along with their properties and benefits. This paper also highlights the effects of composite fibers on the various properties of concrete, such as compressive strength, tensile strength, toughness, and durability. Furthermore, this paper discusses some of the challenges and limitations associated with the use of composite fibers in concrete, including issues related to fiber dispersion, fiber--matrix interactions, and costeffectiveness. Finally, this paper concludes with a discussion of the future directions of research on composite fibers in concrete, focusing on potential advancements in fiber technology, improved manufacturing techniques, and the development of new fiber--matrix systems. Overall, this paper provides a comprehensive overview of the current state of the art in composite fibers in concrete and serves as a valuable resource for researchers and practitioners in the field. [ABSTRACT FROM AUTHOR]

This paper comprehensively summarizes moisture transport, ion transport, and mechanical damage models applied to concrete under sulfate attack and drying–wetting cycles. It highlights the essential aspects and principles of each model, emphasizing their significance in understanding the movement of moisture and ions, as well as the resulting mechanical damage within the concrete during these degradation processes. The paper critically analyzes the assumptions made in each model, shedding light on their limitations and implications for prediction accuracy. Two primary challenges faced by current models under sulfate attack and drying–wetting cycles are identified: the limited consideration of the coupled effects of chemical and physical attacks from sulfate, and the unclear mechanism of the sulfate attacks. Future research directions are proposed, focusing on exploring the transport mechanism of sulfate ions under various driving forces and further clarifying the crystallization process and expansion damage mechanism in concrete pores. Addressing these research directions will advance our understanding of sulfate attack under drying–wetting cycles, leading to improved models and mitigation strategies for enhancing the durability and performance of concrete structures. [ABSTRACT FROM AUTHOR]

Waste ceramic is produced from different sources and, if not reused, is often disposed of in landfills, contributing to the pressure on landfill capacity and potentially releasing toxins into the surrounding environment as ceramics break down over time. The waste can easily be crushed to the required sizes, which has interested many researchers. It has been used as a replacement for concrete constituents, including cement and aggregates. This offers a promising avenue for reducing the environmental impact and promoting sustainable construction practices by reducing the amount of energy consumed and resources required for concrete production, as well as the amount of waste being sent to landfills. This paper aims to provide a review of the use of waste ceramic in concrete. In essence, the paper is divided into several sections. The first section highlights the current environmental issues associated with concrete production and waste disposal. The second section deals with ceramics, its raw materials, production steps, and the different types of waste ceramic used in concrete. A literature review of the use of waste ceramic in concrete was included in the third section. The study reports different research on the use of waste ceramic and its impacts on the mechanical and durability properties of concrete. [ABSTRACT FROM AUTHOR]

Chloride corrosion is a key factor affecting the life of marine concrete, and surface chloride concentration is the main parameter for analyzing its durability. In this paper, we first introduce six erosion mechanism models for surface chloride ion concentration, reveal the convection effect in the diffusion behavior of chloride ions, and then introduce the corrosion mechanisms that occur in different marine exposure environments. On this basis, the analysis is carried out using empirical formulations and machine learning methods, which provides a clearer understanding of the research characteristics and differences between empirical formulas and emerging machine learning techniques. This paper summarizes the time-varying model and multifactor coupling model on the basis of empirical analysis. It is found that the exponential function and the reciprocal function are more consistent with the distribution law of chloride ion concentration, the multifactor model containing the time-varying law is the most effective, and the Chen model is the most reliable. Machine learning, as an emerging method, has been widely used in concrete durability research. It can make up for the shortcomings of the empirical formula method and solve the multifactor coupling problem of surface chloride ion concentration with strong prediction ability. In addition, the difficulty of data acquisition is also a major problem that restricts the development of machine learning and incorporating concrete maintenance conditions into machine learning is a future development direction. Through this study, researchers can systematically understand the characteristics and differences of different research methods and their respective models and choose appropriate techniques to explore the durability of concrete structures. Moreover, intelligent computing will certainly occupy an increasingly important position in marine concrete research. [ABSTRACT FROM AUTHOR]

This paper explores the new potential strategy of using fine recycled aggregates (fRA) derived from waste 3D printed concrete (3DPC) as a substitute for cement in additive manufacturing. This study hypothesizes that fRA can optimize mixture design, reduce cement content, and contribute to sustainable construction practices. Experimental programs were conducted to evaluate the fresh and hardened properties, printability window, and buildability of 3DPC mixes containing fRA. Mixes with replacement rates of cement with fRA by 10 vol%, 20 vol%, 30 vol%, 40 vol%, and 50 vol% were produced. A comprehensive experimental protocol consisting of rheological studies (static and dynamic yield stress), dynamic elastic modulus determination (first 24 h of hydration), flexural and compressive strengths (2 d and 28 d), and an open porosity test was performed. The obtained results were verified by printing tests. In addition, an economic and environmental life cycle assessment (LCA) of the mixes was performed. The results indicate that up to 50 vol% cement replacement with fRA is feasible, albeit with some technical drawbacks. While fRA incorporation enhances sustainability by reducing CO2 emissions and material costs, it adversely affects the printability window, green strength, setting time, and mechanical properties, particularly in the initial curing stages. Therefore, with higher replacement rates (above 20 vol%), potential optimization efforts are needed to mitigate drawbacks such as reduced green strength and buildability. Notably, replacement rates of up to 20 vol% can be successfully used without compromising the overall material properties or altering the mixture design. The LCA analysis shows that reducing the cement content and increasing the fRA addition results in a significant reduction in mix cost (up to 24%) and a substantial decrease in equivalent CO2 emissions (up to 48%). In conclusion, this study underscores the potential of fRA as a sustainable alternative to cement in 3D printed concrete. [ABSTRACT FROM AUTHOR]

By investigating the bond performance between glass-fiber-reinforced polymer (GFRP) bars and concrete, GFRP bars can be better applied to concrete structures as a building material. This paper considered the effects of three different GFRP bar surface treatments, three bonding lengths, corrosive solution, and immersion time on the bonding strength. The test results indicated that the bond strength decreases with the increase in the diameter and bond length. The bonding between GFRP bars and concrete can be improved by treating the surface of the bars in different ways. Compared with the control group, the bond strength of the specimens in the saline solution decreased by 1.3–21.4%, and the bond strength of the specimens in the alkaline solution decreased by 26.5–38.8%. In the corrosive environment, the bond properties are degraded. A bond strength calculation formula considering the surface treatment method of the GFRP bars was proposed. The prediction formula of the bond strength retention rate between the GFRP bar and concrete in the corrosive environment was established. The formula was validated with the available research data and the calculated values agreed well with the test values. The MBPE model and CMR model are modified to establish the bond-slip model of the GFRP bars and concrete in the corrosive environment. The model curve is close to the test curve. This paper provides a theoretical basis for future research on the bond-slip performance of GFRP bars and concrete. [ABSTRACT FROM AUTHOR]

The vibration of concrete is a typical concealed construction process, in which mature supervisory methods are lacking. The quality of vibration relies heavily on the subjective experience and sense of responsibility of the vibration operators. For the widely used hand-held concrete vibrators, existing methods for monitoring the quality of vibration primarily focus on the horizontal positioning of the vibrator. Due to the limited measurable range of vibration depth, these methods are inapplicable for monitoring the vibration depth during the vibration of deeper structures such as walls, columns, and large volumes of concrete. This paper makes the initial attempt to address the issue of monitoring concrete vibration depth, presenting a method that broadens the measurable range of depth in vibration monitoring. Inspired by the principles of optical and magnetic scales, this paper introduces a radio frequency identification (RFID) scales positioning system for the real-time monitoring of vibration depth. The proposed RFID scales vibration depth monitoring method theoretically has no upper limit on the measurable vibration depth, rendering it applicable to monitoring vibration depth of any extent. By comparing the positioning accuracy of different RFID scales hardware compositions, the optimal RFID scales hardware composition and the most effective RFID scales positioning algorithm were identified. The feasibility and accuracy of the vibration depth monitoring method based on RFID scales were validated through engineering field application. This method achieves centimeter-level accuracy in monitoring vibration depth, offers a tool for the precise control of vibration depth, and helps avoid potential quality issues in vibration. [ABSTRACT FROM AUTHOR]

This article addresses the often overlooked but critical long-term factors of creep, shrinkage, ageing and corrosion in civil engineering structures. The paper emphasizes their substantial impact on structural mechanical resistance and safety, drawing attention to key examples like the Civic Tower in Pavia, the Koror-Babeldaob Bridge and dams in the USA. By exploring the challenges faced in modern engineering, the article sheds light on the need to consider these effects. Various models for predicting creep and shrinkage in concrete structures are introduced as potential solutions. In conclusion, the paper highlights the necessity for engineers to navigate the intricacies of material behaviour for successful construction amidst evolving challenges. [ABSTRACT FROM AUTHOR]

The global surge in environmental pollution, largely attributed to industrialization, has fueled a pressing need for sustainable solutions. In response, the construction sector is increasingly focusing on bio-based materials such as hemp, recognized for its low environmental footprint and prominent carbon-negative quality. As designers, housebuilders, and an environmentally conscious society pivot towards ecological alternatives to standard building materials, hempcrete emerges as a promising candidate. As a composite material mainly made from hemp hurd/shiv, water, and lime, hempcrete offers the ability to sequester carbon long after its incorporation into structures. As a result, the hemp cultivation process—which can be completed within less than four months—ensures that more carbon is absorbed during production and deployment than emitted, e.g., per one study, sequestration on the order of 300 kg of CO2 per m3 of hempcrete. In comparison to concrete, hempcrete offers a more sustainable footprint, given its recyclability post life cycle. This state-of-the-art review paper delves deep into different aspects of hempcrete, summarizing its multifaceted attributes, particularly its compressive strength. Based on the study conducted, the paper also suggests strategies to augment this strength, thereby transitioning hempcrete from a non-load-bearing material to one capable of shouldering significant weight. As architects and designers consistently strive to align their projects with high ecological standards, focusing not just on aesthetic appeal but also environmental compatibility, hempcrete becomes an increasingly fitting solution for the future of construction. [ABSTRACT FROM AUTHOR]

Concrete stands as the most widely used construction material globally due to its versatility, encompassing applications ranging from pavement, multifloor structures, and bridges to dams. However, these concrete structures endure structural stress and require close monitoring to prevent accidents and ensure sustainability throughout their complete life cycle. In recent years, artificial intelligence (AI) and computer vision (CV) have demonstrated considerable potential in diverse applications within construction engineering, including structural health monitoring (SHM) and inspection processes such as crack and damage detection, as well as rebar exposure. While it is undeniable that CV and deep learning models are transforming the construction industry by offering robust solutions for complex scenarios, there remain numerous challenges pertinent to their applications that require attention. This paper aims to systematically and critically review the literature of the past decade on the application of deep learning models in the construction industry for SHM purposes in concrete structures. The review delves into proposed methodologies and technologies while identifying opportunities and challenges associated with these applications in practice. Additionally, the paper provides insights to bridge the gap between theory and application. [ABSTRACT FROM AUTHOR]

To obtain predictions closer to concrete behaviour, it is necessary to employ a particle model (PM) that considers contact softening. A bilinear softening contact model (BL) has been adopted in PM studies. Several limitations in PM predictions have been identified that may be due to BL assumptions. For this reason, this paper compares BL predictions with those obtained with more complex models to assess if PM predictions can be improved. As shown, it is possible to calibrate each contact model to reproduce the complex behaviour observed in concrete in uniaxial and biaxial loading. The predicted responses are similar, and the known PM limitations still occur independently of the adopted model. Under biaxial loading, it is shown that a response closer to that observed in concrete can be obtained (higher normal-to-stiffness ratio of ≈0.50, maximum contact compressive strength of ≈60 MPa, and 30% reduction in the number of working contacts). The BL contact model for PM concrete DEM-based simulations is shown to have (i) lower associated computational costs (15% to 50% lower); (ii) a reduced number of contact strength parameters; and (iii) similar responses to those predicted with more complex models. This paper highlights that the BL contact model can be used with confidence in PM fracture studies. [ABSTRACT FROM AUTHOR]

This paper presents original findings on the heterogeneity of the mechanical properties of concrete of an early age, dependent on the evolution of the hydration reaction. The properties investigated are the compressive strength, the Young's modulus, and the flexural tensile strength. To achieve this, we employed a testing apparatus in which the samples underwent curing in a chamber that followed the same temperature profile as an adiabatic calorimeter. This method enabled us to monitor the hydration progress across multiple samples. We used a function derived from the literature, with specific adaptations, to model the evolution of normalized properties in relation to hydration. Heterogeneity was quantified through the use of the dispersion coefficient. The key finding of this study is that the dispersion coefficient for the analyzed mechanical properties diminishes with the advancement of hydration, until reaching a specific threshold. Beyond this point, the impact of microcracking on the various properties becomes increasingly pronounced, varying according to the particular property being examined. Moreover, this paper presents initial functions designed to offer formulas that assist in modeling concrete within probabilistic numerical simulations from the early stages of its development. [ABSTRACT FROM AUTHOR]

This paper is grounded on the following information: (1) Disposable masks primarily consist of polypropylene fiber, which exhibits excellent flexibility. (2) China has extensive coal gangue deposits that pose a significant environmental hazard. (3) Coal gangue concrete exhibits greater fragility compared to regular concrete and demonstrates reduced resistance to deformation. With the consideration of environmental conservation and resource reutilization, a preliminary concept suggests the conversion of discarded masks into fibers, which can be blended with coal gangue concrete to enhance its mechanical characteristics. In this paper, the stress–strain law of different mask fiber–doped coal gangue concrete (DMGC) under uniaxial compression is studied when the matrix strength is C20 and C30, and the effect of mask fiber content on the mechanical behavior and energy conversion relationship of coal gangue concrete is analyzed. The experimental results show that when the content of mask fiber is less than 1.5%, the strength, elastic modulus, deformation resistance, and energy dissipation of the concrete increase with mask fiber content. When the amount of mask fiber is more than 1.5%, because the tensile capacity and energy dissipation level of concrete produced by the mask fiber cannot compensate for the compression and deformation resistance of concrete of the same quantity and because excess fiber is difficult to evenly mix in the concrete, there are pore defects in concrete, which decreases the concrete strength due to the increase in mask fiber. Therefore, adding less than 1.5% mask fiber helps to improve the ductility, toughness, impermeability, and oxidation and control the cracking of coal gangue concrete. Based on Weibull theory, a constitutive model of DMGC is established, which fits well with the results of a uniaxial test, providing support for understanding the mechanical law of mask fiber–doped concrete. [ABSTRACT FROM AUTHOR]

Featured Application: This paper describes the development of the constitutive model for early-aging viscoelastic concrete. And this paper provides the work related to material testing and modeling for identifying the required constitutive properties of early-age concrete. Short-term uniaxial tensile creep tests were conducted for early-age concrete at different ages in an effort to characterize early-age concrete as an aging viscoelastic material. Based on the test results, the viscoelastic material properties of the test concrete were characterized in terms of the Dirichlet series creep compliance and relaxation modulus functions. Applications of the model to the numerical analysis of the test samples showed a good agreement between the tests and computational results for the samples tested at different ages. This paper presents the test procedures and data analysis with a brief introduction of theoretical background. [ABSTRACT FROM AUTHOR]

With a large number of railroad and highway tunnels opening for operation, the diseases caused by hidden lining defects are increasing. The study of flow characteristics of freshly mixed concrete during tunnel lining casting is the key to revealing the formation mechanism of hidden defects. This paper revealed the location of blank lining formation by investigating the circumferential and longitudinal flow characteristics of concrete in the vault during tunnel pouring to provide suggestions for improving the quality of tunnel lining pouring for the various projects. This paper adopted the method of indoor testing, selected the suitable working conditions and flow parameters, validated the accuracy of the test with a numerical simulation, and simulated the secondary lining pouring process of the tunnel arch from the circumferential direction and longitudinal direction. This revealed the flow characteristics of the freshly mixed concrete in the process of pouring the arch lining. The flow of concrete in the arch lining was basically characterized by two major features which were similar to the flow in the pumping pipe and the layered flow. It also revealed the relationship between the concrete flow rate, flow distance, and the location of the formation of the blank lining risk zone with the slump of the concrete, the pumping pressure, and the radius of the tunnel. [ABSTRACT FROM AUTHOR]

Widely used in the making of sculptures and prefabricated building components, ferrocement is considered to be beneficial to environmental preservation. However, there is still little attention paid to the making shape and design of the ferrocement in the literature. Moreover, there are some disadvantages associated with ferrocement, such as the lengthy and complex process of binding poles and nets together. The research question to solve in this paper is about how to study the making shape of ferrocement when solving these disadvantages, so as to improve the characteristics of ferrocement. In this research, a dialogue is conducted between concrete fabrication and ferrocement, the focus of which is placed more on the material and craft instead of robotics as the recent frontier of concrete fabrication. By replacing the standard wire mesh in the ferrocement with steel, how to make the steel plate from two dimensions to three dimensions, and then assemble them into a steel skeleton is explored. Then, the craft of casting is studied for integration of the cement mixture into the steel skeleton and its tight attachment onto the steel surface with spraying. Apart from that, a digital software is applied to the simulation and design accompanied by physical experimentation. To sum up, the research demonstrates the potential of free-forming of the ferrocement and its application in the (prefabricated) building technology, with questions raised for future study. [ABSTRACT FROM AUTHOR]

Precast rectangular reinforced concrete (PRRC) beams are joined on construction sites using concrete in situ to achieve the desired length. Limited research exists on the effect of intermediate connection shapes and the types of infilled concrete on the flexural performance of PRRC beams. This paper presents a comprehensive experimental and numerical investigation into the performance of PRRC beams with various intermediate connection geometries and infilled materials under flexural loading. The study examines rectangular, triangular, and semi-circular intermediate connections, along with the performance of beams infilled with normal concrete (NC), engineered cementitious composites (ECC), ultra-high-performance ECC (UHPECC), and rubberized ECC (RECC). The experimental results indicate that the rectangular intermediate connection exhibits superior performance in terms of strength and energy absorption compared to the triangular and semi-circular shapes. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC for any shape of intermediate connection. Moreover, beams with rectangular connections and UHPECC infill exhibited the most significant increase in energy absorption and ultimate load compared to the beams with ECC and RECC. The ultimate load of the beams with UHPECC and tensile reinforcement bar diameters of 10 mm and 12 mm increased by 13% and 29%, respectively, compared to the control beam. The energy absorption of the beams with tensile reinforcement bar diameters of 10 and 12 mm was found to be 75% and 184% higher, respectively, than the control beam. In addition, an increase in tensile bar diameter was found to enhance both the energy absorption and the ultimate load capacity of the beams, regardless of the type of infill concrete. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC. In particular, beams with rectangular connections and UHPECC infill exhibited an increase in energy absorption and ultimate load of up to 184% and 29%, respectively. UHPC was calculated to be as high as 184%, and 29%, respectively, compared to the control beams. In addition, an increase in tensile bar diameter was found to enhance both energy absorption and ultimate load capacity. Finite element modeling (FEM) was developed and validated against the experimental results to ensure accuracy. A parametric study was conducted to study the effects of various concrete types in triangular and semi-circular connections, as well as the influence of intermediate connection length on semi-circular connections under flexural loads. The findings reveal that increasing the length of intermediate connections increases the ultimate load of the beams. [ABSTRACT FROM AUTHOR]

Phase change materials can be converted between solid, liquid, and gaseous states, absorbing or releasing a large amount of heat. PCM is incorporated into concrete to adjust the temperature difference between inside and outside of concrete, which can reduce cracking. In this paper, the finite element analysis method is used to establish the model of an ordinary concrete structure, doped with phase change materials, on the basis of mechanical properties and a temperature regulation test performed by calculating the adiabatic temperature rise of concrete with different contents of composite phase change material, comparing the experimental and simulation results of the ordinary concrete structures with phase change materials, and analyzing the change in temperature field of the concrete structure with the content of self-prepared composite phase change materials. It is found that the addition of self-prepared composite phase change materials reduces the temperature peak of the concrete structure in the stage of hydration heat and delays the time taken to reach the temperature peak. Then, the temperature field of the phase change mass concrete structure is established, and the influence law of composite phase change material admixture on the temperature field of mass concrete is summarized through the time–temperature curves of different admixture amounts and positions so as to predict the possibility of cracks in mass concrete. [ABSTRACT FROM AUTHOR]

The energy consumption of buildings presents a significant concern, which has led to a demand for materials with better thermal performance. Thermal conductivity (TC), among the most relevant thermal properties, is essential to address this demand. This study introduces a methodology integrating a Multilayer Perceptron (MLP) and a Generative Adversarial Network (GAN) to predict the TC of concrete based on its mass composition and density. Three scenarios using experimental data from published papers and synthetic data are compared and reveal the model's outstanding performance across training, validation, and test datasets. Notably, the MLP trained on the GAN-augmented dataset outperforms the one with the real dataset, demonstrating remarkable consistency between the model's predictions and the actual values. Achieving an RMSE of 0.0244 and an R2 of 0.9975, these outcomes can offer precise quantitative information and advance energy-efficient materials. [ABSTRACT FROM AUTHOR]

It is essential to understand how failure mechanisms work in arch dams and, in particular, their most common manifestation: cracking. In this paper, the different types of cracking are explained in terms of their causes and consequences. Then, an exhaustive literature review is carried out that results in a detailed compilation of the characteristics of 38 cracked arch dams from all over the world, including crack characteristics (zone, position, dimensions and probable cause). This review is restricted to only those dams for which information on the position of the cracks or dam displacements is publicly available. As part of the review, a brief summary of key data for each dam is included, as well as a compilation of published crack diagrams. The positions of the cracks of all the dams are classified using diagrams in relation to the type of dam and the origin of the crack. Finally, the distribution of some dam parameters and crack features is analyzed by studying the relationships between them. [ABSTRACT FROM AUTHOR]

The appearance quality of fair-faced concrete plays a crucial role in evaluating the engineering quality, as the abundance of small-area bubbles generated during construction diminishes the surface quality of concrete. However, existing methods are plagued by sluggish detection speed and inadequate accuracy. Therefore, this paper proposes an improved method based on YOLOv5 to rapidly and accurately detect small bubble defects on the surface of fair-faced concrete. Firstly, to address the issue of YOLOv5 in generating prior boxes for imbalanced samples, we divide the image preprocessing part into small-, medium-, and large-area intervals corresponding to the number of heads. Additionally, we propose an area-based k-means clustering approach specifically tailored for the anchor boxes within each of these intervals. Moreover, we adjust the number of prior boxes generated by k-means clustering according to the training loss function to adapt to bubbles of different sizes. Then, we introduce the ECA (Efficient Channel Attention) mechanism into the neck part of the model to effectively capture inter-channel interactions and enhance feature representation. Subsequently, we incorporate feature concatenation in the neck part to facilitate the fusion of low-level and high-level features, thereby improving the accuracy and generalization ability of the network. Finally, we construct our own dataset containing 980 images of two classes: cement and bubbles. Comparative experiments are conducted on our dataset using YOLOv5s, YOLOv6s, YOLOxs, and our method. Experimental results demonstrate that the proposed method achieves the highest detection accuracy in terms of mAP0.5, mAP0.75, and mAP0.5:0.95. Compared to YOLOv5s, our method achieves a 7.1% improvement in mAP0.5, a 3.7% improvement in mAP0.75, and a 4.5% improvement in mAP0.5:0.95. [ABSTRACT FROM AUTHOR]

This paper investigates the effectiveness of applying continuous high-compression pressure on the initial setting of fresh concrete to produce hardened concrete materials with excellent mechanical properties. A novel experimental apparatus was self-designed and used for the pre-setting pressure application. The utilization of the completely decomposed granite (CDG) soil as an alternative aggregate in concrete production was also explored. A total of twenty-eight specimens were fabricated using two types of fine aggregates, six mix ratios, two initial pressure values, and two distinct durations of the initial pressure application. The density and uniaxial compressive strength (UCS) of the specimens were examined to evaluate their mechanical qualities, while micro-CT tests with image analysis were used to quantify their porosity. The results indicated that the 10 MPa initial pre-setting pressurization can effectively eliminate the excess air and voids within the fresh concrete, therefore enhancing the mechanical properties of the hardened concrete specimens of various types. Compared with non-pressurized specimens, the porosity values of pressurized specimens were reduced by 73.11% to 86.53%, the density values were increased by 1.43% to 8.31%, and the UCS values were increased by 8.42% to 187.43%. These findings provide a reference for using a continuous high pre-setting compression pressure and using CDG soil as an aggregate in the fabrication of concrete materials with improved mechanical performance. [ABSTRACT FROM AUTHOR]

Clays are components in the fine portion of aggregates, less than 75 microns in size (micro-fines), which are usually washed away when producing coarse or fine (manufactured sand) aggregates in quarries. When marginal sources of aggregates are being used, the content of this washed portion can be quite high, and there is an incentive to keep as much of it in the aggregate, including the clays. The present paper presents a comprehensive treatment of the role of clays in terms of the characterization of their composition and quantification of their effects on the rheological and mechanical properties of cementitious systems, as well as the means to mitigate deleterious influences. It is shown that the strategy for neutralizing the effect of micro-fines containing clays on increased water demand in concrete can be quantified in terms of the combination of their content in concrete and their nature as characterized by the methylene blue value (MBV); this is a more rational approach to considering their influence than their content in specific aggregates as specified in standards. The effect of low and medium MBV aggregates on the water requirement can be neutralized by lignosulfonates when their content in the concrete is below a threshold value of about 150 kg/m3; polycarboxylates (PC) are required at higher contents; for high MBV aggregates, a combination of PC and clay mitigating admixture (CMA) is required. It is also demonstrated that with proper treatment, such micro-fines can be turned into useful fillers, enhancing the strength of concrete and thus also serving as a means for reducing cement content. [ABSTRACT FROM AUTHOR]

The degradation of concrete and reinforced concrete structures is a significant technical and economic challenge, requiring continuous repair and rehabilitation throughout their service life. Geopolymers (GPs), known for their high mechanical strength, low shrinkage, and durability, are being increasingly considered as alternatives to traditional repair materials. However, there is currently a lack of understanding regarding the interface bond properties between new geopolymer layers and old concrete substrates. In this paper, using advanced computational techniques, including quantum mechanical calculations and stochastic modeling, we explored the adsorption behavior and interaction mechanism of aluminosilicate oligomers with different Si/Al ratios forming the geopolymer gel structure and calcium silicate hydrate as the substrate at the interface bond region. We analyzed the electron density distributions of the highest occupied and lowest unoccupied molecular orbitals, examined the reactivity indices based on electron density functional theory, performed Mulliken charge population analysis, and evaluated global reactivity descriptors for the considered oligomers. The results elucidate the mechanisms of local and global reactivity of the oligomers, the equilibrium low-energy configurations of the oligomer structures adsorbed on the surface of C-(A)-S-H(I) (100), and their adsorption energies. These findings contribute to a better understanding of the adhesion properties of geopolymers and their potential as effective repair materials. [ABSTRACT FROM AUTHOR]

The accumulation of electronic waste (E-waste) has become a significant global environmental issue, driven by the characteristics of the modern era and the ever-increasing use of electronic devices. Thus, a sustainable approach is necessary to overcome this issue. In this paper, an overview of utilizing E-waste as a sustainable aggregate in concrete production was comprehensively reviewed. The basic composition, characteristics, and production techniques were discussed. In addition to that, the colour, shape, size, aggregate crushing value, and water absorption of E-waste concrete were also discussed. Furthermore, the workability properties such as slump flow, mechanical properties (compressive strength, flexural strength, tensile strength) and thermal resistance of E-waste concrete identified by the various researchers were summarised. Based on the literature review, it is concluded that the shape and size distributions of E-waste particles greatly influenced the aggregate properties, and the percentage of replacement of E-waste aggregate affect the workability and mechanical and thermal properties of E-waste concrete. [ABSTRACT FROM AUTHOR]

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus ( E d ) and internal damping ratio (ξ) were determined through acoustic tests. The results show that the normal-strength concretes ( f c = 42 MPa) exhibited an undamaged internal damping ratio of ξ = 0.5 % , reaching a maximum of ξ = 2.5 % at a damage index of 0.8. Conversely, the high-strength concrete mixtures ( f c = 83 MPa) showed an undamaged internal damping ratio of ξ = 0.29 % , with a peak value of ξ = 0.93 % at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios. [ABSTRACT FROM AUTHOR]

In this paper, steel slag powder was used to replace part of the cement in road concrete, and group tests were carried out on coarse aggregates with different water–cement (W/C) ratios, different steel slag parameters, and different particle sizes. A sample of 100 mm × 100 mm × 100 mm was prepared and cured for 3 days, 7 days, and 28 days. In addition, the fluidity and compressive properties of the samples were also tested. The outcomes of this study revealed that, at a constant W/C ratio, increasing the proportion of steel slag improved the concrete's fluidity but reduced its compressive strength; the 3-day (3 d) compressive strength of 40% steel slag was lower because the early activity of steel slag was lower than that of cement; steel slag also decreased the early-hydration rate of concrete. Comparisons across different W/C ratios demonstrated that steel slag made a more significant contribution to lower W/C ratios than higher ones. The water requirement for steel slag was relatively moderate, and the compressive strength of steel slag concrete with a high W/C ratio notably improved in the later stages. Based on the experimental conditions, the optimal content of steel slag was found to be 35%. Reusing steel slag as a replacement for sand in coarse aggregate can effectively lower costs and offer an innovative approach to steel slag treatment. [ABSTRACT FROM AUTHOR]

Material optimization was one of the challenges for achieving cost-competitive solutions when concrete was introduced in construction, leading to new structural shapes for both civil works and buildings. As concrete construction became dominant, saving material was given less significance, and the selection of the structural typology was mostly influenced by construction or architectural considerations. Simple and non-time-consuming methods for building thus arose as the dominant criteria for design, and this led to the construction of less efficient structures. Currently, the awareness of the environmental footprint in concrete construction has brought the focus again to the topic of structural efficiency and material optimization. In addition, knowledge of material technology is pushing the use of cements and binders with lower environmental impact. Within this framework, Fiber-Reinforced Concrete (FRC) has been identified as a promising evolution of ordinary concrete construction. In this paper, a discussion is presented on the structural properties required for efficient design, focusing on the toughness and deformation capacity of the material. By means of several examples, the benefits and potential application of limit analysis to design at the Ultimate Limit State with FRC are shown. On this basis, the environmental impact of a tailored mix design and structural typology is investigated for the case of slabs in buildings, showing the significant impact that might be expected (potentially reducing CO2-eq emissions to half or even less in slabs when compared to ordinary solutions). [ABSTRACT FROM AUTHOR]

In this paper, the development of a 3D adaptive probabilistic explicit cracking model for concrete is reported. The contribution offered herein consists in a new adaptive mesh strategy designed to optimize the use of interface elements in probabilistic explicit cracking models. The proposed adaptive mesh procedure is markedly different from other strategies found in the literature, since it takes into account possible influences on the redistribution of stresses after cracking and can also be applied to purely deterministic cracking models. The process of obtaining the most appropriate adaptive mesh procedure involved the development and evaluation of three different adaptivity strategies. Two of these adaptivity strategies were shown to be inappropriate due to issues related to stress redistribution after cracking. The validation results demonstrate that the developed adaptive probabilistic model is capable of predicting the scale effect at a level similar to that experimentally observed, considering the tensile failure of plain concrete specimens. The results also show that different softening levels can be obtained. The proposed adaptive mesh strategy proved to be advantageous, being able to promote significant reductions in the simulation time in comparison with the classical strategy commonly used in probabilistic explicit cracking models. [ABSTRACT FROM AUTHOR]

Non-destructive testing (NDT) techniques are crucial in making informed decisions about reconstructing or repairing building structures. The SonReb method, a combination of the rebound hammer (RH) and the ultrasonic pulse velocity (UPV) tests, is widely used for this purpose. To evaluate the compressive strength, C S , of the concrete under investigation, the ultrasonic pulse velocity V p and the rebound index R must be mapped to the compressive strength C S using a suitable conversion model, the identification of which requires supplementing the NDT measurements with destructive-type measurements (DT) on a relatively large number of concrete cores. An approach notably indicated in all cases where the minimization of the number of cores is essential is to employ a pre-existing conversion model, i.e., a model derived from previous studies conducted in the literature, which must be appropriately calibrated. In this paper, we investigate the performance of Gaussian process regression (GPR) in calibrating the pre-existing SonReb conversion models, exploiting their ability to handle nonlinearity and uncertainties. The numerical results obtained using experimental data collected from the literature show that GPR calibration is very effective, outperforming, in most cases, the standard multiplicative and additive techniques used to calibrate the SonReb models. [ABSTRACT FROM AUTHOR]

Selection of the Optimum Carrier for Manufacturing Water-Repellent Concrete and Durabilit... Chang Bok Yoon and Han Seung Lee [[10]] show in their paper that the purpose of this experiment was to complement the shortcomings of existing surface treatment methods and to implement water repellency inside concrete to prevent water penetration and improve the durability of concrete. Properties of a Lightweight Fly Ash-Slag Alkali-Activated Concrete with Three Strength Gra... Wang et al. [[7]] show in their paper that lightweight alkali-activated concrete (LAAC) is a type of highly environmentally friendly concrete, which can provide the benefits of both alkali-activated material and lightweight concrete. The samples were then tested to determine the influence of waste-glass powder on the main properties of the prepared concrete mixes and on the performance of the concrete when hardened. [Extracted from the article]

This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging aspects of current research are knowledge mapping, co-occurrence, and co-citation. The Scopus search engine was used to search for and obtain the data required to meet the goals of the study. During the data evaluation, the relevant publication sources, keyword assessment, productive authors based on publications and citations, top papers based on citations received, and areas vigorously involved in SFRC studies were recognized. The VOSviewer software tool was used to evaluate the literature data from 9562 relevant papers, which included citation, abstract, bibliographic, keywords, funding, and other information. Furthermore, the applications and constraints related to the usage of SFRC in the construction sector were examined, as well as potential solutions to these constraints. It was determined that only 17 publication sources (journals/conferences) had published at least 100 articles on SFRC up to June 2022. Additionally, the mostly employed keywords by authors in SFRC research include steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete. The assessment of authors revealed that 39 authors had published at least 30 articles. Moreover, China, the United States, and India were found to be the most active and participating countries based on publications on SFRC research. This study can assist academics in building collaborative initiatives and communicating new ideas and techniques because of the quantitative and graphical depiction of participating nations and researchers. [ABSTRACT FROM AUTHOR]

Pathologies in concrete structures, such as cracks, splintering, efflorescence, corrosion spots, and exposed steel bars, can be visually evidenced on the concrete surface. This paper proposes a method for automatically detecting these pathologies from images of the concrete structure. The proposed method uses deep neural networks to detect pathologies in these images. This method results in time savings and error reduction. The paper presents results in detecting the pathologies from wide-angle images containing the overall structure and also for the specific pathology identification task for cropped images of the region of the pathology. Identifying pathologies in cropped images, the classification task could be performed with 99.4% accuracy using cross-validation and classifying cracks. Wide images containing no, one, or several pathologies in the same image, the case of pathology detection, could be analyzed with the YOLO network to identify five pathology classes. The results for detection with YOLO were measured with mAP, mean Average Precision, for five classes of concrete pathology, reaching 11.80% for fissure, 19.22% for fragmentation, 5.62% for efflorescence, 27.24% for exposed bar, and 24.44% for corrosion. Pathology identification in concrete photos can be optimized using deep learning. [ABSTRACT FROM AUTHOR]

This state of the art review paper aims to discuss the results of a literature survey on possible ways to reinforce printed concrete based on existing reinforcement strategies. Just as conventional concrete, for 3D printed concrete to be suitable for large-scale construction, reinforcement is needed to increase the tensile capacity of concrete members and reduce temperature and shrinkage cracking. Despite efforts that are currently underway, the development of proper reinforcement suitable for printed concrete is still very active on the research agenda. As an initial step for designing suitable reinforcement for printed concrete, the existing reinforcement methods for printed concrete as well as conventional cast concrete from the literature are reviewed and summarized. Through the preliminary evaluation of the suitability and effectiveness of various reinforcement methods, guidelines are proposed to better understand possible solutions to reinforce printed concrete and inspire new practical ideas to fill the current technology void. The conclusions also include the possible improvements of the existing reinforcement methods to be considered in future applications. [ABSTRACT FROM AUTHOR]

Chemical shrinkage (CS) is an intrinsic parameter that may affect the early age cracking of paste, mortar and concrete. It is well known as the driving force of self-desiccation, autogenous shrinkage (AGS) and drying shrinkage. During the first stage of cement hydration (at the initial setting time), the CS and AGS are equal. In the hardened stages, there is a difference in values between the two shrinkage parameters. This paper is a comprehensive review on CS and AGS, measurement techniques, modeling and prediction of different cementitious systems. Based on the various experimental studies, chemical shrinkage depends on the water to binder ratio (w/b) and is proportional to the degree of hydration. A low w/b ratio leads to high CS and AGS. The composition of cement has an effect on both CS and AGS. Also, incorporating supplementary cementitious materials (SCMs) affects both shrinkage parameters. It is concluded that adding fly ash (FA) to concrete contributes to CS and AGS reductions. However, this is not the case when concrete contains slag. More than 170 references were consulted including 35 which were published after 2020. According to the authors knowledge, there is no published work on the effect of fibers, especially bio-fibers, on the chemical shrinkage of cement-based composites. Therefore, in addition to traditional chemical shrinkage of cementitious systems, this review includes a section on recent papers conducted by the authors on the effect of bio-fibers on the chemical shrinkage of cement composites. [ABSTRACT FROM AUTHOR]

With the increasing complexity of engineering environments in tunnel construction, some projects are located in areas with adverse geological conditions, including areas prone to fault movements and other geological hazards. Fiber-reinforced concrete can significantly enhance structural performance in such challenging conditions. Currently, the application of high-performance steel-polypropylene fiber in tunnel linings and its anti-fault performance are quite limited. Therefore, this paper focuses on studying the application of steel-polypropylene mixed fiber-reinforced concrete in tunnel lining under reverse fault movements. In this paper, the constitutive relationship of mixed fiber-reinforced concrete is modified based on literature data. Utilizing the Najar formula, fiber-related variables were designed, and a three-dimensional numerical simulation model of a reverse fault tunnel was established. By designing various parameter combination cases, the structural response of tunnel linings was calculated and studied. then the influence patterns of mixed fiber parameters on the anti-fault performance of tunnel linings are summarized, the relationships between main variables are explored, and a reasonable value range for the two fibers is determined, which can provide guidance for practical engineering. [ABSTRACT FROM AUTHOR]

The differences in physical properties, chemical properties, and mechanical properties between reclaimed concrete aggregate and natural aggregate are discussed in this paper. In this paper, the commonly used improvement techniques of recycled concrete aggregate are reviewed. Physical modification involves peeling the attached mortar layer using mechanical and thermodynamic means, including mechanical grinding and shaping, heat treatment, and microwave or electric pulse treatment. Chemical modification is based on the chemical reaction of some materials with recycled aggregate attached mortar, including acid treatment removal, water glass strengthening, carbonation strengthening, inorganic slurry strengthening, and polymer strengthening. Microbial modification is mainly based on the metabolic activity of specific microorganisms that induce carbon deposition modification. The results show that the reinforced technology of recycled aggregate has made some progress in improving the performance of recycled aggregate, but there are still some problems, such as inconsistent strengthening effects and the unstable compatibility of composite materials. In this paper, future research directions, such as the development of new strengthening materials and the integration of multi-functional strengthening technology, are described in order to provide some theoretical support for the utilization of recycled concrete aggregate. [ABSTRACT FROM AUTHOR]

This paper is devoted to the fastening system that consists of a number of anchors of approximately equal effective embedment depth, called "anchor group", embedded into hardened concrete, used to transmit forces transverse to the anchors from an attachment to the concrete. The anchor group is far from the edges and is subjected to no more than marginal axial forces. Being post-installed, rather than cast-in, the embedded end of each anchor is not hooked, and no nuts, washers, or plates are attached to the embedded shaft. The paper focuses on the transverse forces that can be transmitted across an anchor group from an attachment to the concrete. The paper provides an analytical model for predicting the maximum (ultimate) shear force that an anchor group can bear, thus called "shear strength". The model hence allows the structural designer to predict the shear strength of an anchor group post-installed into concrete. The model is based on five mechanical assumptions, which were established from a wide-ranging numerical analysis. Model predictions turned out to be, on average, 20% lower than the results of experiments performed on cast-in anchor groups borrowed from literature. The comparison verifies model accuracy, considering that the tested anchor groups benefitted from the extra-strength furnished by nuts and washers attached to the embedded shaft. Model predictions were also compared to code provisions; the former resulted to be up to one third of the latter. The paper presents and comments those comparisons, as well as all mathematical development. Applications of the model to wide-ranging case studies is presented and discussed as well. [ABSTRACT FROM AUTHOR]

In the field of construction, the surface of architectural aluminum formwork for concrete pouring will remain the concrete adhesion layer of heterogeneous composite structures. In view of the difficulty of removing the concrete adhesion layer, we studied the technology and mechanism of removing the concrete adhesion layer by laser cleaning technology in this paper. We analyzed the composition and distribution characteristics of residual concrete on the surface of architectural aluminum formwork, set up a laser cleaning test system, carried out laser cleaning experiments on the concrete layer on the surface of architectural aluminum formwork under different storage times, and analyzed the mechanism of removing the concrete adhesion layer by laser cleaning. The experimental results showed that the residual time of concrete will affect the quality and efficiency of laser cleaning concrete residue on the surface of architectural aluminum formwork for concrete pouring. For concrete residues with short residual time, lasering can achieve efficient and high-quality cleaning. A nanosecond pulsed laser could strengthen the surface hardness of the aluminum alloy template during cleaning, which is helpful in improving the durability of the aluminum alloy template. The main mechanisms of laser cleaning to remove the concrete adhesion layer on the surface of architectural aluminum formwork is that the bubbles and water bubbles in the loose structure of concrete instantly absorb high-energy laser and make the concrete aggregate continuously air-burst. This paper provides technological and theoretical support for the application of laser cleaning technology to remove residual concrete on the surface of architectural aluminum formwork for concrete pouring in the field of construction. [ABSTRACT FROM AUTHOR]

It is an effective method to prepare geopolymer with recycled brick and concrete fine powder (RP) and slag as main materials for the resource utilization of construction waste. However, its hydration products have large drying shrinkage and high efflorescence risk under normal curing conditions. Until now, the durability of recycled brick and concrete fine powder–slag-based geopolymer (RPSG) has not been well documented, such as drying shrinkage and efflorescence. In this study, the effects of slag content, alkali equivalent and modulus on the durability properties of RPSG were evaluated. The results show: (1) Slag can significantly reduce the drying shrinkage and efflorescence of RPSG. (2) The potential for the efflorescence of RPSG increases with increasing alkali equivalent. The drying shrinkage of RPSG increases with the increase of alkali equivalent in the case of a low alkali equivalent (6 wt.% in this paper) and decreases with the increase of alkali equivalent in the case of a high alkali equivalent. (3) The drying shrinkage of RPSG increases with increasing modulus. In contrast, the degree of efflorescence decreases with increasing modulus. In this study, RP-S45-M1.3N6 (slag content: 45 wt.%; alkali equivalent: 6 wt.%; modulus: 1.3) is the best proportional design for RPSG with excellent durability. Compared to RP-S0-M1.3N6, the drying shrinkage of RP-S45-M1.3N6 is reduced by 76.32%, the capillary porosity is reduced by 60.9%, the visual efflorescence is significantly alleviated, and the early pH value is reduced by approximately 2.0. This paper systematically analyzed the drying shrinkage pattern and the efflorescence pattern of RPSG, which has a positive significance for promoting the recycling of RP from construction waste. [ABSTRACT FROM AUTHOR]

The study of the resistance of plain concrete to high temperatures is a current topic across the field of civil engineering diagnostics. It is a type of damage that affects all components in a complex way, and there are many ways to describe and diagnose this degradation process and the resulting condition of the concrete. With regard to resistance to high temperatures, phenomena such as explosive spalling or partial creep of the material may occur. The resulting condition of thermally degraded concrete can be assessed by a number of destructive and nondestructive methods based on either physical or chemical principles. The aim of this paper is to present a comparison of nondestructive testing of selected concrete mixtures and the subsequent classification of the condition after thermal degradation. In this sense, a classification model based on supervised machine learning principles is proposed, in which the thermal degradation of the selected test specimens are known classes. The whole test set was divided into five mixtures, each with seven temperature classes in 200 °C steps from 200 °C up to 1200 °C. The output of the paper is a comparison of the different settings of the classification model and validation algorithm in relation to the observed parameters and the resulting model accuracy. The classification is done by using parameters obtained by the acoustic NDT Impact-Echo method and image-processing tools. [ABSTRACT FROM AUTHOR]

Plastic waste management has received significant attention in recent decades due to the urgent global environmental crisis caused by plastic pollution. The versatile and durable nature of plastic has led to its widespread usage across various sectors. However, its nonbiodegradable nature contributes to unsustainable production practices, leading to extensive landfill usage and posing threats to marine ecosystems and the food chain. To address these environmental concerns, numerous challenges have been recently addressed through investigating alternative approaches for disposing of plastic waste, with the construction sector emerging as a promising option. Incorporating plastic waste materials into concrete not only offers economic benefits but also provides a valid alternative to conventional disposal methods. This paper presents the results of different experimental studies, some of them available in the literature and others new, discussing the feasibility of integrating plastic waste into concrete and its impact on mechanical properties. The influence of different sizes, natures, treatments, and percentages of plastic waste in the concrete mixtures is dealt with in order to provide further data for helping to understand the nonunivocal results in the literature, under the conviction that only further observations can help to understand the mechanics of concrete with plastic aggregates. The experimental investigation highlighted that one parameter that is better than others and can be considered to compare different experimental investigations is the variation in weight (due to the effective volume of plastics in the mix), determining a sort of increasing of porosity that degrades the mechanical characteristics. However, this seems inconsistent in some cases. Therefore, the need for further research is highlighted to refine production methods and optimize mix designs. [ABSTRACT FROM AUTHOR]