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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]

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]

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures. [ABSTRACT FROM AUTHOR]

Rubber concrete has been applied to a certain extent in fatigue-resistant structures due to its good durability. Based on a cohesive model of rubber composed of a five-phase material containing mortar, aggregate, rubber, aggregate-mortar interfacial transition zone (ITZ), and rubber-mortar ITZ, this paper studies the influence of the cohesive parameters in the rubber-mortar ITZ on the fatigue problem of rubber concrete on the mesoscopic scale. As the weak part of cement-based composite materials, the ITZ has a great influence on the mechanical properties and durability of concrete, but the performance of the ITZ is difficult to test in macro experiments, resulting in difficulties in determining its simulation parameters. Based on the cohesive model with a rubber content of 5%, this study uses Monofactor analysis and the Plackett-Burman test to quickly and effectively determine the primary and secondary influences of the cohesive model parameters in the rubber-mortar ITZ; further, the response surface method is used to optimize the cohesive parameters in the rubber-mortar ITZ, and the numerical simulation results after optimizing the cohesive parameters are compared and analyzed with the simulation results before optimization. The results show that, under the setting of the optimized parameters, the simulation results of each item of the optimal cohesive model parameters in the rubber-mortar ITZ are in line with the reality and closer to the experimental data, and they are also applicable to rubber concrete models with different rubber dosing. [ABSTRACT FROM AUTHOR]

The hydraulic concrete in the alpine region is subjected to alternating actions of freeze–thaw (F) and abrasion (W) during operation, resulting in significant deterioration of concrete durability. In this paper, the water/binder ratio (W/B) was employed as the test variable, the working condition F group and W group were set as the control group, and the working condition F-W group was used as the test group. Fast-freezing and underwater methods are used for the alternating test. By measuring the mass loss, relative dynamic elastic modulus (RDEM), surface morphological characteristics, fractal dimension of concrete in each alternating cycle, and the evolution law of concrete performance under the alternating action of F and W was explored. The results show that compared with the control group, the alternating action will accelerate the mass loss of concrete, reduce the RDEM, and cause the deterioration of surface wear. The maximum increase in mass loss and RDEM of concrete is 1.92% and 20.11%, respectively. During this process, the fractal dimension of the concrete increases as the number of alternating cycles increases, but it still does not exceed the limit of 2.4. In addition, a relationship function between the fractal dimension and the mass loss rate, volume loss, was established. It was found that the experimental group had a good linear correlation, and the correlation was close to 95%, which was about 20% higher than that of the control group. [ABSTRACT FROM AUTHOR]

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete. [ABSTRACT FROM AUTHOR]

Concrete can be regarded as a composite material comprising aggregates, cement mortar, and an interfacial transition zone (ITZ) at the mesoscale. The mechanical properties and durability of concrete are influenced by the properties of these three phases. The establishment of a mesoscale model of concrete and the execution of numerical simulations constitute an efficacious research method. It is an efficacious method to research concrete by establishing the mesoscale model of concrete and executing numerical simulations. By this method, the influence of an aggregate shape on concrete performance can be studied. This paper presents a systematic review of mesoscale modeling methods for concrete, with a focus on three aspects: the aggregate modeling method, the collision detection algorithm, and the particle-packing algorithm. The principal processes, advantages, and disadvantages of various methods are discussed for each aspect. The paper concludes by highlighting current challenges in the mesoscale modeling of concrete. [ABSTRACT FROM AUTHOR]

The moisture content within the concrete pore network significantly influences the mechanical, thermal, and durability characteristics of concrete structures. This paper introduces a novel fully embedded wireless temperature and relative humidity sensor connected to an automatic acquisition system designed for continuous concrete monitoring. Relative humidity measurements from this new sensor are compared with those obtained by a commercial system based on the borehole method at different depths (2.5 and 4.0 cm) and exposure conditions (oven drying and humid chamber). The results allow for proving that both systems provide consistent internal relative humidity measurements aligned with the exposure conditions and highlight the capability of fully embedded wireless sensors as a practical and reliable alternative to the conventional borehole method. Additionally, the continuous monitoring of the wireless cast-in sensor exhibits reliability during unintended temperature fluctuations, emphasizing the effectiveness of permanently installed sensors in promptly detecting unintended curing variations in real time. The continuous real-time information provided combined with the practicality of these sensors might assist construction managers to improve the quality control of the concrete curing process and shrinkage behavior, and ensure the integrity of concrete surface finishing. [ABSTRACT FROM AUTHOR]

The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications. [ABSTRACT FROM AUTHOR]

Cold weather conditions pose significant challenges to the performance and durability of concrete materials, construction processes, and structures. This paper aims to provide a comprehensive overview of the material-related challenges in cold weather concrete construction, including slow setting, reduced curing rate, and slower strength development, as well as frost damage, early freezing, and freeze–thaw actions. Various innovative materials and technologies may be implemented to address these challenges, such as optimizing the concrete mix proportions, chemical admixtures, supplementary cementitious materials, and advanced construction techniques. The paper also examines the impact of weather-related challenges for personnel, equipment, and machinery in cold environments and highlights the importance of effective planning, communication, and management strategies. Results indicate that the successful implementation of appropriate strategies can mitigate the challenges, reduce construction time, and enhance the performance, durability, and sustainability of concrete structures in cold and freezing temperatures. The paper emphasizes the importance of staying updated about the latest advancements and best practices in the field. Future trends include the development of smart and functional concrete materials, advanced manufacturing and construction techniques, integrated design, and optimization of tools, all with a strong focus on sustainability and resilience. [ABSTRACT FROM AUTHOR]

Graphene, with its excellent properties and unique structure, has been extensively studied in the context of modifiable cement-based materials. However, a systematic summary of the status of numerous experimental results and applications is lacking. Therefore, this paper reviews the graphene materials that improve the properties of cement-based materials, including workability, mechanical properties, and durability. The influence of graphene material properties, mass ratio, and curing time on the mechanical properties and durability of concrete is discussed. Furthermore, graphene's applications in improving interfacial adhesion, enhancing electrical and thermal conductivity of concrete, absorbing heavy metal ions, and collecting building energy are introduced. Finally, the existing issues in current study are analyzed, and the future development trends are foreseen. [ABSTRACT FROM AUTHOR]

One of the paths to CO2 emissions reduction in the concrete industry is to use low-clinker cements, providing at the same time the performance of concrete that is adequate for application in concrete structures. This paper explores the impact of the clinker replacement with high amounts of limestone powder (21–70% in the powder phase) on concrete carbonation resistance. To quantify this impact, the empirical relationship between the carbonation resistance and the compressive strength of the high-volume limestone powder concrete (HVLPC) was established. For that purpose, the regression analysis was applied on the experimental results collected from the published research. The service life analysis based on the full probabilistic approach was performed using the fib Model Code 2010 prediction model and proposed empirical relationship. The first-order reliability method (FORM) was applied to solve the limit state function of reinforcement depassivation with a reliability index equal to 1.3. The obtained minimum concrete cover depths were 40–110% higher compared to those prescribed in the current European standard EN 1992-1-1:2004 for indicative strength classes. Based on the full probabilistic analysis, recommended cover depths are given for all carbonation exposure classes, commonly applied concrete strength classes, and service lives of 50 and 100 years. [ABSTRACT FROM AUTHOR]

The causes of cracks in concrete are varied, and regardless of their origin, these cracks invariably have a detrimental impact on the durability of concrete structures and escalate their maintenance costs. This paper presents a comprehensive review of current knowledge regarding the methods of self-healing in concrete, ranging from autogenic and improved autogenic self-healing to the autonomous self-healing of concrete. Particular emphasis is placed on the methods of autonomous concrete self-healing: the bacterial healing method, the crystalline hydrophilic additives healing method, and the capsule-based self-healing method. The hypothesis is that applying these self-healing methods could potentially prevent damages or cracks in concrete caused by freeze–thaw cycles, thereby extending the lifespan of concrete structures. The mechanism of action and current achievements in the field are provided for each method. [ABSTRACT FROM AUTHOR]

To address the issues of the brittleness, low tensile strength, insufficient bond strength, and reduced service life associated with ordinary cement concrete being used as a repair material, a water-based epoxy (WBE) and carbon-nanofiber-reinforced concrete composite repair material was designed, and the mechanical properties, bonding performance, and durability of the concrete modified using WBE and carbon fiber under various WBE contents were investigated and evaluated. In this paper, a self-emulsifying water-based epoxy curing agent with reactive, rigid, flexible, and water-soluble chains was obtained via chemical grafting, involving the incorporation of polyethylene glycol chain segments into epoxy resin molecules. The results demonstrated that a WBE has a contributing effect on improving the weak interfacial bond between the carbon fiber and concrete; moreover, the composite admixture of carbon fiber and WBE improves the mechanical properties and durability of concrete, in which the composite admixture of 1% carbon fiber and 10% WBE has the best performance. The flexural strength and chlorine ion permeability resistance of concrete were slightly reduced after more than 10% admixture, but bond strength, tensile strength, compressive strength, dry shrinkage resistance, and frost resistance were promoted. The addition of WBE significantly retards the cement hydration process while greatly improving the compactness and impermeability of the concrete. Furthermore, the combined effects of WBE and carbon fiber effectively prevented the generation and expansion of cracks. The interaction mechanism and microstructure evolution between the WBE, carbon fiber, and cement hydration were described by clarifying the mineral composition, organic–inorganic interactions, the evolution of the hydration products, and composite morphology at different scales. Carbon fiber and WBE exhibited synergistic effects on the tensile strength, ductility, and crack resistance of concrete. In the formed three-dimensional network structural system of concrete, the WBE formed an organic coating layer on the fiber surface and provided fiber protection as well as interfacial bonding reinforcement for the embedded cement particles. [ABSTRACT FROM AUTHOR]

Under corrosive environments, concrete material properties can deteriorate significantly, which can seriously affect structural safety. Therefore, it has important engineering applications to improve the durability performance at a lower economic cost. This paper proposes a new, highly durable concrete using inexpensive construction materials such as basalt fiber, sodium methyl silicate, and inorganic aluminum salt waterproofing agent. With the massive application of sewage treatment projects, the problem of concrete durability degradation is becoming more and more serious. In this paper, five types of concrete are developed for the sewage environment, and the apparent morphology and fine structure of the specimens after corrosion in sewage were analyzed. The density, water absorption, and compressive strength were measured to investigate the deterioration pattern of concrete properties. It was found that ordinary concrete was subject to significant corrosion, generating large deposits of algae on the surface and accompanied by sanding. The new concrete showed superior corrosion resistance compared to conventional concrete. Among other factors, the inorganic aluminum salt waterproofing agent effect was the most prominent. The study found that the strength of ordinary concrete decreased by about 15% in the test environment, while the new concrete had a slight increase. Comprehensive evaluation showed that the combination of basalt fiber and inorganic aluminum salt waterproofing agent had the best effect. Its use is recommended. [ABSTRACT FROM AUTHOR]

The durability and strength of concrete in construction can be significantly compromised by permeability issues, which pose considerable challenges to its long-term effectiveness and reliability. By analyzing six selected articles from the Scopus database, this study meticulously synthesizes findings on the effectiveness of CAs in improving these essential properties of concrete. The research meticulously documents and analyzes key variables such as the CA dosage, water–cement ratio, evaluation duration, and treatment conditions, providing a thorough understanding of the factors that influence the performance of CAs in concrete. The results robustly indicate that CAs significantly reduce concrete permeability, thereby enhancing its resistance to water and other detrimental substances, and simultaneously boosts the compressive strength, leading to stronger and more durable concrete structures. However, the study also reveals that the impact of CAs can vary considerably depending on the specific conditions and methodologies employed in the individual studies. This underscores the importance of standardized testing procedures to ensure consistent and comparable results across different studies. This research provides valuable insights for optimizing the use of CAs in concrete formulations, ultimately aiming to improve the durability, performance, and sustainability of concrete in construction applications. [ABSTRACT FROM AUTHOR]

The deterioration of concrete microstructures in freeze–thaw (F–T) cycles is the primary reason for the reduction in the service life of concrete. This paper reviews recent progress in the theory of damage mechanisms and damage models of concrete in F–T cycles. It is a detailed review of the salt-freeze coupling condition, microstructure testing, and models for the evolution of concrete properties that are subjected to F–T damage. Summarized in this paper are the deterioration theory of water phase transition; the mechanism of chloride-F–T and sulfate-F–T damage; the microstructure testing of hydration products, pore structure, microcracks, and interfacial transition zones (ITZ). Furthermore, F–T damage models for the macrostructure are presented. Finally, the issues that are existing in the research and outlook of concrete F–T damage are highlighted and discussed. This paper is helpful in understanding the evolution of F–T damage, and also provides a comprehensive insight into possible future challenges for the sustainable design and specifications of concrete in cold environments. [ABSTRACT FROM AUTHOR]

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability. [ABSTRACT FROM AUTHOR]

When studying concrete impairment, the carbonation depth of concrete is regarded to be variable. Therefore, a time-varying reliability evaluation is important to perform a structural safety assessment. By analyzing 13,198 data on the carbonation depth of concrete, we propose a time-varying reliability evaluation based on the third-moment (TM) method to predict the service life of concrete. Validated by Monte Carlo (MC) simulation, the errors of the calculated results using time-varying reliability evaluation were within 4%. It is shown that the TM method proposed in this paper is more practical than traditional approaches such as MC simulation and second-moment (SM) methods in probability analysis. In this paper, exponential distribution was used to characterize the distribution of carbonation depths. Since paint was present on the concrete surface, numerous uncarbonized concrete components were found in the experiments; to develop a time-varying model considering the uncarbonized components, a function for evaluating the ratio of carbonized concretes is proposed. Overall, the time-varying TM method provided in this paper can act as a foundation for other investigations on probabilistic analysis, e.g., of compressive strength, deflection, and crack of concrete, which can be used to evaluate the reliability of concrete. [ABSTRACT FROM AUTHOR]

Sulfate attack is one of the main factors affecting the durability of concrete structures. In recent years, multi-walled carbon nanotubes (MWCNTs) have attracted the attention of scholars for their excellent mechanical properties and durability performance. In this paper, the influence of sulfate attack and dry–wet cycles on the performance of multi-walled carbon nanotube–lithium slag concrete (MWCNT-LSC) with varied MWCNT content (0 wt.%, 0.05 wt.%, 0.10 wt.%, and 0.15 wt.%) and varied water–cement ratios (0.35, 0.40, and 0.45) were investigated. In addition, scanning electron microscopy (SEM) and X-ray computed tomography (CT) tests were conducted to analyze the microstructure and pore structure of the concrete. The results showed that concrete incorporated with MWCNTs could effectively mitigate sulfate attack. The resistance to sulfate attack of concrete was negatively related to the water–cement ratio when the dry–wet cycle was fixed. The MWCNT-LSC showed the best compressive strength at the water–cement ratio of 0.35 and 0.10 wt.% MWCNTs. The SEM test results showed that the MWCNTs filled the pores and cracks within the specimen and formed bridges between the cracks, enhancing the resistance to sulfate attack. The CT test results also showed that the addition of MWCNTs could reduce the porosity of concrete, refine the pore size and inhibit the generation and development of cracks, thus optimizing the internal structure of concrete and improving its resistance to sulfate attack. [ABSTRACT FROM AUTHOR]

Micro-nano bubble water (WNBW) in concrete is relatively uncommon due to its newness as a technology. This paper presents the preparation of C60 concrete with 35% fly ash (FA) through WNBW and varying amounts of silica fume (0%, 4%, 7%, and 10% SF). The study examines the impact of WNBW and SF on the working performance, compressive strength, and durability of concrete. The findings indicate that applying WNBW and SF independently or jointly deteriorates the working performance of fresh concrete. However, compared to regular mixing water, WNBW reduces the concrete passing time through the V-funnel, decreasing by 40%, 39.1%, 42.9%, and 50.5% for the four varying SF contents. Furthermore, using WNBW, SF, or both resulted in the increased compressive strength of concrete at 7 days and 28 days, with 7% SF content yielding a 12.2% and 6.6% increase, respectively. Using a combination of WNBW and SF has been shown to decrease the impermeability of concrete effectively. The addition of 4% SF results in the lowest electric flux when using regular mixing water, with a discernible decrease of 30.1% compared to the control group. Conversely, using WNBW as mixing water yields a decrease in electric flux at each SF content, with the maximum decrease being 39.7%. Furthermore, both the single and combined use of these materials can contribute to the reduction in the carbonation resistance of the concrete. C60 concrete mixed with 7% SF and 100% WNBW boasts enhanced frost resistance, as indicated by the mass loss and dynamic elastic modulus loss being the least following freeze–thaw under the same SF content. According to the findings of the tests, there is evidence that the incorporation of 7% SF and 100% WNBW into C60 concrete results in lowered viscosity, a highly advantageous attribute for actual construction. Additionally, this mixture displays impressive compressive strength and durability properties. These results provide technical support regarding the integration of WNBW and SF in C60 concrete. [ABSTRACT FROM AUTHOR]

The incorporation of rubber can enhance concrete's durability and effectively reduce the damage caused by freeze-thaw cycling (FTC). Still, there has been only limited research on the damage mechanism of RC at the fine view level. To gain insight into the expansion process of uniaxial compression damage cracks in rubber concrete (RC) and summarize the internal temperature field distribution law during FTC, a fine RC thermodynamic model containing mortar, aggregate, rubber, water, and interfacial transition zone (ITZ) is established in this paper, and the cohesive element is selected for the ITZ part. The model can be used to study the mechanical properties of concrete before and after FTC. The validity of the calculation method was verified by comparing the calculated results of the compressive strength of concrete before and after FTC with the experimental results. On this basis, this study analyzed the compressive crack extension and internal temperature distribution of RC at 0, 5, 10, and 15% replacement rates before and after 0, 50, 100, and 150 cycles of FTC. The results showed that the fine-scale numerical simulation method can effectively reflect the mechanical properties of RC before and after FTC, and the computational results verify the applicability of the method to rubber concrete. The model can effectively reflect the uniaxial compression cracking pattern of RC before and after FTC. Incorporating rubber can impede temperature transfer and reduce the compressive strength loss caused by FTC in concrete. The FTC damage to RC can be reduced to a greater extent when the rubber incorporation is 10%. [ABSTRACT FROM AUTHOR]

The service environment of concrete in the marine environment is harsh, and demands regarding the durability of marine concrete have increased. Marine concrete in harbor and wharf areas suffers from the combined effect of fatigue load, dry–wet cycles, and Cl− erosion, which can result in spalling of the concrete surface, corrosion of the internal reinforcement, and even concrete damage. This paper reviews recent research results on the durability of concrete and reinforced concrete (RC) under the combined effect of fatigue load, dry–wet cycles, and Cl− erosion. We further assess the variation in Cl− transport properties with fatigue load, the causes behind the reduction in the carrying capacity of RC products under fatigue load, the methods of Cl− erosion on concrete under the pressures imposed by dry–wet cycles, and the damage of the protective layer of concrete due to accelerated Cl− erosion caused by the action of dry–wet cycles. Further studies are needed on the durability of concrete under the action of fatigue load, wet and dry cycles, and Cl− erosion, in addition to the testing of the durability of concrete under the combined effects of the afore-mentioned various factors. [ABSTRACT FROM AUTHOR]

The paper presents the results of tests on concrete with recycled aggregate impregnated with the use of citric acid. Impregnation was carried out in two stages, with a suspension of calcium hydroxide in water (so-called milk of lime) or diluted water glass used as the second impregnant. The mechanical properties of the concrete were carried out: compressive strength, tensile strength and resistance to cyclic freezing. In addition, concrete durability parameters such as water absorption, sorptivity and torrent air permeability were investigated. The tests showed that this type of impregnation did not improve most of the parameters of concrete with impregnated recycled aggregate. The mechanical parameters after 28 days were significantly lower compared to the reference concrete, although after a longer curing period, these differences decreased significantly for some series. The durability parameters of the concrete with impregnated recycled aggregate also deteriorated compared to the reference concrete with the exception of air permeability. The results of the tests carried out indicate that impregnation using water glass in combination with citric acid gives the best results in most cases and that the order in which the impregnation solutions are applied is very important. Tests also showed that the effectiveness of impregnation is very much influenced by the value of the w/c ratio. [ABSTRACT FROM AUTHOR]

Chloride ion attack is a major cause of concrete durability problems, and existing studies have rarely addressed the effects of damage zones. In this paper, an improved mesoscale model including five phases was constructed using the finite element software ABAQUS to study the diffusivity of chloride ions in cracked concrete. It was found that the damage zone is negligible when the crack width is less than 50 μm, while the width and depth of the damage zone are about 15 times the crack width and 15% of the crack depth when the crack is greater than 50 μm. The results show that the diffusion of chloride is greatly influenced by the crack width, while it is little-influenced by the crack shape. Low water–cement ratio and adequate hydration of the concrete are also key factors affecting chloride diffusion. In contrast, regular rounded aggregates have a positive effect on reducing chloride diffusion compared to irregularly shaped aggregates, and this effect becomes weaker with increasing service time. In addition, the protective layer can effectively prevent the diffusion of chloride in concrete. Therefore, when designing marine concrete, efforts should be made to ensure that the concrete has a low water–cement ratio, adequate hydration, less cracking and a protective layer. [ABSTRACT FROM AUTHOR]

Different ecological binders have been used to minimize the negative effects of cement production and use on the environment. Wood ash is one of these alternative binders, and there has been increasing research related to this topic recently. The wood ash utilized in the literature primarily originates from power plants and local bakeries, and predominantly wood fly ash is used. This review paper examines the use of wood ash as an ecological binder in two different applications: as a cement replacement and as an alkali-activated material. Studies have shown that while increased wood ash content in concrete and mortars can have negative effects on strength and durability, it is still a promising and developable material. Depending on the chemical composition of the wood ash, the strength and durability properties of concrete might be slightly improved by utilizing wood ash as a replacement for cement, with an optimal replacement level of 10–20%. However, there is a need for more research regarding the effects of wood ash on the durability of cement-based materials and its use in alkali-activated materials. Overall, this review provides a comprehensive overview of the properties of wood ash and its potential applications in conventional concrete and mortars, as well as in alkali-activated materials. [ABSTRACT FROM AUTHOR]

In order to investigate the law of basalt fibre to enhance the durability of concrete, this paper selects basalt fibre length as the main factor, supplemented by novel research methods such as neural networks, to study the rule of concrete resistance to multiple types of salt erosion. Tests have shown that large doses of mineral admixtures and basalt fibres can prolong the time that concrete is eroded by salt solutions; the age of maintenance has a small effect on the mechanical and durability of the concrete; the increase in length of basalt fibres enhances the mechanical properties of the concrete, but weakens the durability. This is exacerbated by the mixing of fibres, but the increase is not significant; the effect of length on concrete resistance to mass loss, corrosion resistance factor of compressive strength, and resistance to chloride ion attack is ranked as follows: 6 mm > 12 mm > 18 mm > 6 mm + 12 mm > 6 mm + 12 mm + 18 mm. The opposite is true for effective porosity; the highest compressive strength corrosion resistance coefficient was found in the length of 6 mm, with an average increase of 6.2% compared to 18 mm, and the mixed group was generally smaller than the single mixed group. The average increase in chloride content was 25.1% for length 18 mm compared to 6 mm; the triple-doped L6-12-18 group was the largest, with an average increase of 33.9% in effective porosity over the minimum 6 mm group. Based on the data from the above indoor trials, artificial neural network models and grey cluster analysis were used to predict and analyse the data, and the prediction and categorisation results were accurate and reliable, providing a reference for subsequent studies. [ABSTRACT FROM AUTHOR]

Polymer concrete, which contains silica fume powder and vinyl ester resin as two replacements for Portland cement, has improved mechanical properties and durability compared to ordinary concrete. Thus, this kind of concrete is considered to be a high-strength concrete that is resistant to corrosion and chemical attacks. In this paper, the effects of the combination of silica fume powder and vinyl ester resin as two Portland cement replacements on the workability and slump value, initial and final water absorption, compressive and tensile strength, and failure and fracture paths of the polymer concrete have been investigated. All investigations have been based on 16 different polymer concrete mixture designs. The results indicate that the optimum percentages for a combination of silica fume and vinyl ester resin, which has the maximum compressive strength (34.26 MPa) and the maximum tensile strength (4.92 MPa), are a combination of 10% silica fume and 5% vinyl ester resin. To evaluate the durability of polymer concrete, the water absorption of all mixture designs has also been measured. Accordingly, the mixture design, which includes a combination of 15% vinyl ester resin and 5% silica fume, has a minimum initial and final water absorption equal to 0.62% and 1.95%, respectively. [ABSTRACT FROM AUTHOR]

Manufactured sand is one of the effective ways to alleviate the extreme shortage of natural sand in the construction industry. This paper uses granite and limestone manufactured sand to study the effect of high fines content on the durability of high-strength manufactured sand concrete, and analyzes its influence mechanism by combining macro and micro test methods. The results show that the carbonation depth of manufactured sand concrete is the smallest when the fines content is 10%. When the fines content is less than 15%, the chloride and sulfate impermeability of concrete are improved effectively. Through macroscopic and microscopic tests, it is found that the main reason why fines can improve the durability of concrete is the filling effect. Too much fines will inhibit the hydration of cement and adversely affect the durability of concrete. Therefore, the fines content of high-strength manufactured sand concrete should be controlled within 5~15%, and the durability is the best when the fines content is 10%. [ABSTRACT FROM AUTHOR]

Corrosion of steel reinforcement due to chloride attack remains a major reinforced concrete durability concern. The problem is prevalent for concrete structures located within marine environments or frost-prone locations where chlorides containing de-icing salts are used. This paper is a state-of-the-art review into chloride binding in Portland cement concrete, with consideration of the differences induced by the presence of sulphates, such as found in seawater. The review also considers the use of supplementary cementitious materials (SCMs), the use of which has increased because of their potential to enhance durability and reduce the carbon footprint of concrete production. Such materials impact on phase assemblage and microstructure, affecting chloride binding and transport properties. Therefore, field and laboratory studies are critically reviewed to understand how these could help in the design of more durable concretes. The contributions of chloride binding, hydrate compositions and microstructures of the binding materials affecting chloride transport in concretes are also evaluated to suggest a more robust approach for controlling the problem of chloride attack. [ABSTRACT FROM AUTHOR]

Cementitious concrete structures serving in sulfate environments suffer from serious durability challenges caused by chemical sulfate attacks (CSA), which lead to the volume expansion, cracking, and spalling of concrete and the early failure of structures. CSA on concrete involves the behaviors of ion transport, chemical reactions, the crystallization of reaction products, microstructural damage to the cement matrix, and the macroscopic deterioration of concrete, namely the transport-chemo-mechanical behaviors. This paper first introduces the reaction products, such as gypsum, ettringite, brucite, and thaumasite, between sulfate and concrete under different environmental conditions and their formation mechanism. Then, aiming at the ettringite type CSA, the theories of volume increase and crystallization pressure are elaborated to explain it-induced concrete degradation. Additionally, the crystallization pressure theory is used to describe the cracking behavior in the microstructure slurry caused by the ettringite crystal filling pore. Finally, a series of transport-chemo-mechanical models for ettringite type CSA are displaced module by module. It includes the sulfate diffusion-reaction model, the free expansion of concrete, and equivalent expansive force in concrete related to the reaction behavior: the model for chemo-mechanical behavior in concrete caused by CSA. These models can be used to analyze the distribution of sulfate ions and the reaction product content, expansive stress and strain in the concrete, and the cracking and spalling degree of the concrete, which is beneficial to evaluate the durability of concrete structures serving permanently in a sulfate environment. [ABSTRACT FROM AUTHOR]

Chloride penetration resistance is one of the most important performance measures for the evaluation of the durability of concrete under a chloride environment. Due to differences in theory and experimental conditions, the durability index (chloride diffusion coefficient) obtained from laboratory accelerated migration tests cannot reflect the real process of chloride ingress into concrete in the natural environment. The difference in test methods must be considered and the transfer parameter k t should be introduced into the service life prediction model when the test results of accelerated methods are used. According to the test data of coastal exposure in South China, the attenuation rule of the chloride diffusion coefficient of different cement-based materials changed with time and was analyzed in this paper. Based on the diffusion coefficient–time curve, the theoretical natural diffusion coefficients of 28 d and 56 d were deduced, which were compared with the chloride diffusion coefficients obtained from the non-steady-state rapid migration method (RCM) at the same age. Therefore, the transfer parameter k t that expounds the relationship between concrete resistance to chloride permeability under a non-stationary electrical accelerated state and natural diffusion in the marine environment can be calculated; thus, the RCM testing index can be used to evaluate the long-term performance of the concrete structure in the marine environment. The results show that the value of k t was related to environmental conditions, test methods, and binder systems. [ABSTRACT FROM AUTHOR]

Marine concrete structures are subject to the action of multiple environments during their service time. This leads to increased deterioration in the durability of marine concretes under the combined action of bending load and dry–wet cycles, salt freeze–thaw cycles, and salt spray erosion. The main reason for the damage of concrete under the action of the above three environments is Cl- attack. The free Cl- content (Cl-f) and the free Cl- diffusion coefficient (Df) of concrete can explain the diffusion of Cl- in concrete. This paper considers the actual environment of marine concrete structures and develops the Cl- diffusion modified model for nano-marine concretes under the action of dry–wet cycles, salt freeze–thaw cycles, and bending load and salt spray erosion. The nano-SiO2, nano-Fe2O3, and nano-Fe3O4 were firstly incorporated into ordinary marine concrete, then the Cl- content of each group of marine concrete was measured at different depths, and the Cl- diffusion coefficients were calculated; finally, the Cl- diffusion modified model was established under different environmental factors. The test results show that the total and free Cl- diffusion coefficients of nano-marine concretes were lower than those of ordinary marine concrete, and the nano-SiO2, nano-Fe2O3, and nano-Fe3O4 of the optimum dosage were 2%, 1%, and 2%, respectively. The fitting results of Cl- content have a good correlation, and the correlation coefficient (R) is basically above 0.98. [ABSTRACT FROM AUTHOR]

In order to evaluate the influence of freeze–thaw action on the durability of concrete structures, this paper presented an experimental study to investigate the effects of freezing–thawing cycles and concrete strength on the bond behavior between steel bars and concrete confined with stirrups. Through freeze–thaw cycles and center pullout tests, the failure mode of pullout specimen, concrete strength, mass loss, dynamic elastic modulus, and bond–slip curves were analyzed. At last, the bond–slip constitutive model was proposed for specimens with stirrup confinement under freeze–thaw action. Main test results indicate that the failure mode and shape of bond–slip curves are affected by stirrups. The bond strength hasa certain increase after 100 freeze–thaw cycles owing to the constraining force from stirrups, whereas the splitting tensile strength significantly declines. After 100 freeze–thaw cycles, the splitting tensile strength of C20 and C40 decreased by 40.8% and 46.5%, respectively. The formula was provided to calculate the bond strength of constrained concrete after freeze–thaw cycles, and the damage coefficient and other related parameters in the formula were suggested. The predicted bond–slip curves are close to the experimental results, which could provide reference for the related research of bond performance after freeze–thaw action. [ABSTRACT FROM AUTHOR]

Three-dimensional concrete printing (3DCP) is becoming more common in the construction industry nowadays; however, the aspect of durability of printed concrete is not well-studied yet. Frost resistance is a very important factor for durability of concrete structures located in northern regions. Since air-entraining agents (AEAs) are widely used in conventional concrete, this paper focuses on exploring the potential of using AEAs in 3D concrete as well—the main objective is to determine how it affects fresh and hardened properties, including frost resistance of 3D concrete. Three different mixes were printed and cast—the dry mix consisted of ordinary Portland cement (OPC), limestone filler (LF), sand, as well as viscosity modifying agent (VMA) and superplasticizer (SP). Two mixes contained different amounts of AEA, the third one was used as reference. First, fresh state properties were tested—air content, density, and mini cone flow test. Second, 28-day compressive and flexural strength tests were carried out; bulk and particle densities were also determined. Next, both cast and printed concrete samples were subject to freeze–thaw cycles according to provisions of CEN/TS 12390-9, mass loss due to surface scaling was determined for each sample. As a result, printed concrete samples containing AEA in the amount of 0.06% of binder mass showed the highest frost resistance—addition of AEA decreased both flexural and compressive strength of this printed concrete mix by 30–40%. To conclude, the obtained results give an insight of how addition of AEA to printed concrete mix affects its properties both in long and short term. Further research of certain aspects, for instance, the air void system and pore distribution is needed to gain a deeper understanding on how to increase durability of 3D concrete. [ABSTRACT FROM AUTHOR]

The authors of this paper systematically studied the mechanical properties and durability of concrete prepared with copper slag instead of natural aggregates. An analysis index was used to assess compressive strength, and a statistical method was used to establish a mix proportion design theory of copper slag aggregate concrete. The analysis was used to quantify the effect of copper slag aggregate concrete on resistance to chloride ion migration. Combined with the morphological analysis of SEM images and fractal calculations, the tests were used to explain the improvement mechanism of copper slag as a fine aggregate on concrete's mechanics and durability from the microscopic mechanism perspective. The results showed that replacing a natural sand fine aggregate with copper slag improved the compressive strength of concrete, and the optimum replacement rate was found to be 40%. The influence of the water–cement ratio on the strength of copper slag aggregate concrete was exceptionally conspicuous—the more significant the water–cement proportion was the lower the compressive strength of the concrete. The optimum dosage of the water-reducing agent was found to be 3.8 kg/m3. A rapid chloride ion migration test and potential corrosion analysis showed that copper slag aggregate concrete's initial density and corrosion resistance were higher than those of natural aggregate concrete. Electrochemical impedance spectroscopy analysis results showed that the structural concrete comprising copper slag aggregate instead of natural sand had a better anticorrosion effect on embedded steel bars. SEM morphology and fractal dimension analyses showed that the incorporation of steel slag aggregate decreased the initial damage to the concrete internal section. [ABSTRACT FROM AUTHOR]

Concrete is a heterogeneous material that consists of cement, aggregates, and water as basic constituents. Several cementitious materials and additives are added with different volumetric ratios to improve the strength and durability requirements of concrete. Consequently, performance of concrete when exposed to elevated temperature is greatly affected by the concrete type. Moreover, post-fire properties of concrete are influenced by the constituents of each concrete type. Heating rate, days of curing, type of curing, cooling method, and constituents of the mix are some of the factors that impact the post-fire behavior of concrete structures. In this paper, an extensive review was conducted and focused on the effect of concrete constituents on the overall behavior of concrete when exposed to elevated temperature. It was evident that utilizing fibers can improve the tensile capacity of concrete after exposure to higher temperatures. However, there is an increased risk of spalling due to the induced internal stresses. In addition, supplementary cementitious materials such as metakaolin and silica fume enhanced concrete strength, the latter proving to be the most effective. In terms of the heating process, it was clear that several constituents, such as silica fume or fly ash, that decrease absorption affect overall workability, increase the compressive strength of concrete, and can yield an increase in the strength of concrete at 200 °C. Most of the concrete types show a moderate and steady decrease in the strength up until 400 °C. However, the decrease is more rapid until the concrete reaches 800 °C or 1000 °C at which it spalls or cannot take any applied load. This review highlighted the need for more research and codes' provisions to account for different types of concrete constituents and advanced construction materials technology. [ABSTRACT FROM AUTHOR]

With the rapid development of infrastructure construction, it is an inevitable trend to replace natural sand in short supply with manufactured sand to meet sustainable development. In this paper, the relationship between the particle shape characteristics of manufactured sand and concrete performance is discussed using a morphological analysis and concrete experiments. The particle shape parameters of five types of manufactured sand were obtained by using the aggregate image measurement system (AIMS) and digital image processing (DIP) techniques, and the correlations between different parameters were analyzed. Moreover, the properties of concrete with the five kinds of manufactured sand were tested. The results show that particle size and type have a significant impact on particle shape parameters. Particle shape parameters, especially angularity, correlate well with the workability and compressive strength of concrete while having little effect on the durability of concrete. An accurate understanding of the morphological characteristics of manufactured sand is conducive to the optimization of concrete mix designs. Therefore, it is suggested that a manufactured-sand shape test be included in aggregate specification. [ABSTRACT FROM AUTHOR]

The crack and carbonation of concrete pose a great challenge to its durability. Therefore, this paper studies the effect of cracks on the carbonation depth of cement paste under different factors. The relationship between carbonation and cracks was determined, and the carbonation mechanism of cement paste with cracks was clarified. The results show that a small water–binder ratio can effectively inhibit the carbonation process. The bidirectional carbonation enlarged the carbonation area around the crack. Within 21 days of the carbonation, the carbonation depth increased with carbonation time, and the Ca(OH)2 on the surface of the specimen was sufficient, allowing for a convenient chemical reaction with CO2. The influence of crack width on the carbonation process at the crack was greater than the influence of the crack depth. Carbonation influenced the hydration of cement-based materials, altering the types and quantities of hydration products. In conclusion, accurately predicting the regularity of carbonation in cracked structures is critical for improving the durability of concrete. [ABSTRACT FROM AUTHOR]

Coal gangue is a kind of industrial solid waste with serious ecological and environmental implications. Producing concrete with coal gangue aggregate is one of the green sustainable development requirements. This paper reviews the properties and preparation methods of Chinese gangue aggregate, studies the influence of gangue aggregate on concrete properties and the prediction model of gangue concrete, and summarizes the influence of modified materials on gangue concrete. The studies analyzed in this review show that different treatments influence the performance of coal gangue aggregate concrete. With the increase in the replacement ratio of coal gangue aggregate in concrete, the concrete workability and mechanical performance are reduced. Furthermore, the pore structure changes lead to decreased porosity, greatly affecting the durability. Coal gangue is not recommended for producing high-grade concretes. Nevertheless, pore structure can be improved by adding mineral admixtures, fibers, and admixtures to the coal gangue concrete. Hence, the working properties, mechanical properties, and durability of the concrete can be improved effectively, ensuring that coal gangue concrete meets engineering design requirements. Adding modified materials to coal gangue concrete is a viable future development direction. [ABSTRACT FROM AUTHOR]

The corrosion of reinforcement induced by chloride ions is one of the most significant causes of durability deterioration for reinforced concrete (RC) buildings. The concrete material factors, including the water-to-cement ratio (w/c) of concrete, as well as the content, shape, particle grading, and random distribution of coarse aggregate embedded in mortar, have a marked effect on chloride transport performance within concrete. However, comprehensive consideration for the effects of both w/c and coarse aggregate performances on chloride diffusion characteristics in concrete is scarce, especially regarding the chloride diffusion model of concrete. In this paper, an indoor exposure experiment exploring chloride ions intruding into mortar and concrete specimens with w/c = 0.4, 0.5 and 0.6 was carried out, in order to acquire the chloride diffusion parameters for concrete three-phases composites. Based on the numerical algorithm of random generation and placement of two-dimensional random convex polygon coarse aggregate, mesoscopic numerical models for concrete, considering various coarse aggregate contents as well as grading, were established. Using the numerical simulation method of finite element analysis for chloride transport in cement-based materials, which can replace some of the exposure tests, the influences of w/c, coarse aggregate content and grading on chloride diffusion performance in concrete mesoscopic models were systematically probed. According to the Fick's second law, a chloride diffusion model by the consideration of w/c, volume fraction of coarse aggregate (VFCA), and maximum size of coarse aggregate (MSCA) was developed to assess the chloride concentration profiles in concrete under arbitrary w/c, coarse aggregate content, and coarse aggregate grading conditions. Certainly, the precision accuracy for this proposed chloride diffusion model was validated. The research results can provide theoretical support for chloride erosion behavior and structural durability assessment of concrete with different mix proportions. [ABSTRACT FROM AUTHOR]

The alkali–aggregate reaction (AAR) is a harmful chemical reaction that reduces the mechanical properties and weakens the durability of concrete. Different types of activated aggregates may result in various AAR modes, which affect the mechanical deterioration of concrete. In this paper, the aggregate expansion model and the gel pocket model are considered to represent the two well-recognized AAR modes. The mesoscale particle model of concrete was presented to model the AAR expansion process and the splitting tensile behavior of AAR-affected concrete. The numerical results show that different AAR modes have a great influence on the development of AAR in terms of expansion and microcracks and the deterioration of concrete specimens. The AAR mode of the gel pocket model causes slight expansion, but generates microcracks in the concrete at the early stage of AAR. This means there is difficulty in achieving early warning and timely maintenance of AAR-affected concrete structures based on the monitoring expansion. Compared with the aggregate expansion model, more severe cracking can be observed, and a greater loss of tensile strength is achieved at the same AAR expansion in the gel pocket model. AAR modes determine the subsequent reaction process and deterioration, and thus, it is necessary to develop effective detection methods and standards for large concrete projects according to different reactive aggregates. [ABSTRACT FROM AUTHOR]

The durability of a concrete structure is affected by temperature cycles that occur during the structure's service life. This paper presents an experimental and theoretical study of the mechanical properties of seawater sea-sand concrete when exposed to temperature variations. By using compressive tests on cylindrical concrete specimens, the effects of thermal cycling (e.g., the amplitude of temperature variations and cycling times) on the mechanical properties of seawater sea-sand concrete, such as failure modes, compressive strength, stress–strain relationship, Young's modulus, ultimate strain, Poisson's ratio and toughness are investigated. Microstructures of both unconditioned and conditioned concrete samples are examined by using scanning electron microscopy (SEM) to understand the mechanisms behind the strength changes. Finally, the stress–strain model is proposed for seawater sea-sand concrete subjected to daily temperature variations, and the proposed model is verified by the experimental data. [ABSTRACT FROM AUTHOR]

Concrete production consumes enormous amounts of fossil fuels, raw materials, and is energy intensive. Therefore, scientific research is being conducted worldwide regarding the possibility of using by-products in the production of concrete. The objective is not only to identify substitutes for cement clinker, but also to identify materials that can be used as aggregate in mortar and concrete productions. Among the potential alternative materials that can be used in cement composite production is rock dust of different geological origin. However, some adversarial effects may be encountered when using rock dust regarding the properties and durability of mortars and concrete. Therefore, comprehensive research is needed to evaluate the adequacy of rock dust use in cementitious composite production. This paper presents a comprehensive review of the scientific findings from past studies concerning the use of various geological origins of rock dust in the production of mortars and concrete. The influence of rock dust as a replacement of fine aggregates on cementitious composites was analyzed and evaluated. In this assessment and review, fresh concrete and mortar properties, i.e., workability, segregation, and bleeding, mechanical properties, and the durability of hardened concrete and mortar were considered. [ABSTRACT FROM AUTHOR]

The main factor that alters the quality of recycled concrete aggregate (RCA) is the paste adhered to the natural aggregate (NA). Since it causes weakening of the interfacial transition zone (ITZ) between the aggregate and the cementitious paste, it becomes a determining factor for the mechanical behavior of concrete. It turns out that it is critical to enhance this interface by improving the surface of the aggregate or by removing the paste adhered to the NA. Considering the variety of methods for removing paste adhered to RCA—namely using acids such as hydrochloric acid (HCl), sulfuric acid (H2SO4), and phosphoric acid (H3PO4), among others—this paper presents a review of treatments for the removal of adhered paste using acidic solutions on the RCA, and their influence on the mechanical properties and durability of concrete produced with RCA. Pearson's correlation was used in the statistical analysis to determine the linear relationship of the main factors—for instance, immersion time, acidic solution, and aggregate size—involved in the removal of the paste in the RCA. [ABSTRACT FROM AUTHOR]

Currently, natural fibers attract the attention of researchers and builders in the construction industry as they are eco-friendly, cost-effective, lightweight, and renewable resources. The inclusion of natural fibers in the concrete and mortar will contribute to solving the environmental problems associated with dumping or burning them and improve the properties and durability of concrete and mortar. Similar to other natural fibers, Date Palm Fibers (DPF) have been receiving more attention as construction materials. This paper presents a review on the properties of DPF and its effects on the physical, mechanical, and thermal properties of concrete and mortar as well as the processing of DPF and mix design. DPFs can be used in concrete and mortar to improve their properties. However, some of the properties could be reduced. Even though the conducted studies and investigations are promising, it is still not enough to introduce DPF concrete and mortar to the construction industry's applications. [ABSTRACT FROM AUTHOR]

The by-product of the foundry industry is waste foundry sand (WFS). The use of WFS in building materials will safeguard the ecosystem and environmental assets while also durable construction. The use of industrial waste in concrete offsets a shortage of environmental sources, solves the waste dumping trouble and provides another method of protecting the environment. Several researchers have investigated the suitability of WFS in concrete production instead of natural river sand in the last few decades to discover a way out of the trouble of WFS in the foundry region and accomplish its recycling in concrete production. However, a lack of knowledge about the progress of WFS in concrete production is observed and compressive review is required. The current paper examines several properties, such as the physical and chemical composition of WFS, fresh properties, mechanical and durability performance of concrete with partially substituting WFS. The findings from various studies show that replacing WFS up to 30% enhanced the durability and mechanical strength of concrete to some extent, but at the same time reduced the workability of fresh concrete as the replacement level of WFS increased. In addition, this review recommended pozzolanic material or fibre reinforcement in combination with WFS for future research. [ABSTRACT FROM AUTHOR]

Surface damages usually occur in concrete structures. In order to restore the functions and prolong the service life of concrete structures, their surface damages should be repaired in time. This paper reviews the main requirements for repair materials for concrete structures and the most used inorganic repair materials, such as cement-based materials, alkali-activated materials and polymer modified inorganic repair materials. Moreover, techniques to characterize and even improve the interfaces between these repair materials and concrete substrate are summarized. Cement-based material has the advantages of good mechanical properties and consistency with concrete substrate while having the problems of high shrinkage and low flexibility. Polymer modified materials were found as having lower shrinkage and higher flexural strength. Increasing the roughness or humidity of the surface, adding fibers and applying interfacial agents can improve the bond strength between cement-based repair materials and concrete substrates. All of these repair materials and techniques can help to build a good interfacial bonding, and mechanisms of how they improve the interface are discussed in this article. These are of great importance in guaranteeing the effectiveness of the repair of the concrete surface and to guide the research and development of new repair materials. [ABSTRACT FROM AUTHOR]