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Offshore wind turbines operating in harsh marine environments are at risk of corrosion. Thickness loss and perforation caused by corrosion can lead to component failure or structure collapse. An environmental test setup was constructed to simulate various marine corrosion zones. Several experimental studies were conducted on Q355 steel, commonly used in offshore wind turbines. The mass loss and electrochemical properties of the steel specimens were analyzed, including electrochemical impedance spectra and polarization curves. The results indicate that corrosion remains stable in the immersion and tidal zones, whereas corrosion in the splash zone is the most severe, with a corrosion rate as high as 0.70 mm/a. A significant macroscopic corrosion cell effect was observed on the vertical steel strip, accelerating corrosion in the splash zone and at the low tide line. The corrosion product compositions and corrosion morphology of each corrosion zone were characterized and analyzed. Furthermore, a corrosion monitoring sensor based on electromechanical impedance was proposed. A prediction model for the mass loss rate of vertical steel strips was developed based on the conductance peak frequency. This study elucidates the corrosion evolution of wind turbine structural steel and proposes a comprehensive steel corrosion monitoring solution. • The corrosion evolution of Q355 steel under various corrosion zones was elucidated. • Macroscopic corrosion cell effects on vertical steel strips were revealed. • A quantitative corrosion monitoring method for offshore wind turbines was proposed. [ABSTRACT FROM AUTHOR]

Despite extensive academic research on durability issues caused by sulfate attack, deterioration reasons and expansion mechanisms of concrete remain controversial, with descriptions of expansion development still focusing on phenomenological observations. The present study analyzes the macro-micro property changes of concrete and establishes a time-varying expansion prediction model considering environmental and material parameters. The micropore evolution in different pore categories is investigated, and the primary type and precipitation location of expansive products, as well as the expansion mechanism of concrete, are clarified. The results indicate the possibility of thaumasite sulfate attack (TSA) in concrete at low temperatures. The expansion development of concrete under sulfate attack can be divided into two stages: the expansion latency stage explained by crystallization pressure theory, and the significant expansion stage associated with volume increase theory. The expansion level at the inflection point of the expansion rate was solely related to the intrinsic micropore properties of concrete. • The relationship between macroscopic performance changes and micropore evolution was revealed. • A time-varying prediction model for concrete expansion development under sulfate attack was established. • The precipitation location of products and the expansion mechanism were clarified. [ABSTRACT FROM AUTHOR]

Highlights • Effects of content and size of CRT glass aggregate on the concrete were studied. • Finer CRT glass aggregates generally increased the strength and elastic modulus. • CRT glass aggregate content had a limited impact on the damping ratio of concrete. • Reducing the size of CRT glass aggregate generally lowered the damping ratio. Abstract This paper investigates the influences of the content and particle size of recycled cathode ray tube (CRT) glass on the damping ratio of the CRT glass concrete by free vibration attenuation method. The density, water absorption, strength, and elastic modulus were also evaluated. The results show that the water absorption, elastic modulus, compressive strength and tensile strength decreased monotonously with CRT glass content, while the CRT glass content had a limited impact on the damping ratio. In general, hardened density, water absorption and damping ratio would decrease when the maximum particle size reduces from 4.75 mm to 0.60 mm, while the compressive strength, tensile strength and elastic modulus would increase. However, an unexpected decrease in the compressive strength and increase in the damping ratio of CRT glass concrete comes out when the maximum particle size decreases from 1.18 mm to 0.60 mm. The tensile strength of CRT glass concrete is underestimated by most of the existing concrete specifications when using compressive strength to estimate tensile strength. These specifications provide a conservative estimation that allows for the safe application of recycled CRT glass concrete in engineering designs. [ABSTRACT FROM AUTHOR]

Piezoelectric transducers have been widely employed in the field of structural health monitoring (SHM). Currently, most piezoelectric transducers based non-destructive monitoring method lays basis on wave-based method. The change of wave after propagating in the target medium can reflect the internal state of the structure, such as damage and porosity. Owing to that concrete is a severely heterogeneous material at micro scale, the relationship between stress wave parameters and microstructure of concrete such as pores and preexisting cracks in concrete is still unclear, which limits the generalization of monitoring system in different concrete structures. This paper presents an experimental study by setting up a kind of monitoring platform with piezoelectric transducers to investigate the relationship between porosity in cement paste and stress wave parameters. Meanwhile, 3D models of cement paste specimens were built with X-ray computed tomography (CT) scanning method, and the actual pore structure and distribution inside the specimens were obtained. The test and numerical results share similar decreasing trend of amplitude and velocity with an increment of porosity. It indicates that the proposed 3D model building method provides a vivid way to investigate the influence of micro-structure on stress wave transferring in cement based materials. Additionally, it also provides a promising approach to assess the porosity in cementitious materials using smart aggregate (SA)-based non-destructive monitoring method. [ABSTRACT FROM AUTHOR]

The nonlinear constitutive model of the structural plane is very important for the stability evaluation of the geotechnical engineering, and is also the key to the accuracy of the numerical analysis. In this paper, the shear tests are carried out under different roughness and normal stress, and the change laws of the mechanical properties are revealed under the influence of two factors. The relationship equations, with the normal stress (σ n) and the roughness (JRC), are established for various mechanical parameters. Then, on the basis of the statistical damage mechanics, the shear damage nonlinear constitutive model is established, and the accuracy and practicability are verified by different shear test results. The empirical relationships are established for the model parameters (a and r) with the normal stress, roughness and rock wall strength (JCS), by the multi-factor optimization analysis method. Finally, the discrete element is selected, and the C++ is used to compile the running program of the constitutive model to realize numerical application. Different numerically simulated shear tests are carried out to verify the feasibility of the numerical application. The research results are beneficial for the stability evaluation in the geotechnical engineering. [ABSTRACT FROM AUTHOR]

Great autogenous shrinkage has become a common problem in cement-based materials with a low water-to-binder ratio (w/b). To limit the autogenous shrinkage in ultra-high performance concrete (UHPC) during the process of hydration and curing, sustainable use of recycled micropowder (RMP) made from autoclaved aerated concrete waste (AACW) to cure UHPC internally is proposed in this paper. The influence of RMP (at the levels 5%, 10%, and 15% by mass) with three particle size classes ranging from 0 to 600 μm on the autogenous shrinkage, hydration reaction, internal relative humidity, and compressive strength of UHPC were investigated. The results show that mixtures with different dosages and particle sizes improve the fluidity of UHPC, and its internal curing effect can effectively inhibit the early-age autogenous shrinkage of UHPC and maintain a higher internal humidity compared with the control group. The incorporation of RMP can advance the appearance of a hydration peak and increase the cumulative heat of hydration. Microscale analyses show that the curing water released from RMP promotes the hydration of the unhydrated cement around RMP. The generated hydration product filled the surface pores of RMP and weakened the negative effect of the pores introduced by RMP on the compressive strength of UHPC. Thus, RMP can be utilized as internal curing materials for UHPC to reduce autogenous shrinkage. • The potential for internal curing of RMP in UHPC is investigated. • Autogenous shrinkage of UHPC with RMP is reduced by 65%. • The underlying mechanism behind internal curing of RMP has been explored. • Compressive strength of UHPC with RMP can still exceed 160 MPa at 28 days. [ABSTRACT FROM AUTHOR]

• A experimental study is conducted to investigate the mechanism of calcium leaching of cement hydrates exposed to the sodium sulfate solution. • The influences of sulfate ions concentration and environmental temperature are analyzed on calcium leaching process. • The solid–liquid equilibrium curve describing calcium leaching in deionized water is extended to sodium sulfate solutions. Calcium leaching from cement hydrates to pore solution increases the porosity and reduces the bonding strength of cement hydrates, accelerating the degradation of concrete. Calcium leaching can be quantified by solid–liquid equilibrium curves, which have been studied in deionized water or ammonium nitrate. The research of solid–liquid equilibrium curve of calcium under sulfate attack is limited and its mechanism is poorly understood. Reported here provide insights into the dissolution process of calcium from cement hydrates exposed to the sodium sulfate solution. The experimental programme examines the effects of sulfate ion concentration and temperature. An external sulfate attack (ESA) model considering the influence of calcium leaching is established and validated. The results show that, compared to deionized water, sulfate ions impact strongly the leaching process. Qualitatively, the dissolution of calcium in cement hydrates is accelerated by increasing the concentration of sulfate ions and decreasing the environmental temperature. Quantitatively, the presence of sulfate ions modifies the equilibrium curve describing calcium leaching in deionized water. In addition, the prediction results of the ESA model considering the influence of calcium leaching are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of PCT and additives on the compressive strength and permeability was investigated. • Low strength ratios of permeable concrete to cement paste results from the low bonding area. • Enhanced bonding ratio can produce the greatest benefit in terms of strength. • Loss of permeability is the result of both reduced connected porosity and increased tortuosity. • Cement paste thickness distribution and pore size distribution were predicted by lognormal function. The macro performance and mesostructure of permeable concrete are largely determined by the paste coating thickness (PCT) on aggregates within the fresh mixture. Accordingly, in the present study, the strength and permeability of permeable concrete with different paste coating thicknesses were measured. The mesostructure characteristics of cement paste and pore were subsequently quantified by X-ray CT images and image processing techniques. As a result, the influence of PCT on the compressive strength and permeability, the characteristics of cement paste and pore was determined. The distribution of cement paste thickness and total pore size were used as functions of paste coating thickness, which coud be used to predict these mesostructure characteristics at the design stage of permeable concrete. The significance of this paper includes providing a deeper understanding of the relationship between macro performance and mesostructure from the perspective of paste coating thickness within mixtures. [ABSTRACT FROM AUTHOR]

As cities continue to develop, the significance of resilience and intelligence is increasing. In post-earthquake emergency response, there is a continuous demand for efficient and accurate methods of structural state assessment. This study employs deep learning (DL) techniques to propose a multi-scale image-based damage recognition and assessment method for reinforced concrete (RC) structures. First, an RC structural damage recognition task framework and a structural mechanical damage image dataset are established. Second, a DL model is selected to conduct the experiments and enhance its performance through transfer learning. Then, a multi-scale correlated structural state assessment procedure is introduced where local, component, structural, and regional scales are linked. Finally, an engineering case is presented to describe the application steps of the method in real-world scenarios, demonstrating its feasibility. Nevertheless, the proposed method lacks comprehensive validation across various geotechnical conditions and detailed structural configurations, which may limit its generalizability. This study has the potential to enhance the efficiency and scope of post-disaster emergency response and contribute to the development of sustainable cities. • An RC structural damage recognition and assessment method is proposed. • An RC structural damage recognition task framework is constructed. • An RC structural mechanical damage image dataset is established. • A multi-scale correlated structural state assessment procedure is introduced. • An engineering case demonstrates the effectiveness and practicality of the method. [ABSTRACT FROM AUTHOR]

• Silane emulsion modification was used to improve the compressive strength of RA permeable concrete. • Silane emulsion modification was used to improve freeze–thaw durability of RA permeable concrete. • Mechanism of silane modification and freeze–thaw failure were verified. • Microstructure of cement matrix and ITZ were investigated based on BSE-IA technology. Currently, there are few effective methods for improving the freeze–thaw durability of recycled aggregate (RA) permeable concrete without reducing the strength or permeability. Thus, this study aims to improve the freeze–thaw durability of recycled aggregate permeable concrete without the degradation of strength and permeability. Accordingly, two silane emulsion modification methods, namely the surface modification of recycled aggregate and integral modification of cement matrix, were used to raise the freeze–thaw durability. The compressive strength, permeability coefficient, freeze–thaw durability of recycled aggregate permeable concrete were measured. The characteristics of interfacial transition zone (ITZ) and cement matrix were investigated to analyse the modification mechanism. The results indicate that surface modification of recycled aggregate can increase both the compressive strength and freeze–thaw durability of recycled aggregate permeable concrete more effectively than the integral modification of cement matrix. This study provides an effective method to improve the comprehensive performance of recycled aggregate permeable concrete. [ABSTRACT FROM AUTHOR]

The work reports on an experimental programme, conducted to validate comprehensively our previously proposed coupled chemo-transport model for external sulfate attack on concrete. Specifically, the effects of the concentration of sulfate solution and temperature on the distribution of sulfate ions in concrete are experimentally investigated and used to demonstrate the accuracy of the modeling framework. Further, the profile of aluminate depletion and the leaching depth numerically are investigated. For all cases the model predictions are in good agreement with the experimental results, showing increases of the concentration of sulfate ions in concrete with higher concentrations of sulfate solution and higher temperatures. It is concluded that higher sulfate solution concentration and temperature enhance the processes involved in the external sulfate attack on concrete, namely diffusion of sulfate ions and their chemical reactions with concrete. It is found that these parameters affect the external sulfate attack predominantly via the chemical reaction process. [ABSTRACT FROM AUTHOR]

• Cement paste distribution characteristic and its distribution law were clarified. • Mesostructures were predicted by image technology. • Compressive strength and permeability were predicted by models using the mean thickness of cement paste. • Mesostructures and performance can be designed by the proposed method and models. The permeability and compressive strength of pervious concrete are mainly determined by its mesostructures including the pore, cement paste and aggregate. However, most of the current performance prediction methods have not considered the influence of mesostructural characteristics on the performance reasonably and comprehensively. In this study, a novel method based on image processing techniques was proposed to predict the mesostructures of pervious concrete. Experiments were designed to validate the effectiveness and accuracy of the proposed mesostructure prediction method. Furthermore, the prediction models of the permeability and compressive strength are proposed using the predicted characteristics of cement paste distribution. This study provides a novel method that can predict the mesostructures of pervious concrete with various mix design without repeated X-ray scanning, reducing the time and cost of trials. Compared to the reported correlation models between performance and pore characteristics, the proposed models can predict the performance accurately. [ABSTRACT FROM AUTHOR]

Sulfate-induced deterioration can reduce the service life of a concrete structure. A coupled chemo-transport-damage model for external sulfate attack is developed, which predicts the effects of calcium leaching and temperature on the deterioration processes. Specifically, calcium leaching is described using a solid–liquid equilibrium curve, and temperature effects are included in the creation of a temperature gradient and in the rates of chemical reactions, calcium leaching, and ion transport. The model is validated using published experimental results, and the effects of calcium leaching and temperature on expansion are analyzed. The results show that model predictions agree well with the available experimental data. One conclusion is that calcium leaching has a strong effect on deterioration, and therefore should be included when modeling external sulfate attack. Temperature influences sulfate attack, but a more substantial conclusion about the effect of temperature requires further experimental evidence. [ABSTRACT FROM AUTHOR]

This study proposes a model to analyze a deep tunnel embedded in unsaturated soil. Key feature is the consideration of the coupled soil water and air. The analysis emphasizes on the dynamic responses of wave field induced by a unit vertical harmonic point load on the invert level of tunnel. The tunnel is modelled as an infinitely long shell with a circular section. The soil is simulated as an unsaturated poroelastic full-space in which the solid matrix is filled with the coupled soil water and air. Stress compatibility and displacement continuity are used to describe the interaction between the tunnel and the soil. A good agreement regarding the results of soil displacements between the present model and existing models for saturated soil and elastic media confirms the validity of the proposed model. The numerical analysis investigates the effects of water saturation on soil displacements and matric suction under different load frequencies. The results reveal that the dynamic responses of unsaturated soil are different from those in saturated soil. Increased water saturation can vary the value of displacements and matric suction of the soil, but not their distribution pattern around the tunnel. Displacements and matric suction distribution curves along the circumferences of the tunnel have more peak points in the case of higher load frequencies. • Model for deep tunnel embedded in unsaturated full-space is proposed. • The model is validated by existing elastic medium and saturated soil models. • Displacements and matrix suction caused by harmonic point load are given. [ABSTRACT FROM AUTHOR]

Assessing the long-term durability of concrete structures subjected to external sulfate attack (ESA) poses a significant challenge, primarily due to the lack of a well-defined quantitative metric for durability limit states. Traditional performance indicators such as compressive strength, mass loss, and expansion strain are insufficient for providing a comprehensive understanding of the extent of damage and are often difficult to measure accurately in practice. The primary objective of this study is to introduce a novel durability failure indicator, namely the failure thickness of concrete under ESA exposure, designed to quantitatively assess the ultimate limit state of concrete durability. Experiments were conducted and the results confirmed that the failure thickness can reliably reflect changes in both the elastic modulus and compressive strength of concrete exposed to ESA. A prediction model for estimating the failure thickness was subsequently developed, integrating key influencing factors like sulfate concentration, initial aluminate content, and sulfate ion diffusion coefficient. The established model exhibited a high degree of correlation between the predicted and experimental failure thickness values, with a low margin of error. The findings of this research contribute to serve as a foundation for both lifespan prediction and durability design of concrete structures exposed to sulfate-rich environments. • We propose a durability failure indicator based on critical sulfate concentration. • Concrete performance deterioration can be well characterized by failure thickness. • The validity of the prediction model of failure thickness was confirmed. [ABSTRACT FROM AUTHOR]

This study investigates the efficacy of post-fire curing using carbonation with a 20% carbon dioxide concentration and a relative humidity cycle set between 40% and 90% for restoring the mechanical properties of thermally damaged high-performance concrete (HPC) specimens containing 0%–40% silica fume. The HPC specimens were exposed to temperatures of 600, 800, and 1000 °C for 1 h, and the compressive strength recovery was measured. The microstructure, porosity, pore size distribution, and chemical composition of the HPC specimens were analyzed to explore the strength recovery mechanism. After exposure to elevated temperatures, the average compressive strength of samples without silica fume decreased by 49.2 MPa. Subsequent carbonation recuring resulted in a significant recovery of 73.9 MPa in the average compressive strength. This recovery surpassed the original strength for the samples heated to 600 and 800 °C, attributable to the filling and coalescing effects of calcium carbonate polymorphs formed through the carbonation of residual cement particles and β-C 2 S. The samples containing 20% silica fume exhibited the second highest average strength recovery of 34.1 MPa. However, the strength recovery for the samples with 40% silica fume exposed to 800 and 1000 °C was negligible, as the microcracks exceeding 1 μm in width had barely been restored by the carbonation of the low-calcium calcium silicates with low reactivity. Overall, this study presents an exciting future prospect for the labor and cost-effective restoration of thermally damaged concrete structures through the use of carbonation curing. [ABSTRACT FROM AUTHOR]

The applications of pervious concrete made with recycled aggregate (RA) have been hindered by its significantly reduced strength. In this study, a silane polymer emulsion treatment method was used to promote the strength of pervious concrete while maintaining its permeability. The mechanical and physical properties of RA pervious concrete were experimentally investigated. Membrane-forming ability tests and X-ray micro-tomography were conducted to determine the influence of the silane polymer emulsion on the membrane-forming behaviour and thickness distribution of cement paste. The results revealed that silane treatment significantly improved the strength of RA pervious concrete while maintaining acceptable permeability due to the redistribution of the cement paste. Meso-structure analyses confirmed that more cement pastes gathered around the bonding regions between adjacent RA particles. The findings suggest that this method can be used to enhance the strength of RA pervious concrete through effective utilisation of cement paste. Unlabelled Image • Silane polymer emulsion treatment was used to enhance strength of RA pervious concrete. • Strength of RA pervious concrete is obviously enhanced with maintaining desired permeability. • Meso-structural features were obtained with X-ray tomography and lineal analysis method. • Strength enhancement originates from more cement paste gathering around the bonding regions. [ABSTRACT FROM AUTHOR]

Highlights • Actual coarse aggregate shapes were statistically analyzed based on CT technology. • A Polygon aggregate modeling method was proposed considering statistical features. • Proposed polygon aggregate models were verified by an experimental test. • Several meso-scale models with various sizes and cross-section shapes were provided. Abstract Few efforts have been made to study actual coarse aggregate shapes in mesoscopic simulation analysis, whereas it has a significant impact on stress distribution and micro-crack propagation during the failure process of concrete. In this study, the true characteristics of aggregates (i.e. edge number, area, equivalent radius, elongation ratio and size distribution) were statistically analyzed by processing the real 2D slice images of concrete obtained from X-ray computed tomography technology. A polygon random aggregate modeling method, considering above statistical features of aggregate, is proposed and verified by an experimental investigation. The test results show that the established model can give an accurate description of the stress-strain behavior and damage evolution of concrete. Moreover, several representative meso-scale concrete models were established, which provides a reference in building meso-scale models with various sizes and cross-sectional shapes, especially for large-scale concrete members that are unable to undergo CT testing due to limitation of operational space. [ABSTRACT FROM AUTHOR]

Using recycled cathode ray tube (CRT) funnel glass as a substitute for sand contributes to both reducing natural aggregate consumption and the disposal of CRT funnel glass. Currently, most studies have focused on the mechanical and durability properties of mortar or concrete containing CRT glass as fine aggregate. However, the study of the dynamic loadings (e.g., earthquake load, wind load and impact load) of major concrete structures containing CRT glass is still limited. In this paper, a dynamic thermo-mechanical analysis test with various frequencies (0.1 Hz–2.0 Hz) and temperatures (−30 °C−30 °C) is undertaken on mortars with different CRT replacement ratios (0, 20%, 40%, 60%, 80%, and 100%). The test results show that the storage modulus (stiffness) of mortar with incorporated CRT glass is lower than that of control mortar in most cases, but the decreasing trend is not proportional to the CRT replacement ratio. However, the presence of CRT glass in the mix has a negligible impact on the frequency dependence of the storage modulus of mortar. The storage modulus of each replacement ratio is nearly constant for all excitation frequencies. The frequency dependence of loss tangent (damping behavior) is significantly improved with CRT glass under 0 °C. This indicates that a frequency dependent damping model is needed when dynamic analysis is conducted on concrete structures with incorporated CRT glass in cold weather. [ABSTRACT FROM AUTHOR]

• The effect of seawater and sea sand at different stages of preparation on the performance of AWC mortar was systematically studied. • The adverse effect of seawater on the properties of AWC mortar at the molding stage was found for the first time. • The mechanism of the influence of seawater on AWC properties at the molding stage was revealed. Seawater and sea sand are widely used in marine concrete to overcome the shortage of freshwater and river sand. However, the effect of the various salts in seawater and sea sand on the performance of anti-washout underwater concrete (AWC) is unclear. In this study, the influence of seawater and sea sand, as well as the aggressive ions in seawater, on the anti-washout ability, mechanical performance, and microscopic structure of AWC mortar are studied systematically. The AWC mortar molded in seawater has a lower compressive strength even though its indicators of anti-washout ability perform better than that in freshwater. This is because Mg2+ in seawater chemically binds with OH– in cement to form Mg(OH) 2 film absorbed by anti-washout admixture(AWA), which inhibits the release of substances in AWC while also introducing more defects in AWC. This study lays the foundation for promoting the application of seawater and sea sand AWC in marine engineering. [ABSTRACT FROM AUTHOR]

Steel fiber size and fiber distribution synergistically influence the tensile behavior of ultra-high performance concrete (UHPC). The suitable aspect ratio of steel fiber can improve crack-bridging capacity, while the oversized ratio results in poor fiber distribution, degrading tensile performance substantially. Therefore, identifying the synergistic effect of fiber geometry and distribution is key for superior tensile properties, which is quantitatively evaluated here. It is found that the aspect ratio determines the domain of stress distribution, while fiber distribution affects the overlapping domain, leading to variations of tensile properties, which is revealed as the "pile group" working mechanism of fibers. Furthermore, a novel model was proposed to accurately predict the uniaxial tensile strength of UHPC by combining the Gradient Boosting (GB) and statistical approaches. The matrix tensile strength was obtained using the GB algorithm, and the relationship among fiber factor, fiber distribution, and tensile strength was established by the statistical regression method. The findings provide unique insight into how the fiber geometry and distribution govern the tensile properties and inspire a new design scheme of UHPC toward excellent tensile behavior. • The synergistic effect of fiber geometry and distribution is evaluated quantitatively. • The pile group working mechanism of steel fibers in UHPC has been explored. • Model for predicting UHPC tensile strength using statistical and GB approaches is proposed. [ABSTRACT FROM AUTHOR]

Seawater sea-sand concrete (SWSSC) provides an alternative to normal concrete, while Steel-FRP Composite Bars (SFCB) offer corrosion resistance in offshore and marine structures. Despite their benefits, the long-term performance of SFCB-reinforced SWSSC structures remains under-explored. This study evaluated the durability of such beams, particularly focusing on the effects of using Portland cement versus low-alkalinity calcium sulphoaluminate (CSA) cement. The investigation involved tensile and pull-out tests conducted on SFCB, and flexural tests conducted on the beam components after accelerated marine environmental exposure over periods ranging from one to six months. Results highlighted that SFCB embedded in low-alkalinity CSA cement exhibited improved retention of tensile strength, elastic modulus, and bonding strength by 32.0 %, 39.1 %, and 56.7 % respectively, compared to that embedded in normal Portland cement concrete. Microstructural analyses showed much less hydrolysis of the resin matrix and shallower corrosion of the basalt FRP (BFRP) cover on the SFCB. Furthermore, flexural tests demonstrated superior cooperative performance between low-alkalinity CSA concrete with SFCB in beam components, showing only marginal degradation in crack density, crack strength, and yielding points. The ultimate failure load of beams made with CSA concrete was 1.89 times higher than those made with normal SWSSC after 6 months of exposure. These results underscore the potential of low-alkalinity concrete in improving the long-term durability and structural performance of SFCB-reinforced marine concrete infrastructures. • SWSSC beams reinforced with SFCB were assessed for durability under accelerated marine environment. • Low-alkalinity CSA concrete significantly reduced the hydrolysis depth of BFRP covers under accelerated corrosion. • SFCBs embedded in low-alkalinity CSA concrete demonstrated enhanced retention of mechanical properties and bond strength. • Low-alkalinity CSA beams displayed improved structural integrity and sustained higher ultimate loads than normal beams. [ABSTRACT FROM AUTHOR]

The anti-washout concrete (AWC) made with seawater and sea sand has a limited marine infrastructure application due to its unfavorable properties. Our study proposes an effective performance enhancement method for AWC using silica fume. A comprehensive examination was carried out to investigate the effects of silica fume on AWC's flowability, anti-washout ability, compressive strength, microstructure, permeability, and abrasion resistance, with the AWC prepared with seawater and sea sand, and molded in seawater. It was discovered that 10 % silica fume can most effectively improve the performance of AWC. This enhancement is due to the pore structure refinement realized with C-S-H gel generated from pozzolanic reaction. Exceeding 10 % silica fume content can have a detrimental effect on the slump-flow of mixtures, while only providing marginal improvements in impermeability and compressive strength. The study lays a fundamental groundwork for the wide use of sea-based resources and the application of AWC in marine engineering. • The science behind modification of AWC mortar molded in seawater using silica fume was revealed. • The effects of silica fume on the performance of AWC molded in seawater were thoroughly explored. • The optimal content of silica fume to improve performance of AWC molded in seawater was identified. [ABSTRACT FROM AUTHOR]

• The performance of concrete under sulfate attack and dry-wet cycles is investigated. • A newly defined index is proposed to describe the progress of sulfate attack. • A novel method is proposed to assess the performance of sulfate-attacked concrete. Sulfate attack is a major cause of concrete durability deteriorations. Mass loss, strength reductions, and expansive strain of concrete specimens are generally used in laboratory testing to identify the resistance of concrete materials to sulfate attack. However, these indicators cannot be directly used to quantitatively predict the bearing capacity of actual concrete structures under sulfate attack. There exists a significant size effect between laboratory and engineering size concrete components. In this study, the durability performance of concrete specimens, exposed to sulfate attack and dry–wet cycles, was investigated. Mass loss, dynamic elastic modulus, compressive strength, and sulfate ions distributions of deteriorated concrete were measured over time. Test results indicate that the newly defined integral area of sulfate ions distributions is a suitable index to describe the non-uniform deteriorations behavior of sulfate–attacked concrete; and a novel method based on the homogenizations theory is proposed to predict the deteriorations level of components of attacked concrete structures, which provides a potential use in assessing the loading capacity of actual concrete structures based on accelerated test results in a laboratory. [ABSTRACT FROM AUTHOR]

Large-scale expansion of urban underground space has led to the accumulation of substantial sediment. Now the primary disposal approach involves long-distance transport followed by dumping in open areas or landfills, incurring excessive deposition and causing landslides. To tackle this concern, a novel processing scheme that transforms sediment into supplementary cementitious material is proposed for preparing sustainable seawater sea sand concrete (SWSSC). Notably, it is determined that this transformed sediment improves cement hydration and reduces cement dosage, achieving a 35% reduction in CO 2 emissions compared to traditional SWSSC with identical strength according to life cycle assessment. Furthermore, it offers the additional benefit of cost-effective. Microanalysis has demonstrated that the recycled sediment reacts with calcium hydroxide and produces secondary calcium-silicate-hydrate gel, contributing to the mechanical properties and decrease in alkalinity of SWSSC. A design model for SWSSC is proposed, focusing on alkalinity, mechanical strength, and environmental benefits. This proposed model enhances application of SWSSC in construction, catering to specialized marine engineering structures, like artificial islands, harbors and offshore structures. This study contributes to a large-scale processing strategy of sediment and provides an economical and green alternative construction material for sustainable infrastructures. [Display omitted] [ABSTRACT FROM AUTHOR]

Using geopolymer concrete (GC) is a technically feasible decarbonization strategy in the cement and concrete industry shown by numerous papers. A key factor determining its commercial application is whether its cost is competitive. However, related study is scarce. In this paper, we present the analysis of GC's CO 2 avoidance cost, the cost incurred to reduce one metric ton of CO 2 emissions. The results show that among the 486 GC mixtures analyzed, only seven yield negative CO 2 avoidance costs, while 379 are even more expensive than capturing CO 2 from cement plants, which is another technically feasible decarbonization strategy and has been evaluated to have a CO 2 avoidance cost of 55 USD/tCO 2 in Chinese demonstration project. Only a few GC mixtures with lower CO 2 avoidance costs will be considered by the industry, and they are associated with low activator dosage and high compressive strength. To quantify this relationship, we introduce the activator index (Ai), which refers to the activator dosage (kg·m−3) required to achieve 1 MPa of compressive strength. The result shows that Ai values below certain thresholds correspond to lower CO 2 avoidance costs and significant emission reductions of GC. This Ai -based criterion helps identify the optimal GC mixture that effectively reduces CO 2 emissions at the lowest possible cost, thereby promoting its commercial application. [Display omitted] • Only 7 of 486 geopolymer concrete (GC) mixtures have negative CO 2 avoidance costs. • CO 2 avoidance costs of most GC in literature exceed CO 2 capture. • The lower activator dosage per MPa strength, the lower CO 2 avoidance cost of GC. [ABSTRACT FROM AUTHOR]

Cathode ray tube (CRT) funnel glass is classified as a hazardous waste because it contains lead, which can endanger the environment and human health. In this paper, an innovative cementitious material, ultra-high performance concrete (UHPC) was introduced to recycle hazardous waste CRT without lead extraction. Crushed CRT funnel glass without lead extraction was used to replace sand as fine aggregate in various ratios in UHPC. The mechanical properties and toxic heavy metal leachability of UHPC were investigated. Results showed that the addition of CRT glass can increase the flowability and decrease the compressive and flexural strength of UHPC. Analyses by X-ray diffraction and scanning electron microscopy demonstrated that the CRT glass increases the porosity, inhibits cement hydration, and weakens the interfacial transition zone, resulting in the reduced strength of UHPC. Meanwhile, the leached lead concentration of UHPC was still below regulatory limit of U.S. code even when the replacement ratio reaches 100%. The working principle behind the sharp drop in leached lead in UHPC was proposed, that is the dense microstructure and low permeability coefficient of UHPC can effectively restrain the lead leaching from CRT glass. The findings of this study can provide an effective alternative to recycling hazardous waste CRT without limitations on the replacement ratio and safety concern. Image 1 • Recycling of waste CRT funnel glass without lead treatment through UHPC is explored. • The influence of waste CRT funnel glass on the properties of UHPC is investigated. • UHPC with waste CRT funnel glass fulfills safety requirement from US code. • Lead leaching is inhibited in UHPC and its working principle has been revealed. [ABSTRACT FROM AUTHOR]

• Effect of titanium dioxide and graphene on the durability and mechanical properties of polyether sealant is studied. • Tensile strength after ultraviolet exposure of modified sealant improved by 102%. • Water absorption of graphene-modified sealant reduced by 85.7%. • The working mechanism of sealant with titanium dioxide and graphene has been revealed. The silane-modified polyether sealant is widely applied to fill the gaps between external walls in prefabricated buildings and to bear the deformation of joints. However, the weak tensile strength and poor ultraviolet and moisture resistance of sealant lead to severe degradation, posing threat to the building waterproofing and safety. To address the problems, titanium dioxide and graphene were adopted to improve the mechanical properties and durability of sealant. The tack-free time, tensile properties, ultraviolet resistance, and hydrophobic performance of pristine and modified sealant were investigated and the enhancement and erosive resistance mechanisms of modified sealant were revealed by microscale characterization. Results indicated that modified sealant with low content of titanium dioxide had greater tensile strength and ultraviolet resistance. The crystalline form of titanium dioxide and produced Si-O bond enhanced the ultraviolet resistance. Moreover, the 0.8% graphene-modified sealant possessed superior moisture resistance with 23% increased contact angle. Graphene increased the surface roughness and generated π-conjugated structure, improving sealant hydrophobicity. It is revealed that the enhanced properties were ascribed to the spatial structure of fillers and chemical bond energy. This work provides a novel sealant with high ultraviolet resistance and hydrophobicity, facilitating the development of durable and low-maintenance prefabricated buildings. [ABSTRACT FROM AUTHOR]

• The influences of moisture variations on ion transport and physical crystallization were discussed. • The respective contributions of chemical and physical attack to crystallization pressure were distinguished. • The deterioration in concrete performance was considered under the combined impacts of external sulfate attack and drying–wetting cycles. • A transport-chemical-physical–mechanical model was developed to evaluate and predict damage progression to concrete. When coupled with drying–wetting cycles, the deterioration process of concrete subjected to external sulfate attack (ESA) is significantly accelerated. The impact of moisture variations on ion transport was considered to establish a mass conservation equation with pore solution concentration as the variable. The contributions of chemical and physical attack to crystallization pressure were distinguished, and a bulk modulus reduction function was introduced to ascertain the stiffness deterioration. An ESA model was proposed and verified by comparing it to published experimental data, which could accurately predict the deterioration process of concrete under ESA and drying–wetting cycles. [ABSTRACT FROM AUTHOR]

This study investigates the effects of lime-saturated water and water–CO 2 cyclic recuring on strength recovery of thermally damaged high-performance concretes (HPC). The HPC samples were subjected to elevated temperatures up to 1000 °C in 200 °C increments and underwent recuring. Phase assemblage and distribution, microstructure evolution, and pore structure of the HPC samples were identified. According to the results, recovered compressive strength of the HPC samples with low silica content can surpass their original strength after 600 and 800 °C exposure and recuring. In contrast, HPC with high silica content is unfavorable for strength recovery at temperatures above 800 °C because the low-calcium phases formed have low reactivity. After 1000 °C exposure, only water–CO 2 cyclic recuring coalesces the disintegrated microstructure and recovers the compressive strength. Strength recovery primarily depends on healing the microcracks and large pores rather than the coarsened cement paste. [ABSTRACT FROM AUTHOR]

The damping capacity is one of major concerns for structures under dynamic loads, which significantly affects the safety and service life. Ultra-high performance concrete (UHPC) is a new generation of cementitious material characterized by superior mechanical strength and durability, exhibiting enormous potential in application to innovative structures. However, the weak steel fiber-matrix interface within UHPC leads to insufficient damping performance and poses threats to UHPC structures under extreme dynamic loading conditions. In this paper, various interfacial modulation approaches were investigated to improve static and dynamic damping properties of UHPC, including physical shape and chemical modification of steel fibers, macrofibers and microfibers hybridization. Results show that the interfacial modulation can significantly enhance damping ratio, loss factor and energy dissipation ratio of UHPC, where the chemical modification of steel fibers endows the highest damping ratio. The loss factor and energy dissipation ratio of UHPC reach 0.579 and 0.091 after interfacial modulation, which improved by more than 110% and 100%, respectively. The working mechanisms behind variations of damping performance are attributed to the toughening in interfacial bond and load transfer, leading to improvement in energy dissipating ability of interface. Furthermore, a comprehensive comparison between UHPC and existing vibration damping materials was conducted through multi-criteria analysis from the perspectives of damping performance, mechanical strength, processability and economic benefit, and UHPC with chemical modification of steel fibers exhibits the best overall performance. The findings contribute to inspiring a novel structural vibration control strategy through UHPC with enhanced static and dynamic damping properties for resisting extreme loads. [ABSTRACT FROM AUTHOR]

The development of underground space is an important trend for urban infrastructure in cities supporting socio-economic activities, while it also results in an enormous accumulation of sediment waste, which consumes vast land resources, causes serious environmental problems and endangers public safety. It is urgent to explore pathways of recycling sediment waste with low carbon impact for sustainable infrastructure. This study employed calcination and alkali activators to recycle sediment waste into geopolymer paste. The mechanical properties and working performance of recycled geopolymer paste were investigated and the underlying mechanism of this recycling scheme was revealed with microscale characterizations. Results showed that the compressive strength of recycled geopolymer paste could reach 50 MPa. The environmental impact of geopolymer paste and cement-based paste has been analyzed via life cycle assessment (LCA). Recycled geopolymer paste can save 310 kg CO 2 eq/t of carbon emissions, which is 39% lower than that of cement-based material. Moreover, the multi-criteria approach was adopted to evaluate geopolymer paste and cement paste considering mechanical properties, working performance, carbon emissions, energy consumption and cost, and geopolymer paste exhibits better overall performance. The findings inspire a construction waste management strategy and contribute to low-carbon construction materials for sustainable urban infrastructure. • Sediment waste is recycled into geopolymer paste via calcination and alkali activator. • The optimum mix ratio range of geopolymer paste with sediment waste is determined. • Mechanical and environmental performance of geopolymer paste has been studied. • A sustainable sediment waste management strategy and a low-carbon construction material is inspired. [ABSTRACT FROM AUTHOR]

Low-carbon emission mortar samples were prepared using reactivated cementitious materials (RCMs) produced by calcinating hydrated cement paste with adjusted Ca/Si ratios. Carbonation curing was employed to enhance the cementing capacity of the RCMs and to sequestrate CO 2. The compressive strength, phase assemblage, microstructure, and environmental impacts of the mortars were analyzed. According to the results, the mortar sample produced with the RCM with a 10% addition of silica fume during calcination attained the highest compressive strength (35.3 MPa) after water curing, while higher silica contents were unfavorable because the low-lime calcium silicates that formed have limited water reactivity. Carbonation curing significantly promoted reactions of the RCMs and, thus, the compressive strength of the mortars compared to water curing. The amorphous and metastable calcium carbonates contributed more to the densification of the microstructure than the calcite. From the life cycle assessment, the RCM mortars had a significantly lower impact on global warming potential compared to Portland cement mortars. [Display omitted] [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) is a new generation of cementitious composites that exhibit excellent compressive strength and durability. However, the poor bonding between steel fiber and UHPC matrix usually results in insufficient tensile properties and limits its application. Here, the surface of steel fibers is modified with silane coupling agent (SCA) to enhance fiber/matrix bond. The macroscale workability, flexural and tensile properties of UHPC are investigated. It has been found that SCA modifications contribute to strength enhancement and cracking behavior improvement of UHPC, and its energy absorption capacity increases 13.8%. The microscale characterizations of fiber/matrix interface are conducted through scanning electron microscopy, energy dispersive spectrometer and Fourier transform infrared spectroscopy. The mechanisms behind the enhancement have been revealed and classified into mechanical friction, chemical bonding and physical adhesion. This work provides a green and effective approach for promoting tensile properties and an in-depth understanding of SCA modification mechanisms. [ABSTRACT FROM AUTHOR]