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The performance of joint connections in composite slabs is crucial for ensuring their bidirectional load-bearing capacity and overall structural integrity. To effectively address the challenge of protruding rebar in precast components, a new structural form of a tightly connected hollow concrete composite slab without protruding rebar on the slab side is proposed. To investigate the mechanical performance and failure modes of this slab-side tight-joint connected hollow concrete composite slab, bending performance tests under monotonic load were conducted on three tightly connected hollow composite slabs and one seamless hollow composite slab. The analysis focused on the failure modes, crack distribution, bending capacity, and bending stiffness of additional steel bars at the joints of the slabs. The results indicate that, under normal operating conditions, the flexural performance development of concrete hollow composite slabs with tightly connected slab sides is generally consistent with that of the non-spliced cast hollow composite slab. Under ultimate conditions, tearing or brittle fracture failure at the joint interface is likely to occur in the composite slabs, leading to a reduction in flexural bearing capacity. With an increase in joints, the bending capacity of the hollow composite slab decreases by 17.1%, Conversely, when joints are positioned away from the most stressed section, the flexural stiffness of the section increases by 13.5%. A comparison of experimental data and theoretical calculations indicates that the additional rebar at the joints effectively contributes to the lateral load transfer in the hollow composite slab, achieving bidirectional load-bearing capacity. This further validates that the design of the single-joint, tight-joint connected hollow concrete composite slab without protruding rebar meets the requirements for bidirectional load-bearing performance. [ABSTRACT FROM AUTHOR]

Translation abstract Use of 100 % recycled aggregates in concrete – report on practical applicationsThis article reports on eight practical examples of applications for concrete with 100 % recycled aggregates. The applications include reinforced/unreinforced bored piles, foundations, load‐bearing internal/external walls, columns and floor slabs as well as balcony elements. Some components were realised as architectural concrete components. The respective project is summarised together with the results of the concrete development and concrete testing as well as the experience gained from obtaining special approvals in individual cases. Based on the findings from the various practical projects, it can be concluded that concrete with 100 % RC‐GK can be used for a large number of applications, so far limited to up to XC4 and XF3. Compressive strength for ready‐mix concrete up to C35/45 with good workability even with pumped concrete (here: pumping distance 45 m) using 100 % RC‐GK type 1 were possible without any problems. A concrete with sufficient early strength and a final strength of C40/50 was developed for precast elements. In two examples, RC‐GK type 2 was used for the coarse grain fraction and RC‐GK type 1 for the sand. All the projects presented have already been completed or are nearing completion. The feasibility of 100 % RC concrete in practice has thus been successfully demonstrated in several cases. [ABSTRACT FROM AUTHOR]

Translation abstract A modular precast segmental bridge with thermally formed CFRP reinforcement – modularisation approach and precast concrete productionModular construction enables the serial prefabrication of structural elements and transfers manufacturing processes from the construction site to the protected environment of a precast concrete factory. In serial production with sufficient quantities, rationalisation, digitalisation and automation of manufacturing processes becomes viable and economies of scale can be utilised. In the design realisation of modular building structures, the design engineer is faced with the challenge of arranging these into sensible modules and designing robust and durable joints. This article presents a modularisation approach based on the principles of precast segmental construction and discusses the design and precast segment production for an 8.10 m long test bridge. Non‐metallic reinforcement made of carbon fibre reinforced polymers (CFRP) is used in order to create particularly material‐efficient and thin‐walled concrete cross‐sections and to avoid the risk of reinforcement corrosion. The forming of the reinforcement elements, which is currently still a technical challenge in the application of CFRP‐reinforced concrete, was realised by using recently developed processes of thermal forming. With the realisation of a modular segmental bridge with thermally formed CFRP reinforcement, the authors aim to contribute to the development of technical solutions for modular construction and demonstrate new fields of application for non‐metallic reinforcements. [ABSTRACT FROM AUTHOR]

The chloride migration coefficient (CMC) of concrete is crucial for evaluating its durability. This study develops ensemble models to predict the CMC of concrete, addressing the limitations of traditional, labor-intensive laboratory tests. We developed three ensemble models: an inverse variance-based model, an Artificial Neural Network (ANN)-based model, and a tree-based model using the random forest regression algorithm. These models were trained on a dataset comprising 843 concrete mix proportions from existing literature. Results indicate that ensemble models outperform single models such as ANN and Support Vector Regression (SVR) in predicting CMC, with the combined random forest and ANN model showing the highest accuracy. Sensitivity analysis using Shapley Additive Explanations (SHAP) reveals that the CMC is most influenced by the water-to-cement ratio and curing age. Additionally, we designed a graphical user interface (GUI) to facilitate the practical application of our models. This research offers a robust methodology for evaluating concrete durability and potential for extending the prediction to other concrete properties. [ABSTRACT FROM AUTHOR]

Due to the demand for carbon neutrality, concrete carbonation has been reconsidered as an interesting topic because of its potential for capturing carbon dioxide (CO2) from the atmosphere. Concrete carbonation can significantly modify the chemical and microstructure properties of concrete and thus will have important effects on chloride diffusion. This paper presents a chloride diffusion model in which the concrete cover is divided into three different zones, each with their own defined porosity and chloride binding isotherm. The first is the fully carbonated concrete near the surface, where the porosity and chloride binding isotherm can be obtained from the experimental data of fully carbonated concrete. The second is the uncarbonated concrete near the reinforcement, where the porosity and chloride binding isotherm can be obtained from the experimental data of normal concrete. The third is the transition zone between the fully carbonated and uncarbonated concretes, where the porosity and chloride binding isotherm can be assumed to vary continuously from the carbonated concrete to uncarbonated concrete. To validate the present model, a comparison of the present model with published experimental results is provided, which demonstrates the importance of considering different zones in the chloride diffusion model when the concrete has a carbonated layer near the surface. [ABSTRACT FROM AUTHOR]

Purpose: Evaluate the performance of progressive collapse of full-scale three-dimensional structure (3D) beam-slab substructures with and without the presence of reinforced concrete (RC) balconies using two concrete mixes [normal concrete (NC) and rubberized concrete (RuC)]. Design/methodology/approach: This study examines two concrete mixes to evaluate the progressive collapse performance of full-scale 3D beam-slab substructures with and without the presence of RC balconies using the finite element (FE) method. Findings: The results showed that the vertical loads that affect the structures of the specimens after including the balconies in the modeling increased by an average of 29.3% compared with those of the specimens without balconies. The specimens with balconies exhibited higher resistance to progressive collapse in comparison with the specimens without balconies. Moreover, the RuC specimens performed very efficiently during the catenary stage, which significantly enhanced robustness to substantial deformation to delay or mitigate the progressive collapse risk. Originality/value: All the experimental and numerical studies of the RC beam-slab substructures under progressive collapse scenarios are limited and do not consider the balcony's presence in the building. Although balconies represent a common feature of multistory residential buildings, their presence in the building has more likely caused the failure of this building compared with a building without balconies. However, balconies are an external extension of RC slabs, which can provide extra resistance through tensile membrane action (TMA) or compressive membrane action (CMA). All those gaps have not been investigated yet. [ABSTRACT FROM AUTHOR]

A novel analytical model is proposed to improve the accuracy of predicting the mechanical response of a strand with asymmetrically broken wires. This model incorporates a new approach to compute the contact force between the broken wire and the duct. When there is more than one asymmetrically broken wire, the previous method cannot handle this situation due to the large deflection of the center wire near the breaking end. This deflection results in a significant contact force between the center and broken wires. The omission of this force in the previous method leads to unrealistic solutions for two or three asymmetrically broken wires. This paper addresses the issue appropriately. The calculated results have been compared with those from a previous experiment, demonstrating satisfactory agreement. Furthermore, the proposed analytical model has been adopted to predict the mechanical behavior of the broken wire in multi-strand scenarios relevant to a prestressed concrete bridge. The contact force between strands is accurately calculated. The findings indicate that the axial force of the asymmetrically broken wire in multi-strands can recover after a short distance from the broken end. This recovery is attributed to the confinement effect of the other strands. [ABSTRACT FROM AUTHOR]

In this work, a particular type of carbon nano-material, like graphene oxide (GO), is synthesized in different batches by varying oxidation times, ranging from 1 to 4 days. The synthesis process initially starts with the oxidation of commercially available graphite powder and subsequently exfoliates the obtained graphite oxide in an aqueous solution using a high-frequency ultrasonication process. The synthesized GO batches were characterized using different characterization techniques to authenticate the formation of GO. The highly oxidized GO in an aqueous solution was selected and used as a strength-enhancing additive in concrete. The concrete mixes containing highly oxidized GO at the dosage of 0.01% 0.03%, 0.05%, 0.07%, and 0.09%bwoc were prepared to assess the strength and durability parameters. The GO (4 d) with 0.09%bwoc in concrete increases compressive strength by 58%, tensile strength by 41%, and flexural strength by 43% at 56 days. The results proved that the 0.09%bwoc GO dosage in cement concrete could effectively improve mechanical and durability performances compared to other mixes. Furthermore, the results are verified with the microstructural investigation using FE-SEM in secondary electron (SE) and backscattered electron (BSE) mode to monitor the microstructural changes and thickness of the interfacial transition zone (ITZ) during cement hydration. [ABSTRACT FROM AUTHOR]

The escalating use of glass in an ever-evolving world poses a waste management challenge, with glass waste contributing to non-biodegradable landfill growth. Recycling glass waste emerges as a viable solution, combating the need for additional landfills and the environmental repercussions. This study employs a scientometric and content analysis from the Scopus bibliometric database and explores the functional feasibility and performance characteristics of recycled glass waste (RGW) in sustainable concrete production. Results indicate that Asia dominates research contributions to RGW for concrete production compared to other continents. Glass-mixed concrete properties depend on glass type, particle size, shape, surface texture, replacement ratio, and curing age. The pozzolanic reactivity of recycled glass is correlated with its relative fineness. Finer glass particles were considered more suitable for use due to the enhanced alkali-silica interaction. Utilizing glass powder and fine aggregates improves mechanical properties, but high replacement levels could affect concrete strength development. Additionally, using RGA as a cement and fine aggregate replacement reduces concrete's thermal conductivity. This scientometric analysis not only aids in understanding a comprehensive overview of incorporating recycled glass waste into concrete production but also identifies knowledge gaps, guiding sustainable concrete research and development for addressing waste management challenges linked to the growing use of glass in our contemporary society. [ABSTRACT FROM AUTHOR]

The electrochemical indicators including corrosion potential (Ecorr), concrete resistivity (ρ), corrosion current density (icorr), and polarization resistance (Rρ) are pivotal in the evaluation of the degradation state of reinforcements embedded in concrete. Notwithstanding, extensive investigations traditionally hinge on a singular electrochemical metric for the appraisal of rebar corrosion. The current study transcends this conventional approach by integrating multiple electrochemical detections, significantly improving the accuracy in ascertaining the corrosion status of reinforcing bars within concrete. In this paper, a Bayesian network model is developed, synthesizing results from four electrochemical indictors obtained from published literatures. This model effectively addresses the challenge of integrating unmeasured electrochemical parameters in cases where only a limited set is tested in practical engineering, culminating in a more comprehensive assessment dataset. Further, this study progresses to quantitatively assess the reinforcement corrosion status by devising and fine-tuning an integrated model. The Bayesian network notably excels in extrapolating untested results and accurately determining the thresholds for rebar corrosion status, thus significantly improving the overall assessment capability. The Bayesian network, as employed in this study, computes median Ecorr and icorr values at -282mV and 0.168µA/cm², respectively. These computed values exhibit a deviation within 15% of experimental data, aligning with the uncertainty range stipulated by the ASTM C876-91 standards. [ABSTRACT FROM AUTHOR]

Phosphorus tailings are solid wastes generated from mineral processing. It limits the green development of phosphorus chemical industries. Phosphorus tailings mainly consist of dolomite, fluorapatite, and quartzite, so they are used as mineral admixtures to prepare concrete, which not only reduces carbon emissions but also eliminates phosphorus tailings and solves the issues caused by the large accumulation of phosphorus tailings. In this paper, C40 concrete was prepared with different content and fineness of phosphorus tailings, and the effects of phosphorus tailings on its workability, mechanical properties, and durability were investigated. The harm of heavy metals leaching of concrete mixing with phosphorus to the environment was evaluated. The mechanism of the effect of phosphorus tailings on concrete was also analyzed by using characterization methods such as heat of hydration, XRD, and SEM. The results showed that the workability of concrete increased with the phosphorus tailings amount increased, but the mechanical property of concrete decreased. The fineness of phosphorus tailings has little effect on the workability and mechanical properties of concrete. The durability properties of concrete were impaired with the increase in the admixture of phosphorus tailings, but the fineness of phosphorus tailings has no significant effect on the durability properties of concrete. With the increase of the curing time, the structure of the concrete mixed with phosphorus tailings became denser than the concrete without phosphorus tailings incorporated. The concrete mixing with phosphorus tailings had little detriment to the environment. Finally, using the particle size of 20 μm and the content of 20% of phosphorus tailing to replace the cement was suggested. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) is a solid waste generated by phosphate fertilizer industries that is currently used in concrete materials. However, adding PG to concrete usually results in reducing its water resistance and corrosion resistance. This paper presents a new method of applying PG to concrete to improve its water resistance. In this paper, a green superhydrophobic PG (SPG) coating was prepared using modified PG as a hydrophobic medium and cement as the bonding material. The contact angle between the superhydrophobic phosphogypsum coating (SPG coating) and water was 156°, and the coating reached a superhydrophobic state with good self-cleaning ability. Even when sandpaper was used to polish the coating, the water contact angle of the coating was still greater than 150°, indicating that the coating had good wear resistance. In addition, the results of water absorption and electrochemical experiments indicated that mortar coated with SPG had better water resistance and corrosion resistance than ordinary mortar. The SPG coatings with water resistance, wear resistance, and self-cleaning properties have potential applications in building exterior walls. [ABSTRACT FROM AUTHOR]

Based on investigated mechanical properties of alkali residue-based foamed concrete (A-FC), this paper presents a comprehensive examination of the microstructural features of A-FC and their impact on compressive properties. A detailed investigation of the compressive performance and pore structure characteristics was conducted through compression tests and low-field nuclear magnetic resonance (NMR) tests. The results demonstrate that the primary pore size in A-FC falls within the microscale, and the pores can be categorized into three types—gel pores, capillary pores, and air voids. In addition, the T2 spectrum of A-FC exhibits three distinct relaxation peaks, each of which is attributed to different water components, i.e., adsorbed water, pore water, and free water. As the pore size, air void ratio, and porosity increase, the compressive strength of A-FC decreases. The main reasons for the increased in strain in low-strength A-FC include compression at the bottom, internal stress dissipation through the pore structure, and changes in the failure mode. [ABSTRACT FROM AUTHOR]

This study explores the effect of nanosilica (NS) and ground granulated blast furnace slag (GGBFS) in varied quantities (0%–5% NS and 0%–25% GGBFS) on the postfire mechanical and endurance characteristics of concrete at temperatures ranging from 200°C to 1,000°C. To examine bonding performance and structural endurance, a full range of experimental evaluations was methodically carried out, including bond strength evaluations, rapid chloride permeability, chloride attack tests, and water penetration testing. Advanced methods like scanning electron microscopy and X-ray diffraction were used to examine the postfire internal structure. The combination of NS and GGBFS in concrete compositions resulted in noticeable improvements in mechanical resilience and endurance. This was evident by increased bond strength (a notable 12% rise with 4% NS and 20% GGBFS), decreased chloride permeation (a significant 26% drop), and decreased water penetration (about 20% reduction). Interestingly, this optimum concrete mix performed well even at high temperatures, with modest performance improvements at 200°C–400°C but apparent structural deterioration at greater temperature levels. Nonetheless, the composite concrete was demonstrated to perform well at higher temperatures in contrast with control samples. Further, this research develops a reliable correlation for forecasting concrete performance under high heat circumstances as well as providing essential insights critical for the precise design of concrete buildings in extreme situations. [ABSTRACT FROM AUTHOR]

In recent years, the recycling and reutilization of shield tunneling residues (STR) have received extensive attention in underground engineering. To optimize the method of resource utilization of STR, this paper introduces a replacement method of STR slurry. The STR are incorporated into concrete and prepared as STR concrete (STRC) using a coarse and fine aggregate shell production process. By optimizing the mixing method of STR slurry, we obtained the best mixing process, and studied the influence of STR dosage and water–binder ratio (w/b) on the compressive strength of STRC. The results revealed that the air-dried STR preliminarily crushed to about 15 mm can be used to prepare STRC by extending the mixing time of STR slurry. The compressive strength of the concrete significantly depends on the dosage of STR slurry. The strength decreases significantly with the increase of STR dosage, and the recommended dosage is about 10%. The influence of the w/b on compressive strength is similar to that of ordinary concrete. A predictive model for the compressive strength of STRC was established by analyzing the relationship between the dosage of STR, w/b , age, and the strength of STRC. [ABSTRACT FROM AUTHOR]

Digital fabrication of concrete structures has gained substantial research traction over the last decade, enabling efficient material use and adding more architectural freedom. Current research focuses on chemical and mineral admixtures, as well as manipulating the cement hydration reaction to control the yield stress evolution with time in the cement paste. Instead of providing yield stress through the concrete fluid properties, a high yield stress can be provided by interparticle friction from the use of high aggregate volumes and large nominal maximum aggregate size, with flow enhanced for material extrusion by vibration. Granular physics was applied to concrete mixture design to develop concrete mixtures with excellent edge retention abilities that flow easily under vibration. A linear regression analysis of concrete yield stress after vibration revealed that water content is most important, followed by fineness modulus of the aggregate combination and density after vibration. A decrease in water content, increase in fineness modulus and increase in density after vibration were found to increase the static yield stress after vibration. [ABSTRACT FROM AUTHOR]

As a result of firing pulverized coal in thermal power plants, enormous amounts of fly ash (FA) are produced as industrial waste. The release into the atmosphere and storage of this industrial waste remains one of the major environmental problems that threaten human health by contributing to air, water, and soil pollution. The recovery and reuse of FA in the construction industry is the only economic solution to the existing problem. In this study, the potential radiological risk caused by the usage of FA in concrete and cement production as a main component and its storage in landfill sites was evaluated for people and works by estimating radiological parameters (activity concentration and alpha index, annual effective doses, and the corresponding excess lifetime cancer risks) based on activity concentrations of terrestrial radionuclides in FA. Also, the radiological risk to the workers working in the FA landfill site was evaluated using the Residual Radioactivity Onsite 7.2 code. The average activity concentrations of terrestrial radionuclides in FA samples from the Tunçbilek lignite coal-fired thermal power plant at Kütahya province of Turkey were measured as 417, 156 and 454 Bq kg−1 for 226Ra, 232Th and 40K, respectively. When using up to 35% by mass of FA in cement and concrete, the average values of the radiological parameters revealed that they were within the recommended safety limits. However, code estimations showed that a regular worker in FA storage would be exposed to a total effective dose rate greater than 3 mSv y−1. [ABSTRACT FROM AUTHOR]

Backbone curves were generated from previous physical lab tests conducted on identical full-scale RC components utilizing different loading protocols (slab–beam–column and column specimens). These curves were subsequently compared with those prescribed in ASCE 41. It was observed that there was a substantial difference between the two, with ASCE 41 backbones (based on standard tests) showing significantly lower ductility capacity compared to backbones from tests using a loading pattern representative of earthquake demands, leading to a near-collapse condition. A four-story archetype RC building was analyzed to assess the influence of different backbones on its seismic response. The analysis revealed that using backbones representative of earthquake demands produced a median spectral capacity somewhere from 25% to 50% greater than that obtained using ASCE 41 upper bound backbones. Similarly, for drift capacities at incipient collapse, it was found that using backbones representative of earthquake demands resulted in a median capacity somewhere between 1.6 and 2.9 times that of using ASCE 41 upper bound backbones. These differences are significant, implying that ASCE 41 can be overly conservative by rejecting buildings that would otherwise be acceptable if ASCE 41 criteria were based on tests using protocols representative of earthquake demands. Examination of the time-history responses of the study building revealed that earthquake demands were predominantly characterized by relatively few large drift excursions having a one-direction bias. Standard protocols differ significantly from responses observed during actual earthquakes, as they feature numerous symmetrical fully reversed cycles of drifts with progressively increasing amplitudes that are much more demanding. This leads to overly conservative ASCE 41 criteria (too pessimistic). It is concluded that future component lab tests must include protocols representative of earthquake demands to achieve more accurate estimates of component behaviors. Use of such protocols will lead to more appropriate (less conservative) ASCE 41 building evaluations, aligning more consistently with the philosophy of performance-based earthquake engineering. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper was to prepare a ternary hierarchical rough particle to accelerate the anti-corrosive design for coastal concrete infrastructures. Design/methodology/approach: A kind of micro-nano hydrophobic ternary microparticles was fabricated from SiO2/halloysite nanotubes (HNTs) and recycled concrete powders (RCPs), which was then mixed with sodium silicate and silane to form an inorganic slurry. The slurry was further sprayed on the concrete surface to construct a superhydrophobic coating (SHC). Transmission electron microscopy and energy-dispersive X-ray spectroscopy mappings demonstrate that the nano-sized SiO2 has been grafted on the sub-micron HNTs and then further adhered to the surface of micro-sized RCP, forming a kind of superhydrophobic particles (SiO2/HNTs@RCP) featured of abundant micro-nano hierarchical structures. Findings: The SHC surface presents excellent superhydrophobicity with the water contact angle >156°. Electrochemical tests indicate that the corrosion rate of mild steel rebar in coated concrete reduces three-order magnitudes relative to the uncoated one in 3.5% NaCl solution. Water uptake and chloride ion (Cl-) diffusion tests show that the SHC exhibits high H2O and Cl- ions barrier properties thanks to the pore-sealing and water-repellence properties of SiO2/HNTs@RCP particles. Furthermore, the SHC possesses considerable mechanical durability and outstanding self-cleaning ability. Originality/value: SHC inhibits water uptake, Cl- diffusion and rebar corrosion of concrete, which will promote the sustainable application of concrete waste in anti-corrosive concrete projects. [ABSTRACT FROM AUTHOR]

This paper presents the mathematical derivation and numerical implementation of a novel regularized density-driven damage mechanics (D3M) model for simulating failure in concrete members. The novel idea behind the derivation of the approach is that damage is described as a function of the local change in material density. This choice is justified by the fact that the development of local damage directly corresponds to a reduction in local density since undamaged cementitious composites inherently have a higher density than the fluid or gas that occupies damaged regions. For this reason, devising numerical approaches that can predict the material behavior as a function of density could open up new possibilities for the prediction of the nonlinear behavior of concrete structures, as well as the derivation of novel testing procedures for the evaluation of strength by means of direct and indirect measures of density. In this context, a three-phase mesoscopic representation of concrete material is used, where coarse aggregate, mortar, and the interfacial transition zone are explicitly modeled to obtain a realistic representation of the material internal structure. The manuscript first presents the mathematical derivation of the model, with emphasis devoted to the regularization of the computational implementation. This paper then proceeds to demonstrate that the novel regularized D3M is insensitive to the mesh size chosen to represent the three material phases while also predicting realistic compression-to-tension strength ratios and damage patterns at failure. In addition, a parametric study is carried out to illustrate the effect of the relevant mechanical parameters on the observed response. Finally, the proposed model is validated by comparison with experimental results of 3-point bending tests on plain concrete beams of various sizes, also demonstrating that the regularized D3M is capable of predicting size effect in concrete members. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is a potential material for application as nano-reinforcements in cementitious composites owing to its high-water dispersibility, aspect ratio and outstanding mechanical characteristics. In this study, the combined effect of GO and fly ash on strength properties, stress–strain behaviour and static modulus of elasticity of high-strength concrete was investigated. In addition, microstructure has been characterized using SEM and EDS techniques. The addition of GO at 0.15% and the replacement of cement with fly ash at 10, 20 and 30% by weight was considered. The results exhibited that the addition of GO at 0.15% improved the compressive and flexural strength of concrete by 24.3 and 25.2%, respectively, at 7 days. The combined effect of GO and fly ash on the strength properties of concrete at 7 days was greater than control concrete demonstrating that GO can offset the effect of fly ash on delaying the strength growth at an early age. From the experimental results, it can be concluded that the addition of GO and fly ash into the concrete improved both the strength and elastic modulus, consequently exhibiting positive synergy in hybridizing GO and fly ash into the concrete. Also, the microstructure properties indicated that the GO and fly ash-based concrete mixes exhibited a denser microstructure. Furthermore, a nonlinear numerical model was also created for GO and fly ash-based concrete with finite element-based software ATENA-GiD to validate the experimental findings. The nonlinear numerical model successfully predicted the behaviour under monotonic axial compression and was quite beneficial in minimizing the tedious experimental testing. Finally, it is found that the findings of both the experimental and numerical investigations are in good agreement. [ABSTRACT FROM AUTHOR]

Spatially resolved capacitance-based stress self-sensing in unmodified concrete has been demonstrated. The spatial resolution is 45 mm in one dimension, which is in the direction of the capacitance measurement. Parallel coplanar component electrodes (aluminum, 5-mm wide), attached to the concrete using double-sided adhesive tape) separated by 45 mm are used to measure the in-plane capacitance in the direction perpendicular to the length of the electrodes. Combinations of component electrodes are electrically connected to form an electrode. The capacitance ranges from ∼200 pF to ∼750 pF. The greater is the number of component electrodes in an electrode, the higher is the capacitance. The compressive loading is applied at selected areas located between adjacent component electrodes. The stress (defined as load divided by the 300 ×300-mm2 concrete area) is up to 3000 Pa. The load decreases the capacitance monotonically and reversibly. The fractional decrease in capacitance ranges from ∼0.1 % to ∼0.5 %. More spatially concentrated loading, as for loading near the edges of the specimen, gives greater fractional decrease in capacitance. The capacitance decreases with increasing inter-electrode distance. Embedded steel rebars with a 20.0-mm concrete cover do not affect the capacitance or capacitance-based sensing. • Spatially resolved structural self-sensing of stress is reported. • It involves capacitance measurement, as shown for unmodified concrete. • Parallel coplanar component electrodes (aluminum strips) 45 mm apart are used. • Component electrodes are electrically connected to form a composite electrode. • The compressive stress reduces the capacitance reversibly and monotonically. [ABSTRACT FROM AUTHOR]

The magnetite ore was taken as the partial aggregate to prepare two types of concrete specimens mixed with magnetite and without magnetite. Both were cured in water and 5 wt % Na2SO4 solution at 20 and 80°C, respectively, to study the influence on the strength of concrete. In addition, the magnetite ore was ground into powder, and cured in simulated concrete pore solution and 5 wt % Na2SO4 solution respectively, and the mineral and morphological change at different ages was tested by X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). The experimental results show that the strength of concrete with magnetite ore is a little higher than that of concrete without magnetite ore whether cured in water or in Na2SO4 solution, and the magnetite transforms into Fe2O3, ferrihydrite and other minerals in simulated concrete pore solution and in 5 wt % Na2SO4 solution. The experimental results also demonstrate that using some magnetite ore as aggregate for concrete is beneficial for improving the sulfate resistance of concrete. [ABSTRACT FROM AUTHOR]

The blast resistance of a typical two-lane steel girder highway bridge structural system was modeled using a nonlinear finite-element approach that considered material damage, fracture, and separation. Critical blast scenarios were based on field observations of terrorist attacks on bridges in Iraq, while system failure was defined in terms of practical emergency serviceability criteria used on actual blast-damaged bridges. The blast resistance of various design parameters was assessed, including the number of girders, deck concrete strength, reinforcement ratio, slab thickness, girder and reinforcement yield strength, girder sectional dimensions, and pier column width. The presented approach uniquely quantifies structural system blast resistance in terms of the charge weight that can be applied at different locations until failure. A sensitivity analysis was conducted to determine the most influential design parameters. It was found that system blast capacity was primarily influenced by the number of girders and girder yield strength, while additional significant parameters were deck compressive strength, deck thickness, web stiffener width, and girder depth. Secondary parameters were deck reinforcement ratio, girder flange, and web thickness, while deck reinforcement yield stress was found to be insignificant. Based on the results, recommendations for improving blast resistance are provided. [ABSTRACT FROM AUTHOR]

Despite their undeniable potential for promoting sustainability in construction materials, the characteristics of recycled aggregates (RCA), seawater, and sea sand may vary significantly, thereby affecting their use in structural concrete. This study exploits these materials to investigate their performance in producing sustainable concrete and establishing its mechanical and fracture behavior. The so produced material, referred to as seawater sea sand recycled aggregate concrete (SSRAC) could lend a hand in widening the usage of RCA and sea sand in a variety of applications where the use of ever-depleting natural materials as concrete constituents becomes an issue. Consequently, the variables of the study include the type of water (fresh versus seawater), type of coarse aggregate (RCA versus natural coarse aggregate, NCA), and the type of fine aggregate (dune sand versus sea sand). For each water type, three concrete mixtures are produced using NCA-dune sand, RCA-dune sand, and RCA-sea sand combinations. Analyses of the mechanical characteristics of the concrete, including compressive strength, flexural strength, modulus of elasticity, and fracture toughness, were conducted based on experimental tests. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were also conducted on the designed specimens to investigate their microstructure. In terms of fracture characteristics, the use of seawater resulted in improvement in the fracture toughness. The use of recycled aggregate along with seawater resulted in improved compressive strength. However, natural aggregate concrete (NAC) showed higher flexural strengths than recycled aggregate concrete (RAC). The results also revealed that the addition of sea sand had a detrimental impact on all mechanical characteristics. Thus, optimizing the concrete composition in which the investigated materials partially replace the conventional concrete constituents is required in order to consider alternative constituents to generate sustainable concrete for practical applications. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is not widely used in construction because of the concerns related to its quality. This paper investigates the effect of the replacement levels of recycled concrete aggregate (RCA) on bulk and hardened densities of RAC. The analysis of variance (ANOVA) was used to investigate the sensitivity of bulk and hardened densities of concrete to the replacement level of RCA. Predictive equations were developed to estimate the 3-day, 7-day, and 28-day compressive strength of RAC from its fresh properties, which are helpful for early quality control inspection of RAC. Furthermore, a predictive equation has been proposed to determine the flexural strength of RAC based on its 28-day compressive strength. The comparison of the predictive capability of the proposed and widely used code equations showed the incapability of the latter to estimate the flexural strength of RAC. In contrast, the proposed equation demonstrated a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

In this study, the pore structure and gas permeability of river sand concrete and manufactured sand concrete (mixed with various stone powders) are examined under dry and wet conditions. First, the pore structure of concrete was tested using the mercury-in-pressure (MIP), hydrostatic balance (HB), and nuclear magnetic resonance (NMR) methods. Second, the gas permeability of concrete was measured using the quasi-stationary flow method. Finally, a numerical model was developed based on the relationship between the pore structure and gas permeability. The results indicated that the gas permeability of dry concrete has a quadratic linear relationship with the porosity and volumetric characteristic pore size. The pore structure of partially water-saturated concrete can be corrected using a correction factor and the relaxation rate of the dry material. Finally, a random hierarchical bundle model using the HB–NMR method is proposed. The maximum relative deviation between the predicted and experimental values is 48.28%. [ABSTRACT FROM AUTHOR]

The quality of the air void system is essential for the frost resistance of concrete. Therefore, it is crucial to assess the quality of the air void system in hardened concrete in an appropriate way. In this study, the shape from focus (SFF) method is applied to identify the focused image of each point on the polished surface of hardened concrete and thereby acquire the depth information of the entire surface. The performance of various focus measure operators and window sizes is evaluated. Thereafter, the selected focus measure operator and window size are applied for the SFF analysis of all samples. Based on the obtained depth map, the voids are identified, and the void parameters of the hardened concrete are determined by an automated procedure. The main advantage of the SFF method is that it is possible to carry out an automated air void analysis without contrast enhancement. [ABSTRACT FROM AUTHOR]

This paper presents an innovative method to include creep deformations in the prediction of time to corrosion-induced cover cracking. Using experimental results, creep and cracking criteria used in this method are verified. It is argued in the paper that the cover cracking problem under corrosion is close to a relaxation problem and the conventional creep formulations based on the effective elastic modulus cannot be adopted. It is found in the paper that accurate consideration of creep deformation would lead to about 30–40% longer time to cover cracking when compared to no consideration of creep deformations whilst for the currently practiced methods, the time can be up to 200% longer, which is unconservative in predicting time to cover cracking. Results in this paper open the debate on modelling of creep in the analysis of corrosion-affected structures and serve as an important step towards the accurate prediction of corrosion-induced concrete cracking. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the mechanical characteristics of steel-reinforced reactive powder concrete (SRRPC) columns with different geometrical dimensions after high-temperature treatment. The bearing capacity, axial stiffness, and ductility of 35 SRRPC column specimens after high-temperature treatment are investigated, considering two parameters: concrete cover thickness (30–100 mm) and slenderness ratio (3–50). The findings indicate that (1) the ultimate bearing capacity increases by 26.0–135.7% as the concrete cover thickness increases and decreases by 1.5–92.0% as the slenderness ratio increases. (2) The axial stiffness increases by 18.9–92.5% as the concrete cover thickness increases and sharply decreases by 31.9–92.6% as slenderness ratio increases, and change degree decreases. (3) As concrete cover thickness and slenderness ratio increase, the displacement ductility coefficient declines, and degree of decrease in displacement ductility coefficient becomes progressively smaller. (4) The bearing capacity, stiffness, and ductility are extremely sensitive to concrete cover thickness, followed by slenderness ratio. Considering confining effect of stirrups and section steel on concrete in the core area, methods for calculating bearing capacity after high-temperature treatment are proposed. From the perspectives of preventing buckling instability and cracking of components after high temperature, two methods for determining the critical concrete cover thickness are given. Finally, the calculation formula of the stability coefficient corresponding to various slenderness ratios after high-temperature exposure is provided, which provides a reference for postfire evaluation and reinforcement of SRRPC structure. [ABSTRACT FROM AUTHOR]

In this study, the effect of nano-CaCO3 on the durability of concrete was investigated by simulating the attack of semi-buried concrete structures in saline soil. Different nano-CaCO3 contents were used to enhance the durability of concrete. The durability of different areas of nano-CaCO3 modified concrete, partially exposed to sulfate solution, was evaluated, and a reliability analysis was conducted. The results indicated that appropriate nano-CaCO3 content can improve the durability of concrete. In this study, concrete with a nano-CaCO3 content of 1% exhibited the highest durability. The corrosion degrees of different areas of the nano-CaCO3 modified concrete partially exposed to the sulfate solution decreased in the following order: dry–wet transition areas (M area) > fully immersed areas (D area) > exposed air areas (T area). A sulfate chemical attack occurred inside the concrete in the dry–wet transition areas, while a sulfate physical attack occurred on the surface concrete. The predicted values of the model agreed well with the test results. The bivariate Wiener process can effectively describe the whole process of performance deterioration of nano-CaCO3 modified concrete. [ABSTRACT FROM AUTHOR]

This study focuses on the essential task of monitoring the strength of structural concrete in construction and rehabilitation projects. The conventional non-destructive testing (NDT) approach offers an indirect estimation of concrete compressive strength. However, the existing models lack the ability to address the estimation of compressive strength in concrete mixtures containing bottom ash (BA) and recycled coarse aggregate (RCA). This study aims to bridge this gap by accurately estimating the compressive strength of such concrete using the ultrasonic pulse velocity (UPV) technique. To achieve this objective, various concrete specimens with different cement content, water–cement ratios (w/c), recycled coarse aggregate, and bottom ash contents through weight batching, were prepared. UPV and compressive strength measurements were taken on cylindrical concrete specimens after 28 and 90 days of curing. The analysis revealed an exponential relationship between the compressive strength and UPV, with a high correlation coefficient across the evaluated concrete mixes, independent of the curing time. Ultimately, two robust models were developed to predict the compressive strength of concrete mixes containing different percentages of RCA and BA, respectively, at 28 and 90 days of curing. These models offer valuable insights and practical tools for ensuring the structural integrity of concrete in construction and rehabilitation projects involving bottom ash and recycled coarse aggregate. [ABSTRACT FROM AUTHOR]

Concrete is the most commonly used construction material. However, its production leads to high carbon dioxide (CO2) emissions and energy consumption. Therefore, developing waste-substitutable concrete components is necessary. Improving the sustainability and greenness of concrete is the focus of this research. In this regard, 899 data points were collected from existing studies where cement, slag, fly ash, superplasticizer, coarse aggregate, and fine aggregate were considered potential influential factors. The complex relationship between influential factors and concrete compressive strength makes the prediction and estimation of compressive strength difficult. Instead of the traditional compressive strength test, this study combines five novel metaheuristic algorithms with extreme gradient boosting (XGB) to predict the compressive strength of green concrete based on fly ash and blast furnace slag. The intelligent prediction models were assessed using the root mean square error (RMSE), coefficient of determination (R2), mean absolute error (MAE), and variance accounted for (VAF). The results indicated that the squirrel search algorithm-extreme gradient boosting (SSA-XGB) yielded the best overall prediction performance with R2 values of 0.9930 and 0.9576, VAF values of 99.30 and 95.79, MAE values of 0.52 and 2.50, RMSE of 1.34 and 3.31 for the training and testing sets, respectively. The remaining five prediction methods yield promising results. Therefore, the developed hybrid XGB model can be introduced as an accurate and fast technique for the performance prediction of green concrete. Finally, the developed SSA-XGB considered the effects of all the input factors on the compressive strength. The ability of the model to predict the performance of concrete with unknown proportions can play a significant role in accelerating the development and application of sustainable concrete and furthering a sustainable economy. [ABSTRACT FROM AUTHOR]

Freeze–thaw damage gradients lead to non-uniform degradation of concrete mechanical properties at different depths. A study was conducted on the stress–strain relationship of stressed concrete with focus on the freeze–thaw damage gradient. The effects of relative freeze–thaw depths, number of freeze–thaw cycles (FTCs) and stress ratios on the stress–strain curves of concrete were analyzed. The test results demonstrated that freeze–thaw damage was more severe in the surface layers of concrete than in the deeper layers. The relative peak stress and strain of concrete degraded bilinearly with increasing depth. The stress–strain relationship of stressed concrete under FTC was established, and it was found to agree with the experimental results. [ABSTRACT FROM AUTHOR]

Due to the low water-cement ratio of ultra-high-performance concrete (UHPC), fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete. In this study, the effects of different types of cementitious materials, chemical shrinkage-reducing agents (SRA) and steel fiber (SF) were assessed. Compared with M2-UHPC and M3-UHPC, M1-UHPC was found to have better fluidity and shrinkage cracking performance. Moreover, different SRA incorporation methods, dosage and different SF types and aspect ratios were implemented. The incorporation of SRA and SF led to a decrease in the fluidity of UHPC. SRA internal content of 1% (NSRA-1%), SRA external content of 1% (WSRA-1%), STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%, 8.3%, 9.2% and 25%, respectively. However, SRA and SF improved the UHPC shrinkage cracking performance. NSRA-1% and STE-0.7 reduced the shrinkage value of UHPC by 40% and 60%, respectively, and increased the crack resistance by 338% and 175%, respectively. In addition, the addition of SF was observed to make the microstructure of UHPC more compact, and the compressive strength and flexural strength of 28 d were increased by 26.9% and 19.9%, respectively. [ABSTRACT FROM AUTHOR]

Using ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) in profiled slabs, as opposed to normal strength concrete without fibers, has been shown experimentally to significantly increase both the bond between the profiled sheet and the concrete, and the tensile forces across cracked concrete. The consequence of these fiber benefits is to substantially increase the flexural rigidity leading to reduced deflections and also to substantially reduced crack widths leading to improved behavior under serviceability loads and to improved durability. To quantify these benefits so that they can be used in design, a rational partial‐interaction numerical model has been developed that can incorporate the material properties of any type of UHPFRC including time‐effects. This modeling should help in the development of simplified design rules for specific fiber types. [ABSTRACT FROM AUTHOR]

AbstractThe corrosion of concrete and environmental pollution have become major challenges for the conventional concrete used in sea beds. Comprehensive research work has been carried out to enhance the strength and effectiveness of artificial reef (AR) concrete, because of its significant benefits for the sea coastlines to enhance algae growth, fish assembly, rehabilitation, and soil erosion. An experimental investigation of the compressive strength, water absorption, flexural, split tensile strength, and sorptivity of concrete specimens used for artificial reefs concrete immersed in seawater is presented here. Natural recycled materials used in this research work includes fly ash, seashells, rice-husked ash, silica fumes, granite powder, paper pulp, and coconut fiber. To investigate the corrosion behaviors of concrete based on the M20 standard, experiments were conducted using different proportions of raw materials. Concrete strength was observed on different days (7, 14, 28, 56, and 90) and the results showed that artificial reef concrete is stronger than conventional concrete. Moreover, the strength of concrete is increased by 3% due to the addition of 5% of silica fume and granite powder. It also shows that the attack of sulfate in the concrete decreases gradually by the addition of rice husk ash and silica fume. In addition to other recycled biodegradable materials like AR2, AR3, and AR4 have flexural strengths such as 1.90%, 4.08%, and 5.07% which is higher than the conventional concrete, respectively. These approaches were eco-friendly to the ocean, because of the application of silica fumes and flyash and it does not create any type of crack in the reef. It is cost-effective and environmentally favorable. The splitting tensile strength of the traditional mixer after 28 days is measured in 2.94 MPa, which was found to be 2.11%, 4.79%, 4.68%, 23.81%, and 28.78% and it is higher than the values observed in the other specimens. [ABSTRACT FROM AUTHOR]

This research is focused on the development of an eco-friendly low-cost concrete using fly ash (FA) and marble powder waste (MPW) as partial replacements for cement and fine aggregate respectively. The substantial use of cement in concrete makes it expensive and contributes to global warming due to high carbon emissions. Thus, using such waste materials can help reduce the overall carbon footprint. For this purpose, various mix designs of concrete were developed by varying the percentages of FA and MPW. The concrete's fresh and hardened properties were experimentally determined for those mixes. The test results revealed that MPW as a sand substitute increases strength up to 40% and gradually decreases beyond that, but a 60% replacement still has more strength than the control specimen. Similarly, using FA as a cement replacement was found to reduce the strength, but the reduction was not very significant up to 20%. A mixed blend of FA and MPW showed superior results and maximum strength was obtained at F10M40. The optimal mix, with 10% FA and 40% MPW (F10M40), achieved a compressive strength of 4493.46 psi, a 16.21% improvement compared to the control mix proportion. Furthermore, the microstructure of the cementitious material was improved due to the pozzolanic reaction that led to a denser microstructure, as supported by the permeability test and SEM analysis. [ABSTRACT FROM AUTHOR]

This paper explores the creation, development, and dissemination of prefabricated concrete rural houses in Jiangsu Province in East China from 1961 to the 1980s, an example of the technological transition provoked by the depletion of forest and timber in China. Through archival research, fieldwork and interviews, the paper examines the two waves of design and dissemination of prefabricated concrete rural houses between 1961 and 1965 and their subsequent 'vernacularisation' in the 1970s and the 1980s. This research provides a twofold insight into the current scholarly debates surrounding built heritage and global climate change. On one hand, it addresses a historical context of concrete overuse in contemporary China, a matter of critical importance in relation to carbon emissions and global climate change. On the other hand, it offers a counter-argument to today's call for reintroducing timber structures in many places, as evidenced by the case of East China, where the widespread use of materials like concrete was primarily a consequence of the ecological crisis following decades of deforestation and timber resource depletion. In addition, the 'vernacularisation' of concrete structures manifested by this case still provides lessons for today's efforts to popularise more eco-friendly construction materials and technologies, especially in rural areas, and the prefabricated concrete houses possess potential heritage values as trackers of ecological changes. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymers (FRP) for structural elements' strengthening and rehabilitation are increasingly gaining popularity because of their proven efficiency and ease of application. The response of the adhesive joint formed between the FRP and concrete is a crucial factor influencing the overall behavior of FRP structures. The analysis of the interface crack propagation is a complex task involving the consideration of multiple interacting mechanisms. This work aims to provide a background to a recently proposed model that analyzes the behavior of the adhesive joint formed at the interface between the FRP and concrete, by creating its counterpart. The study presented herein discusses a model based on fracture mechanics to obtain a reference point needed to assess the output provided by an algorithm utilizing a damage-based model for concrete and an empirical-based procedure for the loss of bond action. Typically, model validation is performed via a comparison against experimental data. However, additional insights into the interacting phenomena can be provided by comparing the results of various applicable models. [ABSTRACT FROM AUTHOR]

Concrete compressive strength testing is crucial for construction quality control. The traditional methods are both time-consuming and labor-intensive, while machine learning has been proven effective in predicting the compressive strength of concrete. However, current machine learning-based algorithms lack a thorough comparison among various models, and researchers have yet to identify the optimal predictor for concrete compressive strength. In this study, we developed 12 distinct machine learning-based regressors to conduct a thorough comparison and to identify the optimal model. To study the correlation between compressive strength and various factors, we conducted a comprehensive analysis and selected blast furnace slag, superplasticizer, age, cement, and water as the optimized factor subset. Based on this foundation, grid search and fivefold cross-validation were employed to establish the hyperparameters for each model. The results indicate that the Deepforest-based model demonstrates superior performance compared to the 12 models. For a more comprehensive evaluation of the model's performance, we compared its performance with state-of-the-art models using the same independent testing dataset. The results demonstrate that our model achieving the highest performance (R2 of 0.91), indicating its accurate prediction capability for concrete compressive strength. [ABSTRACT FROM AUTHOR]

The microstructure of concrete can be affected by many factors, from non-destructive environmental factors through to destructive damage induced by transient stresses. Coda wave interferometry is a technique that is sensitive enough to detect weak changes within concrete by evaluating the ultrasonic signal perturbation compared to a reference state. As concrete microstructure is sensitive to many factors, it is important to separate their contributions to the observables. In this study, we characterize the relationships between the concrete elastic and inelastic properties, and temperature and relative humidity. We confirm previous theoretical studies that found a linear relationship between temperature changes and velocity variation of the ultrasonic waves for a given concrete mix, and provide scaling factors per Kelvin for multiple settings. We also confirm an anti-correlation with relative humidity using long-term conditioning. Furthermore, we explore beyond the existing studies to establish the relationship linking humidity and temperature changes to ultrasonic wave attenuation. [ABSTRACT FROM AUTHOR]

Sand is frequently used as a fine aggregate in concrete mixtures, but the performance of concrete can be considerably impacted by regional variations in sand gradation. In this work, the effect of sand gradations on the fresh properties of three-dimensionally printable concrete (3DPC) mixtures was systematically investigated. The binder combinations (cement, fly ash, silica fume, limestone powder, ground granulated blast-furnace slag) and the water/binder ratio were kept constant throughout the trials. The sands used in the mixtures were standard Ennore sand (ES) (grades I, II and III) and locally available river sand (RS). The mini-slump heights and flow values of mixes made with RS and with optimal packing of binary and ternary combinations of the standard ESs were evaluated and compared with those of the unary packing of ESs and RS. A correlation between the fineness modulus of different sand gradations and printable flow time was determined. The influence of sand gradations and fineness modulus on buildability, shape retention, open time and extrudability were evaluated. It was found that the performance of the fresh 3DPC was influenced by the aggregate's gradation and grain size in addition to its fineness. In conclusion, different fine aggregate specifications must be chosen depending on the various 3D printing building conditions and design requirements. [ABSTRACT FROM AUTHOR]