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The strength and durability properties of the recycled aggregate concrete (RAC) have been affected by the cracks and the weak interfacial transition zone (ITZ) of the recycled coarse aggregates (RCA). However, the mechanical and physical features of RCA can be improved by microbially induced calcite precipitation (MICP). Therefore, immobilization techniques were used to protect and maintain the high efficiency of Bacillus bacteria for the formation and precipitation of calcium carbonates in self‐healing concrete over a period of time. The objective of the present study was to show the viability of the immobilized bacterial consortium‐enhanced RCA to form self‐healing cracks. Further, the self‐healing capability of enhanced RCA was investigated along with two other immobilization methods, that is, RCA and hydrated lime and brick powder (HBr)‐immobilized bacteria. The experimental results show that the increase in the bio‐deposition time improved the physical and mechanical properties of the RCA. Further, subsequently 56 days of the healing incubation period, the immobilized consortium‐enhanced RCA concrete specimens completely healed the cracks of width 0.58 mm. However, the equivalent cracks of width 0.56 mm were also recovered by the HBr immobilized bacterial cultures. Furthermore, the field emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) and X‐ray diffraction (XRD) analysis revealed that the existence of precipitation at the crack surface was calcium carbonate with a regular cubic‐shaped and lamellar layer morphology. The outcomes of the current study show that consortium‐enhanced RCA has promising potential to develop self‐healing concrete with self‐repaired and improved durability properties in the concrete construction field. [ABSTRACT FROM AUTHOR]

The utilization of recycled aggregate concrete (RAC) within the construction sector has the potential to prevent irreversible harm to the environment and reduce the depletion of natural resources. Nonetheless, it is essential to scrutinize the quality of RAC before utilizing it in practical applications. RAC's most significant design parameter is its elastic modulus, typically determined through time‐consuming and costly experiments. Machine learning (ML) techniques can be a feasible solution to reduce the number of experiments required and obtain accurate estimates. This article employs two robust ML techniques, namely Xtreme Gradient Boosting (XGB) and Adaptive Boosting regression, in three distinct modes, namely individual, hybrid, and ensemble‐hybrid methods. Furthermore, phasor particle swarm optimization (PPSO) and chaos game optimization (CGO) have been utilized in hybrid and ensemble‐hybrid modes to optimize final results, minimize errors, and obtain highly precise outcomes. As mentioned earlier, several evaluators were employed to identify the most appropriate model to compare the modes. The findings suggest that the relevant optimizers significantly contributed to achieving superior metric values. Specifically, the results indicated that PPSO exhibited greater efficacy than CGO in optimizing outputs and enhancing accuracy. The hybrid models, particularly XGB in conjunction with PPSO, yielded the most favorable correlation coefficient and root mean square error values equal to 0.996 and 0.336 and can serve as an effective ML method to determine elastic modulus of recycle aggregate concrete for time and energy storage. [ABSTRACT FROM AUTHOR]

The utilization of recycled aggregates (RA) in producing novel concrete can contribute to the resilience of the building sector. However, it is important to thoroughly evaluate the mechanical properties of this variety of aggregate before incorporating it into various applications. This study used Gaussian process regression (GPR) and Decision Tree (RT) to estimate the ERAC because the current equations for the modulus of elasticity of concrete may not apply to recycled aggregate concrete (RAC) concrete. On the other hand, the Dwarf mongoose optimizer (DMO) and Phasor particle swarm optimizer (PPSO) were combined with related models. They formed hybrid models to improve the accuracy of developed models. In this study, the hybrid models were evaluated and compared in three phases, which 70% of the samples for training, 15% for validation, and the remaining 15% for testing phase. In addition, several statistical evaluation metrics were employed to assess the precision and effectiveness of the established models. The performance of the models was compared with error metrics and coefficient correlation to obtain a suitable model. The results generally indicate that the PPSO algorithm showed a more acceptable performance than other algorithms coupled with models. In general, GPR‐PPSO can obtain R2=0.995 and RMSE=0.423 with 0.62% and 32% difference than RT‐PPSO. [ABSTRACT FROM AUTHOR]

The quantity of recycled concrete aggregates is increasing day by day due to the enhanced demolition rate of old infrastructures, which is dangerous to the environment's sustainability. Therefore, it is essential to handle these recycled aggregates for sustainable development. Furthermore, due to the low compressive strength (COS) of recycled aggregate concrete (RAC), it has always remained an active research area to ameliorate the mechanical performance of such concrete by either adding fibers and/or laterally confining with carbon fiber reinforced polymer (carbon‐FRP) wraps. The main objective of the current investigation is to improve the strength of hybrid fiber‐reinforced recycled aggregate concrete (HFRAC) transversely wrapped with carbon‐FRP wraps. The axial COS, axial strain, and compressive stress–strain graphs of the tested samples were assessed by manufacturing a total sum of 18 cylindrical samples wrapped with either one or two carbon‐FRP wraps. Two different grades of HFRAC were fabricated that is, 15 and 20 MPa containing hybrid fibers (steel and polypropylene fibers). The results showed that the transverse wrapping effectively ameliorated the axial strain, COS, and axial stiffness of HFRAC samples. By using a single layer of carbon‐FRP wraps, an enhancement of 115.7% was observed while using two layers of carbon‐FRP wraps, an enhancement of 130.7% was observed in the COS of 15 MPa group HFRAC samples. Similarly, by using a single layer of carbon‐FRP wraps, an enhancement of 37.4% occurred while using two layers of carbon‐FRP wraps, an enhancement of 112.6% occurred in the COS of 20 MPa group HFRAC samples. Hence, the lateral wrapping of low‐strength HFRAC is more efficient than the high‐strength HFRAC. A theoretical investigation based on the analysis of 11 different models was also performed to predict the COS of carbon‐FRP‐wrapped HFRAC samples. [ABSTRACT FROM AUTHOR]

To investigate the mechanical properties of polypropylene fiber recycled aggregate concrete (PPFRAC) under compression‐shear, 69 recycled aggregate concrete (RAC) specimens were tested with the parameters of polypropylene (PP) fiber volume content (0, 0.6, 0.9, and 1.2 kg/m3), recycled coarse aggregate (RCA) replacement rate (0%, 30%, 50%, 70%, and 100%), and normal stress (0, 3, and 6 MPa). In the tests, the failure pattern of the specimens was observed, and the effects of the polypropylene fiber content on the direct shear stress, compression‐shear stress, initial shear stiffness, and shear ductility coefficient of the PPFRAC were thoroughly investigated. The results show that as the polypropylene fiber content increases, the direct shear stress of concrete (Natural aggregate concrete and 100% recycled coarse aggregate concrete [100%RCA]) first increases and then decreases gradually. Meanwhile, the best PP fiber content is 0.9 kg/m3 in this study. Furthermore, the compression‐shear stress‐displacement curves of specimens were obtained. The compression‐shear strength under normal stress at 6 MPa is approximately 230% greater than at 0 MPa. However, the peak shear stress of concrete is almost not affected by the replacement rate of RCA. Finally, based on the Mohr circle theory, the compression‐shear calculation model of PPFRAC is verified, and the optimal calculation formula is given. [ABSTRACT FROM AUTHOR]

Raw coal gangue (RCG) as one of the solid wastes can result in serious ecological and environmental pollution. Utilization of RCG as coarse aggregates in concrete can mitigate the demand for natural aggregates in engineering construction to a certain extent. This study aims to assess the impact of utilizing raw coal gangue aggregates (RCGAs) on the mechanical behaviors and compressive stress–strain responses of concrete. For this purpose, a total of 90 concrete specimens were prepared, varying in RCGA replacement ratios of 0, 30%, 50%, 70%, and 100% and water‐to‐cement (w/c) ratios of 0.37 and 0.47. The slump, compressive and splitting tensile strengths in cubes, and complete compressive stress–strain curves of RCGA concrete were obtained and discussed. Results indicated that as RCGA was incorporated, the peak stress and elastic modulus of concretes with 0.37 and 0.47 w/c ratios decreased by 26%–51% and 23%–57%, respectively. In addition, the crack development and microstructural characteristics of RCGA concrete were analyzed by digital image correlation and scanning electron microscopy (SEM), respectively. The SEM analysis indicated that the interface transition zone between RCGAs and mortar was relatively thick and loose compared to that between coarse natural aggregates and mortar, indicating the poor mechanical properties of RCGA concrete. Finally, based on the test data, a normalized stress–strain model for RCGA concrete was proposed, taking into account the influence of RCGA replacement. [ABSTRACT FROM AUTHOR]

Concrete constructed using recycled aggregates in place of natural aggregates is an efficient approach to increase the construction sector's sustainability. To improve recycled aggregate concrete (RAC) technologies in permafrost, it is essential to certify the stability in frost‐induced conditions. The main goal of this study was to use support vector regression (SVR) methods to forecast the frost durability (DF) of RAC on the basis of durability agent value in cold climates. Herein, three optimization methods called Ant lion optimization (ALO), Grey wolf optimization (GWO), and Henry Gas Solubility Optimization (HGSO) were employed for indicating optimal values of SVR key parameters. The results depicted that all developed models have capability in predicting the DF of RAC in cold regions. The values of OBJ as a comprehensive index depicted that the GWO−SVR model has the higher value at 0.0571 as the weakest model, then ALO−SVR at 0.0312 recognized as the second‐highest model, and finally the HGSO−SVR system at 0.0224 mentioned as outperformed model. ALO−SVR and GWO−SVR approaches were likewise capable of accurately forecasting the DF of RAC in cold regions, but the created HGSO−SVR method outperformed them all when taking into account the explanations and justifications. [ABSTRACT FROM AUTHOR]

The goal of this study is to propose a robust method for the analysis and design of recycled aggregate reinforced concrete (RAC) beams. For this purpose, a machine‐learning framework, named, GA‐XGBoost was designed. A comprehensive dataset of 276 tests of RAC beams was compiled from available literature for training, validating, and testing the models. The results confirmed that the proposed models can offer a precise tool for failure mode classification and capacity prediction of RAC beams. For the design framework, a Generative Adversarial Network for tabular data was utilized to produce synthetic data. These synthetic data can provide options for the selection of design variables. In this framework, the design variables are selected by specifying the design constraints, the objective function to be optimized, and validating the capacity requirements using the developed GA‐XGBoost models. Lastly, a web application was developed to make the proposed GA‐XGBoost models appropriate for practical design. [ABSTRACT FROM AUTHOR]

Fibers are mixed within reinforced high‐strength recycled aggregate concrete (RHRAC) beams to improve their flexural performance. This study experimentally and analytically investigates the effect of using RAC combined with polyvinyl alcohol fiber (PVAF) and steel fiber (SF) on the flexural performance of RHRAC beams. A total of 11 RHRAC beams (150 × 300 × 2600 mm3) are manufactured and subject to four‐point flexural testing. The parameters of the concrete are investigated, including the volume content of the PVAF and SF. The experimental results show that SF increases the flexural strength of RHRAC beams more than PVAF does. Conversely, the effect of PVAF on deformability is more significant than that of SF. In addition, the positive influences of hybrid fiber (PVAF and SF) on the crack load, flexural capacity, and deformation capacity are superior to those of single‐mixed PVAF or SF. Three different specifications are used to calculate the flexural capacity of the test beams, among which, JGJ/T465‐2019 is the most reliable. [ABSTRACT FROM AUTHOR]

This paper investigates the post‐cracking behavior of glass fiber‐reinforced recycled concrete (FR‐RAC). This was done on eight fiber‐reinforced concrete (FRC) mixtures, with three types of recycled aggregates (RAs), while the used fibers were the CEM‐FIL Minibars™ with a fiber content of 0.50 and 0.75 V%. Based on those investigated mixtures, it was found that the proposed constitutive tensile model of the fib Model Code 2010 and the model of di Prisco overestimate the measured load–CMOD curves. Therefore, the post‐cracking branch of the constitutive tensile model was numerically optimized. This was done by optimizing the ka and kc value in the simplified model (Equations 16 and 17), proposed by Vandevyvere and based on the model of di Prisco. The ka value relates to the tensile strength at serviceability limit state, while the factor kc relates to the tensile strength at ultimate limit state (ULS). The numerically optimized ka and kc value, abbreviated by ka' and kc', indicates a lower ka' value and a higher kc' value than the model of di Prisco et al. In addition, the extensive test data in this study show an increased post‐cracking behavior for the 0.75 V% mixtures with RAs. However, the ka' and kc' values are 0.325 and 0.710 for NAC‐0.75 V%, and only slightly different ka' and kc' values are obtained for the FR‐RAC mixtures. Therefore, one unified constitutive tensile model is proposed for all FRC mixtures. In addition, the numerically optimized model indicates a lower neutral axis location as well as a higher maximum tensile strain (εct,max) and compressive strain (εc,max) for the recycled concrete mixtures. The εc,max value at CMOD3 is 0.074‰ for NAC‐0.75 V%, while the nRAC‐0.75 V% mixture indicates a value of 0.100‰. This explains the improved fiber activation of the fiber‐reinforced recycled concrete mixtures (with 0.75 V% glass fibers). [ABSTRACT FROM AUTHOR]

This study aims to develop a new artificial intelligence model that can produce explainable rules to predict the mix design and early‐age concrete compressive strength classes of recycled aggregate concrete (RAC). Unlike other black‐box machine learning methods and rule‐based algorithms, the study relies on a metaheuristic mechanism for explainability. This metaheuristic mechanism is not used for a traditional parameter optimization, but to automatically extract interpretable and interpretable rules from the experimental data. In the study, 30 series of RACs are produced, and the samples' 1‐ and 3‐day early‐age concrete compressive strength values are determined. Concretes produced using these strength values are classified. The labels defined for each concrete class are Class A (C 8/10), Class B (C 12/15), Class C (C 16/20), and Class D (C 20/25). The proposed intelligent classification model that consists of rule set automatically produces interpretable and comprehensible rules from data to determine the early‐age concrete compressive strength class and RAC mix amounts. In addition, the proposed method eliminates the black‐box disadvantages of classical machine learning methods with its explainability and interpretability feature. The sunflower optimization algorithm is adapted as the metaheuristic mechanism and a special fitness function and representative solution form are developed for automatic extraction of high‐quality comprehensible rules by simultaneously optimizing many different metrics. This paper is the first interpretable and comprehensible artificial intelligence model attempt used for early‐age compressive strength classification and mixture design of recycled aggregate concrete by balancing and optimizing both the accuracy and explainability. Proposed explainable intelligent classification model is tested against both well‐known state‐of‐the‐art machine learning algorithms and standard rule‐based methods on the produced real data. Promising results in terms of accuracy, precision, recall are obtained along with the explainability feature. [ABSTRACT FROM AUTHOR]

As a sustainable concrete material, hemp and recycled aggregate concrete (HRAC) is produced by partial replacement of natural coarse aggregates (NCA) with recycled concrete coarse aggregates (RCA) and industrial hemp fibers. The objective of the reported research was to investigate the structural performance of reinforced concrete beams prepared with HRAC and designed to fail in flexure, shear, or bond splitting modes of failure, and to compare that performance with companion control beams cast with conventional concrete. The significance stems for the fact that no previous research is reported on mixtures using such a combination of hemp fibers and RCA. Test results indicated that HRAC beams with 0.75% volumetric percentage hemp fibers and 50% RCA replacement had comparable peak load capacities to the control beams with no RCA and no fibers, with ±4% difference for all tested modes of failure. Additionally, the fracture energy of the HRAC beam was higher than the control beam by 3.6%, 17.9%, and 14.4% for the flexure, shear, and bond modes of failure, respectively. Moreover, a life cycle analysis (LCA) was considered to compare HRAC mix with conventional concrete mix in terms of the environmental aspects. LCA results indicated that HRAC is a sustainable concrete, specifically with respect to structural performance and lower environmental impact. [ABSTRACT FROM AUTHOR]

Studies have found utilization of recycled aggregate concrete (RAC) for engineering use to be environmentally favorable by preserving natural resources and limiting waste reduction. However, the use of RAC has not been effectively integrated in the industry due to limited research overlying the critical areas of its creep and shrinkage behavior. Hence, this study aims to investigate the natural aggregate concrete creep and shrinkage prediction models and perform recycled concrete aggregate (RCA) replacement level and water absorption modifications to illustrate the presence and behavior of RAC. Comparative analysis was undertaken by establishing comprehensive conventional concrete and RAC experimental databases and investigating several creep and shrinkage prediction models including, ACI 209R‐92, Bazant–Baweja B3, CEB MC 90, GL 2000, MC 2010, and JSCE 2010. The Bazant–Baweja B3 model was found to present the most optimal results by evaluating each conventional model against the RAC databases and performing regression analysis. Hence, the Bazant–Baweja B3 natural aggregate concrete models for creep and shrinkage were then effectively modified to illustrate the presence of RCA replacement level and water absorption. The adjusted models were verified with a set of experimental databases which successfully presented favourable results with coefficient of correlation factors increased from an average of 0.76 to 0.9. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to examine the advantages and disadvantages of the Kömürhan bridge, built with natural aggregate concrete in Elazig, in terms of mechanical, environmental, and economic properties if certain ratios of recycled concrete aggregate (RCA) were used. For this purpose, a detailed laboratory study was designed, and concrete samples were produced, all‐natural, all‐recycled, and both recycled and containing natural aggregates. Different water‐to‐cement, aggregate‐to‐cement, and recycled concrete aggregate‐to‐total aggregate ratios were considered for the mixture designs of these samples, and the fresh and hardened concrete properties of these samples were determined. Then, statistical analyses were made using the response surface method, and numerical models were developed to predict the fresh and hardened concrete properties with high accuracy. Mixtures containing RCA, which have the same fresh and hardened concrete properties as the fresh and hardened concrete properties of the Kömürhan bridge, which was selected as an example structure by using these models, were determined for optimization purposes. A detailed environmental and economic comparison of the optimization and reference mixtures was made. While making environmental assessments, energy consumption, global warming potential, waste generation, and abiotic depletion were considered. It was seen that the optimization mixtures were more economical and more environmentally friendly than the reference mixture. As a result of this study, it was predicted that the use of RCA in buildings constructed using large amounts of concrete could provide significant environmental and economic advantages and was exemplified by the Kömürhan bridge. [ABSTRACT FROM AUTHOR]

The pressed sleeve connection is a new type of connection technique reported in China recently. To explore the possibility of combining the advantages of pressed sleeve connections and recycled aggregate concrete (RAC) in precast concrete, the seismic performance of precast shear walls with pressed sleeves and recycled fine aggregate (RFA) concrete was investigated through a thorough experimental programme. A total of seven precast shear wall specimens and one cast‐in‐situ specimen were fabricated and tested under lateral cyclic loading, considering the effects of the aspect ratio, the axial compression ratio, and the RFA content. The failure modes, hysteretic behavior, bearing capacity, energy dissipation, stiffness and shear distortion of the specimens, as well as the strains of the steels, were reported and discussed. The test results demonstrated that the pressed sleeve connections were capable of transmitting both tensile and compressive forces between reinforcements, and the precast shear walls with pressed sleeve connections exhibited the same hysteresis behavior, strengths, ductility coefficient and energy dissipation capacity as the cast‐in‐situ counterpart. Moreover, the seismic behavior of the precast specimens with the RFA content of 30% was almost the same as those with natural aggregate concrete (NAC). The increase in the axial compression ratio and aspect ratio led to higher peak loads of the precast shear walls. Finally, existing design methods of ordinary reinforced concrete shear walls were evaluated for their application to the design of precast RFA concrete shear walls with pressed sleeves. Overall, the evaluation results revealed that the examined design methods offer generally accurate strength predictions for the proposed shear walls. [ABSTRACT FROM AUTHOR]

Only in Europe, every year around 29 million tons of plastic waste are generated and only about 35% of such waste is collected for recycling. This results in huge amounts of plastic waste threatening the environment. One of the possible solutions for disposal can be represented by the concrete industry. Several research works have already studied the use of plastic waste in concrete mix as partial replacement for aggregates, showing that this use of plastics can contribute to reducing the environmental impact of concrete production by saving non‐renewable resources. At the same time, lightweight concrete can be produced but at a non‐negligible cost of a mechanical strength reduction. This work aims at investigating the effects on concrete physical and mechanical performances resulting from the introduction of recycled plastic aggregates in combination with another kind of waste used as filler, namely biochar. Biochar, which is the solid carbonaceous by‐product resulting from wood‐waste pyro‐gasification, can have the role of carbon sequestrating additive in concrete, being able to fix carbon in a stable form in buildings for decades. The experimental findings obtained in this work show that the combination of biochar and recycled plastic waste, which was never investigated before, can help to obtain concretes with satisfactory mechanical performance, which promote circular economy principles. Thanks to biochar addition, the reduction in mechanical properties due to the presence of plastics is extremely limited with respect to control; moreover, these concretes demonstrate better behavior in terms of fracture energy and ductility. [ABSTRACT FROM AUTHOR]

Since reinforced concrete members suffer from different types of loads during their service life, the steel bars embedded in reinforced concrete members can be easily corroded in chloride‐laden environment. To investigate the influence of combined effect of load and steel corrosion on the flexural stiffness of recycled aggregate concrete (RAC) beams, 12 RAC beams were prepared and tested. The effects of load level (i.e., the ratio of the load applied to beams to the ultimate load) and recycled coarse aggregate (RCA) replacement ratio (i.e., the ratio of RCAs to replace natural coarse aggregates) on the internal force arm coefficient of cracking cross‐section, the elastoplastic resistance moment coefficient of cross‐section, and the strain incongruity coefficient of corroded tensile steel bars were analyzed, and a calculation model for flexural stiffness of RAC beams under combined effect of load and steel corrosion was established. The results showed that when the ratio of bending moment to ultimate bending moment of the pure bending part of beams was within 0.55–0.80 and the average mass loss of tensile steel bars was less than 3.23%, 0.85 could be adopted as the internal force arm coefficient of cracking cross‐section. The elastoplastic resistance moment coefficient of cross‐section was approximately a constant when the corroded RAC beams were in the service stage, while it increased obviously with the load level. There was a strong linear relationship between strain incongruity coefficient and average mass loss of tensile steel bars during the service stage of corroded RAC beams, and the strain incongruity coefficient increased linearly with the load level. The calculated values of the model of flexural stiffness proposed in this paper were in reasonable agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Nowadays, recycled coarse aggregates (RCA) are playing a major role in sustainable construction as compared to natural coarse aggregates (NCA). Researchers use fibers and cementitious materials to improve the mechanical properties of concrete. Nowadays, RCA are playing a major role in a sustainable environment as compared to NCA. This article examines the combined effect of jute fiber (JF) and RCA on the durability and mechanical properties of concrete. A total of 15 concrete mixes are prepared, in which three categories of concrete mixes are prepared by utilizing 100%RCA, 50%RCA, and 0%RCA and in each mix, 0.60%, 0.45%, 0.30%, 0.15%, and 0% of JF by volume of concrete are used. Mechanical properties of concrete are analyzed by flexural strength, split tensile strength, and compressive strength tests whereas durability properties of concrete are analyzed by sorptivity coefficient, porosity, and chloride penetration tests. The experimental results depict that smaller dosages of JF (0.15%) have a positive effect on the mechanical properties of concrete with RCA whereas greater dosages of JF (≥0.30%) have an adverse effect on mechanical concrete properties with RCA. The mechanical properties are increased by more than 4% in the case of a lower percentage of JF. The durability of concrete shows a negative impact on concrete with the increasing percentages of RCA and JF in all types of the mix. The durability of concrete is more affected in the case of higher dosages of JF. [ABSTRACT FROM AUTHOR]

The use of recycled aggregate improves waste management and is a crucial step toward the sustainable development of the concrete industry. Hence, this paper presents the experimental investigation to determine the mechanical properties of concrete with recycled concrete aggregates as the selective substitution for natural aggregates. The slump was observed to decrease by replacing natural coarse aggregates with recycled concrete aggregates. Compressive strength of about 40 MPa was achieved after 56 days of curing with the utilization of 100% recycled concrete aggregates. Besides, a reduction in the splitting tensile strength of 14% was observed due to the incorporation of recycled concrete aggregates. The statistical techniques use various probability distribution models such as Gamma, Lognormal, Weibull, and Normal distributions. Amongst the considered functions, lognormal and Weibull distributions best represent the experimentally obtained compressive strength of concrete with 100% natural aggregates and 50% recycled concrete aggregates, respectively. However, for concrete with 100% recycled aggregates, Weibull distribution represent compressive strength after 28 days of curing, and lognormal distribution is given the best fit for the compressive after 56 days of curing. In the case of split tensile strength, lognormal distribution provided the best representation after 56 days of curing for all specimens. [ABSTRACT FROM AUTHOR]

A beam‐end test is proposed in this paper and in the new fib Model Code 2020 to determine the effects of concrete type, confinement effects, and casting position on the anchorage strength of reinforcing bars. Two bars are cast in each specimen (in the two opposite corners), one in a "good" casting position and the other in "poor" casting position. The proposed test aims to be an economical bond test capable to represent actual conditions of anchored bars in real design practice. The test is also intended to verify whether existing provisions for bond and anchorage in the fib Model Code are suitable in nonconventional concrete. The validity of the proposed beam end type bond test is assessed by the results of more 60 tests on rebars having anchorage length of about 20 times the bar diameter in plain concrete, in fiber reinforced concrete, and in recycled aggregate concrete. Experimental results provide information both on the "top cast effect" in three types of concrete and on the effectiveness of fib Model Code provisions for anchorage when nonconventional concrete is used. [ABSTRACT FROM AUTHOR]

This project investigates the use of foamed glass aggregates in lightweight precast concrete. Precast mixes are evaluated for compression and split‐tension strength, and durability is assessed through rapid chloride permeability, thermal conductivity, alkali silica reactivity, and freeze–thaw performance. Mixes containing a 100% or 50% replacement of gravel with foamed glass aggregates are evaluated. The 100% mixes have a 28‐day compression strength = 23.3–27.89 MPa which is acceptable per structural lightweight concrete standards (ASTM C330), but the split‐tension strength falls short of ASTM C330 requirements. The 50% mixes have acceptable strength but exceed the maximum density allowed for lightweight concrete in ASTM C330. The mixes exhibited low–moderate permeability but poor freeze–thaw resistance. All of the proposed mixes with one exception have acceptable expansion due to alkali silica reactivity. The thermal conductivity of the mixes varies from typical lightweight to normal weight concrete ranges with respect to the aggregate replacement ratio. [ABSTRACT FROM AUTHOR]

Due to the low strain capacity and the weak crack resistance of concrete, fibers are commonly added to concrete to increase its tensile resistance. The most recent standardized constitutive tensile model is given in the fib Model code 2010, which is based on a simplified stress profile at serviceability limit state (SLS) and ultimate limit state (ULS). However, in current research, an improved stress profile at ULS is proposed. Consequently, three new constitutive tensile models, which are valued for a specific FRC class, are developed. Those models are constructed with the test data of fiber‐reinforced concrete with natural aggregates (FR‐NAC) and three types of recycled aggregates (FR‐RAC). In addition, macro glass fibers and macro polypropylene fibers are used. The test data indicate that the lower concrete Young's modulus of FR‐RAC, as well as the crack growth resistance due to plastic work of the recycled concrete mixtures, result in an increased residual tensile strength at SLS and ULS. The residual tensile strength at 2.5 mm CMOD (fFt,2.5) of the normal recycled aggregate concrete (nRAC) mixture with 0.75 V% glass fibers is 0.95 MPa, while the FR‐NAC mixture with the same fiber content only indicates a fFt,2.5‐value of 0.43 MPa. Consequently, higher linear postcracking stresses are observed for the FR‐RAC mixtures, especially for the FR‐RAC mixtures with 0.75 V% glass fibers and the lower quality of recycled aggregates. [ABSTRACT FROM AUTHOR]

The primary purpose of this study is to examine in detail the mechanical, environmental, and economic properties of concrete produced using recycled concrete aggregate (RCA) in different ratios. This study used RCAs obtained from construction and demolition wastes (CDW) that emerged after the 24 January 2020 Sivrice‐Elazig earthquake to produce recycled aggregate concretes. The ultimate aim of this study is to determine the advantages and disadvantages of these structures in terms of mechanical, environmental, and economic properties if RCA will be used at certain rates in high‐rise private buildings built with natural aggregate concrete (NAC) in Elazig. For this purpose, concretes with all natural aggregates, all recycled aggregates, and both natural aggregates and recycled aggregates were produced. A mathematical model was developed using response surface method to predict the mechanical properties of recycled coarse aggregate concretes (RCACs) by utilizing the compressive strength values of the produced concretes. Then, the component amounts of RCACs, which have the same compressive strength as the compressive strength values of the NAC used in Elysium, which was chosen as a sample building in Elazig, were estimated. Considering the estimated component amounts, environmental impact assessments and feasibility analyses were made according to four different scenarios, including parameters such as cement amount, chemical additive amount, the cost difference between RCA‐natural coarse aggregate, and transportation distance. As a result of these evaluations and analyses, it was foresighted that using RCA would provide significant advantages in buildings produced using large amounts of concrete. This foresight is exemplified by the Elysium buildings. As a result, it was determined that the use of RCAs is appropriate, especially the concrete produced with aggregates obtained from CDW is more important for a sustainable environment, and the use of RCAs in high‐rise buildings built using large amounts of concrete can provide significant environmental and economic advantages. [ABSTRACT FROM AUTHOR]

The addition of recycled concrete aggregates together with industrial by‐products for the concrete production is an effective solution to the environmental problems in terms of excess waste materials and massive nonrenewable natural resources consumption. This article investigates the long‐term behavior and microstructure of sustainable self‐compacting concrete (SCC) by substantially substituting natural coarse aggregate with recycled coarse aggregates (RCA) and cement with supplementary cementitious materials (SCM). The influences of RCA and SCM content as well as SCM combination type (fly ash, ground granulated blast furnace slag and/or silica fume) on the mechanical properties and long‐term deformation of recycled aggregate SCC (RA‐SCC) were assessed in detail. Furthermore, scanning electron microscope and x‐ray diffraction were implemented to justify the reasons for improvement on mechanical properties and long‐term behavior of RA‐SCC. The results indicate that the addition of RCA reduces the compressive strength and elastic modulus of RA‐SCC, and increases the creep and shrinkage deformations. However, incorporating SCM with a combination of fly ash, ground granulated blast furnace slag and silica fume compensates for the detrimental effect of RCA and makes considerable improvement in strength and reduction in the long‐term deformations. Microstructure analysis confirms the reasons of improvement, which is mainly attributed to the addition of SCM by adopting a combination type, resulting in a more compact microstructure such as stronger interfacial transition zone. Based on the experimental results, the correction factors of RCA and SCM were introduced in conjunction with fib Model Code 2010 model to evaluate the creep coefficient of RA‐SCC. [ABSTRACT FROM AUTHOR]

To establish a restoring force model for recycled aggregate concrete‐filled steel tube (RACFST) frames, the quasistatic tests on two frames comprising two RACFST columns and a reinforced recycled aggregate concrete (RRAC) beam each was carried out. The recycled coarse aggregate replacement ratio was 100%. The failure mechanism, hysteretic curves, and strain response of the specimens were discussed. By analyzing the degradation of the load bearing capacity with increasing displacement amplitude and combining the hysteretic curves and stiffness degradation relationships, a restoring force model of load versus displacement adopting a trilinear approximation was proposed. The characteristic points of the model were the relative yield point, relative peak point, and relative failure point. Results showed that bending‐shear or bending failure occurred at the ends of specimen beams and plastic hinges formed there earlier than at the column ends. The hysteretic curves of load versus displacement were essentially symmetric in a full shuttle shape. The proposed restoring force model adopting trilinear approximation agreed well with the experimental hysteretic curves under low‐cycle loading and can thus be recommended to perform the elastoplastic analysis of seismic response for this new type of composite structures. [ABSTRACT FROM AUTHOR]

Internal curing (IC) agents such as prewetted lightweight aggregates (LWAs) have been proved to be advantageous in reducing the autogenous shrinkage and early‐age cracking of concrete by introducing additional water. Quantitative analyses of internal relative humidity (IRH) of concrete are essential to better estimate the autogenous shrinkage of early‐age concrete. Existing studies investigate the IRH or autogenous shrinkage of early‐age concrete, respectively; however, the relevance between them of concrete containing prewetted LWAs remain lacking. Accordingly, the IRH, autogenous shrinkage, and the correlation between them for early‐age concrete with various LWAs replacement ratios were investigated. A noncontact device was utilized to measure the IRH and autogenous shrinkage of concrete simultaneously. Test results suggested that: (1) the absolute value of the maximum expansion increased from 0 με to 20, 50, and 96 με when the proportion of prewetted LWAs increased from 0% to 10%, 30%, and 50%, respectively; (2) compared with Mixture LWA00, the autogenous shrinkage at 28 days decreased by 14.7%, 36.3%, and 62.6% for Mixture LWA10, LWA30, and LWA50, respectively; (3) the IRH at 28 days or the critical time of IRH was 88.7%, 90.1%, 93.2%, and 95.9% RH or 5, 6, 8, and 10 days for Mixture LWA00, LWA10, LWA30, and LWA50, respectively; (4) a prediction model for the evaluation of the autogenous shrinkage was constructed based on IRH of early‐age concrete considering the quantity of IC water introduced by various replacement ratios of LWAs. [ABSTRACT FROM AUTHOR]

The improved mechanical properties of recycled aggregate concrete (RAC) by employing the particle packing method (PPM) of the mix design approach encourages its application to study the performance of structural members. The experimental investigation is conducted on the axial compressive behavior of reinforced natural aggregate concrete (NAC) and RAC columns using two different tie spacing conditions. A reduction of 18% in the axial load of RAC columns is observed with respect to the NAC columns and only 2.7% improvement in axial load is recorded as the tie spacing reduces by 22.5%. Subsequently, the finite element (FE) analysis is conducted to investigate the axial compressive strength of both NAC and RAC columns using different tie spacing conditions. The FE analyses of RAC columns with different tie spacing support to modify the spacing of transverse reinforcement as half as that of the spacing specified in the prevailing design for NAC columns. [ABSTRACT FROM AUTHOR]

An effort has been made to enhance the flexural fatigue lives of self compacting concrete (SCC) in which half of the natural aggregates (NA) were substituted with recycled concrete aggregates (RCA) by means of blended cements. Blended SCC mixes containing either silica fume (SF) or metakaolin (MK) along with cement, and fly ash (FA) was also adopted. Fatigue lives have been evaluated as mean value, design value life and theoretical value. The Weibull distribution parameters were utilized for the valuation of mean and design values of fatigue lives for different considered mixes. It has been observed that adding RCA in SCC causes degradation in the fatigue lives, which can be enhanced by adopting the blended mixture comprising of SF or MK, cement and FA. Both SF and MK established a promising result in improving fatigue lives. Still, the blend of MK in SCC contributed most effectively in enhancing the fatigue life of SCC comprising RCA. [ABSTRACT FROM AUTHOR]

The environmental impacts of activities such as raw material extraction, construction of infrastructure, and demolition, place construction as one of the sectors that exert the highest pressures on the environment, society, and economy. Some of the major environmental impacts for which the construction industry is responsible are mineral resource depletion, greenhouse gas emissions, and waste generation. Among the different strategies that exist to decrease such impacts, recycling demolition waste into recycled concrete aggregates has been considered a promising alternative. As such, at present, the literature dealing with the impact assessment of recycled aggregate concrete structures is very extensive. Therefore, the objective of this article is to present a critical view of the state‐of‐the‐art in terms of sustainability assessment of recycled aggregate concrete structures, taking a holistic perspective by considering environmental, social, and economic impacts. [ABSTRACT FROM AUTHOR]

The main relevant difference between recycled concrete aggregates (RCAs) in comparison with the companion natural ones, is the presence of the Attached Mortar content which confers to the RCAs higher porosity and, consequently, higher water absorption capacity. In the last decades, several studies have been performed worldwide for unveiling the role of the employed RCAs on the resulting concrete mixture performances at both fresh and hardened states. On the other hand, the effects of RCA on the early‐age and/or long‐term concrete deformations (e.g., shrinkage) are still very limited. In this context, this article summarizes the results of a wide experimental campaign aimed at evaluating the influence of RCAs on the autogenous and drying shrinkage of normal (35 MPa) and high (60 MPa) strength recycled aggregate concrete (RAC) mixtures. A total of 10 mixtures were realized by considering the variation of both the original source and size of employed RCAs. The results showed a clear correlation between the intrinsic properties (i.e., Attached Mortar content) of the employed RCAs and the resulting concrete deformation. Moreover, although the drying shrinkage is higher for RAC mixtures, the presence of a more porous aggregates mitigates the observed autogenous shrinkage. Consequently, the overall total shrinkage result to be almost unaffected by the presence of the recycled particles. [ABSTRACT FROM AUTHOR]

The promotion of recycled aggregate concrete (RAC) can effectively reduce carbon emissions from the construction industry and increase the recycling rate of waste concrete. Owing to the significantly higher creep of RAC than that of natural aggregate concrete (NAC), the accurate prediction of long‐term RAC creep deformation is vital. Therefore, a predictive model for RAC is investigated in this study. A creep database of RAC with 106 groups of 1309 experimental data points considering 15 influencing parameters is established. Furthermore, back‐propagation neural network (BPNN) and support vector machine (SVM) models are adopted to process and predict data. The accuracies of the prediction of the existing RAC creep, BPNN, and SVM models are comparatively analyzed. The results reveal that for the prediction of RAC creep, the BPNN and SVM models are more accurate than the existing RAC creep model. Finally, the extended parameters of the model are analyzed based on the BPNN model to further clarify the effects of the recycled coarse aggregate (RCA) replacement ratio, RCA residual mortar content, and RAC strength on the creep properties of RAC. [ABSTRACT FROM AUTHOR]

The equivalent mortar volume (EMV) mixing method has been proposed to prepare recycled aggregate concrete (RAC) with comparable mechanical properties to those of reference natural aggregate concrete (NAC). Previous studies primarily focused on the mechanical properties of EMV concrete with a single replacement ratio of recycled coarse aggregate (RCA). This paper investigates how the mechanical properties of EMV concrete vary with the replacement ratios and particle size distributions of RCA. Five different RCA replacement ratios and two RCA particle size distributions were assessed. A material demand coefficient was principally proposed to quantify the contribution of the EMV mixing method to reduce the environmental impact; the maximum RCA replacement ratio was suggested to obtain sufficient workability of EMV concrete using an effective sand ratio; a drying shrinkage model was theoretically proposed for EMV concrete accounting for the drying shrinkage of residual mortar. The obtained results indicated that the compressive strength and elastic modulus properties of EMV concrete decreased with increasing RCA replacement ratios; using the effective sand ratio of EMV concrete, comparable mechanical properties to those of reference NAC could be obtained for EMV concrete; the proposed shrinkage model was consistent with the available experimental data. [ABSTRACT FROM AUTHOR]

Fracture energy (GF) represents the average total energy consumed in the whole process of crack propagation. Using one parameter of GF, it is not sufficient to describe the fracture behavior during crack stable and unstable propagation periods. In this study, the GF, stable fracture energy (GFS) and unstable fracture energy (GFU) of natural and recycled aggregate concrete (RAC) were investigated by using three‐point bending tests. Totally, 128 cubic specimens (100 mm × 100 mm × 100 mm) and 64 notched beams with size of 510 mm × 100 mm × 100 mm were manufactured to test the compressive strength (fcu), splitting tensile strength (ft), load–deflection (P‐δ), and load‐cracking mouth opening displacement (P‐CMOD) curves, considering different replacement levels (0%, 30%, 70%, and 100%) of recycled coarse aggregate (RA) and high temperatures exposure (20, 100, 200, and 300°C). The effects of RA substitutions and temperatures on basic mechanical properties, GF, GFS, and GFU were analyzed. The results demonstrated that the fcu, ft, and elastic modulus (E) decreased with the incremental temperature. The GFS of concrete with different RA substitutions first decreased and then increased, and the minimum value appeared at 200°C. The GF and GFU of concrete with different RA substitutions increased with the elevated temperature, and the increase rate decreased with RA substitutions. When the temperature is less than 100°C, the GF and GFU of concrete remained mostly unchanged with the increase of RA substitutions, while the temperature reached 200 and 300°C, the GF and GFU of concrete increased and decreased with the increase of RA substitutions, respectively. [ABSTRACT FROM AUTHOR]

The application potential of recycled aggregate concrete has been realized with the development and utilization of waste concrete. Fibers are added to concrete made with recycled coarse aggregate to enhance its mechanical properties and broaden its application possibilities. Additionally, in practical applications, parts of structural elements are frequently under compression‐shear stress. As a result, the normal stress ratio k (k = σ/fcu, where σ is axial compressive stress, and fcu is concrete cube compressive strength), coarse aggregate replacement rate, and carbon fiber content are used as design parameters to examine the compressive‐shear mechanical properties of carbon fiber recycled aggregate concrete in this paper. The results show that the normal stress ratio and fiber content affect the whole compression‐shear process curve, shear strength, peak shear displacement, and damage evolution. A compressive shear damage model that takes into account the aggregate replacement rate, normal stress ratio, and fiber content is established. And there is good agreement between the experimental findings and the calculation model. [ABSTRACT FROM AUTHOR]

Nowadays, reducing the waste and recycled material resources in nature and environmental protection, as well as reducing the use of natural resources, has gained the attention of engineers and researchers. One of the ways to reach this goal is to use waste and recycled materials in new concrete members' construction. Additionally, using glass fiber‐reinforced polymer (GFRP) rebars has gained high consideration owing to their advantages such as high tensile strength and corrosion resistance. Therefore, this study aims to measure the influence of recycled coarse aggregates (RCA) on the structural performance of reinforced concrete (RC) columns reinforced by GFRP rebars under concentric and eccentric loading conditions. A total of 24 RC columns were cast and subjected to concentric and eccentric loads with different eccentricity ratios (e/h):0 (no eccentricity), 0.25 (moderate eccentricity), and e/h = 0.5 (high eccentricity). A total of 18 columns were strengthened with longitudinal GFRP rebars, and six specimens were considered control samples reinforced by steel rebars. RCA was used at two contents of 0% and 100% in terms of weight as a substitute for natural coarse aggregates (NCA). In addition, to measure the influence of transverse reinforcement, three different spacings were considered: 60, 120, and 180 mm. Evaluation of axial behavior, the strain of rebars and concrete, and the ductility were the main aims of this study. Moreover, a comparison between the experimental results and existing standards was carried out. Findings revealed the adequate axial resistance of specimens when RCA was used. Therefore, RCA incorporation improved the axial resistance of GFRP‐RC columns by about 25% and 35% when the stirrup spacing declined by 60 and 120 mm, respectively in comparison with the same specimens made with NCA. However, the influence of RCA on the RC columns' axial behavior was declined by raising the eccentricity distance. [ABSTRACT FROM AUTHOR]

To investigate the combined effect of load and steel corrosion on the flexural performance of recycled aggregate concrete beams, considering three types of aggregate replacement ratios (i.e., 0%, 50%, and 100%) and four levels of load (i.e., 0, 0.2, 0.4, and 0.6), 12 beams were designed for accelerated corrosion test and four‐points bending test. The load was applied to beams by using a designed loading device before the accelerated corrosion test. After the accelerated corrosion test, four‐point bending test was conducted to measure the flexural performance of beams. The results showed that, with the increase of load level applied to beams before accelerated corrosion test, the number of bending cracks on the bottom of corroded beams after four‐points bending test decreased, while the average spacing of bending cracks increased. The effect of aggregate replacement ratio on the average spacing of bending cracks was more significant than that of steel corrosion. Yield moment capacity and ultimate moment capacity of corroded beams had a strong linear relationship with the maximum mass loss of tensile reinforcement, and both of which decreased with the increase of load level and aggregate replacement ratio. For every 1% maximum mass loss of the tensile reinforcement, the reduction of ultimate moment capacity of beams was approximately 4–6 times larger than that of ordinary concrete beams. The degradation model for ultimate moment capacity of corroded beams proposed in this paper had satisfactory prediction accuracy. [ABSTRACT FROM AUTHOR]

Alternative aggregates have undergone intensive research work that has led to confidence in its utilization in concrete. Likewise, various polymers have been investigated to enhance the strength parameters of concrete. This study was dedicated to studying the influence of PVA (poly‐vinyl alcohol) on fresh and hardened properties of rubberized concrete. In this study, nine different grades of concrete were cast containing two proportions of rubber, that is, 5% and 10% by mass of fine aggregate, while two dosages of PVA, that is, 1% and 2% by mass of cement. The results obtained for fresh properties of concrete indicate that rubber led to lower the workability and fresh density of concrete while PVA showed to enhance the workability but lowers the fresh density of concrete. Crumb rubber led to a reduction in mechanical strength parameters of concrete which were significantly recovered with the incorporation of PVA. It was witnessed that, both rubber and PVA substantially enhance the resistance of concrete to acid attack and the strain capacity of concrete. Moreover, PVA led to cause a tad increase in the modulus of elasticity (MOE) while rubber causes a dip in MOE. [ABSTRACT FROM AUTHOR]

Reuse and recycling of construction wastes effectively prevent further destruction of the environment and nature due to the construction industry. One of the conventional methods is the reapplication of recycled aggregates (RAs) in concrete mix design and construction. Compressive strength (CS) is a considerable representation of the mechanical properties of recycled aggregate concrete (RAC). The present study is divided into two parts of experimental and predicting. In the laboratory studies phase, RA was used with 100% replacement. Due to the proven defects in RAC, glass fibers and silica fume (variables) have been used to compensate for these defects. Different mixing designs were used to construct concrete samples, and then the CS of each specimen was measured in the laboratory. Afterward, these data were used as training and testing in various conventional, ensembled and hybrid models as the tree‐based learning algorithms, rules, Lazy‐learning Algorithms, Functions, and Meta classifiers. Considering the applied performance statistical criteria (R2, root mean squared error, mean absolute error, and mean absolute percentage error), all models have provided excellent and acceptable results, which the precision of the multilayer perceptron single model and additive regression‐random Forest hybrid model have the best agreement with measured values of CS of RAC. [ABSTRACT FROM AUTHOR]

In the present scenario, sustainable materials which creates less impact on the environment are the need of the hour. Recycled fine aggregate self‐curing concrete (RFA‐SCRC) can play a significant role in reducing the utilization of natural river sand and also plays a vital role in conserving the water used for curing. This research work deals with the experimental investigations on the compressive strength, flexural strength and split tensile strength of RFA‐SCRC for various replacement proportions of RFAs using ordinary portland cement (OPC) and portland pozzolana cement (PPC) as different variants. The replacement proportions of RFAs considered for this study are 0%, 10%, 20%, 30%, 40%, and 50% to the weight of manufactured sand. Strength optimization was carried out by Taguchi optimization method using Minitab software tool. The parameters considered in this study are the replacement proportion of RFA, type of cement and type of curing. The optimization results indicate that, considering compressive and split tensile strength characteristics, RFA concrete produced using 40% RFA, OPC, and self‐curing process is found to be optimum whereas 30% RFA, OPC, and self‐curing process is found to be optimum with respect to flexural strength characteristics. [ABSTRACT FROM AUTHOR]

Recycled aggregates (RAGs) usage in concrete is surging, inspired by environmental and economic concerns. Regarding predicting various models designed the values of modulus of elasticity (MOE) of concrete with natural aggregates and, in conclusion, they would probably be unreliable when used to concrete with RAG. In the present study, two new gray wolf multi‐layer perceptron neural networks (GWMLP) and gray wolf support vector regression (GWSVR) algorithms were proposed to predict RAG concrete's elastic modulus. About 400 records were gathered from published articles to develop these models. The results show that among the GWMLP models with different hidden layers, GWM3L with three hidden layers could get the highest score (TRS) at 39. Simultaneously, in the testing phase, the GWSVR was the first‐rank model because of the lower RMSE (0.6381), MAE (0.1541), and a larger R2 (0.9707) compared with GWMLP models. Therefore, it can result that the GWSVR model could predict the elastic modulus of RAG concrete precisely even better than GWM3L, which is well over the accuracy of the developed models. [ABSTRACT FROM AUTHOR]

There are essential differences between recycled brick aggregate (RBA) and recycled concrete aggregate (RCA). The weak area of RCA is the old mortar attached to the aggregate surface, while the weak area of RBA is its own larger porosity. Silane has a small molecular structure, which can penetrate into the concrete with water as the medium and react with the active functional groups in the concrete to form a network structure of silane polymer. In this paper, 8% silane solution was used to modify recycled brick aggregate concrete (RBAC) in two schemes. The first scheme was that RBA was soaked in 8% silane solution, and the second scheme was that 8% silane solution was added in the mixing process of RBAC instead of water. The results showed that compared with the unmodified RBA, after silane modification of RBA its apparent density increased by 5.48%, water absorption decreased by 61.12%, crushing index decreased by 11.09%. The average compressive strength of RBAC with RBA modified by silane was 11.72% higher than that of unmodified RBAC, and the average compressive strength of RBAC mixed with silane was 9.12% lower than that of unmodified RBAC. The pores and cracks on the surface of RBA were significantly reduced and the interface transition zone (ITZ) of RBA was compacted after silane modification of RBA. RBA contained Si, Fe, Al, Ca elements and a small amount of Na, K, Mg elements brought by mineral powder; the content of Ca, O, Si elements in ITZ and cement mortar were rich, which indicated that there were a large amount of calcium silicate hydrate (C‐S‐H) in ITZ and cement mortar; ITZ and cement mortar contained Al elements, which indicated that there were ettringite and monosulfate; the content of Ca element in RBA and ITZ increased after silane modification of RBA, which indicated that silane hydrolyzed and reacted with free calcium ions to form calcium silicate. [ABSTRACT FROM AUTHOR]

The importance of using sintered fly ash aggregates (SFAs) as coarse aggregate and metakaolin (MK) as partial replacement of cement for generating sustainable concrete has been accessed in this research. For this, concrete mixes are designed by replacing 0%, 15%, 30%, and 45% natural coarse aggregates (NCAs) by SFA and incorporating 0%, 10%, 15%, and 20% MK in place ordinary Portland cement (OPC) along with a constant water‐binder ratio (0.42). Workability, compressive, split tensile and flexural strength, and nondestructive parameters and other characteristics (water absorption, volume of voids, and density) of designated mixes are evaluated by performing various experiments in the laboratory. The study demonstrates that significant degradation in concrete behavior has been observed with the use of 45% SFA and 20% MK. However, usage of 30% SFA in place of NCA and 10–15% MK as cement replacement is beneficial in achieving the desired target strength and fulfills other concrete requirements for practical use. [ABSTRACT FROM AUTHOR]

The 3‐D base force element method (BFEM) for damage problems is proposed, which is applied to analyze the damage mechanism of recycled aggregate concrete (RAC). A piecewise curve damage constitutive model is given to simulate the constitutive relationships of RAC phases. A spatial random aggregate model of RAC is proposed. 3‐D numerical simulations of RAC under uniaxial mechanical stress are carried out. The macroscopic stress–strain relationship and failure process of RAC under uniaxial stress based on the 3‐D BFEM are obtained. The numerical results show a good consistency with the experimental results. This illustrates that the numerical simulation can reflect the nonlinearity deformation, stress redistribution, and crack propagation process of RAC. In addition, the influence of recycled aggregate replacement percentage on strength and elastic modulus is investigated. The results show that the content proportion of recycled aggregate has a great effect on RAC, which have to be considered in the analysis and the application of RAC. [ABSTRACT FROM AUTHOR]

Research argues in favor of using recycled aggregates in structural concrete. However, lack of specific clauses in standards for recycled aggregate concrete design hinders the use of recycled aggregate concrete by the industry. Recycled aggregate concrete‐specific design clauses are hindered because conventional research must be complemented with experiments directed towards stochastic modeling, so that reliability concepts may evaluate whether the probabilities of failure of design comply with the expectations of Society or whether specific design rules are needed. This article compares the within‐batch variability of carbonation under accelerated conditions of four natural aggregate concrete and four analogue recycled aggregate concrete mixes and analyses the reliability of Eurocode 2 cover design for carbonation exposure. In general, the incorporation of coarse recycled concrete aggregates worsened the mean durability behavior of concrete, including resistance to carbonation. However, the variability of carbonation depth was not meaningfully affected by the recycled aggregates used (coarse recycled aggregates produced from concrete waste) and the reliability of concrete cover design only decreased due to the effect of the recycled aggregates on the mean resistance to carbonation. A 5 mm increase of concrete cover was found to more than offset the detrimental influence of full incorporation of recycled aggregates on the reliability of concrete cover design. [ABSTRACT FROM AUTHOR]

The above article, published online on 10 February 2022 in Wiley Online Library {https://onlinelibrary.wiley.com/doi/abs/10.1002/suco.202100681} has been retracted by agreement between the journal's Editor‐in‐Chief, Professor Luc Taerwe, the fib, and John Wiley & Sons Ltd. The retraction has been agreed given the journal has received evidence confirming that the peer review process of this paper was manipulated. As a result, the conclusions reported in the article are not considered reliable. [ABSTRACT FROM AUTHOR]

The above article, published online on 15 November 2021 in Wiley Online Library {https://onlinelibrary.wiley.com/doi/10.1002/suco.202100250} has been retracted by agreement between the journal's Editor‐in‐Chief, Professor Luc Taerwe, the fib, and John Wiley & Sons Ltd. The retraction has been agreed given the journal has received evidence confirming that the peer review process of this paper was manipulated. As a result, the conclusions reported in the article are not considered reliable. [ABSTRACT FROM AUTHOR]

Heavyweight concrete (HWC) is produced by replacing natural aggregates in a concrete mix design with heavyweight aggregates of a higher specific gravity. HWC is mainly used for the prevention of leakage from radioactive containing structures and is hence primarily used in the medical and nuclear energy industries where this property is of particular benefit and importance. Also, high‐strength concrete (HSC) has been increasingly employed in both civil structures, such as high rise buildings and bridges and defense applications. This study makes attempt to develop and evaluate different concrete mixes, which are considered as high‐strength, heavyweight and highly workable in nature. Such mixes use magnetite as the primary aggregate. The three‐mentioned properties of these concrete types have been thoroughly investigated individually; however, there is a limited numbers of literature on the analysis of mix designs dealing with the three‐mentioned properties simultaneously, in which the water/cement ratio variation, and/or variation of the magnetite content have been assessed. In this study, nine highly workable high‐strength HWC mixes have been developed and fresh and hardened properties are discussed. The overall result indicates that the developed mixes satisfied the required high‐strength, heavyweight and highly workable criteria, as well as, compressive strength would increase by increasing the heavyweight aggregate content. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse ash (SBA) is a supplementary material widely used around the world for improving mechanical and durability properties of concrete. Main aim of this study was to examine the potential of SBA for controlling alkali‐silica reaction (ASR) in concrete incorporating reactive aggregates. SBA and reactive aggregates were acquired from local industry and quarry. Mortar bar specimens were cast to investigate various dosages of SBA (i.e., 10, 20, 30, and 40% by cement weight) for mitigating the alkali‐silica reactivity expansion as per ASTM C1260. Petrography analysis of aggregates revealed the presence of deleterious minerals, which are prone to ASR. Strength activity index and thermal analysis results confirmed the pozzolanic activity of SBA. Mortar bar results showed 20 and 40% decrease in ASR expansion for specimens incorporating 10 and 40% of SBA by cement weight, respectively. Moreover, scanning electron microscopy analysis showed no sign of cracks due to ASR for specimens incorporating SBA. The improved behavior of specimens with SBA addition was due to alkali absorption and dilution process leading to low CaO/SiO2 ratio, confirmed through energy disperse X‐ray spectroscopy. Therefore, it can be envisioned that full‐scale implementation of SBA addition in concrete mixtures could mitigate land filling of this by‐product and lead toward the development of eco‐friendly and sustainable technique for controlling the ASR associated damages in concrete structures. [ABSTRACT FROM AUTHOR]