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Copyright of Low-Carbon Materials & Green Construction is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recycling of concrete generated from construction and demolition waste as coarse aggregates in concrete has been a focus of several studies for the evolution of the green concrete and conservation of natural resources. This investigation, therefore, focusses on the study of the behavior of RC beams strengthened with externally bonded CFRP wraps, cast with both natural and recycled aggregates concrete. Furthermore, one-way slabs were strengthened with Near Surface Mounted (NSM) bars, while two-way slabs were strengthened with CFRP strips. One-way and two-way slabs used in the study were cast with both natural and recycled aggregate concrete (RAC). In RAC, natural aggregates were replaced by 30% recycled concrete aggregates. All beams and slabs were cast with concrete mix design of 1:1.24:2.6 and w/c ratio of 0.43. Beams and one-way slabs, control and strengthened, were tested under four-point bending. Whereas, two-way slabs were tested in punching. A significant increase in the load-carrying capacity was observed for both natural and recycled aggregates concrete beams without shear reinforcement and two-way slabs, indicating the effectiveness of strengthening scheme. Increase of 20.5% and 12.6%, respectively, was found in the load-carrying capacities for the cases of both and natural and RAC beams with natural aggregate concrete (NAC) and RAC beams when results were compared for the case of shear deficient control and strengthened RC beams with CFRP wraps. Furthermore, increase of 27 − 37% was noted in load-carrying capacities of both natural and RAC two-way slabs when results were compared for the case of control and strengthened NAC and RAC slabs. [ABSTRACT FROM AUTHOR]

Replacement of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) is an ideal solution to recycle and utilize the huge amount of construction and demolition wastes (CDW). However, due to the relatively higher porosity and cracking of RCA, its application in the construction industry is restricted. In this study, the RCA was used to completely replace natural coarse aggregate (NCA) for preparation of recycled aggregate concrete (RC). The effects of nano-SiO2 (NS) on the hydration characteristics, mechanical properties and permeability and microstructure of RC were investigated by a range of analytical techniques. The results indicated that the incorporated of NS promoted the hydration progress and enhanced the compressive strength at different ages, while it adversely affected the fluidity. Moreover, the microstructure showed less content of calcium hydroxide and dense interfacial transition zone (ITZ) between RCA and matrix in the RC reinforced by NS due to the nucleation effect and the pozzolanic reaction, thus increased the resistance to chloride penetration and capillary water absorption. The maximum efficiency was obtained when 3% NS was used. This method provides the possibility to use 100% RCA in concrete and helps to maintain the better mechanical properties and durability of RC for a longer period. [ABSTRACT FROM AUTHOR]

Soft computing techniques have become popular for solving complex engineering problems and developing models for evaluating structural material properties. There are limitations to the available methods, including semi-empirical equations, such as overestimating or underestimating outputs, and, more importantly, they do not provide predictive mathematical equations. Using gene expression programming (GEP) and artificial neural networks (ANNs), this study proposes models for estimating recycled aggregate concrete (RAC) properties. An experimental database compiled from parallel studies, and a large amount of literature was used to develop the models. For compressive strength prediction, GEP yielded a coefficient of determination (R²) value of 0.95, while ANN achieved an R² value of 0.93, demonstrating high reliability. The proposed predictive models are both simple and robust, enhancing the accuracy of RAC property estimation and offering a valuable tool for sustainable construction. [ABSTRACT FROM AUTHOR]

The effects of dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber on the stress–strain relationship of RAC under cyclic loading were studied. What is more, the characteristics of stress–strain curve, plastic strain, stress degradation and stiffness degradation of RAC under cyclic loading were analyzed. The microstructure of RAC was analyzed. Based on the principle of surface energy, the reason for the decrease in compressive strength of wet concrete was analyzed. In addition, the envelope equation of stress–strain curve under cyclic loading, unloading and reloading curve was established. The test results showed that the peak stress of the envelope line of RAC under cyclic loading was affected by dry or saturated state, water–cement ratio and coarse aggregate type, but the addition of steel fiber could reduce the degradation rate of stress and stiffness of RAC after peak strain. The plastic strain accumulation of RAC before and after the peak stress was quite different, but dry or saturated state, water–cement ratio, coarse aggregate type and steel fiber have no obvious influence on the plastic strain accumulation of RAC. The pores and cracks of RAC provide space and channels for the moisture absorption and water absorption. The Weibull–Lognormal statistical distribution envelope model, unloading curve model and reloading curve model established were in good agreement with the experimental curves. The research results provided a reference for the study of the full curve constitutive model of RAC under cyclic loading. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete contributes to the recovery of construction and demolition waste, which is a growing societal concern. The technical feasibility of recycled aggregate concrete has been extensively tested and validated and the revisions of codes are already including clauses for recycled aggregate concrete specification and design. However, there are still doubts regarding its structural behavior. This article assesses the suitability of Eurocode 2 design clauses for concrete elements under compression when used for recycled aggregate concrete design. This is done through the analysis of model uncertainties that are estimated from a database collected from laboratory experiments on columns. Both the current version of Eurocode 2 (with and without taking confinement into account) and the upcoming (second generation) Eurocode 2 are considered. A database was collected with clearly defined criteria and includes coarse recycled aggregates produced from concrete waste, since columns made with other types of recycled aggregates are scarcely tested and do not represent the current status for structural recycled aggregate concrete design and production. The statistics of the model uncertainty for natural and recycled concrete columns were compared and it was observed that the mean model uncertainty tends to decrease slightly when recycled aggregates are used. However, a preliminary assessment of whether a partial factor for recycled aggregate concrete compression design should be used concluded that this partial factor is not necessary to ensure reliable design and the design of columns may be carried out using the same formulae used for conventional concrete. The format proposed may be used for other resistance models, provided that the partial factor is calibrated for each resistance model. [ABSTRACT FROM AUTHOR]

Life cycle assessment of concrete made of 100 % recycled aggregate compared to normal concrete The construction sector accounts for a significant proportion of the consumption of natural resources and is also the source of the largest waste streams. The aim must therefore be to improve the circular economy in the construction sector. In this context, the Institute for Materials and Building Research (IMB) at Munich University of Applied Sciences (HM) has investigated the use of recycled aggregates beyond the technical building regulations up to 100 % including recycled sand for the production of structural concrete. The first applications of concrete with 100 % recycled aggregate (100 % RC concrete) have already been completed and are presented in this issue. Based on the findings from the research and construction projects, life cycle assessments were performed in which 100 % RC concrete (circular system) was compared with normal concrete (linear system) for the application case C30/37 XC4/XF3 (CEM II/C‐M (S‐LL)). The life cycle assessments of the two product systems were prepared in the form of nomograms so that input parameters such as transport services can be adjusted and a graphical evaluation of GWP can be carried out. This makes it easy to elaborate recommendations for the use of 100 % RC concrete with regard to reducing the environmental impact (GWP) in specific applications based on the life cycle assessments carried out. Other cements can also be taken into account after a simple conversion. The analyses show that the circular system has a slightly lower GWP when assuming the same transport distances and the same cement content but a slightly higher superplasticizer content. [ABSTRACT FROM AUTHOR]

The construction industry contributes the highest carbon dioxide (CO2) emissions, in which concrete production is one of the key components. Extracting and transporting raw materials such as limestone and aggregates contribute to habitat destruction and pollution. This study deals with the relative assessment of a group of commonly used concretes at varied strength levels using emergy analysis and life-cycle assessment (LCA). Six types of concrete are considered for evaluation: normal, binary blended, ternary blended, quaternary blended, alkali-activated and recycled aggregate concrete (RAC). Emergy analysis considers different qualities and quantities of inputs, providing insights on resource-based impacts through emergy indicators. LCA, conducted using the SimaPro software, evaluates the environmental impacts of concrete production using midpoint and endpoint indicators. From emergy analysis, it is observed that concrete with alternative materials such as fly ash, silica fume, ground granulated blast-furnace slag and recycled aggregate exhibits better results in terms of emergy indicators. RAC shows the highest value of emergy sustainability index in all strength ranges. In LCA, higher impacts are seen for normal concrete, followed by those for RAC. To obtain a more inclusive result, an integrated emergy–LCA index is proposed. The results from this index aid in improved decision making regarding the sustainability of the system considered. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The water environment greatly affects the creep deformation of recycled aggregate concrete (RAC). Hence, a humidity–stress–damage coupling numerical model was used for investigating the time-dependent deformation of RAC in the water environment in this study. Firstly, uniaxial compression and water absorption tests were performed to determine the calculation parameters of the creep numerical simulation of RAC in a water environment. Experimental results indicate that the elastic modulus and compressive strength drop as the water content increases. Then, the time-dependent deformation of RAC in a water environment was studied using a numerical simulation test of compressive creep when multiple stress levels were applied, and the critical stress for accelerated creep and the long-term strength of RAC were obtained. Finally, the influence of confining pressures on the long-term deformation of RAC in a water environment was discussed. When there is no confining pressure, the long-term strength of RAC is 23.53 MPa. However, when a confining pressure of 3.921 MPa is loaded onto RAC, the long-term strength of RAC is 47.052 MPa, which increases by 100%. Increasing confining pressures has an obvious effect on ensuring the long-term stable application of RAC in a water environment. Compared with the creep test, the method adopted in this study saves time and money and provides the theoretical basis for evaluating the time-dependent deformation of RAC in a water environment. [ABSTRACT FROM AUTHOR]

The seismic behavior of six corroded recycled aggregate concrete (RAC) columns with ultra-high-strength bars (UHSB) was investigated through quasistatic test and numerical analysis. The main parameters include different corrosion ratios, axial load ratios (ALR), and stirrup ratios. The results revealed that: The damage development of the corroded specimen sped up with increasing corrosion ratio and ALR, and the corroded specimens suffered brittle shear failure due to the stirrup fracture or the concrete failure. The difference in carrying capacity of the specimens with low corrosion ratios and ALR was relatively small, while the deformation capacity was significantly reduced with increasing corrosion ratios and ALR. Reinforcement corrosion had a minor effect on the strength and stiffness degradation but would reduce the maximum cumulative energy dissipation capacity. By combining residual drift and residual crack width, the corroded specimens all could meet the limit of repairable residual drift and crack width before 4% drift, showing satisfactory resilient performance. Based on the modified corrosion models of materials, the numerical analysis showed the detrimental and coupling impact of the high ALR, high corrosion ratio, and low stirrup ratio on the carrying and deformation capacity. Through numerical analysis data, an equation was proposed that can satisfactorily predict the peak drift of the corroded columns with UHSB. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of recycled aggregate concrete according to the mixing ratio of recycled coarse aggregate(RCA) were analyzed for different design strengths to explore the use of recycled materials in the production of ready-mixed concrete. The results show that, depending on the ratio of recycled aggregate, the compressive strength is similar to that of normal concrete and does not deteriorate. Therefore, it is possible to achieve a target design strength. Furthermore, if the ratio of recycled coarse aggregate for concrete is up to 25% of the total aggregate amount (50% of the total coarse aggregate), slump does not cause problems. Our findings show that the higher the design standard strength, the greater the amount of powder, and the more stringent the management of slump reduction, unit quantity, and performance necessary. The obtained results show that recycled aggregate can be used to produce ready-mixed concrete after adjusting its mixing ratio and concrete mix proportions. [ABSTRACT FROM AUTHOR]

Relatively few studies have been conducted on the seismic performance of recycled aggregate concrete (RAC) shear walls with concealed bracing. To promote the development of high-performance green building structures and the application of RAC in structural components, the seismic performance of RAC shear walls under different influencing factors was tested, and low-cycle reversed loading tests were performed on ten RAC shear walls with different shear-to-span ratios. The test parameters included the recycled coarse aggregate (RCA) replacement ratio, the recycled fine aggregate (RFA) replacement ratio, the axial compression ratio, the shear span ratio and whether to set up the concealed bracing. The influence of the above variables on the seismic performance was then assessed. The results revealed that the bearing capacity, ductility, stiffness and energy dissipation capacity of the RAC shear walls decreased in line with an increase in the replacement ratio of the RFA. However, the bearing capacity, energy consumption and stiffness of the RAC shear walls decreased within 10% and the ductility decreased within 15%. The RAC shear walls were able to meet the seismic requirements of the building structure after reasonable design and use. As the axial compression ratio increased, the bearing capacity of the RAC shear walls improved, but their elastic–plastic deformation capacity was reduced. Setting the concealed bracing significantly improved the seismic performance of the RAC shear walls, such that they achieved a seismic performance close to that of the natural aggregate concrete (NAC) shear wall. After setting up the concealed bracing, the load carrying capacity of the RAC shear walls increased by up to 15%, the ductility increased by up to 20% and the energy consumption capacity increased by up to 50%. A mechanical calculation model of the RAC shear wall was then established by considering the effect of recycled aggregate, the calculated results of which were a good match with the test results. [ABSTRACT FROM AUTHOR]

Through the use of recycled aggregates, the construction industry can mitigate its environmental impact. A key consideration for concrete structural engineers when designing and constructing concrete structures is compressive strength. This study aims to accurately forecast the compressive strength of recycled aggregate concrete (RAC) using machine learning techniques. We propose a simplified approach that incorporates a two-layer stacked ensemble learning model to predict RAC compressive strength. In this framework, the first layer consists of ensemble models acting as base learners, while the second layer utilizes a random forest (RF) model as the meta-learner. A comparative analysis with four other ensemble learning models demonstrates the superior performance of the proposed stacked model in effectively integrating predictions from the base learners, resulting in enhanced model accuracy. The model achieves a low mean absolute error (MAE) of 2.599 MPa, a root mean squared error (RMSE) of 3.645 MPa, and a high R-squared (R2) value of 0.964. Additionally, a Shapley (SHAP) additive explanation analysis reveals the influence and interrelationships of various input factors on the compressive strength of RAC, aiding design and construction professionals in optimizing raw material content during the RAC design and production process. [ABSTRACT FROM AUTHOR]

Objective: This study investigates the influence of high-temperature treatment on the deformation properties and structural deformation of recycled aggregate concrete (RAC) in response to potential fire hazards in the construction industry. Methods: Standard-cured 28-day RAC specimens were subjected to microwave heating at 300 °C and 600 °C, with subsequent uniaxial compression tests utilizing a WDW-2000 machine and a VIC 3D strain measurement system to analyze strain data through digital image correlation (DIC) technology. Results: After treatment at 300 °C, recycled aggregate concrete (RAC) demonstrated superior mechanical properties to fresh concrete aggregates. This enhancement may be attributed to the more robust siloxane bonds (Si-O-Si) in the recycled materials. Conversely, exposure to 600 °C intensified internal structural damage, notably lowering the material's elastic modulus and peak stress. DIC analysis highlighted the correlation among temperature, volumetric strain, and crack development patterns, with more extensive cracking at 600 °C. Conclusions: Moderate-temperature treatment enhances RAC's structure and deformation properties, while high-temperature treatment diminishes its performance. These findings provide valuable insights for assessing building safety post-fire and the application of RAC, emphasizing its suitability at moderate temperatures and risks at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract Recycled aggregate concrete (RAC) is recognized as an environmentally friendly construction material derived from reclaimed concrete components. This paper aims to conduct a comprehensive scientometric analysis of RAC research published between 2000 and 2023 in the Web of Science core database. The study includes analyses of publication trends over time, contributions and collaborations among authors, productivity of institutions and countries, co-citation networks, and keyword co-occurrence patterns. Additionally, the research identifies emerging frontiers in RAC studies. The results are visually presented to provide a holistic overview of the current state of RAC research and future developmental trajectories. The study analyzes publication trends over time, with over 80% of the papers published after 2017, reflecting the growing interest in sustainable construction. Key trends identified include the increasing focus on improving the mechanical properties and durability of RAC, microstructural analysis, and innovative manufacturing techniques. While the field has advanced significantly, challenges remain in areas such as the integration of nanoparticles, biomineralization techniques, carbon capture and utilization, and 3D printing technologies. These challenges underscore the need for continued innovation and exploration. With these advancements, RAC has the potential to play a pivotal role in promoting sustainable construction practices in the future.

The pores in steam-cured concrete affect its strength and durability, and optimisation of the steaming system can improve the pore structure to some extent. However, the influence mechanism of evaporation on recycled aggregate concrete (RAC) remains unclear. In this paper, the effects of curing temperature (20°C, 40°C, 60°C and 80°C), steam curing time (6 h, 9 h and 12 h) and pozzolans (slag powder and fly ash) on the compressive strength and pore structure of RAC were studied. The microstructure characteristics such as pore size and pore size distribution were analysed by mercury injection porosimetry. The results show that steam curing can significantly improve the compressive strength and reduce the most probable aperture and average pore sizes of RAC. Moreover, the effect of slag powder on RAC pore structure is better than that of fly ash. Also, there is a linear correlation between the compressive strength and the average pore size of steam-cured RAC. This could be an important parameter for constructing future steam-cured RAC strength prediction models. [ABSTRACT FROM AUTHOR]

The application of recycled aggregate is crucial for waste concrete recycling, while the loading rate significantly influences the fracture behavior of recycled aggregate concrete. Herein, we investigate the effect of loading rate on the flexural and fracture behaviors of recycled aggregate concrete, along with associated acoustic emission characteristics. Results show that the flexural strength and energy absorption capacity maximum increase by 15.18% and 38.39%, respectively, as the loading rate rises. As the loading rate increases from 0.05 to 1 mm/min, peak frequency is primarily clustered in 0 ~ 75 kHz and 75 ~ 225 kHz and tends to be dense, while the b value decreases by 19.28%, 23.30%, and 30.17%, respectively. Additionally, the proportion of shear failure also decreases, which relates to the high energy release rate. Further, the multifractal spectrum α − f(α) resembles a quadratic distribution, with both multifractal intensity ∆f and spectrum width ∆α showing a downward trend as the loading rate rises. Highlights: Interaction of loading rate and recycled coarse aggregate is investigated.Rate effect on flexural and fracture behaviors is analyzed.AE response to rate‐dependent flexural behaviors is analyzed.Rate‐dependent multifractal characteristics of AE signals are explored. [ABSTRACT FROM AUTHOR]

Concrete production contributes significantly to global greenhouse gas emissions, and its manufacture requires substantial natural resources. These concerns can be partly mitigated by recycling construction demolition waste as aggregates to produce Recycled Aggregate Concrete (RAC). RAC has gained momentum due to its lower environmental impact, production costs, and increased sustainability. The aim of this study was to advance the reasonable use of recycled aggregate in concrete and achieve optimal mixture ratio design. Four advanced machine learning algorithms, Support Vector Machine (SVR), Light Gradient Boosting Machine (LGBM), Random Forest (RF), and Multi-Layer Perceptron (MLP), were employed, and the novel optimization algorithms, biogeography-based optimization (BBO), Multi-Verse Optimizer (MVO) and Gravitational Search Algorithm (GSA), were integrated to to predict the compressive strength of RAC. Six potential influential factors for RAC strength were considered in the models. The study employed four evaluation metrics, Taylor diagrams and Regression Error Characteristic plots to compare model performance. The result shows LGBM-based hybrid model outperformed other methods, demonstrating high accuracy in predicting compressive strength. The Shapley Additive Explanation (SHAP) results emphasize the importance of understanding the interactions between the various factors and their effects on the mechanical properties of the RAC. The findings can inform the development of more sustainable and environmentally friendly building materials. [ABSTRACT FROM AUTHOR]

The durability of recycled aggregate concrete (RAC) in the marine environment is mainly influenced by chloride attack. In this paper, the chloride transport law in RAC with different recycled coarse aggregate (RCA) contents was investigated by dry-wet cycling tests considering RCA volume fractions. A five-phase randomly convex polygonal aggregate model was built through a self-compiled program and then a mesoscopic numerical method was established by finite element software development. The proposed numerical model was validated by experimental results and data from other scholars. The impact of interfacial transition zone (ITZ), RCA, new mortar and old mortar were studied. The results showed that: 1) As the thickness of ITZ grows, the chloride diffusion coefficient increases in RAC. When the thickness of the ITZ rises from 25 µm to 100 µm, the chloride diffusion coefficient rises by 37%; 2) The diffusion coefficient of ITZ and mortar have a positive impact on the diffusion of chloride ion in RAC; 3) The chloride diffusion coefficient of RAC is positively correlated with the volume fraction of RCA (VRCA). The chloride diffusion coefficient increases by 102.0% as the VRCA increases from 0% to 50%. The proposed mesoscopic model not only effectively simulates the chloride attack process but also can be used to simulate other ionic attack behaviors and mechanical properties of RAC.

The durability of recycled aggregate concrete (RAC) in the marine environment is mainly influenced by chloride attack. In this paper, the chloride transport law in RAC with different recycled coarse aggregate (RCA) contents was investigated by dry-wet cycling tests considering RCA volume fractions. A five-phase randomly convex polygonal aggregate model was built through a self-compiled program and then a mesoscopic numerical method was established by finite element software development. The proposed numerical model was validated by experimental results and data from other scholars. The impact of interfacial transition zone (ITZ), RCA, new mortar and old mortar were studied. The results showed that: 1) As the thickness of ITZ grows, the chloride diffusion coefficient increases in RAC. When the thickness of the ITZ rises from 25 µm to 100 µm, the chloride diffusion coefficient rises by 37%; 2) The diffusion coefficient of ITZ and mortar have a positive impact on the diffusion of chloride ion in RAC; 3) The chloride diffusion coefficient of RAC is positively correlated with the volume fraction of RCA (V RCA). The chloride diffusion coefficient increases by 102.0% as the V RCA increases from 0% to 50%. The proposed mesoscopic model not only effectively simulates the chloride attack process but also can be used to simulate other ionic attack behaviors and mechanical properties of RAC. [ABSTRACT FROM AUTHOR]

In this paper, five specimens were designed to test under monotonic static loading to study the axial compression performance of steel tube‐reinforced high‐strength recycled aggregate concrete composite columns with steel bars. The design parameters for these specimens include the type of concrete, the sectional shape of the steel tube (circular or square), and the internal structure of the core column, specifically the presence or absence of cross‐shaped tie bars in the square steel tube. The effects of different parameters on the axial load–displacement curve, bearing capacity, and ductility were analyzed. The test results show that the failure of all specimens was caused by the concrete cover spalling of outer reinforced concrete, which occurred after the longitudinal strain of the steel tube exceeded the yield strain. The ultimate bearing capacity of the recycled aggregate concrete (RAC) specimen is higher than that of the natural aggregate concrete (NAC) specimen, but the latter has a more robust deformation performance. Furthermore, under the condition of the same steel tube cross‐sectional area and similar material strength, the bearing capacity and deformation capacity of specimens with circular steel tubes are higher than those of specimens with square steel tubes. A similar conclusion was also obtained for square steel tube specimens with cross‐shaped tie bars. Finally, four international design methods were applied to estimate the axial compression capacity of 40 composite columns, as detailed in this paper and other sources. [ABSTRACT FROM AUTHOR]

In recent years, wind energy has begun to receive a significant amount of attention as clean energy is utilised and demanded in large quantities, resulting in a sharp increase in the use of wind turbines. The demand for wind turbines has gradually risen due to the clean and recyclable nature of wind energy. The current blade life of wind turbines in China is about 20 years, which means that the disposal of obsolete used blades can become a difficult problem in the future. Therefore, this study is of great significance to explore the regeneration performance of the blades after recycling and disposal. In this paper, wind turbine blades were mechanically recycled into recycled macrofibres, which were added to concrete as a reinforcing material to make wind impeller fibre concrete (WIC), and the three proportion ratios of 1%, 1.5%, and 2% were explored to compare the performance. The performance of WIC was also evaluated and its performance was compared to that of glass fibre concrete (GC). In addition, the material physical properties of second-generation recycled aggregate concrete (RAC) based on WIC were explored. The strength and peak strain variations and their causal mechanisms were analysed both macroscopically and microscopically by means of the classical mechanical tests (compression and bending tests), SEM, and XRD. The results show that the compressive strength of WIC was negatively correlated with the fibre content and increased by 6.04–18.12% compared to that of ordinary concrete (OG), with a maximum of 19.25 MPa; the flexural strength was positively correlated with the fibre content, with an increase of 5.37–18.5%. The microstructural analysis confirmed the macroscopic results and the intrinsic model better validated the experimental results. [ABSTRACT FROM AUTHOR]

Rising environmental awareness has prompted in‐depth studies on how the concrete industry affects the environment. Using recycled concrete aggregates (RCAs) and supplementary cementitious materials (SCMs) in concrete manufacturing provides advantages for sustainability. However, the broader chemical composition of SCMs and the inferior qualities of RCAs compared with natural aggregates (NAs) often lead to a decrease in concrete mechanical strength. The difficulty lies in foreseeing how the inclusion of SCMs and RCAs will affect the concrete compressive strength. The artificial neural network (ANN) approach presented herein can precisely forecast the recycled aggregate concrete (RAC) compressive strength, even when incorporates SCMs. The analysis employing the connection weight approach (CWA) determines how input variables influence compressive strength. Results indicate silica fume contributes most to compressive strength, followed by cement content, silica modulus, fine natural aggregate dosage, and coarse natural aggregate. Additionally, the amount of water utilized, the water/cement ratio, and the presence of RCA are all detrimental to compressive strength. The adverse effect of the cementitious materials' alumina modulus can be attributed to increased water demand during their reaction. Performance metrics of the final ANN model on the testing data subset include R2 = 0.94, and RMSE = 3.11, utilizing 834 data observations after outlier treatment for training and validation purposes. In summary, the ANN‐based approach demonstrates its efficacy in predicting concrete compressive strength when incorporating SCMs and RCAs, shedding light on the influential factors in concrete performance. [ABSTRACT FROM AUTHOR]

A branch of artificial intelligence called machine learning is well-positioned as a prediction method that can take into consideration several influencing factors and complex inter-factor connections. Without being specifically trained to do so, these machine learning models have the ability to generalize, predict, and learn from data. Regression theory is a key topic in statistical modelling and machine learning. The main goal of this study is to compare the performance of several popular machine learning regression models for predicting the early-age compressive strength of concretes made from recycled concrete aggregates from a structure that demolished following the Sivrice-Elazig earthquake on January 24, 2020. Early-age concrete compressive strength is even more crucial due to factors like the fact that there are thousands of newly built structures in the aftermath of the earthquake, the quick manufacturing of these structures, and the completion of the project in the lowest amount of time. Determining the early-age concrete strength with high accuracy and in a useful manner is crucial for this reason. Seven different classical machine learning algorithms were employed in this study to achieve all of these goals. Early-age concrete compressive strength values were considered for 1 and 3 days. The relationship between the experimental results and the predicted outcomes of the employed algorithms was investigated, and a thorough comparison of these intelligent regression algorithms was conducted. Within the scope of sustainable development and circular economy goals, it is thought that this article will make significant contributions to the literature in terms of utilizing these waste materials and determining the earlyage compressive strengths of the concretes produced with high accuracy. [ABSTRACT FROM AUTHOR]

The present study illustrates the susceptibility of optimized-quality recycled concrete aggregate (RCA) to supplementary cementitious materials (SCMs), such as silica fume (SF), ground granulated blast slag (GGBS), and mechanically produced recycled fine (M-Fine or MF), in concrete. According to the present research, old interfacial transition zone (OITZ) characteristics may be controlled if RCA is developed in such a way as to reduce mortar adhesion optimally. It may facilitate the penetration of binder particles, strengthening the OITZ even further. A high-quality surface may improve RCA's self-cementing properties, which strengthen the new ITZ (NITZ). The combined effect may yield RCA characteristics equivalent to parent aggregate when interacting with a cement matrix based on SCMs. Substituting the cement with SF (11%), GGBS (14%), and MF (15%) contributes to the compressive strength of recycled aggregate concrete (RAC) up to 11.61% via strengthening the OITZ. SF and GGBS further enhance RAC tensile strength in a similar way to how they enhance natural aggregate concrete (NAC) tensile strength. The elastic modulus (MOE), fracture energy, and durability characteristics of RAC with SF and GGBS are significantly improved. RAC with MF (15%) shows compressive and tensile strength comparable to RAC with GGBS (14%) with marginal reductions in flexural strength. In comparison to RAC, RAC with MF has a 2.9% lower MOE. RAC-MF has 1.82% higher fracture energy than RAC. RAC-SF, RAC-GGBS, and RAC-MF have significantly reduced water absorption and water absorption rate (sorptivity) than RAC. There is a strong correlation between the compressive strength of RAC, RAC-SF, RAC-GGBS, and RAC-MF, and their UPV with R2=0.92. The sorptivity and electrical resistivity are also correlated with R2=0.86. SEM images show uniform and dense microstructure and EDS analyses shows Si-rich C-S-H gel formation, resulting in superior mechanical and durability properties in RAC with SCM compared to RAC. Practical Applications: About 20% to 30% of recycled fines (M-Fines) below 150 μm are generated during RCA processing from construction and demolition waste. In addition, M-Fines are also generated during the removal of the mortar attached to the RCA. Thus, M-Fines as by-products of mechanical processing of RCA could be used as cementitious materials. Despite M-Fine's low reactivity compared to SF, it may produce strength and durability characteristics comparable to other conventional supplementary cementitious materials like GGBS. In structural concrete, optimized-quality recycled concrete aggregates with supplementary cementitious materials, including M-Fines, can be used. In this way, it may be possible to promote construction and demolition waste recycling operations. Moreover, the effectiveness of SF and GGBS with RCA, as well as the performance of RAC-MF, may encourage the use of RAC as structural concretes and M-Fines as supplementary cementitious materials. [ABSTRACT FROM AUTHOR]

The effect of binary blending of recycled aggregates and nylon fibers on the workability and flexural strength of concrete has been investigated in this work. An equal dosage of recycled aggregates from demolished wastes and conventional aggregates was used with 0.5 water cement ratio in preparing a mix of 1:2:4. Nylon fibers were used from 0% to 2% with an increment of 0.25% by weight of cement to reinforce the concrete. The slump cone test was determined for all nine batches of the concrete. Workability was observed to reduce with an increase in the content of nylon fibers. Flexural strength was evaluated by testing three prism specimens of 150mm x 150mm x 500mm size in each batch. A comparison of test results with control concrete (0% nylon fibers) and recycled aggregate concrete (with 50% recycled aggregates and without fibers) showed that nylon fibers helped in overcoming the loss of flexural strength due to the addition of recycled aggregates. The optimum dosage was recorded as equal to 1.5% with an increase in strength equal to 19.13% and 52.45% in comparison to conventional and recycled aggregate concrete. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recycled aggregate concrete (RAC) is increasingly being used in the construction of structural elements. However, the performance of RAC elements under fire is usually considered to be inferior to that of normal concrete (NC) elements. This study investigates the fire behavior of RAC composite steel slabs with and without openings. Ten slabs of size of 1.0 m × 2.2 m were cast either with no opening, one or two circular openings, and one or two square openings. Five of the slabs were manufactured with 100% RAC, while the other five slabs were made with NC. The concrete slabs were loaded and subjected to fire tests at a temperature of about 900°C for 120 min. Test results show that RAC composite slabs have lower stiffness (thus larger mid‐span deflections) under fire exposure compared to their counterpart NC slabs. In terms of the recorded temperature–time curves, RAC slabs showed similar performance to that of NC slabs. The ratio of soffit temperature to the temperature at the top of slab was considerably smaller for RAC slabs compared to NC slabs. RAC slabs also showed more spalling than NC slabs. Experimental test results were numerically verified using PyroSim® software with the two showing good agreement. A series of new design charts for composite RAC slabs with desired fire endurance are proposed. This study is expected to promote the wider use of RAC in construction of structural elements, particularly of composite slabs exposed to extreme temperatures. [ABSTRACT FROM AUTHOR]

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]

Adding polypropylene fibre (PPF) to recycled aggregate concrete (RAC) not only improves performance but also has economic benefits. The effects of single-blend and double-blend micro- and macro-PPFs in RAC specimens were studied. Micro- and macro-PPFs were used to design and produce 30 groups of PPF-reinforced RAC specimens with 0%, 25% and 50% coarse aggregate (CA) substitution rates. Controlling the fibre mixing proportions, the stress–strain curve, elastic modulus, peak strength, peak strain and acoustic emission amplitude–frequency extremum (AFE) of each group of specimens were obtained. The elastic modulus and peak stress of specimens without PPFs decreases gradually with an increase of the CA substitution rate. However, there was a certain increase in elastic modulus and peak stress when PPFs were added. A damage constitutive model for PPF-reinforced RAC was established. By fitting this model, it was found that although the elastic modulus and peak stress of the RAC specimens increased by a certain extent, the fitting parameters of RAC were greater than those of ordinary concrete and the RAC post-peak strength was lower. The evolution law of acoustic emission AFE of PPF-reinforced RAC was studied. It was found that the cumulative AFE of RAC with PPF was larger, indicating that the PPFs limited crack propagation and increased the fracture energy. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The modification methods of pozzolan slurry combined with sodium silicate and silicon-based additive were respectively adopted to treat recycled coarse brick-mixed aggregate (RCBA) in this study. The compressive strength and chloride permeability resistance of recycled aggregate concrete (RAC) before and after modification treatment were tested, and the microstructure of RAC was analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The results show that the physical properties of RCBA strengthened by modification treatment are improved, and the compressive strength and chloride permeability resistance of treated RAC are also significantly improved. The modification treatment optimizes the pore size distribution of RAC, which increases the number of gel pores and transition pores, and decreases the number of capillary pores and macro pores. The surface fractal dimension shows a significant correlation with chloride diffusion coefficient, indicating that the variation of chloride permeability of treated RAC is consistent with the microstructure evolution. [ABSTRACT FROM AUTHOR]

With the increasing scarcity of natural gravel resources and increased production of construction and demolition waste, recycled aggregates offer prospects for concrete structures. However, the adhered loose and porous mortar and microcracks in recycled aggregates led to impaired mechanical behavior of recycled aggregate concrete (RAC) and reduced durability in harsh environments, significantly restricting its engineering application. Compression-casting can solve the problems of low strength and poor durability of RAC; however, it induces significant brittleness of concrete in compression. This study proposed an improvement in the ductility of compression-cast RAC through confinement using fiber-reinforced polymer (FRP) laminates. A total of 32 FRP-confined compression-cast cylinder specimens were tested under uniaxial compression, with variables including concrete mixture proportion, FRP thickness, and concrete casting method. The experimental results showed that the ultimate axial stresses of the unconfined RAC and FRP-confined RAC increased by up to 34.8% and 14.5%, respectively, and the ultimate axial strain decreased by up to 49.0% with compression-casting. Furthermore, the compression-casting method resulted in an 8.5% reduction in the measured average rupture strain of the FRP. The confinement efficiency was not significantly affected by compression-casting, as indicated by a slightly greater slope of the strength enhancement ratio with an increase in the confinement ratio for FRP-confined compression-cast RAC. Stress–strain models of FRP-confined compression-cast and normal RAC were proposed based on test data from this study and the literature. It was found that the proposed model improved the prediction accuracy of the stress–strain behavior compared with existing models. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The employment of recycled materials from construction and demolition waste (CDW) for mixing recycled aggregate concrete (RAC) is widely practiced in developed countries. In Vietnam, however, being a developing country with a rapid rate of urbanization, especially in major cities, the substantial amount of CDW generated is still mainly treated by landfilling. To promote the recycling of CDW, studies of the performance of structural members fabricated with recycled aggregates must be conducted, which are lacking in quantity in Vietnam. Adopting a standard experiment set up of reinforced beams, the study employed local recycled coarse aggregates in Hanoi, Vietnam, produced from crushed concrete and crushed brick (which is mixed with crushed concrete at controlled percentages) to conduct experiments to observe flexural behaviors with reference to equivalent natural aggregate concrete (NAC) such as cracking load, ultimate load, crack pattern, crack width, etc. The results showed that the ultimate loads were only reduced by less than 10% for all percentages of recycled coarse aggregate produced from crushed brick in the concrete mix, compared to the reference beams using NAC. However, the cracking loads of RAC beams were significantly reduced by 17.86% to 50.45% when increasing the content of crushed brick from 0% to 70%. Moreover, together with an increase in the number of flexural cracks, the deflections of RAC beams also increased with increasing content of crushed brick, demonstrating a reduction in the stiffness of the beams. These observations may serve as recommendations to structural engineers in Vietnam when designing flexural RAC members. [ABSTRACT FROM AUTHOR]

Soft computing techniques have become popular for solving complex engineering problems and developing models for evaluating structural material properties. There are limitations to the available methods, including semi-empirical equations, such as overestimating or underestimating outputs, and, more importantly, they do not provide predictive mathematical equations. Using gene expression programming (GEP) and artificial neural networks (ANNs), this study proposes models for estimating recycled aggregate concrete (RAC) properties. An experimental database compiled from parallel studies, and a large amount of literature was used to develop the models. For compressive strength prediction, GEP yielded a coefficient of determination (R2) value of 0.95, while ANN achieved an R2 value of 0.93, demonstrating high reliability. The proposed predictive models are both simple and robust, enhancing the accuracy of RAC property estimation and offering a valuable tool for sustainable construction.

It is important to clarify the uniaxial compressive mechanical properties and fracture mechanism of recycled aggregate concrete (RAC) from a mesoscale perspective for its further application in engineering. In this study, the cohesive zone model (CZM) based on the Benzeggagh–Kenane (B–K) criterion was used to simulate the RAC's complex fracture behavior. Meanwhile, the effects of cohesive element parameters and mechanical properties of mesoscale components on macroscopic mechanical properties and damage modes of RAC were investigated. The results show that the CZM based on the B–K criterion can be used to characterize the whole fracture process of RAC. The RAC's compressive strength has an exponential relationship with the shear strengths of the mortars as well as the ITZs and is quadratically related to the logarithm of cohesive element stiffness. The RAC's damage morphology is more sensitive to the change of element stiffness, Mode II fracture energy and hybrid fracture energy ratio.

The construction industry is shifting towards sustainability, emphasizing the need for innovative materials. Recycled Aggregate Concrete (RAC), utilizing recycled aggregates, emerges as a promising eco-friendly solution to minimize waste and resource utilization. However, accurately predicting its compressive strength (CS) is challenging due to varying composition and properties. This study addresses this issue by employing machine learning models, specifically five gradient boosting algorithms: Gradient Boosting Machine (GBM), LightGBM, XGBoost, Categorical Gradient Boost (CGB), and HistGradientBoosting (HGB). A total of 314 mixes from relevant published literature were aggregated to train the models. These models are meticulously fine-tuned through hyperparameter optimization for optimal predictive performance. The study also introduces SHAP (SHapley Additive exPlanations) algorithms for model interpretability, elucidating feature contributions to predictions. The results revealed that among the five gradient boosting models, CGB demonstrated the highest R2 value of 92% on the testing set, while LightGBM exhibited the lowest Coefficient of Determination (R2) value of 88%. Additionally, CGB achieved the lowest Root Mean Square Error (RMSE) of approximately 4.05, whereas XGBoost showed the highest RMSE of around 4.8. Furthermore, for Mean Absolute Error (MAE), LightGBM recorded the lowest value of approximately 3.16, while HGB yielded the highest MAE of about 3.8. The SHAP analyses reveal influential features impacting RAC strength, highlighting the significance of cement, water, sand, and recycled aggregate water absorption in predicting RAC compressive strength.