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Concrete waste recycling processes involve multiple stages, equipment, and procedures which produce Fine Recycled Concrete Aggregates (FRCA) for use in construction. This research aims at performing a comprehensive overview of the recycling technologies, recycling processes, and normative requirements to produce high-quality FRCA and to investigate the influence of these processes on their physical properties. The properties investigated were the particle size distribution (PSD), water absorption, oven-dry density, and adhered paste. The correlations between these properties were also investigated. The results indicate that the recycling processes with the highest potential for producing high-quality aggregates demand jaw crusher and impact crusher combinations. These processes are better suited for achieving FRCA with the desired particle size distribution and oven-dry density. However, water absorption and adhered paste, which are critical factors for obtaining high-quality FRCA, seem to be more dependent on the original material than on the recycling process.

Using recycled aggregates is crucial for a more sustainable environment and economy. In this study, the properties of recycled aggregate-based SIFCONs were examined. In the scope of the study, compressive strength, high-temperature resistance, sorptivity, and fracture energy of SIFCONs produced with recycled aggregate were investigated. The results were compared with those of the limestone-bearing SIFCONs. It was determined that the compressive strength and fracture energy of SIFCONs produced with recycled aggregate were 61.2 MPa and 14.9 N/mm, respectively. Although these values are lower than those of SIFCONs produced with limestone, it has been determined that recycled aggregates are advantageous in high-temperature resistance. The results demonstrated that the recycled aggregate could be used to produce SIFCON.

Accelerated carbonation is suggested as a potential alternative for carbon dioxide sequestration, which also improves the microstructure of recycled concrete aggregates. In this study, the carbonation parameters of model aggregates derived from cement pastes with two different water/cement ratios (i.e., 0.5 and 0.7) were evaluated in order to maximize the benefits of the carbonation process on their density and absorption. For this purpose, in a first phase, the initial moisture content of the model aggregates and the reaction time were evaluated. Furthermore, in a second phase of mortar production, the fraction of fine natural aggregates was replaced, considering each type of unprocessed and carbonated model aggregate at volumetric replacement percentages of 50% and 100%, varying the amount of water in the mortar mix to maintain a similar workability in all the series. In this way, the properties of the eight series of mortars are evaluated in comparison with the control series made only with natural aggregates. The results indicate that the accelerated carbonation process positively influences density and absorption in the model aggregate. Regarding the parameters of the accelerated carbonation environment analyzed, for a higher w/c ratio in the original model aggregate, higher initial water content was necessary for the carbonation process to be efficient. As for the mechanical performance of the mortars with model aggregate, the series that incorporated model aggregate aggregates with a w/c ratio of 0.5 achieved better mechanical behavior compared to the series replacing model aggregate with a w/c ratio of 0.7; this was related to the formation of a more compact matrix in the mortar with model aggregate of cementitious pastes.

This study used recycled aggregate (RA) and mineral additions to design large-pore sandy recycled concrete (LPSRC) using a design porosity (DP) of 25 %, 20 %, and 15 %. Thus, the related effects of recycled coarse aggregate (RCA), recycled fine aggregate (RFA) and fly ash (FA) on the compressive strength, frost resistance (using slow and fast freezing methods), and sulfate attack properties of LPSRC were systematically studied. Moreover, to reduce the error between the design and theoretical porosity values, the bulk density ratio adjustment method was employed to design the theoretical porosity. The results of binarization analysis demonstrated that the deviation of the actual porosity caused by the sidewall effect was ∼2 %, which should be considered during DP design and performance evaluation. The compressive strength of the LPSRC after 56 curing days increased by 35.9 % on average as the DP was reduced from 25 % to 15 %. In a freeze–thaw cycle test, the slow freezing method was more accurate for evaluating the frost resistance of the LPSRC. Under the same conditions, the mass loss rate of the LPSRC calculated using the slow and fast freezing methods was 3.2 % and 7.62 %, respectively. This distinction is pivotal for establishing reliable frost resistance criteria for LPSRC in cold-weather applications, complementing previous research in the field. In terms of sulfate deterioration resistance, compressive strength corrosion factors decreased with increasing DP. Additionally, damage was mainly concentrated at the contact interface between RCA and the cement matrix, while the aggregate itself showed relatively little damage, suggesting RCA application has a positive effect on improving preparation of the LPSRC. Specifically, as DP increased from 15 % to 25 %, the average reduction in the compressive strength corrosion factors for LPSRC after 30 and 60 times of dry–wet cycle were 9.64 % and 8.37 %, respectively, illustrating a clear correlation between higher DP and reduced sulfate resistance. This study contributed to the LPSRC design and production using RCA, RCF and FA, that positively impacts to the sustainable development of the construction industry and helps to evaluate the effectiveness of RA in macroporous concrete. Moreover, the strategic implementation of design porosity has been shown to optimize the structural integrity and performance of the concrete, achieving a balance between strength and workability, which is crucial for the concrete's durability and its ability to adapt to various environmental conditions.

In this research, sustainable sand was developed using desert sand with recycled fine aggregate. Developing sustainable sand can solve environmental issues caused by excessive river sand mining. For this purpose, four types of sustainable sand have been developed. The present study has developed a method to optimize desert sand by incorporating recycled crushed sand from demolished concrete. The developed sand properties were well within the ASTM and British standards recommendations. A chemical analysis of SEM-EDS and FTIR was also performed on the developed sand. The 50 % addition of desert sand separately with 50 % recycled crushed sand is effected to reach the fineness modulus well within the specified range (2.4–3.0) set by the standard code. Four concrete mixes were prepared with developed sand using the absolute volume method. The compressive strength increment was evaluated at 3, 7, 28, 56, 91, and 360 days of curing. The developed sand mixes with fineness modulus values 2.6, 2.7, and 2.8 successfully pass criteria 1 and 2 set for this study at 28 days of curing. The prepared mix with the lowest fineness modulus value of 2.4 successfully achieved criterion 1 and failed to reach criterion 2. It shows that the fineness modulus value significantly influences the concrete strength. The flexural strength of all mixes surpassed the standard requirement. The study concluded that desert sand is a useful fine aggregate with recycled crushed sand when utilized at the optimum value. Hence, the developed sustainable sand can replace river sand in concrete production.

This study addresses the critical challenge of estimating compressive stress in rubberized recycled aggregate concrete, a key concern for sustainable construction. By integrating empirical data and machine learning techniques, particularly Extra Gradient Boosting (XGBoost), this research aims to enhance predictive models for structural performance assurance. Utilizing a dataset comprising 3840 stress-strain responses collected from 60 rubberized concrete mixtures, with 12 input variables, the study employs statistical analyses and regression to validate the model's performance. The XGBoost model demonstrates robust predictive capability, with low mean absolute error values (1.551 for testing and 0.967 for training) and high a20−index (0.917 for testing and 0.933 for training), effectively predicting compressive stress. Key factors influencing compressive stress were identified through Shapley's additive explanations. The developed model offers a practical tool for predicting stress-strain behavior in rubberized concrete formulations, with implications for mix design optimization and testing cost reduction. Additionally, the introduction of a user-friendly GUI facilitates interaction with the developed XGBoost model, further enhancing its practical application in sustainable construction practices. This study also includes the comprehensive database utilized in modeling, along with the developed Python code, provided as supplementary files. Future directions include exploring the influence of different types and sizes of rubber aggregates on concrete, particularly in high-strength and ultra-high-strength mixtures, and investigating the impact of outliers on model prediction performance.

Copyright of GeSec: Revista de Gestao e Secretariado is the property of Sindicato das Secretarias e Secretarios do Estado de Sao Paulo (SINSESP) 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.)

In the present study, we investigated the mechanical performance of concrete composed of non-selected construction and demolition waste (C&DW) sourced from both old and new sections of an inactive waste landfill site in Karaj, Iran. Initially, we determined the composition of the coarse and fine C&DW used in concrete production. Subsequently, we meticulously examined the physical and chemical properties of both the C&DW and virgin materials to enable thorough comparisons of the results. We then conducted experimental analyses on 33 concrete mixtures containing recycled C&DW, utilizing various tests, including a compressive strength test (CST) for cylindrical and cubic samples, modulus of elasticity (MOE), wide wheel abrasion test (Capon test), British pendulum number (BPN), and ultrasonic pulse velocity (UPV) test. We considered both non-separated fine and coarse C&DW at different replacement ratios in the recycled concrete (RC). Our findings indicate that using non-separated coarse and fine C&DW in concrete yielded satisfactory results, leading to significant savings in virgin materials required for concrete preparation and promoting sustainable development. Furthermore, non-selected C&DW proved to be a viable sustainable material for similar concrete applications. The results revealed a decrease in brick material consumption in various constructions over the past 20 years in Karaj, contributing to the enhanced strength of C&DW concrete. However, the presence of clay minerals in aged landfill sites can adversely affect concrete performance as a potential destructive factor. Despite the possible negative impact of incorporating fine recycled C&DW materials on concrete mechanical performance, the Capon test results demonstrated that the presence of coarse C&DW can enhance concrete's wear resistance. [ABSTRACT FROM AUTHOR]

Copyright of Tikrit Journal of Engineering Sciences is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) 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 purpose of this study is to investigate the macro and micro properties of stabilized recycled aggregate base layers using gypsum slag cement (GSC) and compare them with ordinary Portland cement (OPC). To achieve this, four levels of recycled aggregate content (0%, 50%, 60%, 70%) and three levels of binder materials (3.5%, 4.5%, 5.5%) were designed, where the binding materials included OPC and GSC. When GSC is used as the binding material with 0% recycled content, two scenarios for the ratio of slag to activator are considered: 4:1 and 4:2. For recycled content of 50%, 60%, and 70%, only the 4:1 ratio is considered. The macro-mechanical properties of the composite material were studied through compaction tests, unconfined compressive strength tests, and indirect tensile strength tests. Microscopic properties were investigated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Macroscopic test results indicate that, at an equal binder content, GSC exhibits a higher moisture content and maximum dry density compared to OPC. Moreover, the unconfined compressive strength and indirect tensile strength of GSC are higher than those of OPC. Microscopic test results reveal that the hydration products of both binding materials are essentially similar; however, under identical curing conditions, the hydration products of GSC are more abundant than those of OPC. [ABSTRACT FROM AUTHOR]

The road network in Colombia, as reported by the National Roads Institute of Colombia (INVIAS), comprises a total of 206,708 kilometers, with 142,284 kilometers falling under the rural roads with low traffic volume network category. Sadly, an estimated of 96% of these roads are in poor condition. The primary reason behind this issue is the presence of subgrades that exhibit inadequate mechanical performance, largely due to the lack of proper stabilization methods. Moreover, these roads often serve as the sole access and exit routes for rural communities, significantly impacting their connectivity with nearby urban centers. Recognizing this critical issue, this article proposes the use of coal ash for subgrade stabilization during the construction of low-traffic-volume roads. The study conducted demonstrates that coal ash can enhance the mechanical properties of subgrades, leading to an increase in strength and load-bearing capacity. The improved mechanical properties are attributed to the binding and reactive characteristics displayed by the coal ashes, which greatly contribute to soil stabilization. To verify these claims, a series of physical, mechanical, and strength characterization tests were conducted on both natural and treated clayey sand samples obtained from a rural population in Colombia. The detailed analysis of the results shows an improvement in the mechanical properties of the soil due to the use of coal ash as a stabilizing agent. [ABSTRACT FROM AUTHOR]

Construction, demolition, and renovation activities generate a significant amount of waste, posing serious environmental risks. The scarcity of recycling facilities makes it difficult to implement the new legislation, which calls for producing recycled aggregates. Moreover, the lack of studies on the environmental feasibility of recycling construction and demolition waste in regions with plentiful natural resources of aggregates is a contributing factor to this scarcity. Therefore, this paper studies the environmental feasibility of establishing a construction and demolition waste (CDW) recycling plant. A case study approach compares the CDW recycling process against the traditional quarrying process for generating aggregates. The lifecycle assessment method is used for evaluating both scenarios. Contribution analysis is performed to infer the factors influencing the viability of the recycling process. Thereafter, a sensitivity analysis is conducted to determine the suitability of the proposed location for the recycling facility. As revealed by the single score, the recycling alternative has a 23% more negative environmental impact than quarrying. Nevertheless, there is a chance that the recycling process could be environmentally advantageous. Findings indicated that a total travel distance of 70 km between the demolition site and the construction site is recommended to guarantee environmental feasibility. The transportation distance is found to be the most critical element influencing the environmental feasibility of recycling CDW. The findings of this study help the decision-makers in environmental affairs to consider the influencing factors when constructing a CDW recycling plant. [ABSTRACT FROM AUTHOR]

In order to study the improvement effect of nano-clay and polypropylene fiber on the mechanical properties of recycled aggregates, unconfined compression tests and triaxial shear tests were conducted. The experimental results show that adding polypropylene fibers to recycled aggregates increases the unconfined compressive strength by 27% and significantly improves ductility. We added 6% nano-clay to fiber-reinforced recycled aggregates, which increased the unconfined compressive strength of the recycled aggregates by 49% and the residual stress by 146%. However, the ductility decreased. Under low confining pressures, with the addition of nano-clay, the peak deviatoric stress strength of the fiber-reinforced recycled aggregates first decreased and then increased. When the nano-clay content was 8%, this reached a maximum value. However, under high confining pressures, the recycled aggregate particles were tightly interlocked, so that the improvement effect of the fiber and nano-clay was not obvious. As more nano-clay was added, the friction angle of the fiber-reinforced recycled aggregates decreased, while the cohesion increased. When the content of nano-clay was 8%, the cohesive force increased by 110%. The results of this research indicate that adding both polypropylene fibers and nano-clay to recycled aggregates has a better improvement effect on their strength characteristics than adding only polypropylene fibers. This study can provide a reference for improving the mechanical properties of recycled aggregates and the use of roadbeds. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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 New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials 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.)

Alkali-activated concrete (AAC) features excellent mechanical properties and sustainability. The incorporation of crumb rubber (CR), recycled concrete aggregates (RCAs), and recycled steel fibers (RSFs) can further enhance environmental sustainability. This paper mainly investigated the dynamic behaviors of a novel rubberized AAC incorporating RCAs and RSFs (RuAAC) through Split-Hopkinson Pressure Bar (SHPB) tests. The variables included three types of RSF content (1%, 2% and 3%), five types of rubber content (0%, 5%, 20%, 35% and 50%) and five impact pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa and 0.9 MPa). Dynamic stress–strain curves, dynamic strength, the dynamic increase factor (DIF), impact toughness and the synergistic effects of RSF and CR were discussed. The results show that increasing RSF and CR contents could improve the impact resistance of RuAAC under impact loading. The RuAAC exhibited significant strain rate sensitivity, and the sensitivity increased with larger contents of RSF and CR. The increase in strain rate sensitivity was more pronounced with higher CR contents, which was reflected in larger dynamic increase factor (DIF) values. Under high impact pressure, the impact toughness was obviously enhanced with higher RSF contents, while the contribution of increased CR content to impact toughness was not apparent, which may be attributed to the fact that this study only calculated the integral under the dynamic stress–strain curve before the peak stress to determine impact toughness, neglecting the potential contribution of CR particles after the peak point. The obvious strain sensitivity exhibited by the RuAAC in the SHPB tests indicated superior impact performance, making it particularly suitable for architectural structures prone to seismic or explosive impacts. [ABSTRACT FROM AUTHOR]

Copyright of Materiały Budowlane is the property of Wydawnictwo SIGMA-NOT 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.)

ContextBulk mineral waste materials such as construction and demolition waste are Germany’s largest waste stream. Despite the availability of high-quality recycling pathways such as road base layers, waste concrete is predominantly recycled into lower-quality recycling pathways like earthworks or unbound road construction. This is due to low demand for recycled aggregates in road base layers and frost protection layers, especially in public procurement.PurposeThis study assesses the environmental consequences of increasing high-quality recycling of waste concrete in the near future to provide decision support for public procurement in Germany. The focus lies on climate change due to its importance for decision-makers. However, 17 other impact categories were assessed to avoid problem shifting.MethodsLife cycle assessment (LCA) is applied with background data from ecoinvent 3.9.1. Impact assessment was conducted at midpoint level using IPCC 2021 and ReCiPe Midpoint (H). Foreground data were taken from literature and expert interviews. In line with the goal of this LCA, a consequential modeling approach was followed to account for changes in the material flow system. Substitution creates a cascade effect previously omitted in consequential LCA studies, in which lower quality recycling materials replace higher quality recycling materials in their respective utilization pathways.Results and discussionIncreasing the high-quality recycling of waste concrete into road base layers causes a reduction in environmental impacts for all 18 impact categories, as it replaces natural aggregate and avoids backfilling of mixed mineral waste and excavated earth through substitution effects. Transport distances and ferrous metal recovery were identified as hot spots. Sensitivity analyses show that only transport is a significant issue.ConclusionIncreasing the high-quality recycling of waste concrete in Germany is recommended in terms of environmental impacts. Lower-quality recycling is environmentally feasible only in cases where the avoided transport distances for natural aggregates and backfilling are significantly lower than the additional transport distances for high-quality recycling.

Recycled aggregate (RA) and recycled concrete powder (RCP) hold significant potential as environmentally sustainable raw materials for asphalt mixtures. In this study, a comprehensive investigation was conducted on the bonding properties between RA and RCP-filled asphalt mastic (RCPAM). This investigation utilized an image processing-assisted modified water boiling test, binder bond strength (BBS) tests, and the surface free energy (SFE) method. The results indicate that the boiling water test method, even with the assistance of 2D image processing analysis, cannot adequately evaluate the adhesive characteristics of the RA-RCPAM interface. This limitation could be attributed to the relatively small number of samples tested and the significant variation in surface properties of RA. Increasing both the filler-to-asphalt (F/A) ratio and RCP replacement ratio adversely affected the interfacial bond strength of the RA-RCPAM interface. On the other hand, an increase in RA surface roughness contributed to a higher bond strength. Based on the experimental results, a best-fit multivariate mixed model was proposed to predict the interfacial bond strength between RCP-filled asphalt mastic and recycled aggregate within a given range of RCP replacement ratio, surface roughness, and filler-to-asphalt (F/A) ratios. The analysis of SFE suggested that moisture damage to RCPAM was caused by both cohesive and adhesive failure. Additionally, the minimal impact of adhesion work in wet condition with increasing RCP content suggested that adhesion failure energy was only marginally affected by the inclusion of RCP, even in the presence of moisture. These findings are expected to enhance the understanding of interfacial adhesion characteristics and moisture susceptibility of the RA-RCPAM interface.

Due to low density, large pores, and numerous cracks, recycled aggregate mortar has defects of lower fluidity and lower strength compared to natural aggregate mortar. In order to modify inherent defects of recycled aggregates, nanosilica (NS) with different dosages (0%, 0.6%, 1.2%, 1.8%, 2.4% and 3%) was added to recycled aggregate mortar (RNC), and 40% natural sand in RNC was replaced by recycled aggregates. Then consistency test, compressive strength test and microscopic tests (SEM, EDS and XRD) were conducted to investigate working performance and microscopic mechanism. It was found that the addition of NS can improve the flowability of RNC, and the consistency value reaches the maximum (53 mm) while NS content is 2.4%, which increases by 14% comparing to the specimen without NS. The compressive strength of RNC increases and decreases with increasing NS content in the ranges of 0–1.8% and 1.8–3% respectively, and compressive strength is 3.3 and 5.9 MPa at curing ages of 7 d and 28 d respectively while NS content is 1.8%, which increase 50% and 14% comparing to the specimen without NS. Meanwhile, the consistency value of the specimen with NS content of 1.8% is 51 mm, which is close the maximum value corresponding to NS content of 2.4%. For that, 1.8% is suggested as the optimal content of NS. Moreover, the addition of NS can reduce the brittleness index and mechanical damage degree, and enhance the energy absorption effect. Microscopic analysis reveals that NS can not only fill the inherent cracks and pores of recycled aggregates, but also promote cement hydration reaction, and more hydration products (C-S-H) can efficiently reduce the cracks and pores of recycled aggregates. It is believed that the finds of this paper can provide theoretical support for the application of recycled aggregates in practical engineering.

As many residential homes and structures were destroyed or badly damaged because of the military battle in Iraq, it is critical to recycle construction debris widely in the rebuilding and decoration of buildings and infrastructure. This battle resulted in the buildup of massive construction debris, and recycling this waste allows for a cleaner environment. Recycling the construction waste of various installations is an urgent need to decrease the consumption of natural materials and landfills of construction waste, and as a result reduce the environmental pollution. Therefore, this study is a local focus on using concrete debris to obtain high packing density recycled coarse and fine aggregates in various fractions of (0.16 mm - 10 mm) by selecting high-density packing materials that was developed by Kharkhadin A.N in laboratories of Belgorod State Technical University in Russia to preparing of reference mix from ordinary density recycled aggregate. The new concrete samples for two concrete mixtures were prepared, to identify and study the important specifications. Models of cubes and standard prisms were prepared to evaluate the compressive strength and the splitting tensile strength. Also, the modulus of rupture and the unit weight were conducted. The results indicated an increase in the concrete’s mechanical properties using the high-packing density recycled aggregate. The obtained compressive strength, splitting tensile strength and modulus of rupture were (49) MPa, (3.6) MPa, and (7.1) MPa compared with a reference mix (39) MPa, (3.3) MPa and (6.3) MPa, respectively. The reference mix corresponding properties were (39) MPa, (3.3) MPa, and (6.3) MPa, respectively. Also the values of an oven-dry density were (2340) kg/m3 compared with the reference mix (2260kg/m³). These results proved that increasing the packing density of recycled aggregate enhanced the concrete’s strength properties.

Abstract Fracture parameters of fiber concrete (FC) are currently a hot research area. Fracture mechanics is the field of solid mechanics that helps to study the type and propagation of cracks in materials. It uses methods of calculating the driving force on a crack and characterizes the material's resistance to fracture. Behavioral characteristics are determined by crack mouth opening displacement and the load–deflection method. This research identifies the fracture parameters of 33 notched simply supported beams made by recycled aggregate cement concrete with steel fiber. The recycled aggregate ratio in concrete has been altered to determine the effect on the mechanical and fracture properties. For determining fracture parameters, a 3-point bending single-edge notched fracture test was used. The results indicated that the steel fiber-reinforced concrete made with recycled aggregate showed similar performance and fracture characteristics compared to normal concrete. Thus, adding steel fibers to various concrete mixes considerably improved the fracture characteristics, while the brittleness was reduced with increased steel fiber content. Linear regression analysis also showed the accuracy of mechanical strength results as the value of R-square was close to unity. Displacement, ultimate load, brittleness (B), fracture toughness (K IC), crack mouth opening displacement (CMOD), fracture energy (G F), modulus of elasticity (E), and characteristic length (l ch), were determined for both conventional and recycled aggregate specimens. The “work of fracture"—by definition the formula—is the most reliable to calculate the fracture energy as the nonlinearity is related to the performance of FC.

Three types of aggregate, including metallurgical slag aggregate (steel slag, copper slag, and iron sand), rare earth porcelain sand (REPS) aggregate as artificial aggregate, and recycled aggregate, were selected to produce concrete with the same basic mixture proportions in order to investigate the influence of aggregate types and aggregate replacement rates on their mechanical properties. Three levels of aggregate replacement rate—20%, 35%, and 50% for coarse aggregate (CA) and 20%, 30%, and 40% for fine aggregate (FA)—were employed in this study. The results indicate that replacing natural sand with metallurgical slag aggregate as FA enhances the mechanical properties of concrete. Among these, iron sand (IS) shows superior enhancement effects compared with copper slag (CS), and CS outperforms steel slag (SS). Specifically, at a 30% IS replacement rate, the compressive strength and splitting tensile strength of IS aggregate concrete are 32.8% and 35.6% higher than those of natural aggregate concrete, respectively. REPS used as CA demonstrates significant improvements in compressive strength, while REPS used as FA notably enhances splitting tensile strength. For recycled aggregate concrete with recycled coarse aggregate replacement rates of 35% and 50%, mechanical properties are effectively strengthened by incorporating CS as FA at a 30% replacement rate and REPS as CA at a 20% substitution ratio, respectively. Additionally, XRF and XRD techniques were employed to confirm aggregate composition and were combined with SEM and EDS techniques to analyze the concrete microstructure, clarifying the strengthening mechanisms of metallurgical and artificial aggregates on concrete.

The objective of the research outlined in this paper is to propose an eco-friendly solution that simultaneously contributes to improving the characteristics of polymer composites. The analyzed solution entails the use of recycled aggregate from crushed concrete rubble. The authors conducted experiments to test the consistency, density, flexural strength, compressive strength, and microstructure of polymer concrete (PC) with different proportions of recycled aggregate (RA). It was found that PC with RA had a higher compressive strength, 96 MPa, than PC with natural aggregate, 89.1 MPa, owing to the formation of a double-layer shell of resin and calcium filler on the surface of porous RA grains. Using a resin with a lower viscosity could improve the performance of PC with RA by filling the cracks and penetrating deeper into the pores. RA is a valuable material for PC production, especially when it contains porous grains with poor mechanical properties, which are otherwise unsuitable for other applications. This article also highlights the environmental and economic benefits of using RA in PC, as it can reduce waste generation and natural resource consumption.

In recent years, the use of recycled aggregate (RA) in roller-compacted concrete (RCC) for pavement construction has been increasingly attractive due to various environmental and economic benefits. Early determination of the compressive strength (CS) is crucial for the construction and maintenance of pavement. This paper presents the idea of combining metaheuristics and an advanced gradient boosting regressor for estimating the compressive strength of roller-compacted concrete containing RA. A dataset, including 270 samples, has been collected from previous experimental works. Recycled aggregates of construction demolition waste, reclaimed asphalt pavement, and industrial slag waste are considered in this dataset. The extreme gradient boosting machine (XGBoost) is employed to generalize a functional mapping between the CS and its influencing factors. A recently proposed gradient-based optimizer (GBO) is used to fine-tune the training phase of XGBoost in a data-driven manner. Experimental results show that the hybrid GBO-XGBoost model achieves outstanding prediction accuracy with a root mean square error of 2.64 and a mean absolute percentage error less than 8%. The proposed method is capable of explaining up to 94% of the variation in the CS. Additionally, an asymmetric loss function is implemented with GBO-XGBoost to mitigate the overestimation of CS values. It was found that the proposed model trained with the asymmetric loss function helped reduce overestimated cases by 17%. Hence, the newly developed GBO-XGBoost can be a robust and reliable approach for predicting the CS of RCC using RA.

Recycling concrete with reinforcement made of basalt fibre polymers: investigations on the composite and tensile load‐bearing behaviour The use of recycling concrete is subject to restrictions in Germany, which prevent its use in environmental conditions containing de‐icing salt of exposure classes XD3 and XS3. To overcome these normative barriers, the Munich UAS is conducting research on the use of alternative reinforcement materials that completely eliminate reinforcement corrosion induced by chlorides. In this regard, non‐corrosive fibre composite bars, made of basalt, are employed, which offer ecological advantages over reinforcements made of stainless steel, glass fibre or carbon. The investigations presented here on the composite and tensile load‐bearing behaviour of basalt fibre‐reinforced polymers have arisen as part of a current research project examining the use of this type of reinforcement in bridge caps made of recycling concrete. In addition to preliminary concrete technology studies on the use of up to 100 % recycled aggregates, composite specimens made of recycled concrete and basalt fibre reinforced polymer were tested to provide insights on the load‐bearing behaviour under static and cyclic conditions. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society 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.)

Reusing recycled aggregate (RA) and recycled powder (RP) for fully recycled mortar can effectively reduce the amount of construction and demolition waste. This work studied the chloride transport and resistance improvement of fully recycled mortar incorporating both RA and RP. The results showed that RP had certain nucleation and filler effects.. The addition of RA or RP had an increase in chloride diffusion of mortar. Including RA improved the chloride binding capacity, but mixing RP reduced the chloride binding capacity. At equal waste powder content, recycled paste powder blended mortar owned superior chloride binding capacity to recycled mortar/concrete powder blended mortar. The chloride diffusion of fully recycled mortar with both RA and RP were much higher than that of plain mortar. Mixing various RPs could reduce chloride diffusion of fully recycled mortar, and a significant decrease in chloride diffusion occurred as silica fume or metakaolin was incorporated. [ABSTRACT FROM AUTHOR]

This study investigates the factors influencing the permeability and water storage capabilities of Recycled Graded Crushed Stone Layer (RGCSL) materials, which are crucial for constructing sustainable "sponge cities". The research focuses on how aggregate characteristics, such as particle size and filling sequence, affect the porosity structure of RGCSL and, consequently, its permeability and water storage performance. The findings reveal significant impacts of these factors on material performance, leading to the development of a performance prediction model based on the principle of superposition and backpropagation neural networks. The model's efficacy was validated through simulation experiments, indicating that the water storage capacity of recycled sand is significantly higher than that of coarse aggregates, with the model achieving an accuracy of 89.1%. This study is vital for advancing environmental restoration and sustainable urban development. [ABSTRACT FROM AUTHOR]

The use of recycled aggregate obtained from the crushing of construction solid waste can not only save natural sand and gravel resources, but also promote the recycling of construction solid waste. The quality of recycled aggregate determines the performance of recycled aggregate concrete. There are many factors affecting the quality of recycled aggregate, and the strength of parent concrete is one of the important influencing factors. The article takes strength of parent concrete as the research object, and summarizes its influence law on the properties of recycled aggregate and recycled aggregate concrete. Different strengths of parent concrete affect the quality and content of recycled aggregate adhesive mortar, which in turn affects the properties of recycled aggregate and recycled aggregate concrete. When the strength of parent concrete increases, the quality and content of adhesive mortar are improved. While the quality of adhesive mortar is improved, the properties of recycled aggregate and recycled aggregate concrete are strengthened. The increase in the content of adhesive mortar deteriorates the physical properties of recycled aggregate, increases the porosity and water absorption of recycled aggregate, but strengthens the internal curing effect of concrete, which contributes to the mechanical properties of recycled aggregate concrete. Using microscopic analysis, it is found that different strength of parent concrete make a difference in the content of hydration products in the interfacial transition zone of recycled aggregate concrete, which has an impact on the mechanical properties of concrete. The article provides a theoretical basis for further grading and utilization of recycled aggregate. [ABSTRACT FROM AUTHOR]

In order to increase the utilization rate of recycled aggregates from construction solid waste, this paper adopts ordinary mixing and vibration mixing processes, and investigates the effect of recycled aggregate substitution rates and mixing time on the mechanical properties of concrete through comparative tests. The results show that: with the increase of the proportion of recycled aggregate, the compressive strength of concrete in different mixing methods are reduced, in which the reduction in ordinary mixing process is more obvious; compared with the ordinary mixing, vibration mixing compressive strength of recycled concrete in the recycled aggregate substitution rate of 0, 20%, 40%, 60%, 80%, 100%, respectively, increased by 10.59%, 7.87%, 9.09%, 4.99%, 5.43%, and 6.1%, respectively. When vibration mixing times were 50 s, the 7 d and 28 d compressive strength of concrete was the highest. The above studies show that vibration mixing can inhibit the decline of mechanical properties of recycled aggregate concrete and save mixing time. [ABSTRACT FROM AUTHOR]

Rice husk ash (RHA), an agricultural by‐product, has been added as supplementary cementitious material (SCM) in concrete mixture to improve the compressive properties of recycled aggregate concrete (RAC) in recent years. This study aimed to optimise the mixture design of RAC considering two variables: the replacement ratio (wt.%) of recycled aggregate (RA) to natural aggregate (NA) with three levels (0%, 50% and 100%) and the replacement ratio (wt.%) of RHA to cement with three levels (0%, 10% and 20%). Compression test was implemented at concrete age of 28 days based on the full factorial experiment. By means of response surface methodology (RSM), the optimised RA replacement ratio and RHA replacement ratio can be calculated with respect to the compressive strength and E‐modulus at 28 days, and vice versa the compressive strength and E‐modulus at 28 days of RAC containing RHA can also be predicted. According to response surface modelling, the compressive strength reaches the maximum value when the RA replacement ratio is 0% and the RHA replacement ratio is 7%, and the E‐modulus would reach the maximum when the RA replacement ratio is 17% and the RHA replacement ratio is 7%. The determination coefficient (R2) and adjusted coefficient (R2adj) for the compressive strength model are 0.9632 and 0.9544 respectively, and for the E‐modulus model are 0.9319 and 0.9157 respectively, showing that the models developed by RSM are relatively well correlated with the experimental results. [ABSTRACT FROM AUTHOR]

In Germany the use of recycled aggregates is possible within certain limits since the introduction of the DAfStb guideline in 1998. Due to increasing demands of concretes fulfilling requirements regarding sustainability, conservation of resources and avoidance of waste the topic of recycled aggregates has again become the focus of public, economic, and political interest in recent years. Although the results of the BMBF research project "R‐Beton" have led to positive changes with respect to the regulation gap in environmentally relevant characteristics several certain barriers still prevent the broad use of recycled aggregates in the German concrete market. In the forthcoming DIN 1045, regulations will be created which, particularly in concrete class BK‐N in the application range of up to 25 % volume fraction, will permit simple and thus practical use of recycled aggregates. In addition, fine recycled aggregates of type 1 may be used, which was previously not permitted. Here, changes in the regulatory framework of DIN 1045 will be discussed in the sense of a broader use of recycled aggregates in Germany as well as the context of other national regulations. An outlook regarding further need of research is also given. [ABSTRACT FROM AUTHOR]

The differences in physical properties, chemical properties, and mechanical properties between reclaimed concrete aggregate and natural aggregate are discussed in this paper. In this paper, the commonly used improvement techniques of recycled concrete aggregate are reviewed. Physical modification involves peeling the attached mortar layer using mechanical and thermodynamic means, including mechanical grinding and shaping, heat treatment, and microwave or electric pulse treatment. Chemical modification is based on the chemical reaction of some materials with recycled aggregate attached mortar, including acid treatment removal, water glass strengthening, carbonation strengthening, inorganic slurry strengthening, and polymer strengthening. Microbial modification is mainly based on the metabolic activity of specific microorganisms that induce carbon deposition modification. The results show that the reinforced technology of recycled aggregate has made some progress in improving the performance of recycled aggregate, but there are still some problems, such as inconsistent strengthening effects and the unstable compatibility of composite materials. In this paper, future research directions, such as the development of new strengthening materials and the integration of multi-functional strengthening technology, are described in order to provide some theoretical support for the utilization of recycled concrete aggregate. [ABSTRACT FROM AUTHOR]

Fracture parameters of fiber concrete (FC) are currently a hot research area. Fracture mechanics is the field of solid mechanics that helps to study the type and propagation of cracks in materials. It uses methods of calculating the driving force on a crack and characterizes the material's resistance to fracture. Behavioral characteristics are determined by crack mouth opening displacement and the load–deflection method. This research identifies the fracture parameters of 33 notched simply supported beams made by recycled aggregate cement concrete with steel fiber. The recycled aggregate ratio in concrete has been altered to determine the effect on the mechanical and fracture properties. For determining fracture parameters, a 3-point bending single-edge notched fracture test was used. The results indicated that the steel fiber-reinforced concrete made with recycled aggregate showed similar performance and fracture characteristics compared to normal concrete. Thus, adding steel fibers to various concrete mixes considerably improved the fracture characteristics, while the brittleness was reduced with increased steel fiber content. Linear regression analysis also showed the accuracy of mechanical strength results as the value of R-square was close to unity. Displacement, ultimate load, brittleness (B), fracture toughness (KIC), crack mouth opening displacement (CMOD), fracture energy (GF), modulus of elasticity (E), and characteristic length (lch), were determined for both conventional and recycled aggregate specimens. The "work of fracture"—by definition the formula—is the most reliable to calculate the fracture energy as the nonlinearity is related to the performance of FC. [ABSTRACT FROM AUTHOR]