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

In this paper, the possibility of utilising coarse recycled concrete aggregate (CRCA) obtained from a construction and demolition waste (CDW) plant in Delhi to make 60 MPa self-compacted concrete (SCC) was evaluated. The CRCA was used in as-collected condition and was not processed any further. The aggregate packing (bulk) density (APD) method was adopted to prepare the SCC-CRCA mixture in order to obtain an aggregate mixture exhibiting maximum bulk density/least void content (45%). In addition, SCC was made using aggregate mixtures in which the natural coarse aggregate (NCA) was replaced with CRCA at 0%, 20% and 100% of the total coarse aggregate content by weight. The cement, fly ash, silica fume and water were kept constant for all SCC mixtures. The effects of CRCA on the flow behaviour, mechanical strength, shrinkage characteristics and microstructure properties of SCC mixtures were evaluated. The test results indicated that SCC mixtures made with up to 45% CRCA replacement can be used for structural concrete, which is higher than that recommended in Indian (20%) and international specifications (35%) for traditionally vibrated (conventional) concrete. [ABSTRACT FROM AUTHOR]

The recycling of construction wastes holds significant importance both environmentally and economically. While extensive research has been conducted on aggregates derived from various wastes, the recycling of pervious concretes (PC) has been largely overlooked. This study addresses this gap by examining the porosity and mechanical properties of PC manufactured using aggregates obtained from recycled PC. The investigation focuses on three key factors: aggregate size (5/15, 10/15, and 15/25 mm size fractions), fiber inclusion (dosages of 0.1%, 0.2%, and 0.3% by volume), and aggregate type (limestone aggregate and recycled aggregate). Through image processing techniques, void characteristics including amount, structure, and homogeneity were quantified. Results indicate that the use of recycled aggregate led to a decrease in compressive strength ranging from 29% to 65%, depending on aggregate size fraction and fiber content. Porosity assessments revealed higher porosity in concrete utilizing recycled aggregate, with computer-based methods yielding values closely aligned with volumetric results. [ABSTRACT FROM AUTHOR]

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

The administration of waste from constructing-demolition and the reuse of industrial waste materials are the main focuses of the sustainability initiatives. There are economic and environmental benefits to using recycled concrete aggregates (RCA). Nevertheless, the RCA mixes' poor performance necessitates the addition of more enhanced substances. This study investigated the moisture resistance of asphaltic mixes that included RCA and silica fume (SF). Coarse aggregates were replaced with RCA at three different percentages 15%, 30%, and 45%, which were pre-treated by immersing it in acid with a concentration of 0.1 mol. for a duration of 24 hours. Then the mixes containing RCA were incorporated with various amounts of SF, with 3%, 6%, and 9% of the binder's weight. These mixes were used to measure the Marshall characteristics and evaluate moisture resistance using indirect tensile strength, compresive strength tests. A thermal camera was employed to assess the modified asphalt's homogeneity. The thermal images demonstrated that after 30 minutes of mixing SF at 160 ℃, the asphalt cement has been uniformly distributed SF particles, as evident by the colour convergence. The findings revealed that the addition of RCA to the asphalt mix increased TSR and IRS levels by 6.68% and 8.93%, respectively, at RCA 30% compared to the original mixture. Additionally, the inclusion of silica fume led to a rise in TSR and IRS until 6%, after which there was a drop, but the levels remained above the original mix. The use of 30% RCA ratio with 6% silica fume resulted in the highest improvement in TSR and IRS, with a rise of 13.72% and 14.13%, respectively. [ABSTRACT FROM AUTHOR]

Extrusion tests were conducted on recycled coarse aggregate concrete with circular steel tubes (RCCST, 100% replacement of recycled coarse aggregate) to investigate the impact of freeze–thaw cycles on bond properties. RCCST samples were subjected to 0, 25, 50, 75, 100, 125 and 150 freeze–thaw cycles and their bond properties were then compared with those of natural coarse aggregate concrete with circular steel tubes (NCCST) after 0, 100 and 150 freeze–thaw cycles. The experimental results indicate that freeze–thaw cycling damages the internal structure of RCCST, causing a significant decrease in interfacial bond strength with an increase in the number of freeze–thaw cycles. Freeze–thaw RCCST exhibits lower peak load and higher peak slip compared to NCCST, with increases of 25.2%, 73.2%, and 70.3% after 0, 100, and 150 freeze–thaw cycles, respectively. Regression analysis was used to derive an exponential equation that describes the relationship between longitudinal strain and strain gauge position. Additionally, a segmented fitting method was employed to obtain an expression for the bond slip of the freeze–thaw RCCST with a circular steel pipe. [ABSTRACT FROM AUTHOR]

The cracking of recycled aggregate concrete (RAC) is well known to promotes the chloride diffusion, accelerates the corrosion of reinforcement embedded in RAC. To reveal the mechanism of chloride diffusion in RAC under cracking, a multiphase mesoscopic model for chloride diffusion in RAC was proposed. It should be noted that RAC is regarded as eight-phase composite materials consisting of coarse aggregate, reinforcement, new and old mortar, new and old interface transition zones (ITZ), cracks, and damage zones. The effects of the width and depth of cracks and damage zones on chloride diffusion behavior in RAC after cracking were further investigated. The numerical simulation results show that the damage zones accelerate the chloride diffusion and exacerbates the accumulation effect of chloride at the crack tip. Compared to the crack depth, the crack width of RAC has a small effect on chloride diffusion behavior, especially, the crack width is less than 50 μm. More importantly, the chloride diffusion streamline generated by numerical simulation reveals the mechanism of cracks promoting chloride diffusion. The research in this paper provides new insights into the durability design of RAC by revealing the diffusion behavior of chloride ions in RAC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recycled concrete is a new and environmentally friendly material for future construction. When applying recycled concrete to cold and severe regions, it is necessary to consider the freeze–thaw resistance of recycled concrete. Using an indoor freeze–thaw cycle test system, the rapid freezing method was used to conduct rapid freeze–thaw tests on recycled concrete specimens under set freeze–thaw cycle conditions. Relevant parameters (such as compressive strength, quality loss rate, rebound value) were tested on recycled concrete specimens that completed the set number of freeze–thaw cycles. The influence of various factors (freeze–thaw cycle number, replacement rate of recycled aggregates) on the compressive strength, quality loss rate, and rebound value of recycled concrete was analyzed. The results indicate that with the increase of freeze–thaw cycles and recycled aggregate content, the workability, rebound value, and compressive strength of the specimens decrease, and the quality loss rate increases. The changes in workability of concrete are sharp, with a slump difference of 21 mm between concrete with 100% recycled coarse aggregate and concrete using natural coarse aggregate. The rebound value of the specimen shows a decreasing trend overall, but the rebound value varies for different measuring points on the same specimen. The attenuation of compressive strength is significant. When fully using recycled aggregates to prepare concrete, the compressive strength after 30 freeze–thaw cycles decreases by 49.42% compared to the compressive strength after 0 freeze–thaw cycles. The overall quality loss rate shows a decreasing trend, but the quality loss is not severe. [ABSTRACT FROM AUTHOR]

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. [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 (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]

There has been a significant interest in the development of eco-friendly building materials. Recyclable and environmentally friendly, geopolymer composites are extraordinary binding materials. The purpose of this experimental study was to examine the mechanical and durability properties of metakaolin based self-compacting geopolymer concrete (SCGPC) comprising steel fibers (SF) and recycled aggregate concrete (RCA) varying percentages of recycled coarse aggregate. The mechanical and durability properties of the geopolymer composites, including fracturing tensile strength, and flexural strength, were subsequently evaluated. At weight proportions of 0%, 25%, 50%, 75% and 100%, the recycled coarse aggregates were substituted for the natural coarse aggregates. The amounts of SF incorporated into the mixtures were 0, 0.5, 1.0, and 1.5% by volume fraction. While the incorporation of SF does not yield a substantial improvement in compressive strength, it substantially enhances fracture tensile strength and flexural behavior. The load-displacement graph demonstrated that the incorporation of steel fibers into geopolymer composites increased their fracture toughness, resulting in a higher maximal load capacity. The findings suggest that the incorporation of RCA into SCGPC reduces its flexural behavior, splitting and compressive tensile strengths, and durability, particularly under peak load, deflection, and load. Furthermore, it is observed that RCA negatively synergize with respect to compressive and fracturing tensile strength. However, SF exhibit a significant positive synergy in terms of flexural properties. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregates (RCA) provide an environmentally friendly solution by reducing the depletion of natural resources. This study investigates the impact of the expansion history of RCA on its reactivity with alkalis in newly produced concrete. Parent concrete samples were collected from the RILEM AAR‐4 curing cabinet (60°C and >90% RH) to produce coarse RCA with four different expansion levels (0.00%, 0.05%, 0.12%, and 0.20%). The results show that the expansion levels of the new concrete mixtures decreased as the ASR expansion history of parent concrete increased. The 20‐week compressive strength and elastic modulus of the reactive aggregate concrete containing no mineral admixture and exposed to AAR‐4 test conditions were lower than those of their water‐cured counterparts. However, no decrease was observed in the elastic modulus of concrete mixtures that showed an expansion level lower than 0.03% (the maximum expansion for nonreactive aggregate as recommended by the RILEM AAR‐4 standard). [ABSTRACT FROM AUTHOR]

The main objective of this paper is to use the data‐driven approach to predict and evaluate the mechanical properties of concrete made with recycled concrete aggregate (RCA), including compressive strength and elastic modulus. Using 358 data samples, including 10 input variables, 10 popular machine learning (ML) algorithms are introduced to select the best ML performance model for predicting RCA concrete's compressive strength and elastic modulus. Gradient Boosting and Categorial Boosting have the best performance in predicting the compressive strength of RCA concrete, with R2 = 0.9112, RMSE = 5.3464 MPa, MAE = 4.0845 MPa, and R2 = 0.9175, RMSE = 5.1520 MPa, MAE = 3.7567 MPa, respectively. Light Gradient Boosting and Categorial Boosting have the best performance in predicting the elastic modulus of RCA concrete, with R2 = 0.8775, RMSE = 2.3560 GPa, MAE = 1.8330 GPa, and R2 = 0.9300, RMSE = 2.3560 MPa, MAE = 1.2589 MPa, respectively. Based on the Shapley Additive Explanation analysis, the influence of main factors on compressive strength and elastic modulus of RCA concrete values has been analyzed qualitatively and quantitatively. RCA replacement level and cement/sand ratio slightly affect compressive strength but have a dominant influence on the elastic modulus of RCA concrete. [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]

Currently, microscopic research on the tensile fracture properties of recycled brick coarse aggregate concrete has mainly adopted microscopy techniques, which can clearly observe the actual damage situations of each phase material but are unable to individually analyze the effect of a specific material factor on the tensile properties of recycled concrete. This brings much uncertainty to the practical application of recycled concrete. Therefore, this study proposes a cohesive zone model (CZM) for simulating the tensile fracture of recycled brick coarse aggregate (RBCA) concrete. To this end, the study explores the effects of various critical factors on the fracture mode and bearing capacity of recycled brick aggregate concrete, including the replacement rate of recycled brick coarse aggregate, pore structure, interfacial transition zone (ITZ) strength, mortar strength, and volume fraction of brick aggregate. The results indicate that, when the minor to major axis ratio of elliptical pores is 0.5 ≤ K < 1, the following order of influence can be observed: random convex polygonal pores, circular pores, and elliptical pores. Moreover, excessively strengthening the ITZ and mortar does not significantly enhance the tensile performance of RBCA concrete. The distribution location of aggregate has a significant impact on the crack shape of recycled concrete, as does the pore structure, due to their randomness. Therefore, this article also discusses these. These findings contribute to a comprehensive understanding of the tensile properties of recycled brick coarse aggregate and provide insights into optimizing its behavior. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of quarry waste sand (QWS) on the physical and mechanical properties of recycled aggregates concrete (RAC). Two sets of concretes were made one with natural sand (NS) and another with QWS sand. Five mixes with replacement ratios of 20%, 40%, 60%, 80% and 100% of ordinary coarse aggregates (OCA) by recycled concrete aggregates (RCA) were produced for each set. Tests were performed to determine slump, compressive strength, flexural strength, water absorption by immersion and shrinkage. The results showed that the mixes produced with QWS sand exhibited slightly better fresh and hardened properties. The combination of QWS sand and RCA aggregates reduces the degradation often recorded and makes RAC concrete to have the same level of performance as concrete with ordinary aggregates. Some relationships were deduced to express each performance of QWS sand-based concrete with that of NS sand-based concrete. This makes the use of this sand very practical and its modifications easily quantifiable. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the impact splitting tensile property and microstructure characteristics of steel fiber recycled aggregate concrete (SFRAC) based on the split Hopkinson pressure bar (SHPB) and scanning electron microscope (SEM). The effects of fiber content, strain rate, and recycled aggregate replacement ratio on the mechanical parameters (static and dynamic splitting tensile strength, peak strain and ultimate strain, peak toughness and ultimate toughness) were analyzed. Then the microstructure characteristics of SFRAC at different interfaces were observed via SEM, and energy spectrum analysis of the interface transition zone (ITZ) was carried out. The results show that SFRAC is a strain-rate sensitive material whose mechanical properties are affected by the strain rate and improved with its increase. It is also found that steel fibers play a role in improving dynamic splitting tensile strength and toughness, and the optimal fiber content is about 1.0%. However, increasing the recycled aggregate replacement ratio will weaken the good effect of steel fibers on the mechanical properties. Furthermore, it can be seen by means of SEM that the fracture area of steel fiber is mostly pulled out. Also, there are more cracks and pores in the cement paste of recycled aggregate concrete (RAC) compared with normal concrete (NC), and the hydration products in the ITZ are significantly decreased. With the incorporation of steel fibers, the calcium content of the ITZ can be reduced. [ABSTRACT FROM AUTHOR]

The mechanical properties of porous concrete, such as strength and durability, are significantly influenced by moisture transport, particularly in the case of recycled aggregate concretes. The pore distribution and pore size of the concrete, as well as the ambient temperature in the surrounding environment, exert a significant influence on the moisture transport. This paper establishes the fractal Fick’s law, the fractal Darcy law, and the fractal Richards equation. In conclusion, a fractal model for the diffusion and permeability in porous concrete is established. This study examines the mechanisms of moisture diffusion and water permeability in concrete. The comparison of the theoretical prediction with the experimental data indicates a high degree of congruence, thereby suggesting that the concrete’s relative humidity response can be predicted by the established model. This provides a foundation for the optimal design of concrete with required mechanical properties in special applications. [ABSTRACT FROM AUTHOR]

In this study, the performance of recycled concrete aggregate (RCA/RSA) available in Agartala, Tripura (north-eastern regions of India), was studied in reinforced concrete members subjected to a severe artificially induced corrosive environment. The performance test was based on the non-destructive and destructive parameters of concrete. Due to the scarcity of normal stone aggregate (NSA) in this region, studying the effect of using such type of aggregate in reinforced concrete members help not only to mitigate the demand but also assists in waste management. The study also presents an innovative application of micro-bend opticalfibre sensors for corrosion monitoring and validated using other non-destructive instruments. The study presents an effective application of the micro-bend optical fibre sensor to predict the initiation of corrosion (de-passivation) and initiation of cracking (critical stress) due to corrosion in reinforced concrete specimens. Later, the results were validated using half-cell potentiometer and electrical strain gauge values. The specimen also presented different mechanical and durability properties with varying RCA percentages. A regression model to predict mechanical properties and corrosion amount (hoop strain) in reinforcement for different RCA-replaced concrete has been presented. The sorptivity and other porosity-related results were also presented for different RCA replacement percentage specimens. [ABSTRACT FROM AUTHOR]

This study demonstrates an integrated thermomechanical treatment process to produce high quality recycled concrete aggregate (RCA) for structural concrete. RCA is mechanically treated after 90 min of heating at 250 °C in this process. The material properties of RCA produced through 15 combinations of charges and drum revolutions are compared using a statistical method. The highest ranking of an RCA identifies it as a high-quality class. Concrete composed of 100% RCA (recycled aggregate concrete, RAC) has 1.7% higher compressive strength than natural aggregate concrete (NAC). RAC has tensile and flexural strengths of 0.95 and 1.03 in fraction of NAC. RAC meets durability criteria such as UPV greater than 4.4 km/s, rapid chloride ion penetration test (RCPT) less than 1000 C, electrical resistivity greater than 208 Ohm-m, and sorptivity closer to NAC. Water absorption and abrasion resistance are similar to or superior to those of NAC. Coherent and uniform surface morphology of RCA enhances the ITZ microstructure in RAC. [ABSTRACT FROM AUTHOR]

The bond strength of tension lap splices in recycled-coarse-aggregate-reinforced concrete strengthened with hybrid (steel–polyolefin) fibers was experimentally investigated. This study was conducted with the help of twelve lap-spliced beam specimens. The replacement level of coarse natural aggregates with recycled concrete aggregate (RCA) was 100%. The following variables were investigated: various ranges of steel–polyolefin fibers—100–0%, 75–25%, 50–50%, 25–75%, and 0–100%—in which the total volume fraction of fibers ( V f ) remains constant at 1%; and two lengths of lap splices for rebars of 16 mm diameter ( d b ): 10 d b and 15 d b . The test results showed that the best range of steel–polyolefin fibers that gave the highest bond strength was 50–50%. The ductility of the fiber-reinforced recycled-aggregate (FR-RA) concrete was significantly improved for all the cases of various relative ratios of steel and polyolefin fibers. The bond strength was also predicted using three empirical equations proposed by Orangun et al., Darwin et al., and Harajli. This study showed that the Harajli equation gave a more accurate estimation of the bond strength of reinforcing bars embedded in FR-RA concrete than those proposed by Orangun et al. and Darwin et al. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Driven by the insatiable demand for construction materials, excessive quarrying for natural aggregates and the demand for raw materials for cement production pose significant environmental challenges, including habitat loss and resource depletion. To address these concerns, this study investigates the use of fibre-reinforced self-compacting concrete (FR-SCC) with high-volume fly ash (HVFA) and varying levels of recycled concrete aggregates (RCA) as substitutes for fine and coarse aggregates. This approach aims to simultaneously address environmental concerns by reducing reliance on virgin resources by utilizing the recycled aggregates and enhancing the performance of concrete through the combined benefits of fly ash and fibre reinforcement. In this study, Self-Compacting Concrete (SCC) mixes were created with 50% of fly ash replaced with conventional cement content, which was taken from the previous literature. Fine and coarse aggregate utilized in this investigation were replaced with processed recycled aggregates at varying levels from 0% to 100% at an interval of 25%, offering a promising solution to alleviate the environmental burden associated with excessive quarrying while contributing to sustainable construction practices. Additionally, replacement levels of aggregate synthetic polypropylene fibres (PF) were added into the concrete matrix up to 1% at an interval of 0.25%. This research contributes to the development of sustainable construction practices by promoting resource efficiency and minimizing environmental impact. The study found that SCC mixes with fibres and recycled aggregates maintained self-compactability, with polypropylene fibres and fly ash improving workability and cohesion. With this combination of materials, the highest strength value of 55.31 MPa was observed and the study promotes sustainable construction by reducing reliance on virgin resources and minimizing environmental impact. [ABSTRACT FROM AUTHOR]

This study aims to enhance the durability, cost-effectiveness, and sustainability of recycled fine aggregate concrete (RFAC) subjected to the combined effects of wet-dry cycles and sulfate erosion. Dry–wet cycle tests were conducted in RFAC with different admixtures of biotite metakaolin (MK) and 15% fly ash (FA) mix (M) under 5% sulfate erosion environment. The effect of 0%, 30%, 60% and 90% recycled fine aggregate (RFA) replacement of natural fine aggregate on mass loss, cubic compressive strength, relative dynamic modulus test of RFAC, damage modeling and prediction of damage life of concrete were investigated. The results showed that the concrete cubic compressive strength and relative dynamic modulus were optimal for recycled concrete at 15% MK biotite dosing and 60% RFA substitution, and its maximum service life was accurately predicted to be about 578 cycles under 5% sulfate dry–wet cycling using Weibull function model. This study is pioneering in addressing the durability of RFAC under sulfate attack combined with wet-dry cycling, employing a novel approach of incorporating MK and FA into RFAC. The findings highlight the practical application potential for using MK and FA in RFAC to produce durable and sustainable construction materials, particularly in sulfate-exposed environments. This research addresses a critical challenge in the construction industry, providing valuable insights for developing more durable and eco-friendly construction materials and contributing to long-term sustainability goals. [ABSTRACT FROM AUTHOR]

The increasing demand for concrete reduces natural resources, such as sand and gravel, and also leads to a sharp increase in the amount of waste concrete produced. Due to the fact that the physical and mechanical properties of waste concrete made of recycled aggregates (RAs) differ greatly, it is difficult to use directly as a raw material for reinforced concrete (RC) components, which greatly restricts the popularization and application of RAs in actual projects. Utilizing the alkali aggregate properties of RAs to capture CO2 from industrial waste gases is an innovative way of enhancing their properties and promoting their application in real projects. However, the extent of the influence of original concrete strength (OCS) and coarse aggregate size (CAS) on the accelerated carbonation modification of RA is not clear, and a quantitative description is still required. For this purpose, accelerated carbonation tests on recycled coarse aggregate (RCA) samples under completely dry condition were carried out, and the variation laws for the physical property indicators of RCA samples before and after accelerated carbonation versus the OCS and CAS were revealed. Moreover, the influence degrees of the two factors, OCS and CAS, on the property enhancement of RCAs after accelerated carbonation were clarified, and the results of OCS and CAS corresponding to the best accelerated carbonation effects of RCAs were determined. By analyzing the micromorphology of RCA before and after accelerated carbonation, the reasons for property enhancement of RCAs with various OCSs and CASs under the best carbonation modifications were clarified. The findings will contribute to the development of basic theoretical research on accelerated carbonation modification of RA and have important scientific value. [ABSTRACT FROM AUTHOR]

In order to meet the needs of low-impact development and sustainable development, there is an urgent desire to develop an innovative recycled aggregate pervious concrete (I-RAPC) that is of high strength and permeability. In this study, I-RAPC was prepared based on response surface methodology (RSM) using recycled aggregate, river sand, and different types of pipes as the materials, and the effects of different pipe parameters (number, diameter, material, and distribution form) on the performance of I-RAPC were investigated. In addition, the calculation model of the compressive strength and the permeability coefficient of I-RAPC were proposed. The results showed that the frontal- and lateral-compressive strengths of I-RAPC were 39.8 MPa and 42.5 MPa, respectively, when the pipe material was acrylic, the position was 1EM, and the diameter was 10 mm—at which time the permeability coefficient was 3.02 mm/s, which was the highest in this study. The maximum relative errors of the compressive strength calculation model and the permeability coefficient calculation model were only 7.52% and 4.42%, respectively, as shown by the post hoc test. Therefore, I-RAPC has the advantages of high strength and permeability and is expected to be applied in low-impact development in cities with heavy surface sediment content and rainfall. [ABSTRACT FROM AUTHOR]

Concrete sustainability and performance under extreme conditions are of growing interest in construction engineering. This study delves into the influence of recycled coarse aggregate (RCA) content and elevated temperatures on normal‐strength concrete containing RCA. Five different concrete compositions, featuring varying content of RCA (ranging from 0% to 100%), were examined. The heating and subsequent cooling followed the ISO‐834 temperature–time graph up to 800°C. The primary objective was to evaluate residual properties, including the stress–strain behavior, compressive and tensile strength, secant elastic modulus, peak strain, and bond strength of RCA concrete. The findings reveal a consistent decrease in both strength and stiffness parameters of RCA concrete with rising temperatures, while peak strain exhibits a rapid increase at elevated temperatures. Interestingly, RCA content had a negligible impact on the relative deterioration of high‐temperature exposed RCA concrete compared to that at ambient conditions. Moreover, the bond behavior closely resembled that of natural aggregate concrete when used in moderate proportions. Degradation models based on regression analysis of the data were used to quantify the bond strength reduction for RCA‐based concrete and the slip of rebar concerning various temperatures. Importantly, these models demonstrated consistency with those applicable to conventional concrete. [ABSTRACT FROM AUTHOR]

The European Green Deal establishes the efficient management of construction resources as one of its main lines of action. In this sense, the recovery of construction and demolition waste for its reincorporation into the manufacturing process of new sustainable materials has become necessary for the industry. This work deals with the physical and mechanical characterization of cement mortars made with recycled concrete aggregates and reinforced with natural fibers. The reinforcement fibers used (abaca, coconut, and toquilla) are more environmentally friendly compared to traditional synthetic reinforcements. The aim of this research is to analyze the main physico-mechanical properties of these sustainable cement mortars. The results show that mortars made with recycled sand have a lower density and better thermal performance than traditional mortars. In addition, with the incorporation of these natural fibers, the flexural strength of the mortars with recycled aggregate increased by up to 37.6%. Another advantage obtained from the incorporation of these natural fibers is the reduction in shrinkage in the masonry mortars during the drying process, giving them greater dimensional stability and making their behavior similar to that of traditional mortars. Thus, this work shows the potential application of masonry mortars produced under circular economy criteria and their application in the building sector. [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]

Producing recycled aggregate from construction and demolition waste generated by earthquakes and using it as raw material in concrete production would be effective for urgent waste management after disasters and to reduce the environmental impact of concrete production by decreasing resource use. In this study, the life cycle assessment (LCA) method was used to examine the environmental implications of concrete produced using recycled aggregates (RA) derived from construction and demolition waste (CDW) of buildings demolished after the earthquake that struck Iskenderun and was centered in Kahramanmaraş. In addition, the environmental consequences of an equal volume of concrete produced in the same location utilizing natural aggregates (NA) were assessed. For the LCA of these two types of concrete, openLCA software and the ReCiPe midpoint database were used. LCA was conducted considering terrestrial ecotoxicity, climate change, terrestrial acidification, photochemical oxidant formation, marine ecotoxicity, human toxicity, freshwater ecotoxicity, ozone depletion, particulate matter formation, marine eutrophication, and ionizing radiation impact factors. The results show that cement has the highest impact on the environment by far. [ABSTRACT FROM AUTHOR]

This study focused on the problem of recycling construction and demolition wastes as well as industrial waste by-products into sustainable concrete materials. By combining addition of three different industrial waste by-products, an environmentally friendly recycled aggregate self-compacting concrete (RA-SCC) mix was put forward. Carbonation resistance and microstructure of SCC incorporating high volumes of industry by-products and recycled aggregates were studied in this paper. A total of 9 RA-SCC with 50%, 75% supplementary cementitious materials (SCMs) and different SCM combinations were prepared, which consist of binary mix with fly ash (FA), ternary mix with FA and ground granulated blast-furnace slag (GGBS), and quaternary mix with FA, GGBS, and silica fume (SF). An exposure period of 3, 7, 14, and 28 days was adopted for accelerated carbonation tests. The test results indicate that, as RCAs content increased, RA-SCC carbonation depth increased. The carbonation depth of SCC with 100% RCAs increased by 49.35% compared to that of normal SCC. In addition, carbonation resistance of RA-SCC mixes with a given compressive strength decreased with increasing SCM content. However, the loss in carbonation resistance was greatly mitigated by the combined addition of different SCMs, on account of the substitution of cement with industrial by-products and natural aggregates with RCAs. The combined addition of different SCMs enhanced the carbonation resistance of RA-SCC mixes. The test results were validated through microstructural analysis using scanning electron microscopy (SEM), and X-ray diffraction (XRD). A comparison between predictions calculated using existing models and measured carbonation depth was implemented. By taking into account the effect of RCAs and SCMs, a modified carbonation model in conjunction with fib carbonation model was put forward. [ABSTRACT FROM AUTHOR]

Recycling construction wastes for their utilisation as aggregates will overcome the dumping and scarcity problems. However, their higher porosity affects the properties of concrete. Hence, this study examines the potential use of microbial-induced calcium carbonate precipitation techniques to improve the quality of recycled coarse aggregates (RCA). The natural coarse aggregate (NCA) was replaced with 50, 100% of RCA and bio-deposited recycled coarse aggregate (BRCA). The aggregate properties were tested and observed that the water absorption and crushing index of RCA were increased by 85.10% and 19.10%, whereas for BRCA, the water absorption and crushing index were increased by only 5.20% and 5.80%. The concrete mixture prepared with optimised and complete percentages of RCA and BRCA was tested for their fresh, hardened, and durable properties. It is observed that the strength of the RAC was 36% lesser than NAC, whereas the strength of the BRAC was 33.40% more compared to the RAC at 28 days. Also, the water absorption and sorptivity of BRAC were reduced by 33.68% and 15.50% and the resistance to carbonation and chloride ingression of BRAC was enhanced by 15.50% and 29.73% when compared to RAC. The microstructural investigations performed through SEM and XRD evident the CaCO3 precipitation that improves the quality of RCA. [ABSTRACT FROM AUTHOR]

The objective of the current study is to evaluate the performance of Recycled Concrete Aggregates (RCA) based Self-compacting Concrete (RCA-SCC) comprising coal ashes and Silica Fume (SF). Coal ashes [Fly Ash (FA) and Coal Bottom Ash (CBA)] were incorporated as partial replacement for Ordinary Portland Cement (OPC) and Fine Natural Aggregates (FNA), respectively, while RCA were incorporated in place of Coarse Natural Aggregates (CNA). In order to compensate for the anticipated performance loss caused by the incorporation of RCA, a fixed percentage (10%) of SF was used as filler. The performance of aforesaid SCC was evaluated through various laboratory tests in fresh and hardened state. Five different substitution levels of CNA with RCA (0–100%), parallel with constant substitution level of FNA with CBA (10%) and OPC with SF + FA (10% + 20%) have been used throughout the investigation. Overall, the experimental outcomes along with regression results confirmed the potential of RCA-SCC prepared with CBA. RCA-SCC mix (25%) with coal ashes (FA + CBA) resulted in nearly equivalent performance to that of the reference SCC mix. Finally, the outcomes imply the successful contribution of SF, coal ashes (CBA + FA), and RCA leading towards the sustainable development of non-conventional SCC with identical performance. [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]

Concrete made using recycled aggregates may become less durable due to sulfate attack. In this study, the degradation of recycled aggregate concrete (RAC) under external sulfate assault was investigated using a mesoscale numerical analysis method. A random convex polygon aggregate model with five phases—(1) aggregate, (2) aggregate–old bonded mortar interface transition zone (ITZ), (3) old bonded mortar, (4) old bonded mortar–new bonded mortar ITZ, and (5) new bonded mortar—was established using a self-compiled program in order to take into account the heterogeneity of RAC. The aggregate was considered an impervious phase, but the four other phases were considered pervious. In the model, the only chemical byproduct was the ettringite that causes expansion. The proposed method for modeling sulfate attack on RAC was validated by experiments. Sulfate diffusion, the impact of ITZ thickness, water:cement ratio, and surface sulfate content were investigated. The simulation results showed that (1) there was limited influence of surface sulfate ion concentration on the rate of sulfate erosion in RAC, (2) water:cement ratio has a significant impact on sulfate resistance in RAC, and (3) the sulfate attack procedure is largely unaffected by ITZ thickness. [ABSTRACT FROM AUTHOR]

Modulus of elasticity of recycled concrete Recycled concrete can differ in hardened concrete properties from concrete only with natural aggregate. For this reason, when ordering recycled concrete, Switzerland requires the specification of an E‐modulus class. The modulus of elasticity must be determined in accordance with SN EN 12390‐13, i. e. on test specimens that are stored under water. Therefore, the question arose as to whether the modulus of elasticity determined on water‐saturated test specimens is meaningful for structural members with dry exposure conditions. For this reason, investigations were carried out on recycled concrete with recycled aggregates made from crushed concrete and from mixed granulate. For this purpose, test specimens were stored under water until the test was carried out and further specimens were dried before the test. It was shown that the modulus of elasticity is higher with water storage than after dry storage, but the differences are not very large. [ABSTRACT FROM AUTHOR]

Basalt fiber reinforced recycled aggregate concrete (BFRAC) is a high-performance, environmentally friendly material that combines lightweight, high-strength fibers with low-carbon recycled aggregates (RAs), positioned for extensive use in building structures. However, research on its constitutive relationships is currently scarce, which partly restricts component design and analysis. In this context, the current study thoroughly explores the stress–strain relationship and variability of BFRAC under compression, using 240 cylinders for testing to investigate the influence of factors like coarse/fine RA sources, RA replacement rates, and fiber dosage. The study found that the addition of RAs and fibers reduced the workability of the mixture, particularly with the inclusion of fine RAs and short-cut fibers. Using coarse and fine RAs generally reduces the material's elastic modulus, compressive strength, and post-peak ductility. Adding fibers can slightly improve compressive strength and peak strain, significantly reduce material brittleness, and have a minimal impact on elastic modulus. Importantly, the study noted that the pre-peak segment of the stress–strain curve of BFRAC is most sensitive to the addition of fine RAs, while the post-peak segment is most sensitive to fiber content. Despite this, using high-quality RAs up to 50% replacement and adding 0.4% by volume of fiber can make BFRAC with mechanical properties comparable to natural aggregate concrete. Based on the observed tests, this paper proposes constitutive relationships that incorporate skeleton curves and variability at different points for the compressive stress–strain behavior of BFRAC. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregate instead of natural coarse aggregate is of great interest from a sustainability perspective. The present study investigates the flexural design of unbonded, post-tensioned, precast recycled concrete beams. It also evaluates the application of unbonded prestressed tendons in recycled concrete beams. Flexural behavior tests were performed on 13 beams with different prestressed reinforcement indices, section heights, and comprehensive reinforcement indices. We thoroughly investigated stress changes in prestressed steel strands, beam failure forms, and crack development during loading. The results demonstrate that under the same load level, the average crack width of recycled concrete beams is 36% higher than that of conventional concrete beams. A theoretical analysis indicates that the factors affecting the stress increment of unbonded prestressed tendons are the comprehensive and prestressed reinforcement indexes. A theoretical model of stress increment during loading of prestressed reinforcement was obtained, allowing derivation of an ultimate bearing capacity formula for unbonded, post-tensioned, precast, recycled concrete beams. An influence coefficient for recycled coarse aggregate is introduced and set to 1.14, the experimental data is fitted to derive the calculation formula for the average crack spacing and width. The theoretical model of the stress increment in prestressed steel strands and the proposed crack width model provide a valuable design reference and theoretical support for engineering applications. [ABSTRACT FROM AUTHOR]

As a developing nation, Pakistan faces financial obstacles in road construction, which is essential for economic growth but costly. A sustainable approach to address environmental concerns involves using recycled materials in road construction. The construction industry has largely overlooked recycling despite the significant amount of debris generated during construction and demolition. Repurposing materials from building and demolition activities, such as rubber from tires and drywall waste, can serve as viable materials for subbase layers in roads. These recycled materials can improve road quality and performance while mitigating environmental and health risks associated with stockpiling and disposal. This research evaluates the physical and mechanical properties of recycled concrete aggregates (RCA) combined with drywall waste (DW), waste tire rubber (WTR), and quarry dust (QD) for flexible pavement subbases. The study investigated the effect of adding 0.5%, 1%, 1.5%, and 2% crumb rubber with 5%, 10%, 15%, and 20% DW as a percentage of fine aggregate with QD in RCA. By subjecting RCA to a series of tests, their strength, durability, and stability are thoroughly assessed to determine the optimal ratios of WCR and DW. As a result of these evaluations, a notable improvement in compressive strength is observed. Cost analysis demonstrates the economic feasibility of using recycled materials in pavement subbase construction, offering a cost-effective, sustainable, and environmentally safe solution that reduces reliance on fresh aggregates (FA). [ABSTRACT FROM AUTHOR]

Significant construction and demolition waste (CDW) is produced by many useless concrete buildings, bridges, airports, highways, railways, industrial mining, etc. The rising need for new construction has increased the use of natural materials, impacting the ecosystem and incurring high costs from mining natural aggregates (NA) and processing CDW. The concept and implementation of recycled aggregate concrete (RAC) offer a sustainable solution for the concrete industry. Crushed concrete, made from recycled concrete, can be used instead of natural aggregates in structural concrete. This sustainable byproduct, recycled concrete aggregate (RCA), has the potential to replace natural aggregate. This paper examines the benefits of RAC from economic, social, environmental, and technological perspectives and discusses the replacement ratio (RR)—the weight percentage of natural aggregate replaced by recycled aggregate—which is crucial to RAC performance. A collection of used data on mechanical properties and economic performance, national specifications, standards, and guidelines is reviewed to determine the optimal replacement ratio for RCA, which was found to be 20%. Finally, we discuss the challenges and future of using RAC in structural concrete. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregates are potentially interesting for the precast concrete industry as they provide a new use for high-quality waste from its products' life cycle. In precast concrete structures, it is common to use headed bars in several connection types between structural members. This paper presents the results of experimental tests to investigate the impact of replacing coarse natural aggregates with coarse recycled concrete aggregates in the concrete breakout strength of cast-in headed bars embedded in slender structural elements. Results of 12 tests on 16 mm headed bars embedded in 500 × 200 × 900 mm concrete members with an effective embedment depth of 110 mm are presented. The percentage of replacement of natural aggregates by recycled concrete aggregates was 0%, 30%, and 100%, and the flexural reinforcement ratio of the structural elements varied from 0.5% to 3.5%. The behavior and strength of the tested specimens are discussed, and comparisons with theoretical strength estimates are presented. The results showed that the concrete breakout strength of the headed bars was not affected by the use of recycled concrete aggregates and that the flexural reinforcement ratio significantly impacts the load-carrying capacity of the headed bars as they control the crack widths before failure. [ABSTRACT FROM AUTHOR]