Recycled Concrete Research Articles

Development of Sustainable Construction Materials from Inert Waste Mixtures Using the Mechanosynthesis Process.

This research investigates the potential of mechanosynthesis to transform inert waste mixtures into sustainable construction materials. Three waste streams were employed: recycled glass, recycled concrete, and excavated soils. Two alternative material formulations, F1 (50% recycled concrete, 30% recycled glass, 20% excavated soil) and F2 (60% excavated soil, 20% recycled concrete, 20% recycled glass), were developed. Cement pastes were produced by partially substituting cement (CEM I) with 50% of either F1 or F2. Characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), and mechanical testing, were performed. Cement pastes incorporating milled waste materials exhibited significantly enhanced compressive strength compared to their unmilled counterparts. At 28 curing days, compressive strengths reached 44, 47, 45, and 49.7 MPa, and at 90 curing days, they increased to 47.5, 50, 55, and 61 MPa for milling conditions of 200 rpm for 5 min, 200 rpm for 15 min, 400 rpm for 5 min, and 400 rpm for 15 min, respectively. In addition, F1 formulations showed higher compressive strengths than the reference CEM II and CEM III pastes. These results highlight the efficacy of mechanosynthesis in valorizing construction waste, mitigating CO2 emissions, and creating environmentally friendly construction materials.

Enhancing Sustainable Concrete Production by Utilizing Fly Ash and Recycled Concrete Aggregate with Experimental Investigation and Machine Learning Modeling

Enhancing Sustainable Concrete Production by Utilizing Fly Ash and Recycled Concrete Aggregate with Experimental Investigation and Machine Learning Modeling

Fracture properties and acoustic emission characteristics of manufactured sand recycled fine aggregate concrete

To promote the application of recycled fine aggregates, fracture characteristics of concrete beams containing manufactured sand (MS) and recycled fine aggregate (RFA) were investigated. The fracture properties and acoustic emission (AE) characteristics of manufactured sand recycled fine aggregate concrete (MSRFAC) with 0 %, 25 %, 50 %, 75 % and 100 % RFA replacement rates were evaluated by three-point bending test of single-sided notched beams. The fracture mechanisms of MSRFAC beams were explored using AE and digital image correlation (DIC) techniques, and fracture process zone (FPZ) was qualitatively and quantitatively analyzed. The results indicated that the critical nominal stiffness, initial fracture toughness, fracture energy and characteristic length of MSRFAC decreased significantly with the increase of RFA replacement rate, up to 20.2 %, 37.7 %, 22.8 %, and 26.6 %, respectively, while the unstable fracture toughness was insensitive to the variation of RFA. Moreover, the AE activity, the tensile crack, large-scale crack, high amplitude, and high peak frequency in MSRFAC increased with increasing RFA replacement rate. According to the FPZ characteristics of MSRFAC, its FPZ length increased with the increase of RFA replacement rate, while the FPZ width decreased with the increase of RFA replacement rate. The critical FPZ lengths of MSRFAC with different RFA replacement rates were about 20.2–30.0 mm, and the maximum FPZ widths were about 26.0–36.7 mm. The RFA weakened the friction mechanism and interlocking effect between aggregates of MSRFAC, resulting in a faster FPZ propagation rate and smaller damage width of MSRFAC than normal manufactured sand concrete.

The Use of Ground Recycled Concrete Cement as an Eco-Friendly Alternative Cement Material in Mortar Production

The Use of Ground Recycled Concrete Cement as an Eco-Friendly Alternative Cement Material in Mortar Production

Optimisation of Parameters and Application of Green Recyclable Precast Hollow Steel Pipe Concrete Supports

Underground space development is a crucial approach to addressing traffic congestion in China’s cities, especially through underground construction. However, the traditional pit internal support system, particularly the concrete internal support system, has significant drawbacks. These include high energy consumption and carbon emissions, which are increasingly prominent issues. In this paper, a hollow precast concrete-filled steel tube (H-CFST) internal support system is proposed and a node connection scheme is designed. Through numerical simulation, the load-bearing characteristics of H-CFST with different aspect ratios, hollow ratios, hoop thicknesses, and hoop lengths are investigated, and the optimal design parameters are obtained. Finally, following a field application, monitoring data reveal that the precast H-CFST internal support demonstrates superior load-bearing capacity compared to the concrete internal support, successfully meeting the criteria for replacement of the concrete support.

Experimental study on the effect of carbonate ions on ITZs of geopolymeric recycled concrete

In this study, carbonated recycled aggregates (CRA) were used in preparing geopolymeric recycled concrete (GRC). The influence of CRA with different carbonation durations on the compressive strength of GRC was studied, and the physical properties of CRA were tested. Bi-material Brazilian disc (BBD) was explored to simulate interfacial transition zones (ITZ). According to the test results, CRA was found to introduce quantities of carbonate ions, causing a similar adverse effect of efflorescence in GRC. Therefore, the compressive strength decreased in the first 24 h of carbonation. After 96 h carbonation, the reduction in compressive strength was insignificant. When using CRA to prepare GRC, it would be advisable to carbonate recycled aggregates for longer than 96 h. The results of the splitting tensile tests and nanoindentation test of BBD revealed that the carbonate ions introduced by carbonation treatment could slightly weaken the bonding properties of ITZ in GRC.

Natural carbonation boost for hardened cement fines by dripping technique

This study proposes a dripping technique to improve the carbonation efficiency of hardened cement fine (HCF), which mimicked the binder part of waste concrete, sized between 0.6 mm and 1.18 mm under atmospheric CO2 concentration. After a 7-day carbonation using the dripping technique, the carbonation degree doubled compared with that at 85 % relative humidity (RH). This improved carbonation efficiency can be attributed to two factors: 1) The pores created during drying accelerate the infiltration of the solution, releasing more calcium ions; 2) The difference in calcium ion concentration between the surface aqueous film and pore solution causes calcium ions to migrate to the surface, accelerating the dissolution of calcium-bearing hydrates in the pore solution and releasing more calcium ions. Adjusting the dripping interval and drying conditions according to the particle size and amount of carbonatable calcium improves the carbonation efficiency. This strategic approach offers a practical means to contribute to the sustainable recycling of waste concrete.

Microscopic interface deterioration mechanism and damage behavior of high-toughness recycled aggregate concrete based on 4D in-situ CT experiments

High-toughness recycled aggregate concrete (HTRAC), as an innovative green building material, showcases outstanding performance and environmental attributes. To investigate its microscopic structural characteristics and the mechanisms of damage evolution under loading, a series of 4D in-situ X-ray computed tomography (CT) experiments were conducted under uniaxial compression conditions. During the experimental process, detailed scans were performed on six key loading points (0 %, 30 %, 60 %, and 100 % of the peak load, 70 % and 40 % of the post-peak load of the specimen). Advanced three-dimensional image processing techniques were utilized to conduct a comprehensive analysis of internal features within the specimen, including pores, steel fibers, and cracks. The evolution of damage in HTRAC was characterized by both qualitative 2D crack slice analysis and quantitative 3D reconstruction analysis of cracks. Changes in the average grayscale values of CT cross-sectional images were also examined. The deterioration mechanism of recycled aggregate concrete interface cracks was elucidated by the combination of CT images and modeled HTRAC. Furthermore, a statistics model illustrating the interaction mechanism between damage, cracks, and strain was proposed. This study provides technical and theoretical support for the further promotion and application of high-toughness recycled aggregate concrete.

Investigating the impact of carbonation curing concentrations on the mechanical properties and microstructure of recycled concrete

This investigation examines the impact of different CO2 curing concentrations on the mechanical and microstructural properties of recycled concrete aggregates, aiming to optimize the carbonation process for enhanced practicality. Utilizing 25 recycled concrete samples, the study varied CO2 concentrations (20 %, 40 %, 50 %, 60 %, and 95 %) and pre-conservation durations (24–120 h), conducting tests for carbon sequestration, compressive strength, and splitting tensile strength to determine the effects on recycled concrete's performance. Key findings reveal a direct correlation between increased CO2 curing concentrations and carbon sequestration levels, with an observed pattern of initial increase followed by a plateau or decrease in sequestration with extended pre-conditioning. Interestingly, while compressive strength generally improved with higher CO2 concentrations, splitting tensile strength showed a decrease, suggesting different impacts of CO2 concentration on various mechanical properties. A notable observation was that at 60 % CO2 concentration, compressive strength was slightly lower (by 2.46 %) compared to the 95 % concentration, yet the splitting tensile strength was 2.84 % higher at 60 %, indicating that a 60 % CO2 curing concentration might offer an optimal balance between economic efficiency and material performance enhancement. This balance suggests significant improvements in resource utilization compared to traditional pure CO2 curing methods. In conclusion, this study provides substantial evidence supporting the optimization of CO2 curing for recycled concrete, advocating for a 60 % concentration as the most effective strategy to enhance both the environmental sustainability and the mechanical performance of recycled aggregates. These insights significantly contribute to advancing low-carbon and sustainable practices within the construction industry.

Tensile properties of steel fiber reinforced recycled concrete under bending and uniaxial tensile tests

It is important to study the tensile behavior of steel fiber reinforced recycled concrete (SFRRC) for the reliability of structural design. This paper investigates the effects of different mixture systems, including full-NA, full-RCA, full-RFA, full-RA, and full-RA+10%RP, on the tensile behavior of recycled concrete through uniaxial tensile and three-point bending tests. In addition, the effects of the volume content of steel fiber on tensile behavior are investigated. The uniaxial tensile strength and stress-strain curves of SFRRC were tested and the load-deflection, P-CMOD, double K fracture parameter and fracture energy under flexural tensile load were measured. The results show that the incorporation of recycled materials may negatively affect the tensile strength of recycled concrete. Compared with natural concrete, the uniaxial tensile strength decreased by 28.4%–50.2 % and the flexural tensile strength decreased by 17%–42.52 %. In addition, tensile properties, such as initial crack stress, peak strain, double K fracture toughness, and fracture energy, will also decline. The effect of the volume content of steel fibers on the tensile properties of recycled concrete with different mixed systems is analyzed. The steel fiber changes the tensile cracking mode of recycled concrete. When the content of steel fiber exceeds 1 %, the SFRRC of different mixed systems has the phenomenon of deflection hardening. When the fiber content is 2 %, the uniaxial tensile strength is increased by 13.83%–69.07 %. Contrasting with the control group, the recycled concrete group containing 2 % steel fiber showed enhanced fracture energy, which was increased by 15–23 times with different mixture systems. Uniaxial tensile constitutive models of SFRRC have been established under different mixture systems. The tensile stress-strain response of SFRRC was obtained indirectly by inverse analysis. It has been found that flexural tensile tests overestimate the post-crack properties of materials, and this phenomenon is more obvious in recycled concrete. This research is of great significance for the structural design of SFRRC.

Experimental Study of Recycled Concrete under Freeze-Thaw Conditions.

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.

Analysis of Workability and Mechanical Properties of Alkali-Activated Recycled Aggregate Fiber Concrete

Alkali-activated recycled aggregate fiber concrete is an innovative material that combines alkali activation technology, recycled aggregates, and fiber reinforcement. This paper systematically analyzes the workability and mechanical properties of this concrete. Experimental studies assessed the workability of alkali-activated recycled aggregate fiber concrete, including its flowability and workability, and explored how these characteristics impact construction and use. Additionally, a detailed analysis of the concrete's mechanical properties, such as compressive strength, tensile strength, and flexural strength, was conducted. The results indicate that alkali-activated recycled aggregate fiber concrete maintains good workability while significantly enhancing mechanical properties, with excellent crack resistance and toughness. The paper also discusses the key factors affecting these properties and provides an outlook on future research directions and practical applications.

Mesoscopic numerical simulation of chloride diffusion behavior in cracked recycled aggregate concrete

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.

Effects of aggregate's type and orientation on stress concentration and crack propagation of modeled concrete applied a shear force

This study focused on planarizing natural modeled aggregate concrete (NMC), recycled modeled aggregate concrete (RMC), and brick modeled aggregate concrete (BMC) for analyzing the influences of aggregates on shearing failure mechanism. A designed apparatus was used to load a shear force for the specimens and analyzed the global and local strain fields near the interface transition zone (ITZ) using digital image correlation (DIC) analysis. Additionally, we employed COMSOL software simulation to understand the crack initiation process and damage evolution mechanism of related concrete. Our findings revealed that the brick aggregate leaded to the lowest modulus of elasticity and compressive strength, resulting in poor shear resistance. However, the recycled aggregate model exhibited the highest shear resistance, primarily due to the old mortar acting as a buffer layer in the ITZ. During loading, the stress in the NMC model concentrated in the load transfer zone and gradually moved to the left and right sides of the built-in aggregate model until fracture, as observed through DIC analysis. The stress distribution of the RMC was similar with those of the NMC, but the BMC showed a distinct stress distribution pattern. Furthermore, the corner of the built-in modeled aggregate significantly influenced the crack propagating path and stress distribution. Therefore, the modeled aggregate corner plays a crucial role in the shear behavior of concrete, affecting both crack propagation and overall mechanical performance. The practical implications of our study can inform the design and application of recycled concrete.

Effect of chloride ion corrosion on the microstructure of multiple interfaces of alkali-activated GGBS/FA based recycled concrete

In this paper, the resistance to chloride ion permeability of multiple interfaces in alkali-activated slag/fly ash (GGBS/FA) based full recycled concrete was investigated using the immersion method. In order to objectively and accurately reflect the microhardness and width of the interface transition zone (ITZ), box plots were used to process the measured point data. The results indicated that the microhardness of the interface was significantly lower than that of the matrix. The microhardness of the old aggregate interface (ITZOA-OM), the new aggregate interface (ITZOA-NM) and the new mortar interface (ITZOM-NM) all decreased to varying degrees with the extension of the immersion ages, but remained higher than that of the uneroded specimens. Chloride ions penetrated into ITZOA-OM and reacted with a large amount of enriched Ca (OH)2 to form an expansive composite salt (CaCl2.Ca(OH)2.H2O), which improved the microstructure of the ITZ, increased the microhardness and decreased the width of the ITZ. The dense structure of ITZOA-NM and ITZOM-NM inhibited the migration of chloride ions to a certain extent. leading to minimal changes in the width and microhardness of the ITZ. The micro mechanisms of chloride ion penetration resistance at the interfaces of alkali-activated GGBS/FA-based recycled concrete were investigated using BSE and EDS. More reaction products were generated at the interfaces after chloride ion erosion, and the newly generated substances continuously filled the microcracks, resulting in a more uniform bond at the interfaces. This contributed to the improvement of the microstructure and the resistance to chloride ion penetration of alkali-activated GGBS/FA based recycled concrete.

Effect of silica fume on the microstructural and mechanical properties of concrete made with 100% recycled aggregates

Recycled concrete aggregate can be utilized in structural concrete in order to reduce the use of natural resources and the harmful impacts of waste concrete on the environment. This present research aimed to assess the effectiveness of using recycled aggregate concrete with the partial replacement of cement by silica fume (SF) to analyze the microstructural and mechanical properties of recycled aggregate concrete (RAC). In this study, recycled stone was used as coarse aggregate. The main variables of the study included the dosage of silica fume that was employed as a partial replacement of ordinary Portland cement (OPC) with four different percentages: 4%, 8%, 12%, and 16% by weight. Five different mixes were prepared, with four mixes created by varying amounts of silica fume, which were designated as RSACSF4, RSACSF8, RSACSF12, and RSACSF16. The other mix was created as a reference mix without silica fume and designated RSACSF0. Slump test was conducted to investigate the workability of concrete mixes. From the test result, a decreasing trend was found after adding more percentage of SF. Compressive and splitting tensile tests were conducted to analyze the mechanical properties of RSAC at 7 and 28 days. The results showed that the addition of SF improved the performance of RSAC at early and later curing ages, and a 12% addition of SF showed the best result. Scanning electron microscopy and X-ray diffraction analysis were performed to explore SF's microstructural performance and effect on RSAC. The results showed that silica fume showed a positive pozzolanic impact, and when combined with calcium hydroxide, it underwent a secondary hydration reaction that boosted the generation of calcium silicate hydrate and improved the parameters of the interface transition zone. X-ray diffraction analysis showed that silica fume and silica fume have similar pattern intensities. Finally, 12% SF is recommended as a partial replacement for cement in RSAC.

Optimisation of the performance of alkali-activated mortars using CDW binders from different sources

This study investigates the fresh-state properties and the hardened-state physical and mechanical properties of a total of 64 alkali-activated mortars incorporating different wastes as binders, such as fly ash (FA), recycled concrete (RC), recycled brick (RB), and recycled tile (RT). These waste materials were activated using sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). Linear regression analysis was employed to evaluate the impact and significance of Na2O concentration (9 % or 15 %), modulus of silica (0.5 or 1), curing time in the oven (24 or 48 h), and temperature (50 °C or 70 °C) on the properties of the mortars. The results, analysed using ANOVA, indicate that all properties were affected by these parameters, except for the initial curing time in the oven for mortars made with construction and demolition waste (CDW), which showed no significant differences between periods of 24 and 48 h. Compared to mortars produced with RC, the contribution of these parameters to mechanical properties was more prominent in the mixes with RT and RB. The highest compressive strength at 28 days, for the mortars with CDW binders, was obtained by incorporating RT with 12 % of Na2O, modulus of silica of 1 and 70 °C for 48 h of initial curing, reaching 12.5 MPa. This value is 2.1 times higher than the strength obtained in mixes with RB or RC. The results also show that the performance of the mortars is highly related to the reactivity of the waste material (mortars with RT performed better) and prove that each raw material has its own optimum criterion.

Strength development of MgO recycled aggregate concrete with recycled sand from WRSG and compressive behavior of recycled lump-aggregate concrete

The existing literature suggests that natural aggregate concrete demonstrates the least shrinkage, followed by recycled aggregate concrete (RAC) prepared using natural sand, with RAC prepared using recycled sand (RS) from the weathered residual soil of granite demonstrating the greatest shrinkage. Internal incorporation of a MgO expansion agent (MEA) effectively compensates for the excessive shrinkage of the latter; however, the influence of the MEA on the strength development of RAC prepared using RS after natural curing, rather than accelerated carbonation curing, remains unclear. In this study, compression tests of RAC prepared using RS at different stages of natural curing were performed and the corresponding material compositions of RAC were determined and quantified via X-ray diffraction and thermogravimetry-differential thermogravimetry. The soluble carbonate content in RS was determined by ion chromatography, and the morphology of RAC was observed using scanning electron microscopy. The mechanism of strength development of RAC during aging was determined. Furthermore, compressive tests of recycled lump-aggregate concrete (RLAC) were performed to investigate the influencing degree of RAC as fresh concrete on the compressive properties of RLAC. The following key results were noted: (a) the MEA impairs the compressive strength of concrete, but the degree of impairment decreases with curing, and this is attributed to the transformation of Mg(OH)2 to MgCO3. (b) The presence of soluble carbonates in RS (7.2 %) is the main source of carbonate in the conversion of Mg(OH)2 to MgCO3. Mg(OH)2 particles adhere to the surface of RS particles and react with soluble carbonate to generate MgCO3. (c) At 56 days of curing, the addition of 6 % MEA or increasing the replacement ratio of RS impaired the compressive strength of RLAC to a certain extent. However, even with 100 % RS, the compressive strength and elastic modulus of RLAC were impaired by only 7.4 % and 5.8 %, respectively. With 6 % MEA, the impairments were even smaller and negligible.

Assessing the Impact of Fly Ash and Recycled Concrete Aggregates on Fibre-Reinforced Self-Compacting Concrete Strength and Durability

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.

Experimental investigation on mechanical properties of fiber recycled concrete filled-square steel tube columns under pure flexural based on acoustic emission technique

Currently, global countries are actively focusing on carbon emission reduction. Utilizing recycled aggregate concrete (RAC) is expected to realize global carbon neutrality objectives. However, due to its inherent mechanical limitations, its application in structural contexts is restricted. This study aimed to enhance the mechanical attributes of RAC and expand its utility beyond low-strength applications. By employing recycled aggregates, steel fibers, and ordinary Portland cement, a novel eco-friendly composite filler was developed for steel- tube filling. A comprehensive study on 16 concrete mix ratios and 23 steel-tube recycled concrete columns was conducted. The parameters included the recycled aggregate volume, steel fiber content, and steel pipe thickness. The results revealed that reasonable mix design enabled RAC to exhibit flexural performance similar to that of conventional steel-tube concrete. Moreover, while increasing the recycled aggregate content deteriorated the overall mechanical properties, incorporating steel fibers extended the elastic stage and enhanced the flexural characteristics. Optimal results were achieved with 1.2 % steel fiber addition and 75 % recycled aggregate. The comparison between the derived equation and the experimental data demonstrated a high level of agreement, confirming the accuracy of the equation. Furthermore, acoustic emission technology was employed in this experiment to monitor the failure progression of steel tube recycled concrete columns subjected to a pure bending load. The findings revealed a triphasic failure process: elastic, elastic-plastic, and strengthening stages. The analysis demonstrated a consistent correlation between acoustic emission parameters and waveform characteristics with the failure process of the specimen. Empirical evidence demonstrated the efficacy of acoustic emission technology in effectively monitoring the damage severity and failure chronology in recycled concrete steel pipe columns during bending.