High-strength Recycled Aggregate Concrete Research Articles

Axial compressive performance of low-carbon high-strength recycled aggregate concrete

AbstractThis paper introduces a novel material, low-carbon high-strength recycled aggregate concrete (LCHRAC), developed by activating ground granulated blast-furnace slag (GGBS) and silica fume (SF) in an alkaline environment and integrating recycled aggregate. To evaluate its mechanical properties, uniaxial compressive tests were performed, systematically analyzing the effects of recycled concrete aggregate (RCA) substitution ratios, as well as the characteristic parameters of steel and polypropylene(PP) fibers, on LCHRAC’s mechanical behavior. The results indicated that compressive strength shows a gradual decline as the RCA substitution ratio increases, with a moderate reduction of 7.1% up to 50% replacement, and a more significant drop, retaining only 68.6% at 100% replacement. In contrast, the peak strain increases linearly, showing a 29% improvement at full replacement, while the toughness index exhibits a consistent upward trend, increasing by approximately 123% at a 100% replacement rate. Based on experimental data, empirical models were developed to predict the influence of key control variables on the compressive strength, peak strain, elastic modulus, and the uniaxial compressive stress–strain behavior of LCHRAC. Additionally, advanced characterization techniques, including X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), were employed to elucidate the hydration mechanisms of the slag-silica fume composite system. These findings provide a comprehensive understanding of the mechanical performance and microstructural characteristics of LCHRAC, contributing to its potential application in sustainable construction practices.

Axial compression behaviour of square steel tubes encased by and filled with high-strength recycled aggregate concrete

The axial compression behaviour of square steel tube (SST) columns encased with recycled aggregate concrete (RAC) and filled with RAC (RAC-encased RACFSST) columns was investigated. Using high-strength concrete, five specimens were tested under axial compression until failure. The experimental parameters included the coarse aggregate type, stirrup spacing, wall thickness of the SST and the existence of cross-tie bars in the SST. The failure mode, load–displacement curves, load–strain curves and ductility of the composite columns were obtained. The impacts of the various parameters on the mechanical performance of the RAC-encased RACFSST columns were evaluated. The failure modes of the composite columns were comparable. The inclusion of RAC enhanced the load-bearing capacity (LBC) of the column, but negatively affects its ductility and deformation capacity. Increasing the wall thickness of the SST and reducing the stirrup spacing significantly improved the axial compressive performance of the columns, as mainly reflected in the axial compressive capacity and ductility, respectively. Cross-tie bars inside the SST improved the LBC and deformation capacity. The axial bearing capacities of the columns and those in other studies were determined using existing codes. The computed results were very consistent with the experimental data.

Seismic performance of earthquake-damaged HSRAC beam-column interior joints rehabilitated by bonding steel plates in the plastic hinge of beams

In order to investigate the seismic performance of earthquake-damaged high-strength recycled aggregate concrete (HSRAC) beam-column interior joints employing ultra-high strength bars (UHSB) in columns, four specimens were designed and manufactured. The research variables included whether the steel tube was encased in the column and whether beams were rehabilitated by bonding steel plates. Among them, the rehabilitated specimens were firstly loaded to 1.0 % drift ratio, and then loaded to failure after rehabilitating the plastic hinge of beams. The test results showed that the beam hinge failure mode occurred in the specimens loaded directly to failure. The damage of columns and joint cores was relatively slight, and the crack width satisfied the repairability limits before 2.0 % drift ratio. The shear failure of the joint core occurred in the rehabilitated specimen without steel tube, as shear deformation and stirrup strain in the joint core increased. The shear bearing capacity of joints increased after steel tubes were encased in columns, and the damage of joint cores was reduced. The bearing capacity and deformation capacity of specimens improved after rehabilitating. Finite element models were established and verified with experiment results. Parameter analysis was conducted for different pre-damage degrees, and the results indicated that as pre-damage degree increased, the bearing capacity of specimens decreased.

Bond stress-slip behavior of ultrahigh-strength steel bars with spiral grooves embedded in plain and steel fiber high-strength recycled aggregate concrete

This study investigated the bond behavior of ultrahigh-strength steel bars with spiral grooves (UHSSBs) embedded in high-strength recycled aggregate concrete (RAC). Forty-five pullout specimens under monotonic loadings were designed to evaluate the effect of several parameters on the bond strength. The variables included concrete strength (50 MPa–60 MPa); recycled concrete aggregate (RCA) replacement ratio (0 %, 50 %, and 100 %); embedment length (5db, 10db, and 20db); concrete cover (25 mm, 45 mm, and 68.7 mm); surface treatment; volume fraction of steel fibers in RAC and stirrup ratio. The failure modes of these tests mainly concentrated on two types, pullout-type bond failure and splitting-type bond failure. According to the typical bond stress-slip curves and trendlines of plotted values, the bond strength increased with increasing of concrete compressive strength. For specimens with splitting-type bond failure, the higher normalized bond strength was observed in higher RCA replacement ratio and concrete cover thickness. The factors of embedment length and surface treatment were also proven to be effective for bond strength. For specimens with pullout-type bond failure, the presence of steel fibers and stirrups substantially restricted the splitting crack growth and improved the bond failure modes. Combined with previous experimental results, simple empirical equations for the average bond strength and bond stress-slip relationship between UHSSBs and RAC under different types of bond failure were developed by regression analysis, which can capture the experimental data with high accuracy.

Seismic Behavior of High-Strength Recycled Aggregate Concrete Columns with High-Strength Reinforcement

ABSTRACT This study investigated the seismic performance of high-strength recycled aggregate concrete (RAC) columns with high-strength reinforcement under cyclic loading. Five full-scale columns were carried out, and the results revealed that the lateral loading capacity of RAC column was slightly lower than that of natural aggregate concrete column. Increasing the axial load, the lateral loading capacity of RAC columns increased significantly. Increasing the concrete strength under the same axial load, the lateral loading capacity was slightly increased. Based on the test results, a numerical simulation model was established. Finally, a flexural capacity calculation model and an N–M curve calculation model are proposed.

Stress–Strain Relationship in Axial Compression for Confined High-Strength Recycled Aggregate Concrete

Stress–Strain Relationship in Axial Compression for Confined High-Strength Recycled Aggregate Concrete

Experimental research and finite element analysis on seismic performance of resilient columns applying high-strength recycled aggregate concrete

To promote the green development of resilient cities and achieve resilient buildings constructed with recycled materials, it is necessary to further extend the engineering application technology of high-strength recycled aggregate concrete (HSRAC) in resilient structures. In this paper, pseudostatic tests were carried out on six HSRAC columns with ultra-high-strength steel bars (UHSS). The test variables include the UHSS percentage, stirrup ratio, axial compression ratio and UHSS bond strength. In addition, finite element models were developed to conduct the parametric analysis and optimization assessment. Based on the experimental research and finite element analysis, the seismic performance and repairability of HSRAC columns were discussed. The results revealed that HSRAC columns employing the UHSS possessed excellent self-centering capability and remarkable drift-hardening property. Well-designed HSRAC resilient columns can be repaired within 4.0% drift. In addition, the engineering design references were recommended based on reliable simulation results.

Seismic performance and damage assessment of earthquake-damaged HSRAC columns with UHSS repaired by CFRP jackets

In this paper, ultra-high-strength steel bars (UHSS) were innovatively applied to the high-strength recycled aggregate concrete (HSRAC) columns to achieve resilient structures cast from green building materials. Quasi-static tests were conducted to investigate the seismic performance and reparability of HSRAC columns with UHSS under the first-excursion failure mode, and to analyze and discuss the effect of cumulative damage on earthquake-damaged resilient columns repaired by carbon fiber-reinforced polymer (CFRP) composites jackets. The research showed that the damage state of HSRAC columns at 2% drift ratio was mild, and residual displacement satisfied the reparability limit. And the earthquake-damaged resilient columns possessed satisfactory seismic performance after rapid repaired by CFRP jackets. Based on the experiment results and observations, a lateral load carrying capacity prediction model for HSRAC columns with UHSS under first and non-first seismic action was established, and fatigue damage energy was defined. In addition, damage model was introduced to assess the performance degradation of resilient column under first and non-first earthquake effects. The models were then verified by comparing prediction results with test results.

Seismic performance and reparability assessment of recycled aggregate concrete columns with ultra-high-strength steel bars

In this paper, ultra-high-strength steel bars (UHSS) were innovatively applied to the high-strength recycled aggregate concrete (HSRAC) columns to achieve resilient structures cast from green building materials. Quasi-static tests of five new pattern columns were conducted to investigate the seismic performance and reparability. The influence of UHSS substitution ratio and the recycled coarse aggregate replacement ratio on seismic response and damage evolution of HSRAC columns were discussed. The research showed that configuring UHSS in the HSRAC columns could obtain drift-hardening property, and the residual displacement and crack width meet the requirements of repairable limit at the drift ratio less than 3%. The application of recycled aggregate concrete had negligible effect on the seismic performance and reparability of columns, and even contributed to improve their reparability probability. Moreover, reparability assessment methods were established based on the damage evolution theory and measured results, the prediction models of skeleton curve and reparability probability of HSRAC columns were proposed. The models were then verified by comparing the prediction results with test results.

Experimental investigation of bond performance between BFRP and different strength recycled-aggregate concrete

In recent years, there has been a large number of studies on recycled-aggregate concrete as a potential solution to the problem of a scarcity natural resources. This study investigated the bonding performance of a new reinforcement material employed in medium and high-strength recycled aggregate concrete. The pull-out test was carried out by employing basalt fiber-reinforced polymer (BFRP) bars with different diameters (12, 14, and 20 mm) in medium and high-strength concrete with different ratios of recycled coarse aggregate replacement (0, 25, 50, 75, and 100%). Based on the concrete bond damage, the failure modes were identified, the corresponding bond mechanism was analyzed and the bond stress–slip characteristics were summarized. The effect of each parameter on the failure mode, bond strength, and the bond-slip curve between recycled-aggregate concrete and BFRP bars was evaluated. Results indicated that as the diameter of the BFRP bar increased, the failure mode was shifted, the uneven distribution of bond stress became more pronounced, and the bond strength showed a decreasing trend. Two distinct situations of medium to high-strength concrete with very different relative bond strengths at different replacement ratios were found. The relative bond strength of medium-strength concrete increased at first and then decreased with the increase of the replacement ratio of recycled coarse aggregate. A non-linear relationship between the bond strength of recycled concrete and its compressive strength was found. The two-stage model was proposed to describe the bonding behaviour more accurately between BFRP bar and medium to high-strength recycled aggregate concrete.

Experiment and numerical analysis on seismic performance of resilient shear walls using high strength recycled aggregate concrete

In this paper, ultra-high strength bars (UHSB) was innovatively applied to the high-strength recycled aggregate concrete (RAC) shear walls to achieve resilient performance. In order to explore the resilient and seismic performance of the shear wall, five specimens with shear span ratio of 2.2 were tested under cyclic loading. The variables also included the type of longitudinal reinforcement in boundary elements, the presence of anti-corrosion coating in UHSB and the replacement ratio of recycled coarse aggregate (RCA). The results showed that the use of UHSB in the boundary elements significantly improved secondary stiffness and reduced the residual displacement and residual crack width of the shear walls. The anti-corrosion coating decreased bond strength between UHSB and RAC, but it had negligible effect on the seismic and resilient performance of the specimens before 2% drift ratio. Increasing replacement ratio of RCA slightly decreased the lateral force of the specimens under the same drift ratio, but the walls represented satisfactory resilient performance. In addition, finite element models were established in ABAQUS, and the effect of UHSB bond performance, the strength of longitudinal reinforcement with anti-corrosion coating, and the substitution rate of UHSB were analyzed. The results showed that the numerical analysis results were in good agreement with experiment results.

Bond Behavior Between High-Strength Recycled Aggregate Concrete and UHSSB Using Beam Test

Bond Behavior Between High-Strength Recycled Aggregate Concrete and UHSSB Using Beam Test

Analytical and experimental investigation of the bond behavior of confined high-strength recycled aggregate concrete

This study investigates the bond behavior between 600 MPa grade reinforcement and high-strength recycled aggregate concrete (RAC) by carrying out 22 beam tests. Test parameters include the recycled coarse aggregate (RCA) replacement ratio, reinforcement diameter, concrete cover thickness, stirrup ratio, concrete strength and the addition of steel fibers. The influences of different parameters on the failure modes, bond-slip curves and bond strength are discussed. The results indicate that the RCA replacement ratio has little effect on the failure mode and the bond-slip curve, while the bond strength decreases with its increase. Similar to normal aggregate concrete, the bond strength is positively correlated with f′c1/2. Increasing the concrete cover thickness or the stirrup ratio can significantly improve the bond strength and decrease the crack width. The addition of steel fibers can avoid specimen splitting, but this addition will disturb the reinforcement-concrete interface, which has little effect on the bond strength of 50 MPa grade RAC, however, the addition slightly increases the bond strength of 70 MPa grade RAC. The design bond strength of steel fiber concrete should not be lower than the design bond strength of plain concrete with the same compressive strength. The splitting failure of specimens is further classified, and the effective confinement Factor K for predicting the failure mode is presented. In view of different confinement conditions, bond-slip models between the 600 MPa grade reinforcement and high-strength recycled concrete are established.

Seismic performance of semi-precast high-strength recycled aggregate concrete columns with high-strength reinforcement

There is a growing interest in the development of precast structures. In this paper, a semi-precast high-strength recycled aggregate concrete (RAC) column with high-strength reinforcement was studied, which was consisted of cast-in-situ core concrete surrounded by a precast external shell. Six full-scale columns were fabricated and tested under cyclic lateral load, of which two were cast-in-situ columns and four were semi-precast columns. The penetration of shear reinforcement between precast external shell and cast-in-situ core column, core column diameter and axial load were the major design parameters. The test results showed that all specimens exhibited a good deformation capacity with an ultimate drift ratio greater than 3%. The semi-precast columns had comparable seismic performance with the cast-in-situ columns, indicating that the penetrating shear reinforcement and the core column diameter had little effect on the seismic performance. The core column diameter could be selected according to the practical engineering requirements. Increasing the axial load can significantly improve the lateral load-carrying capacity of the specimens, but would result in larger residual drift ratio, which was adverse to the repairability of the specimens. The flexural deformation and the deformation resulting from slippage of longitudinal reinforcement in the concrete foundation accounted for 50%–80% and 10%–20% of the lateral displacement, respectively, which should not be ignored in the deformation calculation; however, the shear deformation can be ignored. The optimized models applicable to calculate the F-Δ curves of semi-precast high-strength RAC columns with high-strength reinforcement were proposed. Parametric analysis based on the optimized models was carried out to develop N-M curves for various precast external shell or core column concrete strength, and core column diameters.

Experimental investigation for splice strength of deformed steel bars in normal-, medium- and high-strength recycled aggregate concrete

Experimental investigation has been carried out to calculate the splice strength in bond of deformed steel bars in recycled aggregate concrete (RAC) using 132 singly reinforced bottom cast splice beam specimens. The testing of the splice beam specimens have been carried out under four-point bending with splicing being carried out at the constant moment region. The parameters investigated in the experiment were: grade of concrete (normal-, medium and high-strength), recycled concrete aggregate replacement level (0%, 50% and 100%), rebar diameter (db) (12 mm and 20 mm), splice length (5 db,10 db, 15 db and 25 db), rebar surface characteristics and concrete cover (c) – to – rebar diameter (c/db = 1.25 and 2.00). Descriptive bond strength equations have been proposed for RAC in which the effect of concrete grade on bond strength is best represented by f'c1/2 and f'c3/4. Amongst various bond strength equations available in the literature, the one proposed by Orangun et al. which has been developed for conventional concrete gave the most accurate and conservative splice bond strength estimate when applied to the concrete obtained by the substitution of natural aggregate to selected levels of RCA replacement level under experimental investigation.

Interfacial bond-slip behaviour between reinforced high-strength concrete and built-in steel plate with studs

Steel-plate-reinforced concrete composite shear walls have been widely used in high-rise and super-high-rise buildings. To improve the bond behaviour between the steel plate and high-strength concrete (HSC) in shear walls, 13 steel-plate HSC shear wall (SPHSCSW) specimens with group studs were designed for push-out tests. Specimens were constructed using HSC or high-strength recycled aggregate concrete (HSRAC). Concrete strength, concrete type, stud length-to-diameter ratio, and replacement of studs with tie bar connectors are considered. The influence of different parameters on the interfacial bond behaviour of specimens is discussed by analysing the load-slip curves, bond strength, and interface damage energy dissipation. The equations for the shearing capacity of studs and the interfacial bond-slip constitutive relationship under different connectors were obtained. Results show that the influence of concrete strength on the bond strength of SPHSCSWs is positively correlated, and the bond behaviour with HSRAC is similar to that of normal HSC. When the stud length-to-diameter ratio exceeds four, increasing the ratio has little effect on improving the shearing capacity, and a further increase reduces the residual bond strength. Replacing some studs with tie bars can significantly improve the residual bond strength and interfacial bond energy dissipation capacity. The proposed equations for the shearing capacity of studs in SPHSCSWs and the bond-slip constitutive relationship agree well with the test results, which can be used for engineering applications and further research.

Bond behavior of high-strength recycled aggregate concrete-filled large square steel tubes with different connectors

To solve the problem of insufficient interface bond strength of concrete-filled square steel tubes (CFSSTs), 16 large CFSST specimens with eight different types of connectors (no additional connectors, built-in studs, built-in circular ribs, built-in vertical ribs, built-in reinforcement cage, and various combinations of the above) were designed for push-out testing. Specimens were constructed using high-strength concrete or high-strength recycled aggregate concrete (RAC). The bond behavior and slip failure mechanism were analyzed by comparing the force-slip curves, slip displacements, and steel tube strains. The bond strength calculation method and bond-slip constitutive relationship of the interface under multiple parameters were obtained. Experiments revealed the following: bond-slip curves for CFSST without additional connectors were composed of an ascending section and a residual section; for tubes with different connectors, the peak values of the curves were higher; the performance-price ratio of studs and circular ribs for improving bond strength was high, and the combined use of studs and circular ribs can work well; the combination of circular ribs and vertical ribs can significantly improve bond strength and energy dissipation capacity; RAC had better bond behavior than normal concrete in HSCFSST without additional connectors or built-in vertical ribs. The predicted force-slip curves agreed well with the test curves, providing a theoretical basis for CFSST applications.

Flexural behavior of large scale semi-precast reinforced concrete T-beams made of natural and recycled aggregate concrete

This study aimed to investigate the flexural behavior of T-section semi-precast reinforced concrete (RC) beams composed of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). The experimental program consisted of four large-scale T beams, including three semi-precast T-beams and a reference RC T-beam made of traditionally cast high strength natural aggregate concrete (HSNAC). The web of all the semi-precast beams composed of a precast U-shaped part, which contained the longitudinal and transverse reinforcement and was cast of HSNAC, and an inner RAC core. Normal strength RAC (NSRAC) or high strength RAC (HSRAC) was used as web core filler, and HSNAC or HSRAC was used for the beam flange. Two techniques were adopted to fill the web core: the traditional concrete casting and the placement of well-sized precast concrete blocks. The results indicated the applicability of RAC and NAC in one section to achieve comparable strength, deformability, and failure mode to those of the monolithically cast beam with NAC. In addition, using precast RAC blocks as filler in the web core of RC beams is a promising construction technique, which can be adopted as a critical design parameter to control development, propagation, and width of flexural and shear cracks to a large extent.

Parametric sensitivity analysis and modelling of mechanical properties of normal- and high-strength recycled aggregate concrete using grey theory, multiple nonlinear regression and artificial neural networks

Abstract It is well-understood that the incorporation of recycled concrete aggregates (RCAs) in a concrete mix can lead to some impacts on the mechanical properties of the concrete due to the inferior characteristics of the RCAs. In this study, the performances of available code-based and empirical models reported in the literature on recycled aggregate concrete (RAC) mechanical properties (i.e., compressive strength, elastic modulus, flexural strength and splitting tensile strength) are first assessed using extensive experimental data collected from the literature, and the assessments indicate that these models cannot achieve a desirable accuracy for their predictions. Aiming to develop more reliable approaches for predicting RAC’s mechanical properties with higher accuracy and to cover wide-range of influential parameters of RAC mixes in the model expressions, a mathematical approach, namely grey system theory (GST) is used to examine the parametric sensitivity of the mechanical properties of RACs. The results of GST indicate that the overall mechanical properties of RACs depend on the geometrical indices of aggregates and also the concrete mixture proportions. The evaluation of GST also confirms the facts that the effect of RCA is different for the concrete at normal and high strength grades due to the difference in the failure mechanism of the concrete at different strength grades. Finally, multiple nonlinear regression (MNR) and artificial neural networks (ANN) are employed to simulate the mechanical properties of RACs using the key parameters of RAC mixes identified using GST. The results demonstrate that the proposed MNR and ANN approaches can provide more accurate predictions for the mechanical properties of RACs compared to previous models reported in the literature.

Diversified Production of Recycled Aggregate Concrete Mixture with the Addition of Single and Hybrid Fibers

The low strength property of recycled concrete aggregates (RCAs) limits its widespread application in the production of high-strength recycled aggregate concrete (RAC). In this study, RCA properties were improved prior to its incorporation into an RAC mixture through surface treatment. This mixture was subsequently diversified considering the benefits of adding various fiber-reinforced systems to enhance RAC performance. Two types of short discrete synthetic fibers, namely, polyolefin and polypropylene, were added in single and hybrid forms. This study aimed to investigate the effectiveness of the diversified modification of RAC mixture production on the mechanical strength of the resulting RAC. Various properties of the modified RAC were analyzed. Although the modified RAC mixture using treated RCA significantly enhanced the mechanical strength of this RAC, the diversification of the RAC mixture with additional polyolefin and polypropylene fibers, particularly in the hybrid form, further optimized the RAC performance.