Recycled Coarse Aggregate Replacement Research Articles

Experimental study on dynamic properties of flax fiber reinforced recycled aggregate concrete

Recycling waste concrete is critical to land use and reduction of landfills. It is a good option to recycle the waste coarse aggregates from it and add them to the concrete matrix. Due to the existence of new and old interface transition zones (ITZs), the quasi-static compressive strength of recycled aggregate concrete is lower than that of natural aggregate concrete, which limits the widespread application of recycled aggregate concrete. In order to improve its engineering application of recycled aggregate concrete, the dynamic compressive properties were studied. Thus, based on a Split Hopkinson Pressure Bar (SHPB) device, the effects of strain rate and recycled coarse aggregate (RCA) replacement ratio on the failure mode, dynamic compressive strength, critical strain and toughness were investigated. It was found that increasing the strain rate led to the aggravation of the specimen damage and growth of the dynamic compressive strength, toughness and critical strain. At a high strain rate, the strain rate effect changed the failure mode of recycled aggregate concrete. This reduced the performance difference between recycled and natural aggregate concrete, in terms of the dynamic compressive strength. The recycled aggregate concrete had a similar toughness to the natural aggregate concrete. Although the growth of the RCA replacement ratio decreased the dynamic compressive strength and increased the critical strain, it had a little effect on the toughness. In order to reduce the brittleness of the recycled aggregate concrete and improve its deformability, non-synthetic, green and low-consumption flax fibers were incorporated into the concrete matrix, and its dynamic compressive behaviors were studied experimentally accordingly. Tests verified that the addition of flax fibers significantly reduced the damage and increased the critical strain. Especially when the strain rate was greater than 200 s-1, flax fiber reinforced recycled aggregate concrete exhibited a superior energy consumption ability. Based on the experimental data, empirical equations were proposed to describe the dynamic compressive strength, critical strain and toughness at different strain rates.

Effect of carbonated recycled coarse aggregates on the mechanical properties of 3D printed recycled concrete

A modification method of carbonation combined with presoaking in nano-SiO2 solution was employed to enhance the recycled coarse aggregates (RCA). The water absorption, apparent density and crushing index of RCA before and after carbonation were tested. The water absorption, compressive strength, flexural strength and splitting tensile strength of 3D printed recycled aggregate concrete (3DPRAC) with different RCA replacement rates were further investigated. Microscopic tests including X-ray diffraction and scanning electron microscopy were performed to analyze the changes in phase composition and microstructure of RCA, while X-ray computed tomography was utilized to explore the pore defect evolution of 3DPRAC. The results demonstrated the method of carbonation combined with presoaking in nano-SiO2 solution significantly improved the physical characteristics of RCA and densified the microstructure of 3DPRAC. With an increase in RCA replacement rate, there was a decrease in the mechanical properties in all directions. At the RCA replacement rate of 100 %, the compressive strength, flexural strength and splitting tensile strength increased by a maximum of 24.71 % in the X direction, 12.95 % in the Y direction and 18.27 % in the Z direction after RCA carbonation, respectively. The pore defects of 3DPRAC were effectively optimized by the inclusion of carbonated RCA. The modification mechanism was explained based on the enhanced performance of RCA and pore defect evolution.

Study on Mechanical Properties and Erosion Resistance of Self-Compacting Concrete with Different Replacement Rates of Recycled Coarse Aggregates under Dry and Wet Cycles

Concrete that self-compacts is frequently utilized in engineering construction. Recycled coarse aggregate self-compacting concrete (RCASCC) is made by partially substituting recycled coarse aggregates (RCA) for natural coarse aggregates in order to conserve construction resources. This study examines the impact of linked sulfate erosion, dry and wet cycles, and RCA replacement rates of 0%, 25%, 50%, 75%, and 100% on the mechanical properties and durability of RCASCC. By using the mass loss rate, relative dynamic elastic modulus, corrosion resistance factor, X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM) analyses, as well as other macroscopic and microscopic methods, it is possible to examine the deterioration patterns of RCASCC under dry and wet cycles. The results demonstrate that the addition of RCA has a notable impact on concrete’s resistance to sulfate attack during both dry and wet cycles. The erosion products steadily rise, the interfacial transition zone (ITZ) becomes rougher, and the sulfate resistance falls as the replacement rate of RCA rises. According to the findings of SiO2, AFt, and CaCO3, the examination of corrosion products from XRD and microstructure from SEM and EDS is carried out. The old mortar that has adhered to the surface of RCA, as shown by the AFM analysis of ITZ and the SEM analysis of RCA, can significantly affect the roughness of ITZ inside RCASCC.

Machine learning approach for investigating compressive strength of self-compacting concrete containing supplementary cementitious materials and recycled aggregate

Supplementary cementitious materials (SCMs) and recycled coarse aggregate (RCA) have the potential for sustainable development and resource utilization and have been widely applied in self-compacting concrete (SCC). However, traditional experiment approaches for predicting its compressive strength suffer from inefficiency, time-consuming, and high cost. To address these issues, machine learning (ML) models are employed, evaluated, and compared in this paper. First, a database of 337 samples with 10 features is collected and established. Then, the 12 ML models, including SVM, KNN, DT, RF, ANN, GBoost, XGBoost, AdaBoost, CatBoost, LightGBM, HistGBM, and GEP are applied for modeling to predict the compressive strength. Finally, both feature importance, individual conditional expectation, and partial dependence plot are utilized to assess the importance and the effect of each and coupled parameters. The results show that the CatBoost and LightGBM models generally possess superior performance in various aspects, including higher R2 values, lower RMSE, MSE, and MAE values, as well as smaller errors. Among the Boosting models, except for the AdaBoost model, satisfactory predictive ability is observed. The ANN and RF models also demonstrate relatively good performance, and the SVM, DT, KNN, and GEP models present relatively poorer performance. Curing age and W/CMs exhibit the most pivotal features on model prediction. Furthermore, RCA replacement ratio plays a more prominent role than CA, and SCMs contribute somewhat to the compressive strength of concrete, but not as much compared to cement. Also, it is important to acknowledge the significant contribution of SP. This study offers a systematic evaluation of the prediction of compressive strength in SCC containing SCMs and RCA, making a notable contribution to both the existing literature and practical applications.

Optimization on the mix design method of self-compacting concrete with recycled coarse aggregate based on paste rheological threshold theory and material packing characteristics

This study aims to use the mixture design method to optimize self-compacting concrete (SCC) and manufacture SCC with excellent workability using recycled coarse aggregate (RCA) and a ternary cementitious system. The influences of incorporated RCA on the rheological thresholds of SCC with a fixed content of fly ash (FA) and blast furnace slag (BFS) are investigated based on paste rheological threshold theory and material packing characteristics. The original rheological model is improved by introducing the volume of adhesive mortar and modifying the equivalent packing density and mortar film thickness. The improved model is incorporated into the original theoretical system to apply the optimized mix design method to SCC. Moreover, experiments are conducted with different volumes of water, water-powder ratios and RCA replacement levels to verify the applicability of the optimized method. The results indicate that the proposed models can accurately predict the yield strength threshold and plastic viscosity threshold of fresh SCC. Furthermore, compared to the original model, predictions are 53% more accurate with the modified model.

Frost Durability of Self-Compacting Concrete Prepared with Aeolian Sand and Recycled Coarse Aggregate.

Aeolian sand (AS) and recycled coarse aggregate (RCA) can be reasonably utilized as green materials for concrete modification. The paucity of natural sand and gravel in the construction industry is anticipated to be remedied by the use of these two eco-friendly concrete ingredients. This is incredibly important for environmental protection. Study on the damage law of self-compacting concrete with the addition of AS and RCA (ARSCC) under severely cold conditions is of great significance for the promotion and implementation of this material. In this study, 12 groups of ARSCC specimens were prepared for freeze-thaw cycle experiments, with AS substitution rates of 0, 20%, 40%, and 60% as well as RCA replacement rates of 0, 25%, and 50%. Then, the degradation mechanism of ARSCC freeze-thaw damage was discussed from both macroscopic and microscopic perspectives via mass loss rate (Wn), relative dynamic modulus of elasticity (Pn), bubble spacing factor, and SEM analysis. Finally, the response surface method was utilized to determine the damage variable. A freeze-thaw damage model for ARSCC was developed based on the Weibull distribution and Grey theories. The results showed that the Pn could reflect the evolution law of the internal structure of ARSCC. Appropriate addition of AS to fill the large, harmful pores in RCA would inhibit freeze-thaw damage of ARSCC. The optimum substitution rates of AS and RCA were determined to be 20-40% and 25-50%, respectively. In addition, the values obtained from theoretical damage modeling and experiments were in good agreement. The acquired damage model had the potential to predict ARSCC damage under freeze-thaw cycles.

Flexural and bond-slip responses of reinforced concrete beams containing recycled coarse aggregate and polypropylene plastic

Reusing non-biodegradable plastic waste and recycled concrete as a substitute for natural aggregates can help alleviate the pressure on natural resources. Therefore, this study aims to incorporate polypropylene plastic aggregate (PPA) and recycled coarse aggregate (RCA) in concrete mixtures. The PPA is used as a partial replacement of RCA in reinforced concrete (RC) beams. The flexural responses and bond behaviors of RCA based PPA concrete (RPC) beams are investigated. The main variables are PPA percentages (0, 5, and 10%) and shear span to effective depth ratios (a/d = 2.13, 1.52, 1.07). Nine 1100 mm long RC beams are fabricated for bending tests, and nine 350 mm long RC beams are cast for pull-out tests. Results indicate that the ultimate moment capacity is increased by up to 28.6% for 5% PPA content depending on the beam depths, and for 10% PPA content, it is decreased by up to 15%. Ductility and toughness are increased by up to 11.7% and 113.6%, depending on the PPA contents and beam depths. Bond strength is increased by up to 16.6% for 5% PPA content and then decreased for 10% PPA by up to 37.5% depending on different beam depths. It is recommended that 5% PPA be used in concrete to improve the overall performance of the RPC beams.

Simultaneous influence of processed cellulose acetate fiber reinforcement and recycled aggregate replacement on mechanical and durability performances of concrete

The poor performance of virgin cement concrete and its significant carbon footprint have prompted researchers to explore the concurrent integration of recycled coarse aggregates (RCA) or recycled fine aggregates (RFA) along with fibers. This study aims to investigate the mechanical and durability performance of various cement concrete mixes prepared using 53-grade cement with various percentages (0%, 30%, 50%, 70%, and 100%) integration of RCA or RFA and varying volume fractions (0.5%, 1%, 1.5%, 2%, and 2.5%) of processed Cellulose Acetate Fiber (CAF) derived from waste cigarette filters. RCA50CAF1.5 exhibits highest compressive strength and flexural strength among all RCA based concrete mix. RFA30CAF1.5 possess maximum tensile strength by about 3.45% higher compared to reference mix. The increase in CAF with % replacement of RCA or RFA cause decrease in the short term durability performance of the concrete mix. The developed correlations for mechanical and durability performances can serve as a valuable tool for designing concrete mixes with improved mechanical and durability performances for CAF-reinforced concrete.

Cyclic compressive behavior of hook-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete

One widely accepted strategy is to add fiber into recycled aggregate concrete (RAC) to improve compressive strength. Few existing investigations have focused on the cyclic compressive behavior of hybrid fiber reinforced recycled aggregate concrete (HFRRAC). A total of eighteen groups of prismatic specimens with different fiber combinations and recycled coarse aggregate (RCA) replacement rates were conducted under cyclic compression to investigate the mechanical properties of hooked-end steel and macro-polypropylene hybrid fiber reinforced recycled aggregate concrete. Results indicate that specimens under cyclic loading fail similarly to those subjected to monotonic loading. The envelope curve of the cyclic stress-strain curve for HFRRAC closely resembles the corresponding monotonic stress-strain curve. RCA replacement rates and fiber combinations do not significantly affect plastic strain and stress deterioration. Fibers added to specimens mitigate stiffness degradation and improve hysteretic energy dissipation. The proposed constitutive equations can be used to describe the cyclic compressive behavior of HFRRAC. The fibers improve the density and structure of mortar and aggregate-paste interfaces from the microstructure morphologies. The fracture mechanisms of HFRRAC were also studied using mesoscale numerical models under uniaxial compression loading. The cohesive zone model is suitable for simulating the compressive behavior of HFRRAC. Numerical specimens fail in mixed fracture modes, primarily mode II fractures.

Mechanical properties of recycled aggregate concrete prepared from waste concrete treated at high temperature

The ever-increasing generation of construction and demolition (C&D) waste caused by the frequent occurrence of building fires has posed a threat to environmental protection and waste management over the last few decades. The shortage of natural resources provides an impetus for the utilization of C&D waste after fire. Aiming to provide a cleaner option for waste concrete after fire, the viability of using waste concrete after fire as a substitute for coarse aggregate in the production of recycled aggregate concrete (RAC) was investigated and analyzed in detail. The failure mode, stress–strain behavior, mechanical properties and microstructure of the RAC was evaluated with the variation of four different replacement ratios (0%, 25%, 50%, and 100%) and five different treatment temperatures (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). The experimental results showed despite the failure mode of RAC being similar to that of natural concrete (NC), an increase in the recycled coarse aggregate (RCA) replacement ratio would decrease the slope of curves and strength, and the fcu and fc with 25% replacement ratio for RAC decrease by about 15% and 10% respectively as compared to those for NC. Nevertheless, treatment of elevated temperature for waste concrete can eliminate the damage of replacement ratio to mechanical properties, and the fcu and fc with 25% replacement ratio after 400 °C increased by approximately 12% and 8% respectively as compared with untreated RAC. Against the test result, a series of calculation formulas is proposed to predict the mechanical properties of the RAC whilst a constitutive model is modified with the existing standard to describe the stress–strain behavior of that with the consideration of replacement ratio and treatment temperature. The microstructure analysis indicated that the increase in the RCA replacement ratio would result in the increasing content of adhered mortar characterized by numerous poles and less bond on RCA, whereas treatment of high temperature for waste concrete can decrease the content of adhered mortar on RCA, which makes the microstructure of the RAC more densified.

Material properties of ITRAC and cyclic behavior of double steel plate composite shear wall filled with ITRAC

An innovative iron tailing and recycled aggregate concrete (ITRAC)-filled double steel plate composite shear wall (ITRAC-CSW) was proposed to promote the application of the fabricated composite structures and the green build materials. Firstly, the mix proportion of ITRAC was studied through the test of six groups of ITRAC samples by changing the recycled coarse aggregate (RCA) replacement ratio and water-binder ratio. Favorable mechanical properties and the corresponding mix proportion was obtained. The elastic modulus calculation and the constitutive model of the ITRAC were obtained based on the test results. Subsequently, three full-scale ITRAC-CSW specimens were fabricated using ITRAC with the 100% RCA replacement ratio and tested under the cyclic lateral load and constant axial load. The failure mode and deformation mechanism of the specimens were analyzed through experimental phenomena. The seismic performance of the specimen was explored by comparing the load–displacement curves, stiffness degradation, and energy dissipation capacity. The analysis revealed that the ITRAC-CSW exhibits good bearing capacity, stiffness, and energy dissipation capacity which can be used in practical project.

High temperature behaviour of basalt fibre-steel tube reinforced concrete columns with recycled aggregates under monotonous and fatigue loading

Experimental and numerical investigations were carried out to evaluate the effects of incorporating recycled coarse aggregates (RCA) on the mechanical behaviour of inner steel-tube reinforced concrete columns exposed to high temperature. The specimens were reinforced with basalt fibres (BF) and strengthened by carbon fibre reinforced polymer (CFRP) sheets, which were subjected to mechanical loading in monotonous and cyclic arrangements. Test results show that at room temperature (RT), incorporation of the chopped BF has reduced both the tensile strength and flexural strength of concrete specimens prepared with recycled aggregate concrete (RAC) but not their static elastic modulus. On the other hand, the BF has improved crack resistance of the steel tube reinforced RAC (STRC) column specimens. Also, the reduction in mass and dynamic elastic modulus of BF reinforced STRC specimens are lower than those of STRC at a given RCA replacement ratio and exposure temperature. Furthermore, improvements in mechanical performance under monotonous and fatigue loading was observed for STRC columns reinforced with BF and externally bonded CFRP sheets with high-temperature exposure (HTE). Therefore, it is possible that BF reinforced STRC columns could be used to reduce risk of brittle structural collapse when exposed to fire or elevated temperature.

Comparative Study of Concrete Using Recycled Coarse Aggregate

Abstract: Recycled coarse aggregate (RCA) is produced by crushing the demolition waste from concrete structures. The construction and demolition waste is primarily used for landfill sites which are causing significant damage to the environment and developing serious problems. The use of the RCAs created from the processing of construction and demolition waste in new construction has become more important over the last two decades as it conserves the non-renewable natural resource of virgin aggregates. With a view to the above needs, the present study is aimed to determine the strength properties of RCA concrete depending on the various content of RCA and to compare them to the strength properties of concrete made with natural coarse aggregates (NCA). The fine aggregates of high FM of 3.0 were used for recycled and natural concrete. After performing the compressive strength test, it was found that concrete made with fully replaced RCA has less strength than concrete made with NCA but not much. So, RCA can be used as a replacement for NCA in concrete production. In addition, full replacement of RCA can be used in structures of less importance such as temporary walls, the base of roads, light traffic roads, pavements in college campuses etc.

Mechanical behavior of multiscale hybrid fiber reinforced recycled aggregate concrete subject to uniaxial compression

This paper presents a multiscale hybrid fiber reinforcing strategy that can remarkably compensate for the adverse effects of recycled coarse aggregate (RA) on the performance of concrete. The hybrid fibers including macro steel fiber (SF), micro polypropylene fiber (PPF), and cellulose nanofiber (CNF) were utilized for crack arresting at multi-levels and improving the mechanical properties of RA concrete (RAC). This work aims to investigate the mechanical performance of multiscale hybrid fiber reinforced RAC (MFRRAC) under uniaxial compression and unveil the multiscale hybrid fiber reinforcement mechanism. A total of 34 groups of prismatic specimens were tested, with an emphasis on the effects of RA replacement rate and fiber parameters on the failure mode, compressive strength, deformation ability, and stress-strain curve. The results showed that the incorporation of multiscale hybrid fibers has a marked impact on the compressive properties of RAC. Specifically, the addition of multiscale hybrid fibers could significantly alter the failure pattern of RAC. In addition, compared with RAC without fibers, the axial compressive strength and peak strain of MFRRAC could be increased by up to 39.34% and 24.85%, respectively. Furthermore, the hybrid fiber reinforcement mechanism on the mechanical enhancement in a physical-chemical manner was revealed, in particular, multiscale crack resistance and hybrid fiber synergetic effect. Finally, a stress-strain model was developed with RA replacement rates and fiber parameters taken into account, and the predictions can correlate well with available experimental results with wide applicability. This research work lays a foundation for the accurate design and analysis of MFRRAC structures.

Relationship between chloride ion permeation resistance of recycled aggregate thermal insulation concrete and pore structure parameters

The incorporation of recycled coarse aggregate (RCA) and glazed hollow bead (GHB) leads to a different internal pore structure of recycled aggregate thermal insulating concrete (RATIC) than that of normal concrete (NC), which is the fundamental reason for the different chloride ion transport mechanisms between the two. To investigate the quantitative relationship between the fine pore structure of RATIC and its resistance to chloride ion permeation in this study, chloride ion permeation tests were conducted on 10 sets of RATIC specimens with different RCA replacement ratios and GHB contents. The pore structure of the specimens, including their quantity and porosity, was also systematically analyzed using nuclear magnetic resonance (NMR) spectroscopy. A model for chloride ion permeation resistance of RATIC that considered RCA replacement and GHB content was proposed, and grey correlation analysis was used to relate the chloride ion permeation resistance of RATIC to the pore structure and establish a suitable chloride ion diffusion coefficient model for RATIC. The results showed that: (1) increasing RCA replacement weakened the resistance of RATIC to chloride ion permeation. Compared to normal concrete (NC), the chloride diffusion coefficient of RATIC increased by 18.73 % when the RCA substitution ratio rose from 0 % to 100 %, while the overall number of internal pores increased by 14.32 %, with the greatest increase in harmful pores under the same RCA replacement conditions; (2) increasing the GHB content effectively improved the chloride ion permeation resistance of RATIC, and the chloride ion diffusion coefficient decreased by 11.49 % when the GHB ratio rose from 0 kg/m3 to 130 kg/m3. The number of RATIC internal pores increased by a total of 20.29 %, with the largest increase in multiple harmful pores. The present authors concluded that establishing the two-parameter model of chloride ion diffusion coefficient/pore structure of RATIC could serve to predict the resistance of RATIC to chloride ion permeation, which could in turn provide a reasonable basis for further research on the durability of RATIC.

Corrosion depth of steel bars in recycled aggregate concrete beams under static load

To study the distribution of corrosion depth along the longitudinal direction of tensile steel bars embedded in recycled aggregate concrete (RAC) beams under static loads, a total of 12 RAC beams were designed for accelerated corrosion testing by considering three types of recycled coarse aggregate (RCA) replacement ratios (i.e. 0%, 50% and 100%) and four kinds of static load levels (i.e. 0, 0.2, 0.4 and 0.6). The results demonstrated that the corrosion depth of tensile reinforcement showed an increasing trend with the increase of static load level. The maximum corrosion depth had a good quadratic polynomial relationship with the average corrosion depth of tensile reinforcement and increased with the average corrosion depth. For beams with the same RCA replacement ratio, there was a good linear relationship between the overall uneven corrosion coefficient and average mass loss of tensile reinforcement. The probability distribution type of corrosion depth along the longitudinal direction of tensile reinforcement was mainly a lognormal distribution. An increase in both RCA replacement ratio and static load level could make the probability distribution curve of corrosion depth move to the right, as well as increase the dispersion of corrosion depth around its mean value.

Recycled concrete beams subjected to combined reinforcement corrosion and static pre-loading

To investigate the flexural behavioural characteristics of recycled concrete beams under the combined action of steel corrosion and static pre-loading, 12 recycled concrete beam specimens, encompassing a combination of three recycled coarse aggregate (RCA) replacement ratios (0, 50 and 100%) and four static pre-load levels expressed as ratio of the ultimate moment capacity (0, 0.2, 0.4 and 0.6), were prepared for accelerated corrosion test and four-point bending test. The test results indicated that under a given RCA replacement ratio of the beams, the maximum width of corrosion-induced longitudinal cracks exhibited a linear relationship with the corresponding corrosion depth of longitudinal tension reinforcement. For the beams with 50% RCA replacement ratio, when the applied static pre-load level increased from 0 to 0.6, the ultimate load and ultimate deflection reduced by 10.4% and 21.2%, respectively, whereas for the beams with 100% RCA replacement ratio, the corresponding reduction in ultimate load and ultimate deflection were respectively 8.9% and 35.5%. Theoretical degradation models for the ultimate moment capacity and yield moment capacity of corroded beams were proposed, whereby the analytical values were in good agreement with the experimental values. This study provides useful reference for practical analysis of recycled concrete beams, which promote sustainable concrete construction.

Long-term behaviour of recycled aggregate concrete beams prestressed with carbon fibre-reinforced polymer (CFRP) tendons

The utilisation of recycled aggregate concrete (RAC) is commonly recognised as one of the most effective means to achieve cleaner and sustainable development in civil engineering. To promote the application of RAC, prestressing technique can be employed to overcome the inherent disadvantages of RAC beams associated with poor cracking resistance and large deflections. However, the research on the prestressed RAC beam is quite limited, and no research has been performed on their long-term behaviour. This paper presents a finite element (FE) analysis for investigating the long-term behaviour of RAC beams prestressed with carbon fibre-reinforced polymer (CFRP) tendons considering the effects of concrete creep, concrete shrinkage, tendon relaxation as well as the cracking and tension stiffening of concrete. Based on the principle of superposition, the variations of the stress and strain with time are considered in the numerical analysis using step-by-step method. The FE model is calibrated with the experimental results obtained from the literature. Based on the validated model, a comprehensive parametric study is performed to investigate the effects of the replacement ratio of recycled coarse aggregate (RCA), concrete strength, reinforcement ratio, prestress level, and sustained load level on the long-term behaviour of prestressed RAC beams. The obtained results demonstrate that increasing the prestress load is an effective way to reduce the long-term deflection of RAC beams, and the use of RAC with low RCA replacement ratio is suggested. Besides, the main causes of the long-term deflection and axial shorting of the CFRP prestressed RAC beams are also studied. This research provides a pioneering and insightful study of the long-term behaviour of CFRP prestressed RAC beams. The obtained results demonstrate that the time-dependent effects should be well considered in the design before the prestressed RAC beam is used in practice.

Cyclic behavior of full‐scale reinforced high‐strength recycled aggregate concrete columns

SummaryIn order to expand the application of high‐strength recycled concrete, five full‐scale square high‐strength recycled concrete columns (600 × 600 mm) were tested under the experimental axial compression ratio (ACR) of 0.54. The seismic behavior of reinforced high‐strength recycled aggregate concrete columns under high ACR and the effects of recycled coarse aggregate (RCA) replacement ratio and ACR on the seismic behavior were analyzed. The results showed that the high‐strength recycled concrete columns have potential to collapse‐resistance capacity subjected to strong earthquakes. Under the similar concrete strengths, the mechanical properties of high‐strength recycled aggregate concrete columns and ordinary concrete columns were comparable even under high ACR. As the ACR increased from 0.35 to 0.54, the bearing capacity increased by up to 12.6%, while the ductility decreased by up to 32.8%. The specimens with 100% RCA were more sensitive to ACR than those with 50% RCA. A four‐fold restoring force model considering the effects of axial load, reinforcement ratio, shear span, and RCA replacement ratio was established, which was in good agreement with the experimental curves.

Effects of replacement ratio and particle size distribution of recycled coarse aggregate on mechanical properties of concrete designed using equivalent mortar volume method

AbstractThe equivalent mortar volume (EMV) mixing method has been proposed to prepare recycled aggregate concrete (RAC) with comparable mechanical properties to those of reference natural aggregate concrete (NAC). Previous studies primarily focused on the mechanical properties of EMV concrete with a single replacement ratio of recycled coarse aggregate (RCA). This paper investigates how the mechanical properties of EMV concrete vary with the replacement ratios and particle size distributions of RCA. Five different RCA replacement ratios and two RCA particle size distributions were assessed. A material demand coefficient was principally proposed to quantify the contribution of the EMV mixing method to reduce the environmental impact; the maximum RCA replacement ratio was suggested to obtain sufficient workability of EMV concrete using an effective sand ratio; a drying shrinkage model was theoretically proposed for EMV concrete accounting for the drying shrinkage of residual mortar. The obtained results indicated that the compressive strength and elastic modulus properties of EMV concrete decreased with increasing RCA replacement ratios; using the effective sand ratio of EMV concrete, comparable mechanical properties to those of reference NAC could be obtained for EMV concrete; the proposed shrinkage model was consistent with the available experimental data.