Recycled Aggregate Concrete Beams Research Articles

Fracture analysis of seawater sea-sand recycled aggregate concrete beams: Experimental study and analytical model

Seawater sea-sand recycled aggregate concrete (SSRAC) has garnered significant attention from engineers involved in various coastal engineering projects. Fracture constitutes one of the primary failure modes of SSRAC, and the accurate analysis of its fracture behavior is crucial for application. In this present study, SSRAC with 50% aggregate replacement was subjected to three-point bending tests to evaluate its fracture performance. Specific methodologies for calculating SSRAC fracture toughness were introduced, taking into account the effects of material microstructures and specimen boundaries. By comparing the fracture properties of SSRAC specimens with varying initial notch lengths, the size effect was addressed by using established methods, resulting in a constant fracture toughness value. Furthermore, the methods for analyzing the fracture of un-notched specimens were developed, considering fracture path analysis and the influence of internal defects. Notably, this research demonstrated that small specimens and established methodologies efficiently predict the fracture behavior of larger specimens, providing practical insights for engineering applications.

Effect Of Openings On Shear Strength Of Sustainable Recycled Aggregate Concrete Beams

Effect Of Openings On Shear Strength Of Sustainable Recycled Aggregate Concrete Beams

Research on the flexural performance of recycled coarse aggregate concrete beams after carbonation

This paper discusses the flexural behavior of carbonated recycled aggregate concrete (RAC) beams through experimental data. We produced fifteen beams, each varying in recycled aggregate replacement ratios: 0 %, 30 %, 50 %, 70 %, and 100 %. Each replacement ratio included three beams, amounting to different levels of carbonation: non-carbonated, partially carbonated, and completely carbonated. Post accelerated carbonation processes; flexural testing was conducted. The findings reveal that beams incorporating varying amounts of recycled coarse aggregates (RCA) but maintaining identical carbonation levels exhibited a minor reduction in the cracking moment, with negligible variations in ultimate flexural strength and deflection. Moreover, beams sharing the same RCA replacement ratio demonstrated increased cracking moment, ultimate flexural strength, and stiffness with advancing carbonation levels, while deflection tended to decrease. Based on these findings, predictive models for cracking moment and ultimate flexural strength of carbonated RAC beams were developed. Comparisons between experimental outcomes and numerical simulations, particularly within the RAC50 group, indicated nearly identical results.

Effect of using normal concrete or recycled concrete layer on behavior of repaired projectile bullet damaged reinforced concrete beams

AbstractThis study utilized experimental research to investigate the efficiency of using normal aggregate concrete (NAC) or recycled aggregate concrete (RAC) as a new concrete layer for repairing projectile bullet damage to strengthening reinforced concrete (RC) beams. This study comprised the construction and testing of eight RC beams made of RAC and NAC. They are initially subjected to projectile bullets and after that tested with flexure load to evaluate the effect of using RAC and NAC that was investigated. The findings of test results demonstrate that the repaired specimens with RAC or NAC experienced a higher load capacity than the damaged control specimens. As such, this approach could potentially use to restore RAC or NAC beams were previously damaged by projectile bullets. In addition, the findings of this research indicate that the load capacity of the damaged RC beams that were previously repaired using the NAC layer was higher than the load capacity of the damaged RC beams that were repaired using the RAC layer. The load capacity enhanced significantly of (106%–118%) and (104%–113%), respectively, when NAC and RAC are utilized in repairs. Therefore, using either NAC or RAC concrete is more economical, environmentally friendly, and efficient than demolishing.

Monotonic and Cyclic Behaviors of Reinforced Recycled Aggregate Concrete Beams

Monotonic and Cyclic Behaviors of Reinforced Recycled Aggregate Concrete Beams

Interpretability Analysis of Shear Capacity in Reinforced Recycled Aggregate Concrete Beams Using Tree Models

Interpretability Analysis of Shear Capacity in Reinforced Recycled Aggregate Concrete Beams Using Tree Models

Research on the flexural capacity of corroded recycled aggregate concrete beams by finite elements method

In this paper, based on the experimental fitting method of recycled concrete beams with corroded rebar, finite element analysis by changing the values of factors affecting the flexural capacity was conducted. The results showed that the flexural capacity of recycled concrete beams increased with the increase of section width and height.

Study on Crack Resistance and Calculation Model of RAC Beams Strengthened with Prestressed CFRP

With the development of recycled aggregate concrete (RAC), the recovery rate of construction waste is improved, and the pollution problem is alleviated. In particular, RAC beams strengthened with prestressed carbon fiber reinforced plastics (CFRP) can exhibit improved mechanical properties, expanding RAC application. Four groups of reinforced RAC beam specimens contained 0%, 40%, 70%, and 100% recycled coarse aggregate, respectively. Each group of beams was first pre-cracked and then strengthened by prestressed CFRP with one layer and two layers respectively. Finally, the bearing capacity tests were performed for these beams. The test results show that as the recycled coarse aggregate content increases, the cracking moment and ultimate load capacity of the beam decrease, while its crack width increases. As the CFRP layer increases, the deformation and crack width of the beam decreases, while the number of cracks increases. The prestressed CFRP also exhibited tensile and peeling failure. A beam deflection calculation model was established by introducing a coefficient k representing the interaction between recycled aggregate and CFRP. The influence coefficient of concrete elongation on the crack width and average crack spacing of the beam was modified, and the crack width analysis model of the beam was established. The calculated results are in good agreement with the experimental observations. It can provide reference for the application and design of recycled concrete beams strengthened with prestressed CFRP.

Shear strength of stirrup-free recycled aggregate concrete beams reinforced with steel fibers

Shear strength of stirrup-free recycled aggregate concrete beams reinforced with steel fibers

Experimental and numerical evaluations of the shear performance of recycled aggregate RC beams strengthened using CFRP sheets

Conserving the ecosystems of the globe, protecting natural resources, and improving environmental conditions can all be achieved by considering sustainability in the construction industry. Recycling of building and demolition waste is one of the key approaches being investigated to accomplish this target. Twelve reinforced concrete (RC) beams were constructed for the current study in order to analyze the shear behavior of recycled aggregate concrete (RAC) beams externally strengthened with carbon fiber reinforced polymer (CFRP) sheets. The main goal of the experimental matrix was to investigate the effect of the recycled aggregate ratio on the shear response of RAC, where three recycled coarse aggregate ratios of 20%, 60%, and 100% were suggested. Additionally, the effects of incorporating two or four CFRP strengthening layers on the ultimate load, failure pattern, load-deflection responses, and stiffness of RAC beams were also investigated. Results revealed that, when different ratios of recycled aggregate estimated at 20%, 60%, and 100% were substituted for natural aggregates, the compressive strength decreased by 4.3%, 24.2%, and 40.0%, respectively, compared to natural aggregate concrete. Moreover, the RC beam that was cast utilizing 20% recycled aggregates and strengthened with four CFRP sheets exhibited the highest ultimate load among all the tested RAC beams of 84.8 kN, which was 22.9% higher than the un-strengthened specimen totally cast with natural aggregate. Furthermore, a three-dimensional (3D) non-linear finite element model (FEM) was constructed using the ABAQUS program in order to compare the effects of employing continuous CFRP sheets for the whole critical shear span length to intermittent strips that had been experimentally tested.

Enhancing performance and sustainability: CRB600H high-strength reinforcement in recycled concrete

This paper addresses the urgent need for high-performance, eco-friendly construction materials due to increasing urbanization. It introduces CRB600H high-strength reinforcement to enhance recycled aggregate concrete (RAC) beam performance. Comparative analysis with conventional concrete (CC) beams demonstrates RAC's inferior shear performance, which CRB600H reinforcement effectively improves. A novel optimization method for high-strength reinforcement is established based on equal strength principles, demonstrating cost-efficiency. Economic analysis reveals that despite rising production costs with increased recycled aggregate replacement ratios, CRB600H reinforcement substantially reduces expenses, even when more expensive than HRB400 reinforcement. The environmental analysis reveals that the CRB600H reinforcement significantly influences the environmental performance of reinforced concrete beams. Utilizing 100% RAC beam with CRB600H as an illustrative example, the contribution rates of steel bars to Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), and Cumulative Energy Demand (CED) are determined as 39.30%, 56.85%, 51.87%, and 55.76%, respectively. In comparison to CC beam with HRB400, the 100% RAC beam with CRB600H exhibit reductions of 10.27%, 18.59%, 19.03%, and 16.93% in terms of GWP, AP, EP, and CED, respectively. In conclusion, CRB600H reinforcement offers cost-effective, eco-friendly solutions, promising significant advancements in RAC applications.

Behavior of reinforced recycled aggregate concrete beams and slabs strengthened in flexure and punching with CFRP composites

Recycling of concrete generated from construction and demolition waste as coarse aggregates in concrete has been a focus of several studies for the evolution of the green concrete and conservation of natural resources. This investigation, therefore, focusses on the study of the behavior of RC beams strengthened with externally bonded CFRP wraps, cast with both natural and recycled aggregates concrete. Furthermore, one-way slabs were strengthened with Near Surface Mounted (NSM) bars, while two-way slabs were strengthened with CFRP strips. One-way and two-way slabs used in the study were cast with both natural and recycled aggregate concrete (RAC). In RAC, natural aggregates were replaced by 30% recycled concrete aggregates. All beams and slabs were cast with concrete mix design of 1:1.24:2.6 and w/c ratio of 0.43. Beams and one-way slabs, control and strengthened, were tested under four-point bending. Whereas, two-way slabs were tested in punching. A significant increase in the load-carrying capacity was observed for both natural and recycled aggregates concrete beams without shear reinforcement and two-way slabs, indicating the effectiveness of strengthening scheme. Increase of 20.5% and 12.6%, respectively, was found in the load-carrying capacities for the cases of both and natural and RAC beams with natural aggregate concrete (NAC) and RAC beams when results were compared for the case of shear deficient control and strengthened RC beams with CFRP wraps. Furthermore, increase of 27 − 37% was noted in load-carrying capacities of both natural and RAC two-way slabs when results were compared for the case of control and strengthened NAC and RAC slabs.

Behavior of Shear-Critical Recycled Aggregate Concrete Beams Containing BFRP Reinforcement

The shear performance of recycled aggregates beams reinforced with basalt fiber-reinforced polymer (BFRP) bars is evaluated and compared with that of similar beams made with natural aggregates (NA). Six beams with a shear span-to-effective depth ratio (a/d) of 3.0 were tested to failure. Test variables consisted of the recycled concrete aggregate (RCA) replacement percentage (60 and 100%) and the presence of BFRP stirrups in the shear span. Experimental results showed that a RCA replacement of 60% marginally reduced (5%) the shear capacity. However, the reduction in the shear capacity was more pronounced (17%) for the specimen made with 100% RCA. The contribution of BFRP stirrups to the shear capacity decreased with an increase in the RCA replacement percentage. The width of the major shear crack at a given value of load was higher for the beams with RCA. The deflection values at the ultimate load were greater for beams made with RCA. A codified analytical approach as well as a model published in the literature were employed to predict the shear capacity of the tested beams. Predictions of the codified analytical approach were very conservative. The analytical model published in the literature provided a more reasonable prediction for the shear capacity of the tested beams than that of the codified analytical approach.

Finite Element Analysis of the Shear Capacity of Recycled Aggregate Concrete Beams with Corroded Stirrups

In this paper, a model to predict the residual shear capacity of RAC beams with corroded stirrups was established, and the simulation analysis was conducted on recycled concrete beams with different corrosion level using ANSYS. The reliability of the finite element analysis model was verified by comparing the finite element results with experimental results.

Effect of hybrid fibers on the flexural performance of high‐strength recycled aggregate concrete beams

AbstractFibers are mixed within reinforced high‐strength recycled aggregate concrete (RHRAC) beams to improve their flexural performance. This study experimentally and analytically investigates the effect of using RAC combined with polyvinyl alcohol fiber (PVAF) and steel fiber (SF) on the flexural performance of RHRAC beams. A total of 11 RHRAC beams (150 × 300 × 2600 mm3) are manufactured and subject to four‐point flexural testing. The parameters of the concrete are investigated, including the volume content of the PVAF and SF. The experimental results show that SF increases the flexural strength of RHRAC beams more than PVAF does. Conversely, the effect of PVAF on deformability is more significant than that of SF. In addition, the positive influences of hybrid fiber (PVAF and SF) on the crack load, flexural capacity, and deformation capacity are superior to those of single‐mixed PVAF or SF. Three different specifications are used to calculate the flexural capacity of the test beams, among which, JGJ/T465‐2019 is the most reliable.

Improving the Shear Capacity of Recycled Aggregate Concrete Beams with NSM-CFRP Strip

Improving the Shear Capacity of Recycled Aggregate Concrete Beams with NSM-CFRP Strip

Analysis of the shear behavior of reinforced recycled aggregate concrete beams based on shear transfer mechanisms

This study aims to contribute to a more rational understanding of the shear behavior of reinforced recycled (concrete) aggregate concrete beams. Twelve reinforced concrete beams - six with natural aggregate concrete (NAC) and six with 100% coarse recycled concrete aggregates (RAC) - with same concrete compressive strength (38 MPa) and proportions of cement and aggregates per volume, varying the longitudinal (1.15%, 1.75%, and 2.50%) and transverse (0%, 0.086%, and 0.114%) reinforcement ratios, were tested under a 4-point bending setup with a full-field displacement monitoring. A thorough examination of the failure span along the tests, associating critical crack shape and kinematics with an investigation of the shear transfer mechanisms provided by mechanical models from the literature was conducted. Direct shear tests on push-off specimens followed by analyses of their failure surface evaluated the characteristics of shear crack surfaces and a proper modeling of the aggregate interlock contribution. The results showed a 28% average reduction in the shear strength of RAC beams with no stirrups in comparison with their reference beams (NAC), whereas beams with stirrups of same characteristics showed a similar shear strength, regardless of the type of coarse aggregate. The evaluation of the shear transfer mechanisms enabled an understanding of the reasons for those behaviors. Experimental results were also compared with those predicted in design codes. They were conservative for beams with stirrups, and, in general, less accurate than those obtained by the shear transfer mechanisms.

Shear design of recycled aggregate concrete beams using a data-driven optimization method

Under the umbrella of sustainable development, recycled aggregate concrete (RAC) is a building material that has attracted a lot of interest. This study proposes a data-driven methodology for shear capacity prediction and design optimization for RAC beams. A comprehensive test dataset with 232 samples was gathered based on clear criteria. Geometric and materials factors are identified as inputs to develop four machine learning (ML) prediction models including artificial neural network, Gaussian process regression, random forest, and categorical gradient boosting (CGB). The winner of ML models is combined with the nondominated sorting genetic algorithm II (NSGA-II) to establish a dual-objective design optimization of RAC beams subjected to shear. Results show that the CGB model achieved the highest accuracy (R2 = 0.972, RMSE = 14.909, and MAPE = 0.086) among four ML models and its standard deviation was more than 80% lower than the five existing equations. The SHapley Additive exPlanations interpreted the CGB model and identified the beam width, nominal strength of stirrups, shear-span ratio, and nominal strength of longitudinal reinforcement are the four main features affecting the shear capacity of a RAC beam. Finally, the Pareto front was created by combining the CGB model with the NSGA-II algorithm. The suggested framework provides a novel route for the structural design of RAC beams subject to shear.

Flexural stiffness of recycled aggregate concrete beams under combined effect of load and steel corrosion

AbstractSince reinforced concrete members suffer from different types of loads during their service life, the steel bars embedded in reinforced concrete members can be easily corroded in chloride‐laden environment. To investigate the influence of combined effect of load and steel corrosion on the flexural stiffness of recycled aggregate concrete (RAC) beams, 12 RAC beams were prepared and tested. The effects of load level (i.e., the ratio of the load applied to beams to the ultimate load) and recycled coarse aggregate (RCA) replacement ratio (i.e., the ratio of RCAs to replace natural coarse aggregates) on the internal force arm coefficient of cracking cross‐section, the elastoplastic resistance moment coefficient of cross‐section, and the strain incongruity coefficient of corroded tensile steel bars were analyzed, and a calculation model for flexural stiffness of RAC beams under combined effect of load and steel corrosion was established. The results showed that when the ratio of bending moment to ultimate bending moment of the pure bending part of beams was within 0.55–0.80 and the average mass loss of tensile steel bars was less than 3.23%, 0.85 could be adopted as the internal force arm coefficient of cracking cross‐section. The elastoplastic resistance moment coefficient of cross‐section was approximately a constant when the corroded RAC beams were in the service stage, while it increased obviously with the load level. There was a strong linear relationship between strain incongruity coefficient and average mass loss of tensile steel bars during the service stage of corroded RAC beams, and the strain incongruity coefficient increased linearly with the load level. The calculated values of the model of flexural stiffness proposed in this paper were in reasonable agreement with the experimental values.

Data-driven shear strength predictions of recycled aggregate concrete beams with /without shear reinforcement by applying machine learning approaches

Recycled aggregate concrete (RAC) has gradually received attention in recent years for sustainable development. However, the adaptation of RAC for structural elements is becoming less popular due to the lack of proper design guidelines. Thus, to encourage the structural application of RAC, it is essential to develop a framework for predicting the shear capacity of RAC beams. The data-driven prediction has demonstrated excellent accuracy compared to traditional empirical equations. This study proposed a data-driven framework using machine learning. In this paper, 401 samples of different RAC beams are analysed, including 264 slender beams and 137 deep beams. Eight machine learning (ML) algorithms namely Linear Regression, K-nearest neighbour, Random Forest, Adaptive boosting, Gradient Boosting, Extreme gradient boosting (XGBoost), Category Boosting, and Light Gradient Boosting Machine were employed to develop the best ML-based framework. Having the best prediction output (R2 score: 0.95 in slender beam, 0.78 in deep beam), XGBoost is selected to further analyse the feature importance and parametric study with SHapley Additive exPlanations (SHAP). Simultaneously, the experiment values were compared with calculated values according to the codes in different regions, such as ACI-381-19, AS3600-2018, Eurocode 2, and GB50010-2010. The results of SHAP from XGBoost indicate that the replacement ratio of RCA has limited influence on normalized shear strength value, Vu/bd, and it is applicable to adopt RAC without shear strength reduction if the replacement ratio of RA is lower than 40%. Nevertheless, the comparison of experiment value from the database and calculated value according to classical analytical methods demonstrates the necessity for adjustment to existing design codes against RAC replacement ratio. Some suggestions which could further improve the accuracy of results are provided at the end of this paper as well.