Recycled Aggregate Concrete Beams Research Articles

Finite Element Analysis on Cracking Resistances of Recycled Aggregate Concrete Beams with Hybrid Fibers

In order to improve the mechanical properties and cracking resistances of recycled aggregate concrete, the influences of the volume incorporation rates of polypropylene fibers and steel fibers on the hybrid fiber recycled aggregate concrete beams are analyzed by finite element. The results show that: Compared with the ordinary RAC beams, the cracking load, the mid span deflection and the maximum compressive stress of HFRAC beams are larger under the initial cracking state. The yield load and maximum compressive stress of HFRAC beams vary little, and the mid span deflection increases or decreases under the yield state. HFRAC beams have greater stiffness and better ductility. Through theoretical calculation and finite element analysis, the formula for calculating the cracking moment of HFRAC beams is derived.

Experimental Investigation and Analytical Study on the Flexural Behavior of Reinforced Recycled Aggregate Concrete Beams

The paper presents an experimental study on the flexural behavior of reinforced beams made of natural and recycled gravels under monotonic loading. 20x25x170 cm beams specimens were prepared using two reinforcement ratios and were cast from two concrete mixtures. The two concretes are respectively a mixture of natural aggregates and a concrete with 100% recycled gravels of C35/45 strength class, S4 class of workability and a constant W/C ratio. The results reported in this paper are those of experiments performed in the framework of this study beside 118 data sets taken from the literature on the flexural behavior of natural (NAC) and recycled aggregate concrete (RAC). The principal results of bending tests show that flexural capacity of recycled aggregate concrete beams is similar to the flexural capacity of natural aggregate concrete beams for the service and ultimate loading. However, cracking moment, maximum crack spacing, crack heights and deflection under serviceable load are affected by the use of recycled aggregates. Experimental results of the extensive data base were compared to load-carrying capacities and deflections calculated according to Eurocode 2 (EC2). The comparisons show that the method of deflection calculation does not correctly predict the experimental results.

Behaviour of recycled aggregate concrete under combined compression and shear stresses

To investigate the behaviour of recycled aggregate concrete (RAC) under combined compression and shear stresses, 75 hollow cylinder specimens prepared with various replacement ratios of recycled coarse aggregate (RCA) were tested with a self-designed loading device. The results showed that the failure pattern was similar for RAC with different replacement ratios of RCA. The ultimate shear stress improved with an increasing axial compression ratio of less than 0.6 and declined after exceeding 0.6. A modified failure criterion for RAC with normal strength under combined compression and shear stresses was proposed. A new procedure to predict the shear strength for RAC beams without stirrups was developed based on the proposed failure criterion, showing a better correlation with the experimental results than the predictions calculated by GB50010, Eurocode 2, fib Model Code 2010 and ACI 318-11.

Shear performance of recycled aggregate concrete beams: An insight for design aspects

The shear failure of reinforced concrete beam is a brittle type of failure and can be dangerous if it is not properly designed. The inherent inferior quality of recycled coarse aggregate (RCA) makes the recycled aggregate concrete (RAC) beams even more vulnerable in shear resistance. This persuades the structural designers to account each of the contributing components in the shear resistance mechanisms seriously, especially that of concrete. In this regard, an experimental investigation was carried out on fourteen beams to examine the shear performance of RAC beams in the absence and presence of transverse reinforcement. Six numbers of beams without transverse reinforcement were tested to examine the contribution of RAC in shear resistance mechanisms and eight beams with shear reinforcement were tested to verify the applicability of the prevailing shear design provisions for RAC beams. The inferior mechanical properties of the RAC are improved satisfactorily by implementing the Particle Packing Method of mix design approach along with the established Two Stage Mixing Approach. However, even with the improved mechanical properties of RAC, the poor performance of RAC beams in shear could not be avoided and a drop of 14% was recorded in the ultimate shear strength of RAC beams without stirrups. A database is prepared by compiling the reported test results of RAC beams with and without transverse reinforcement. An alternative equation is proposed to predict the diagonal tension cracking strength of RAC beams, by using the database of RAC beams without transverse reinforcement and it exhibits a better correlation with the experimental results. Further, in the shear resistance mechanisms of RAC beams the effectiveness of stirrups is studied using the database of RAC beams without and with transverse reinforcement.

Flexural Behavior of Corroded Reinforced Recycled Aggregate Concrete Beams

Recycling concrete not only reduces the use of virgin aggregate but also decreases the pressure on landfills. As a result, recycled coarse aggregate (RCA) is extensively recommended for new construction projects. However, the flexural behavior of corroded reinforced recycled aggregate concrete (RAC) beams is uncertain. The experimental research presented in this paper was performed to investigate the flexural behavior of corroded reinforced RAC beams compared to that of corroded reinforced natural aggregate concrete (NAC) beams and consequently explore the possibility of using RAC beams in corrosive environments. Four different percentages of RCA in total mass of coarse aggregate in concrete mixtures (0%, 33%, 66%, and 100%) and two different concrete strengths (C30, C60) were the governing parameters. The electrochemical method was adopted to accelerate steel corrosion. Full‐scale tests were performed on eight simply supported beams until the failure load was reached. Comparison of load‐deflection behavior, crack patterns, failure modes, ductility, and ultimate flexural capacity of corroded reinforced NAC and RAC beams was made based on the experimental results obtained. The comparison results show that the flexural behavior of corroded reinforced RAC beams with an appropriate percentage of RCA is satisfactory compared to the behavior of NAC beams.

Shear behaviour of recycled aggregate concrete beams with and without shear reinforcement

An experimental study of the shear behaviour of recycled aggregate concrete (RAC) beams with and without shear reinforcement is presented. Nine full-scale simply supported beams were loaded in four-point bending tests until failure. Three different replacement ratios of coarse natural with coarse recycled concrete aggregate (0%, 50% and 100%), and three different shear reinforcement ratios (0%, 0.14% and 0.19%) were the main parameters. All natural aggregate concretes (NAC) and recycled aggregate concretes (RAC) were designed and experimentally verified to have similar compressive strength and workability. It was found that the shear behaviour and the shear strength of the beams with 50% and 100% of recycled concrete aggregate were very similar to that of the corresponding natural aggregate concrete beams. The applicability of different code provisions for shear strength predictions of the RAC beams with and without shear reinforcement was tested by comparison with test results obtained on 85 beams, 58 RAC and 27 corresponding NAC beams. The shear strength of RAC50 and RAC100 beams with and without shear reinforcement was conservatively predicted by the analyzed codes with similar reliability as for the corresponding NAC beams shear strength. At this state-of-knowledge, the application of the analyzed codes’ provisions for NAC beams shear strength can be recommended both for the RAC50 and the RAC100 beams.

Cyclic torsion performance of recycled aggregate concrete beams with or without fly ash

Although the material property and structural behavior of recycled aggregate concrete (RAC) and modified RAC (MRAC) have been widely investigated, the research on seismic performance of RAC and MRAC members under combined flexure-shear-torsion cyclic loading is still very limited. In this paper, the failure mode, hysteresis loop, strain of steel reinforcement, energy dissipation capacity, skeleton curve, deterioration, stiffness and ductility factor and torsional bearing capacity calculation of RAC and MRAC beams subjected to combined cyclic torsion were compared and investigated. The results indicate that the addition of fly ash didn’t bring an obvious effect to the failure mode of test beams. Although the bearing capacity of MRAC beams is lower than that of RAC beams, the ductility factor and energy dissipation capacity of MRAC beams are larger than those of RAC beams. The addition of fly ash will weaken the hysteretic performance to some extent. The larger the torsion-shear ratio is, the more serious deterioration of stiffness is. The addition of fly ash does not bring apparent influence on the deterioration of stiffness. The variable angle space truss model was employed to calculate the torsional bearing capacity of RAC and MRAC beams subjected to combined cyclic torsion. The predictions agree well with the test results of the torsional beams.

Seismic behavior of recycled aggregate concrete beams under cyclic torsion

Although the material property and structural behavior of recycled aggregate concrete (RAC) have been widely investigated, the research on seismic performance of RAC members under cyclic torsion is still very limited. In this paper, the failure mode, hysteresis loop, strain of steel reinforcement, principal strain of concrete, energy dissipation capacity, skeleton curve, deterioration of stiffness and ductility factor of RAC beams and natural aggregate concrete (NAC) beams under cyclic torsion were compared and investigated. The results indicate that although both the RAC and NAC torsional beams present a torsional failure mode with spiral cracks, the cracks of RAC beams are larger than that of NAC beams. The hysteresis loop shape and corresponding inflection points of NAC and RAC torsional beams are very similar, but the energy dissipation capacity and ductility factor of RAC torsional beams are about 20% and 7% higher than those of NAC beams, respectively. The use of RAC in cyclic torsional beams does not bring apparent influence on the deterioration of stiffness, but the bearing capacity of RAC torsional beams is lower than that of NAC beams.

Performance of recycled concrete beams under sustained loads coupled with chloride ion (Cl−) ingress

This paper presents the experimental results of the cracking propagation and flexural performance degradation of reinforced concrete beams with recycled aggregates (RA), under long-term coupled effects of sustained loads and chloride ion (Cl−) ingress. Test results show that the load-induced cracking damages of recycled aggregate concrete (RAC) beams were slightly lower while the corrosion-induced cracking damages were larger than the natural aggregate concrete (NAC) beams, through the 20-month coupled damage history. The flexural capacity was found comparable among damaged beams with different RA replacements. Therefore, this paper suggests the mechanical properties of RAC beams should be acceptable, given that they served under sustained loads and the corrosion of the longitudinal reinforcements was relatively low (less than 3%). However, RAC beams’ inferior durability against cracking by steel bar corrosion should be considered with great cautious.

A database on flexural and shear strength of reinforced recycled aggregate concrete beams and comparison to Eurocode 2 predictions

A comprehensive database of recycled aggregate concrete and companion natural aggregate concrete beams’ flexural and shear strength was compiled from 217 experimental results. Strict criteria were applied to determine the failure type. Sub-databases were formed with beams failing in flexure and shear with and without stirrups. On each sub-database the applicability of Eurocode 2 provisions for flexural and shear strength to recycled aggregate concrete beams was tested. The results show that flexural and shear strength of recycled aggregate concrete beams without stirrups is successfully predicted by Eurocode 2. As for beams with stirrups, further research and experimental results are necessary.

Bond position function between corroded reinforcement and recycled aggregate concrete using beam tests

Twelve beam tests were carried out in order to investigate the bond strength and bond position function between corroded rebar and recycled aggregate concrete (RAC), with the electrochemical method adopted to accelerate steel corrosion. Three recycled coarse aggregate (RCA) replacement percentages (i.e., 0%, 50% and 100%) and 4 expected corrosion crack widths of RAC (i.e., 0mm, 0.05mm, 0.3mm, and 0.6mm) were considered. Test data was used to calculate the bond stress along the anchorage length, and the influence of both RCA replacement percentages and the corrosion cracking widths on the bond strength and bond position function between the RAC and rebar. The bond position functions for different corrosion levels of reinforced RAC were also established. The results indicated that the ultimate bond strength of reinforced RAC beams decreased overall with an increase of the RCA replacement percentage and corrosion crack width, but that the rate of decline reduced with an increase of RCA and corrosion level. The bond position curve of the reinforced RAC beams was similar to that of natural aggregate concrete (NAC) beams subjected to bending and shear stresses before and after steel corrosion, with a sharp increase of the relative bond stiffness at both anchorage ends, and an almost linear decrease of relative bond stiffness in the range of 0.15–0.85 times the anchorage length. Increasing the RCA substitution rate had little effect on the bond position curves, and the bond distribution became more uniform as the crack widths increased.

Shear Behavior of Recycled Aggregate Concrete Beams

Shear Behavior of Recycled Aggregate Concrete Beams

Numeral modeling of fracture failure of recycled aggregate concrete beams under high loading rates

Fracture tests of recycled aggregate concrete (RAC) beams of different sizes were conducted under high loading rates. In order to characterize the effect of high loading rate on the behavior of RAC beams, two new material models were used together with the commercial finite element software \(\hbox {ABAQUS}^{\mathrm{R}}\). One model is a viscoelastic model that can predict the increase of stiffness (modulus of elasticity) of RAC with increasing loading rate, and the other model is a multiphase composite model that can determine the effective stiffness of RAC taking into account the special internal structure of recycled aggregate. Two different cases were considered in the numerical simulation. Case 1 is for fixed beam size under different loading rates, and Case 2 is for fixed loading rate with different beam sizes. For Case 1, the simulation results of the maximum loads under three different strain rates agreed with test data quite well. The Force-CMOD curves of the numerical simulation and test data showed similar trends. The higher the strain rates, the wider the high stresses spread in the crack propagation zone. The good agreements with the test data indicated that the two new material models can characterize the effect of high loading rate on RAC beams very well. For Case 2, three beam sizes and one loading rate was studied. The post-peak Force versus CMOD curves from the simulation follow the same trend of the test data. The stress distributions in the beams of different sizes are similar. On the other hand, the maximum loads predicted by the numerical model did not agree very well with test data. This is due to the fact that the maximum forces of RAC notched beams exhibited size effect, which was not considered in the fracture criteria adopted in \(\hbox {ABAQUS}^{\mathrm{R}}\) and not in the two new material models. This will be a topic for future research.

Reliability Analysis for Flexural Capacity of Recycled Aggregate Concrete Beams

Concrete made of recycled coarse aggregate (RCA) derived from multiple sources can have relative variation in mechanical properties compared with natural aggregate concrete (NAC), resulting in a lower reliability of a recycled aggregate concrete (RAC) beam than that of NAC beam. In this paper, a method is proposed to improve the reliability of beams made with RAC by increasing the reinforcement ratio. According to the equilibrium equations of beams subjected to bending moment, the increase in reinforcement ratio can be achieved by decreasing the RAC design strength. Same mean compressive strengths are assumed for RAC and NAC and four factors are considered including concrete grade, reinforcement grade, reinforcement ratio and the ratio of external loads in reliability analysis. Using NAC beams as a reference and keeping the target reliability index the same as that of RAC beams, the analysis results show that RAC design strength decreases with increase in coefficient of variation (CoV) of RAC compressive strength. When the CoV of RAC compressive strength is 20%, the RAC design strengths are 0.93 and 0.90 times of the NAC design strength with a 95% confidence level for grade C30 and C40 concrete, respectively.

Fracture of Recycled Aggregate Concrete under High Loading Rates

AbstractUsing renewed materials in the construction industry is very important for sustainable development. Recycled aggregate concrete (RAC) is one of the renewed materials. RAC uses demolished concrete as aggregate to make concrete. Previous studies showed that the strength of RAC can be improved and made comparable to regular concrete. This study examines the rate effect on fracture properties of RAC using an available improvement method. The RAC was made of 100% recycled coarse aggregate pretreated by a surface coating method. The fracture properties of RAC were tested based on the size effect method. Three different sizes of notched RAC beams were tested under three different strain rates, from 10−5/s to 10−2/s, controlled by crack-mouth-opening-displacement (CMOD). For the beams under high loading rates, the fracture properties were found to be rate-dependent. The critical stress intensity factor, KIc, and the fracture energy release rate, Gf, increase with increasing loading rate. Two empirical equ...

Structural Behaviour of Composite Members with Recycled Aggregate Concrete — An Overview

A series of investigations on structural behaviour, durability, fire-resistance and seismic performance of composite members with recycled aggregate concrete (RAC) have been carried out in the past 10 years (2005–2014). This paper is consisted of three parts: the first part introduces and discusses the research progress in regard to the structural behaviour of RAC filled steel tubular columns and beams; the second part concentrates on the structural behaviour of steel-reinforced RAC members, including columns, beams, shear walls and slabs; and the third part focuses on the long-term performance of composite members with RAC, involving fire resistance, durability and seismic performance. It seems that RAC composite members with different replacement ratios of recycled coarse aggregate have slightly lower or similar structural behaviour compared to that of normal concrete composite members. Review results reveal that it is feasible to apply steel-RAC composite members as structural applications. This intensive review provides a reasonable knowledge of the structural behaviour of steel-RAC composite members, and recommends further investigations on the failure mechanics and durability of steel-RAC composite members which are needed to promote safe and economic application in the future.

Performance of Recycled Aggregate Concrete in a Real Project

Though a large amount of research has been carried out on recycled aggregate concrete (RAC) during recent years, the application cases of RAC in real structures are still very few in China. This paper reports the application of RAC in a real project. Two beams made of RAC and commercial natural aggregate concrete (NAC) respectively were cast in-situ to carry out the tests. The two beams were subjected to the similar service loading, so that the performance of the RAC beam could be compared with that of the NAC one. Compressive strength, degree of density and uniformity were tested for both types of concrete at representative ages, and concrete strain of the two target beams was monitored regularly from the age from 1 d to 420 d. The results from laboratory tests and on-site monitoring have proved the feasibility and reliability of the application of RAC in real structures though RAC is generally inferior to NAC.

Experimental Study of the Recycled Aggregate Concrete Beam Flexural Performance

Using the same water to binder ratio and the same ratio of reinforcement, the three recycled aggregate concrete are made in different replacement ratio of recycled coarse aggregate which is 0%, 30%, 75% and 100%. Through experimental the beams flexural performance is researched, the right sections bearing deformation performance and damage distinction. The result shows that the damage model and the damage process are basically the same; the right sections mean strain is uniform to plane section assumption. With the increase in the replacement ratio of recycled coarse aggregate, the value of recycled concrete beams cracking moment, yielding bend moment and ultimate moment are all decreasing, the deflection and the maximum crack depth is increasing and the maximum crack depth is decreasing. The experimental and theoretical analysis shows that the existing norms formula is accurately applied in calculating the recycled concrete beams ultimate moment, and the formula is need to be amendment when calculating the cracking moment.

Long-term deflection and flexural behavior of reinforced concrete beams with recycled aggregate

This paper presents experimental results on the long-term deformations of recycled aggregate concrete (RAC) beams for over 1year (380days) and flexural behavior of RAC beams after exposure to sustained loading. Three reinforced concrete (RC) beam specimens were fabricated with replacement percentage of aggregate (100% natural aggregate, 100% recycled coarse aggregate, and 50% recycled fine aggregate) and subjected to sustained loading that is 50% of the nominal flexural capacity. During the sustained loading period (380days), the long-term deflection due to creep and shrinkage was recorded and compared with predicted behavior that was determined based on current specifications (ACI 318 Code). After measuring the long-term deflection for 380days, four-point bending tests were conducted to investigate the flexural behavior of RC beams after exposure to sustained loading and determine any reduction in flexural capacity. A modified equation to predict the long-term deflection values for RC beams with recycled aggregate is proposed, and the experimental results are compared with the predictions calculated using the ACI 318 Code provisions.

Efficiency factors of recycled concrete aggregate concrete bottle-shaped struts

A comparison with code-based predictions of efficiency factors of bottle-shaped struts computed using strut-and-tie models from shear test results of coarse recycled concrete aggregate concrete beams reported in the literature is presented. The objective of the comparison was to ascertain whether strut efficiency factors in current design codes originally meant for natural coarse aggregate concrete can be conservatively applied to concrete made with coarse recycled concrete aggregate or not. In addition to the codal provisions, a strut efficiency factor model developed from first principles was also used in the comparative study. The results of the comparison indicate that the AASHTO LRFD code provisions and the proposed efficiency factor model gave conservative predictions for the coarse recycled concrete aggregate concrete bottle-shaped struts although the ACI 318-08 predictions were unconservative. The most accurate predictions were obtained from the Eurocode 2 model, although with an erratic degree of conservatism. The lack of conservatism vis-à-vis the ACI code recommended strut efficiency factors does not per se indicate inferior strength of coarse recycled concrete aggregate concrete but may be attributed to the insensitivity of the ACI code efficiency factors to strut inclination with adjoining tie(s).