Recycled Coarse Aggregate Replacement Research Articles

Analysis on Mechanical Properties of Recycled Aggregate Concrete Members after Exposure to High Temperatures

In order to study the mechanical properties of recycled aggregate concrete (RAC) specimens after exposure to high temperatures, 120 RAC prism specimens, 57 reinforced recycled aggregate concrete (RRAC) specimens, and 56 steel reinforced recycled aggregate concrete (SRRAC) specimens were designed, involving two varying parameters such as recycled coarse aggregate (RCA) replacement percentage and temperature. The performance degradation of RCA materials, RRAC members, and SRRAC members after exposure to high temperatures was analyzed in depth. The research results show that after exposure to high temperatures the surface color of members may change from cinereous to gray-white. Some cracks may appear on surface of members and the mass of members may be lighter. With the increase of the experiencing temperatures, the bearing capacity (compressive, bending, and shearing) of RAC and its members are reduced, but their ductility and energy dissipation capacity have little effect on the change of high temperature. With the increase of the RCA replacement percentage, the mass loss ratio, ultimate bearing capacity, and peak deformation of each RAC and its members increase slightly, and the displacement ductility and energy dissipation capacity of the RRAC members decrease slightly. With the increase in replacement percentage of RCA, mechanical properties of RAC and their members have little effect after exposure to elevated temperatures, and the fluctuation range is within 20%.

Dynamic behaviour and energy dissipation of reinforced recycled aggregate concrete beams under impact

Abstract In order to study the dynamic behaviour and energy dissipation of reinforced recycled aggregate concrete (RAC) beams under impact, four groups of reinforced RAC simply supported beams with various recycled coarse aggregate (RCA) replacement percentages are designed and tested under drop weight impact at the mid-span of beams and corresponding another four groups of beam specimens under static loading. The static resistance versus mid-span displacement curves are obtained from static loading test to analyse the effect of RCA replacement percentage on the beam's mechanical performance. It is concluded that the static resistance and stiffness of the RAC beam decrease slightly as the RCA replacement percentage increases and the deformation curve of reinforced RAC beam conforms to the classical bending theory of beam. In the drop weight impact test, the reinforced RAC beams failed with both global and local damage, and in bending controlled mode. The time history of impact forces, mid-span displacements and stress states of the beams are investigated. The mid-span displacement of the beams increases with the increase of RCA replacement percentage. The energy dissipation of the beams under impact is discussed based on the simplified resistance model. A concept of global damage energy dissipation is introduced and the method for calculating the global damage energy dissipation of the reinforced RAC beam under impact is proposed. The global damage energy dissipation ratio is defined and used to measure the proportion of global damage and local damage on reinforced RAC beam under impact. The experimental results presented here provide benchmark data for the further research work on the dynamic response of reinforced RAC beam under impact.

Flexural bond behavior of reinforced recycled aggregate concrete

Abstract Replacing natural aggregate concrete with recycled aggregate concrete (RAC) can effectively solve aggregate shortage problems. However, application of recycled aggregate in engineering structures requires analysis of the interaction between steel bars and RAC. The bond behavior under flexure is similar to the actual state of stress in structural members. 15 beam specimens were designed and tested to investigate the RAC-reinforcement bond behavior and the constitutive relationship at the interface between them. Test parameters include water-binder ratio, recycled coarse aggregate (RCA) replacement percentage, recycled fine aggregate (RFA) replacement percentage, bar surface shape, and anchorage length of reinforcements. The influence of the above variables on the load to slip curves, bond strength, and the bond efficiency coefficient is discussed. Bond strength between reinforcements and concrete decreases with increasing RCA replacement percentage, however, the rate of decrease is reduced for specimens with low water-binder ratio. The addition of RFA significantly degrades bond behavior. The bond strength between deformed reinforcements and RAC is approximately 2 times of that of plain reinforcements. With increasing anchorage length, the interface bond behavior between the reinforcements and RAC decreases.

Uniaxial Damaged Plastic Constitutive Relation of Recycled Aggregate Concrete

This paper presents a proposed uniaxial damaged plastic constitutive relation of recycled aggregate concrete (RAC) based on the experimental studies. A total of five groups of RAC specimens with different recycled coarse aggregate (RCA) replacement percentages of 0, 25%, 50%, 75%, and 100%, respectively, are tested under both monotonic loading and cyclic loading. The effect of the RCA replacement percentage is thoroughly investigated on a variety of mechanical properties, including the compressive strength, the peak strain, and the elastic modulus. Based on the test results, a uniaxial damage plastic constitutive relation of the RAC is proposed within the continuous thermodynamics framework. After validated by the experimental results, the proposed damaged plastic constitutive relation of the RAC is applied to perform nonlinear analysis of the RAC columns under cyclic loading, which provides close predictions of the hysteresis behavior of the RAC columns.

Seismic fragility analysis of deteriorating recycled aggregate concrete bridge columns subjected to freeze-thaw cycles

In cold regions, concrete structural deterioration due to freeze-thaw damage is a common problem. To investigate the seismic performance of recycled aggregate concrete (RAC) members in a freeze-thaw environment, the seismic fragility analysis of RAC bridge columns with different recycled coarse aggregate (RCA) replacement ratios subjected to freeze-thaw cycles (FTCs) was performed by the cloud analysis method. The results show that, compared with peak ground acceleration, setting the peak ground velocity as the intensity measurement provided a better correlation with the damage measure when developing the probabilistic seismic demand model. Additionally, the fragility of all RAC bridge columns before FTCs were almost the same; as the FTCs increased, the fragility gradually increased and became increasingly significant as the RCA replacement ratios increased. Finally, the fragility analysis in this paper can provide a good reference for the seismic performance evaluation of RAC members in cold regions.

Effect of Recycled Concrete on the Flexural Behavior of Concrete-Filled FRP Tubes

This paper presents the results of short span concrete-filled fiber reinforced polymer (FRP) tubes filled with different recycled coarse aggregate (RCA) replacement ratios. The mechanical response of recycled concrete-filled FRP tubes (RCFFTs) under flexural load was examined to investigate the influence of RCA as an in-filled material. The experimental results were compared with the simplified finite element model to estimate the failure behavior of the test units. RCFFTs with a 100% RCA replacement ratio showed a similar bending behavior compared to natural aggregate concrete-filled FRP tubes. The flexural behavior of 100% recycled aggregate concrete could be complemented and utilized because of the high strength and high stiffness of the FRPs.

Performance Evaluation of Fiber and Silica fume on Pervious Concrete Pavements Containing Waste Recycled Concrete Aggregate

Pervious concrete as a paving material rehabilitate on a new interest due to its efficiency to permit water to drainage over itself to flow groundwater and reducing storm water runoff. The employment of Recycled Coarse Aggregates (RCA) from site of construction and destruction wastes to product green concrete as a sustainable solve with varied environmental interests. Three different series (A, B, and C) of pervious concrete were used in this work, every series consisting of four mixtures, The (series A) mixtures with RCA replacement were 25%, 50%, 75% and 100% by weight of Natural Coarse Aggregate (NA), and (series B) mixtures using the same replacement ratios of RCA in addition of (silica fume SF) of 2.5%, 5%, 10%, and 12% by weight of cement to strengthen the cement past of pervious concrete. Finally, the (series C) mixtures were included the similar ratios of RCA and SF in addition to glass fibers of volume fraction 0.05%, 0.1%, 0.15%, and 0.2%. The properties of RCA pervious concrete investigated from density, hydraulic conductivity coefficient, porosity, and strength indices were compressive, flexural, and splitting tensile strengths. The test results shows that the use of RCA slightly affect hydraulic conductivity and nugatory effect on compressive, tensile, and flexural strengths where the use of silica fume and glass fibres more strong effect on the hydraulic conductivity and positive effect on pervious concrete flexural, splitting tensile strengths.

Effect of recycled coarse aggregate on the properties of C40 self-compacting concrete

The effect of recycled coarse aggregate (RCA) on the fresh and hardened properties of C40 self-compacting concrete (SCC) was investigated in this paper. The slump, T 500 (the time needed for SCC to spread into a round configuration with a nominal diameter of 500 mm), the slump flow and the flow time of fresh C40 SCC as well as the compressive strength and modulus of elasticity of hardened C40 SCC were studied. The modulus of elasticity of C40 SCC was calculated by theoretical formula, and the calculated values were compared with the experimental values. Mechanisms that effect on the C40 SCC properties at fresh and hardened states were also explored. The experimental results showed that the slump values of the C40 SCC are beyond 250 mm. The C40 SCC with RCA replacement content of 50% showed the highest slump value of 275 mm. All T 500 values of the C40 SCC are within 5 s. The slump flow of the C40 SCC slightly increases with the increase of replacement content of the RCA. In contrast, the compressive strength and modulus of elasticity of the C40 SCC slightly decrease with the increase of replacement content. The experimental values of modulus of elasticity are lower than that of the calculated values. Submerged in water before mixing of RCA leading to the slump flow of the C40 SCC increases with the increasing replacement content of the RCA. The old cement mortar attached to the RCA surface is the main reason that weakens the mechanical properties. The lower amount of coarse aggregate and the higher amount of cement paste attribute to the lower values of modulus of elasticity. This study implied that RCA can be effectively used in the production of C40 SCC without any significant sacrifice on workability and mechanical properties.

Finite element analysis and axial bearing capacity of steel reinforced recycled concrete filled square steel tube columns

This paper presents a finite element model which can simulate the axial compression behavior of steel reinforced recycled concrete (SRRC) filled square steel tube columns using the ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of material in the columns. The nonlinear analysis of failure modes, deformation characteristics, stress nephogram, and load-strain curves of columns under axial loads was performed in detail. Meanwhile, the influences of recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, width thickness ratio of square steel tube, RAC strength and slenderness ratio on the axial compression behavior of columns were also analyzed carefully. It shows that the results of finite element analysis are in good agreement with the experimental results, which verifies the validity of the analytical model. The axial bearing capacity of columns decreased with the increase of RCA replacement percentage. While the increase of wall thickness of square steel tube, profile steel ratio and RAC strength were all beneficial to improve the bearing capacity of columns. Additionally, the parameter analysis of finite element analysis on the columns was also carried out by using the above numerical model. In general, the SRRC filled square steel tube columns have high bearing capacity and good deformation ability. On the basis of the above analysis, a modified formula based on the American ANSI/AISC 360-10 was proposed to calculate the nominal axial bearing capacity of the columns under axial loads. The research conclusions can provide some references for the engineering application of this kind of columns.

Cyclic load tests and seismic performance of recycled aggregate concrete (RAC) columns

In this paper, four one-two-scale recycled aggregate concrete (RAC) columns were prepared and tested under reversed quasi-static cyclic loading. Three levels of recycled coarse aggregate (RCA) replacement ratios (0%, 50% and 100%) and two axial load ratios (0.15 and 0.35) were considered to investigate and analyze the seismic performance of RAC columns. The test results indicate that the failure process of RAC columns is similar to that of natural aggregate concrete (NAC) columns and presented satisfactory seismic requirements in terms of hysteresis behavior, ductility and energy dissipation capacity. The results also show that the RCA replacement ratios effect on seismic is significant, and the axial load ratio had an obvious influence on the energy dissipation capacity and shear deformation of the columns. Therefore, the axial load ratio must be controlled strictly in seismic design.

Punching shear behavior of recycled aggregate concrete slabs with and without steel fibres

A study on the punching shear behavior of 8 slabs with recycled aggregate concrete (RAC) was carried out. The two main factors considered were the recycled coarse aggregate (RCA) replacement percentage and the steel fibre volumetric ratio. The failure pattern, load-displacement curves, energy consumption, and the punching shear capacity of the slabs were intensively investigated. It was concluded that the punching shear capacity, ductility and energy consumption decreased with the increase of RCA replacement percentage. Research findings indicated that the incorporation of steel fibres could not only improve the energy dissipation capacity and the punching shear capacity of the slab, but also effectively improve the integrity of the slab tension surface and thereby changing the trend from typical punching failure pattern to bending-punching failure pattern. On the basis of the test, the punching shear capacity formula of RAC slabs with and without steel fibres was proposed and discussed.

Axial compression performance of composite short columns composed of RAC-filled square steel tube and profile steel

An axial compression test was conducted for 11 composite short columns composed of recycled aggregate concrete (RAC)-filled square steel tube and profile steel, to explore their axial compression behaviour. The following main design parameters of columns were considered: recycled coarse aggregate (RCA) replacement percentage, width-thickness ratio of square steel tube, profile steel ratio and RAC strength. The failure process and modes, load-displacement and load-strain curves and axial stiffness of specimens were obtained and analysed in detail. Results showed the similar failure process and modes of each specimen. Specifically, the profile steel yielded before the square steel tube, and the internal RAC was crushed subsequently. Bulging deformation was evident on square steel tube, thus indicating that the column lost its bearing capacity. With the increase in RCA replacement percentage and width-thickness ratio of the square steel tube, the axial bearing capacity of specimens decreased remarkably. However, the axial bearing capacity of columns increased with the increase in profile steel ratio and RAC strength. These design parameters remarkably influenced the initial stiffness of the short columns, but exerted minimal effect on stiffness degradation at the latter stage of loading. Overall, the composite short columns exhibited high bearing capacity and good deformability in the tests. On this basis, a calculation formula for the axial bearing capacity of the columns was established through theoretical analysis and by considering the adverse effects of RCA replacement percentage. The calculated results showed good agreement with the experimental findings, thus verifying the validity of the established formula. The research conclusions can provide references for engineering applications on this type of columns.

Compressive stress-strain relation of recycled aggregate concrete under cyclic loading

This paper has focused on the structural performance of recycled aggregate concrete (RAC) under both cyclic and monotonic loading. RAC specimens with different recycled coarse aggregate (RCA) replacement percentages of 0%, 25%, 50%, 75% and 100% were cast and tested. The compressive stress-strain relationship and the failure mode were investigated for each RCA replacement ratio. The effects of the RCA replacement percentage on the compressive mechanical properties of the RAC specimens including the strength, elastic modulus, peak strain, ultimate strain and Poisson's ratio were also studied. The RAC specimens have shown similar failure characteristics regardless of monotonic or cyclic loading. In addition, the compression skeleton curves of the RAC specimens under cyclic loading agree well with those under monotonic loading. Based on the experimental results, the characteristic points pertaining to the hysteresis loop were defined and their relations were established. Furthermore, the constitutive equations of the RAC as well as its simplified form were proposed and applied in numerical simulations of RAC columns and frames under cyclic loading. The proposed constitutive equations have shown promising accuracy in predicting the hysteresis performance of RAC on both component and structural levels.

Carbonated recycled coarse aggregate and uniaxial compressive stress-strain relation of recycled aggregate concrete

Carbonation treatment was employed to improve the quality of recycled coarse aggregate (RCA), and the RCA or carbonated RCA (CRCA) was used to prepare recycled aggregate concrete (RAC or RAC-C). The influence of the RCA replacement rate and CRCA on the mechanical properties and stress-strain relation of concrete was investigated. The results have shown that carbonation treatment enhances the physical properties and interfacial transition zone (ITZ) of CRCA, and effectively prevents the degradation in mechanical properties of concrete. Increased RCA or CRCA replacement rate reduces the peak stress and ascending slope and increases the peak strain of RAC or RAC-C. The stress-strain curve of RAC-C has higher ascending slope, peak stress and lower peak strain than that of RAC and is closer to that of natural aggregate concrete (NAC) due to the improved new ITZ. The stress-strain relation result agrees well with the proposed model.

Workability and mechanical property of low grade pumping concrete modified by recycled coarse aggregate

In recent years, the construction industry has entered a stage of rapid development in Chinawith more and more construction waste, which has a great negative impact on natural resources and environment. These building wastes can be processed into recycled aggregate by sorting, crushing and processing. This kind of technology can realize the recycling of construction waste [1]. In order to promote the research and application of recycled aggregate concrete, this paper probes into the effect of recycled coarse aggregate (RCA) on the performance of pump concrete. By using the orthogonal test to studied the impact of the amount of fly ash, replacement of RCA and change of sand rate on the mechanical properties of C30 recycled pump concrete (RPC). By adjusting water consumption to ensured RPC pump requirements. The pump concrete prepared by natural coarse aggregate (NCA) was treated as a control group, which was called natural pump concrete (NPC). The experimental results show that the best proportion of RPC, fly ash content, recycled aggregate content, sand rate respectively are 40wt%, 50wt% and 45wt%.

Experimental Study of Post-heated Steel Reinforced Recycled Concrete Columns Repaired with CFRP

The mechanical and thermal properties of steel reinforced concrete columns with CFRP reinforcement were examined after exposure to a high temperature of 500 oC. The concrete made with normal and recycled coarse aggregate (RCA) was fabricated and three different RCA replacement ratios (0, 50%, and 100%) were investigated. The fatigue properties of steel reinforced concrete with RCA and CFRP reinforcement were tested for two million cycles at a frequency of 2.5 Hz. The test results show that the failure of strengthened specimens is mainly caused by rupture of CFRP jacket and buckling of inner section steel reinforcement. However, for the unstrengthened specimen, both of inner steel buckling and core concrete cracking are the main contributors to the damage. The load-bearing capacity, deformation and energy dissipation of the specimens during the fatigue test could be strengthened greatly by CFRP reinforcement. However, the CFRP reinforcement has little influence on the improvement of the stiffness of the specimens, which may be caused by a plastic damage accumulation during the early cycles of fatigue tests. Finally, a static test was conducted on the post-fatigue specimens, the results showed that a large decrease in stiffness was observed for the specimens subjected to high temperature and fatigue, and the fatigue loading had a higher influence on the specimens than the high temperature.

Mechanical properties of sea sand recycled aggregate concrete under axial compression

The properties of axially loaded sea sand recycled aggregate concrete (SSRAC) were experimentally and theoretically investigated in this paper. The main parameters in the test are the sea sand chloride ions (Cl−) content and the recycled coarse aggregate (RCA) replacement percentage. The influences of sea sand Cl− and RCA content on the compressive strength, stress-strain relation and failure pattern of SSRAC were studied. Test results showed that both the strength and deformation of specimen changed with the variation of sea sand Cl− content and RCA replacement percentage. The compressive strength of SSRAC was higher than that of ordinary concrete. The elastic modulus increased, while the peak strain decreased due to the effect of sea sand. It was also indicated that the influence of recycled coarse aggregate replacement percentage on the properties of SSRAC decreased with increasing sea sand Cl− content. The Poisson's ratio and stress-strain curve of SSRAC were similar to those of ordinary concrete. Finally, a numerical expression for the stress-strain curves of SSRAC under axial loading was presented, which could be used in the theoretical and practical studies.

Influence of recycled coarse aggregate replacement percentage on fatigue performance of recycled aggregate concrete

The fatigue residual strength or stiffness of concrete refers to its strength or stiffness after a certain extent of fatigue loading. They decrease with loading cycles, a distinct feature of the fatigue process. To investigate the influence of recycled coarse aggregate (RCA) content on the fatigue performance of recycled aggregate concrete (RAC), an experiment about compressive fatigue residual strength on RAC with different replacement percentages was conducted. The results show that fatigue life, residual strength, and residual stiffness all decrease with an increase in RCA replacement percentage, with the smallest effect on stiffness. The residual strength and stiffness degradation curves of RAC were obtained by regression analysis and the replacement percentage effect on degradation laws was discussed. Furthermore, fatigue damage evolution was analyzed by defining the damage variable based on residual strength.

Characterization of pervious concrete with blended natural aggregate and recycled concrete aggregates

Abstract The utilization of recycled coarse aggregates (RCA) from construction and demolition wastes to produce green concrete serves as a sustainable solution with manifold environmental benefits. This study aims to widen the potential uses of RCA to fabricate pervious concrete for non-structural applications. The mechanical and surface properties, permeability, and greenhouse gases assessment of pervious concrete made with blended normal granite aggregates and RCA were investigated in this work. RCA replacement levels of 20%, 40%, 60%, 80% and 100% were used. Experimental results show that the RCA mixes have lower mechanical properties. Microscopic analyses show that the lower strength of RCA mixes was attributed to the failure path of RCA specimens which occurred at the weaker adhered mortar on RCA. Despite the drop in strength, all RCA-mixes attained the minimum BS EN 1338 requirements in terms of skid and abrasion resistance. In the mix with 100% RCA, the waste content in the pervious concrete mix was 87% by weight and 73% by volume. The greenhouse gases assessment also shows that the CO2 emission of this 100% RCA mix is 24% lower than the control mix.

Variability of stress-strain relationship for recycled aggregate concrete under uniaxial compression loading

Abstract Uniaxial compression loading tests were carried out to investigate the variability in stress-strain relationship of recycled aggregate concrete (RAC) due to intrinsic variability in properties of recycled coarse aggregates (RCAs). RCAs were selected from a single source to minimize the effects of potential variations in properties of waste concrete. Natural aggregate concrete (NAC) and RAC prisms were designed with different RCA replacement ratios but similar compressive strength. The results show that the RAC prisms have a similar failure pattern with that of NAC specimens. The RAC specimens were however found to have a lower elastic modulus and a higher peak strain. The variability of the peak stress, peak strain, elastic modulus and ultimate strain was found to follow a normal distribution. Based on the collected experimental data, a modified RAC stress-strain model was proposed. The RAC was found to possess a bit more brittle properties than NAC, as indicated by the steeper stress-strain curve's descending branch for the RAC. The variability of RAC stress-strain model was evaluated and the corresponding probability density function (PDF) and cumulative distribution function (CDF) were discussed.