Mechanical Properties Of Recycled Aggregate Concrete Research Articles

Experimental evaluation of mechanical properties and microstructure for recycled aggregate concrete collaboratively modified with nano-silica and mixed fibers

The present study was conducted to meet the demand of the construction schedule for emergency repair and construction in special projects by using the recycled aggregates produced by mechanically crushing the demolished materials on-site. The study aims to modify recycled aggregate concrete (RAC) by incorporating silica nanoparticles (NS) and mixed fibers together to meet the needs of the above special project. Here, the properties of 21 kinds of concrete with different NS contents and mixed proportions of fibers were tested, including their fresh properties, hardening properties and microstructure. Their working properties in the fresh state were studied by measuring slump and unit weight; while the mechanical properties after hardening were mainly evaluated in terms of compressive strength, splitting tensile strength, modulus of elasticity and flexural strength, and here the flexural toughness as well as the residual strength of the specimens were calculated using two methods. In addition, the effects of different NS contents, steel fibers and polyvinyl alcohol (PVA) fibers on crack development and water absorption were investigated in the microstructure. The pores between the cement matrix, interfacial transition zone (ITZ) and fibers and how they are alteredby NS were characterized by SEM and 3D-CT scans. All these results indicate that NS content has a significant effect on both the workability and mechanical properties of RAC, that steel fibers are beneficial to improve the overall mechanical index of RAC, while PVA fibers have a limited enhancement effect, and that NS particles in the microstructure help to fill the pores of 0.001–0.01 mm3 volume in the cement matrix and improve the performance of the ITZ.

Effect of nano-SiO2 modified recycled coarse aggregate on the mechanical properties of recycled concrete

Improving the performance of the interface between old mortar and recycled coarse aggregate (RCA) is a hot topic and important to enhance the properties of recycled aggregate concrete (RAC). In this paper, the RCA was soaked by nano-SiO2 (NS-RCA) then the water absorption and crushing index of NS-RCA were investigated. The mechanical properties, such as compressive strength, flexural strength, and elastic modulus of RAC prepared by NS-RCA (NS-RAC) were studied. The Thermogravimetric and Differential Thermal Analysis (TG-DTA) and scanning electron microscopy (SEM) were applied to analyze the properties of the interface transition zone (ITZ) around unmodified RAC and NS-RAC. A modified stress–strain model of NS-RAC was proposed considering the concentration of nano-SiO2 and soaking time. The testing results showed that the concentration of nano-SiO2 and soaking time had significant effects on the strength and durability of RCA and the mechanical properties of RAC. The 2% concentration of nano-SiO2 and 48 h soaking time had the best modification effect on RCA. The compressive strength, flexural strength, and elastic modulus of NS-RAC with best modification were 31.8%, 33.2%, and 89.6% higher than those of unmodified RAC respectively. The TG-DTA and SEM analyses indicated that NS-RAC had the denser microstructure of ITZ. This study is conducive to enrich the knowledge about using NS-RAC and supplying guidance for its mix design.

Bio-deposition approaches for sustainable execution of recycled aggregates in concretes

Our study offers a quantitative framework for microbial-induced calcium carbonate precipitation (MICP) to uplift the properties of recycled aggregate concrete (RAC). In this regard, a marine alkalophilic bacterium Bacillus sp. B6 was employed, and its growth and mineralization efficiency under seawater conditions was investigated. Optimization of MICP was achieved with different nutrient sources and bacterial introduction methods (dip and spray). The efficiency of treated recycled aggregates (RA) was determined by using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) in combination with basic technologies of density improvement and water absorption. The results show that the optimal nutrient sources of carbon and nitrogen are glucose (7 g L−1) and tryptone (5 gL−1), respectively. Spray treated recycled aggregate (RA) is reported to be efficient with a reduction in water absorption (∼19%), and improvement in bulk (∼2.4%) and apparent density (∼1.7%). The effectiveness of the MICP treatment process is confirmed with SEM and EDX observations, indicating the filling of microcracks with calcium carbonates. As such, the mechanical properties of RAC with spray treated RA significantly increase by up to ∼24% in compressive strength as compared to the control treatment. Current findings will help revitalize the construction industry by utilizing the MICP-treated RA and minimizing the load on natural aggregates.

Changing the soaking method of microbially induced calcium carbonate precipitation technology to improve the reinforcement effect of recycled concrete aggregates

In this study, the effects of the soaking method employed during the concrete reinforcement process on the properties of recycled concrete aggregates (RCAs) with different particle sizes were investigated based on biodeposited calcium carbonate technology. The microstructure and properties of RCAs and the macroscopic properties of recycled aggregate concrete (RAC) before and after the enhancement treatment were studied. The results showed that the presoaked bacterial solution can improve the reinforcement of RCAs, and the best performance of RCAs was obtained after reinforcement by soaking twice (first time, soaking RCAs into nutrient solution after presoaking with the bacterial solution (Method B), the next time soaking RCAs directly into mixed culture solution (Method A)). After immersing twice, the biodeposited calcium carbonate reinforced the defects of RCAs and coated the surface of RCAs. The mechanical properties of RAC were significantly improved owing to the use of the enhanced RCAs, and the RCAs with secondary soaking treatment endowed the concrete with superior mechanical performance.

Mechanical behavior and constitutive model of sustainable concrete: Seawater and sea-sand recycled aggregate concrete

Resources such as fresh water and river sand have become scarce in some areas around the world because of the considerable increase in infrastructural construction. To overcome this issue, the utilization of recycled aggregates (RAs) in concrete is considered a sustainable construction method. Due to the growing scarcity of river sand and fresh water, this study explores the mechanical properties of recycled aggregate concrete (RAC) incorporated with seawater (SW) and sea sand (SS), referred to as SWSSRAC. To this end, a total of 18 mix ratios were designed to analyze the effects of different water-to-cement ratios, curing ages, and RA replacement rates on the mechanical properties of the SWSSRAC. The results suggest that the fluidity of SWSSRAC is slightly worse than that of RAC; further, the effect of the RA replacement rate on the fluidity of concrete is greater than that of SW and SS. The stress–strain relationship reveals that the deformation capacity of SWSSRAC at curing ages of 28 and 180 days show a higher improvement attributed to SW and SS for RAC compared to that for natural aggregate concrete (NAC). In addition, using SW and SS improves the compressive strength and elastic modulus of RAC, particularly after curing for 28 days; the enhancement effect of SW and SS on the mechanical properties of RAC is higher than that of NAC. Although the unloading segments in the stress–strain relationship of SWSSRAC are different from those of RAC at the 28-day curing age, it is necessary to use constitutive models of RAC for SWSSRAC considering long-term use. According to the findings of this study, SW and SS are more suited for RAC than NAC.

Influence on mechanical properties and microstructure analysis of hybrid fiber recycled aggregate concrete after exposure to elevated temperature

The use of recycled aggregate concrete (RAC) in construction is one of the most effective ways to solve the environmental problems of concrete waste. The purpose of the present study is to improve the high-temperature resistance of RAC by incorporating hybrid cellulose and basalt fibers. The mechanical properties of the specimens with different volume fractions of cellulose and basalt fibers after high temperature were studied. Additionally, in order to study the degradation behavior of the specimens, the microstructure of interface between fibers and the cement matrix of RAC was examined by scanning electron microscope. Results show that hybrid fiber can reduce the explosive spalling and mass loss of RAC after being subjected to high temperatures. Compared with the brittle failure of RAC, the failure mode of hybrid fiber recycled aggregate concrete (HFRAC) was transformed into ductile failure under compression and splitting test. After high temperature, the compressive strength and splitting tensile strength of HFRAC were higher than those of RAC, and the cellulose–basalt fibers displayed an excellent synergistic effect on the mechanical properties of RAC. Among all the RAC specimens with different volume fractions of cellulose and basalt fibers, specimen hybrid with 0.15% cellulose fiber and 0.15% basalt fiber showed the best mechanical properties. Microstructure analysis research shows that small channels can be left in the matrix after the melting of cellulose fiber after elevated temperature, which improves the permeability of concrete and reduces the spalling damage of RAC.

Review of the Strengthening Methods and Mechanical Properties of Recycled Aggregate Concrete (RAC)

Replacing natural aggregate (NA) with recycled aggregate (RA) has contributed to the trend of sustainable development in civil construction. With this background, improvements in the mechanical properties of recycled aggregate concrete (RAC) and the scientific design of the mixture ratio are attracting more concern in recent years. This paper is a review of the recent research, including the following aspects: the mixture design of RAC; the improved mechanical properties of recycled concrete with steel fibers; and the performance of the main components. In addition, the primary composition materials, properties, and calculation methods of the mixture ratio of RAC are summarized. The mechanical properties, durability and microscopic analysis of RAC are also discussed. The accurate calculation of mixture proportion can significantly facilitate the work of preparing a test mix of RAC. Through the mixture-ratio optimization and physical and chemical strengthening of RA, the mechanical properties of RAC can be improved to promote the wider application of this eco-friendly material.

Utilization of molybdenum tailings as fine aggregate in recycled aggregate concrete

The increasing emissions of construction waste and industrial by-products have caused a serious burden on the environment. The shortage of natural coarse aggregate (NCA) and river sand provides the impetus for the reuse of solid waste. This research provides a cleaner option for the production of recycled aggregate concrete (RAC) from industrial by-product molybdenum tailings (MTs). MTs are used as alternative material to river sand (10%, 30%, 50%, 70% and 100%). Three types of concrete natural aggregate concrete (NAC), RAC, and MTs recycled aggregate concrete (MTs-RAC) were prepared. Firstly, the mechanical properties of the specimens were tested, including compressive strength (fcu) and splitting tensile strength (fst), and the digital image correlation (DIC) system was used to evaluate the strain field distribution. Then, the freeze-thaw (F-T) cycle corrosion resistance of concrete was evaluated. Subsequently, the pore structure was visualized and quantitatively analyzed based on industrial CT technology. The evolution of corrosion resistance of MTs-RAC was confirmed by microstructure. Finally, the economic efficiency factor (EEF) and environmental impact (EI) were evaluated. The experimental results showed that the appropriate amount of MTs significantly improved the pore structure and mechanical properties of RAC, and the fcu of RAC with a 50% MTs replacement rate increased by a maximum of 14.4%, which could achieve the same mechanical properties as NAC. However, the combination of excess MTs and recycled coarse aggregate (RCA) increases the porosity of concrete. The F-T cycle resistance of RAC decreased with the increase of MTs replacement rate. The increase in the proportion of large pores (>10 mm3) is the main factor leading to the destruction of F-T cycles. On balance, the replacement rate of MTs for use in RAC should not exceed 50% in salt lakes and cold regions. The results are helpful to understand the influence mechanism of MTs on RAC performance and provide the theoretical basis for the application of MTs in RAC.

Mechanical properties and microstructure of nano-strengthened recycled aggregate concrete

Abstract The surface adhesion mortar of recycled coarse aggregate (RCA) is the main factor leading to poor aggregate quality, and it also affects the internal structure and mechanical properties of recycled aggregate concrete (RAC). To improve the quality of RCA and mechanical properties of RAC, self-developed mortar removal equipment was used to strengthen the RCA. Then, the RCA was soaked in 1, 2, and 3% nano-silica solutions, and the vibration-mixing process was used to improve the quality of RAC. In addition, the microstructure of the RAC was examined via scanning electron microscopy to observe its improvement effect on the microstructure of the RAC. The results indicated that the quality of the RCA was improved by mechanical and physical strengthening, and the water-absorption rate and crushing value decreased by 32.9 and 23.9%, respectively. The improvement effect of nano-immersion on the RAC was obvious. The optimal condition was a combination of physical strengthening, 2 days of immersion in 2% NS solution, and vibration stirring. The 28 day compressive strength increased by 31.3%, the splitting tensile strength increased by 23%, and the flexural strength increased by 49%. The proposed strengthening method improves the mechanical properties and microstructure of RAC. The results of this study provided a technical reference for the mechanical strengthening of RAC and promotion of the application and popularization of RAC.

Efficiencies of carbonation and nano silica treatment methods in enhancing the performance of recycled aggregate concrete

This study compared the efficiencies of five recycled aggregate treatment methods (pressurized gas–solid carbonation (PC), flow-through gas–solid carbonation (FC), wet carbonation (WC), nano-silica (NS) spraying and combined PC with NS spraying (PCNS)) in enhancing the performance of recycled aggregate concrete (RAC). Mechanical properties, durability and microhardness of RACs were evaluated. The results showed that PC method recorded higher enhancing efficiency than both FC and WC method. NS spraying method caused higher improvement in mechanical properties of RAC than three carbonation methods. Because of the synergistic effect of enhanced old mortar and new ITZ, PCNS method recorded the highest efficiency.

The Simple Mix Design Method and Confined Behavior Analysis for Recycled Aggregate Concrete.

For the environment protection and sustainable development in building construction, waste concrete can be processed into recycled aggregate to mix the recycled aggregate concrete (RAC). However, the existing mix design methods of RAC were complex, and the mechanical properties of RAC were more weakened than ordinary concrete. This paper presents a simple mix design method for RAC, including orthogonal test and single-factor test. Then, in order to study the behavior of confined RAC, this paper presents a comprehensive experimental study on the RAC filled in steel tube (RCFST) specimens and the RAC filled in GFRP tube (RCFST) specimens. The results show that the proposed mix design method can mix different stable strength grades of RAC promptly and efficiently. In addition, the steel tube and GFRP tube can provide a well confining effect on core RAC to improve the mechanical behavior of column. Moreover, the properties of core RAC in steel tube are the same as the common passive confined concrete, and the properties of core RAC in the GFRP tube are the same as the common active confined concrete. The study results can provide reference for other kinds of RAC mixtures as well as be a foundation for theoretical studies on confined RAC.

Effects of aggregate packing optimization and cement paste volume on the properties of natural and recycled aggregate concrete

AbstractThis paper investigates the influence of aggregate packing optimization based on a particle packing method (PPM) and cement paste volume (CPV) on the workability and mechanical properties of both natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). The slump, compressive strength, flexural strength and Young's modulus of concrete were first examined, followed with the characterization of macro‐pore structure inside RAC by using X‐ray computed tomography (CT). The results indicate that the PPM can help to densify the granular skeleton of aggregates in concrete by reducing the void around the aggregates and the cement paste film thickness, and subsequently enhances the mechanical properties of the concrete with a constant CPV. This enhancement is higher for RAC than NAC, particularly for the Young's modulus. The particle packing optimization can also decrease the number of macro pores in RAC, contributing to the enhancement in the mechanical properties of RAC. Moreover, increasing CPV in concrete with a maximum aggregate packing status considerably decreases the mechanical properties of concrete, whereas increases its workability. This is mainly caused by the increased number of macro pores in the cement paste and at the interfaces between RCAs and hardened cement paste.

The mechanical and interfacial properties of concrete prepared by recycled aggregates with chloride corrosion media

Abstract Recycled aggregates (RA) prepared by concrete suffering a long-term service inevitably carried chloride corrosion media, which would lead to some effects on performance of recycled aggregate concrete (RAC) – concrete prepared by RA- from the inside. Hence, this research evaluated the effect of RA with different corrosion degree, which were soaked in 3%, 5% and 7% NaCl solution for 120 days respectively, on the mechanical properties of RAC and analyzed the dissolution characteristics of chloride element in cement mortar by SEM-EDS, moreover, the performance change of interfacial transition zones (ITZs) was also studied via microhardness test and micro tests (SEM, EDS and XRD). The results showed that Cl− carried by RA partly diffused into the cement mortar, while most of them distributed in the ITZs, and the Cl− accelerated the cement hydration and produced a small amount of Friedel’s salt to optimize the pore structure, which did well in improving the strength and the performance of ITZs between old mortar and new mortar (OM-NM), old aggregate and new mortar (OA-NM), in early stage. However, with the increase of RA’s corrosion degree and concrete’s ages, the amount of internal corrosion products, Friedel’s salt etc., would be more, and it caused the later strength reduction and the interfacial performance in OM-NM and OA-NM to became poor.

New hybrid basalt/E-glass FRP jacketing for enhanced confinement of recycled aggregate concrete with clay brick aggregate

Recycled aggregate concrete (RAC) is more sustainable, eco-friendly, and cost-effective as compared to natural aggregate concrete (NAC). Among recycled aggregates (RAs), clay brick aggregate (CBA) has the potential of being the most widely used RAs because of the considerable amount of clay brick waste generated in many countries. The compressive behavior and mechanical properties of RAC with CBA are highly influenced by the mechanical properties of bricks. The stiffness and compressive strength of RAC with CBA are reported marginally lower than the natural aggregate concrete (NAC). In the past, different types of fiber reinforced polymer (FRP) composites such as carbon FRP, glass FRP, and aramid FRP have been investigated to enhance the strength and stiffness of the RAC with CBA. However, the behavior of hybrid FRP confined RAC with CBA is not yet clear. In this study, the performance of a new, low-cost and high-performance hybrid composite to enhance the strength and stiffness of the RAC with CBA is investigated. Hybrid composite is developed by using natural Basalt fiber and E-glass fibers (Chopped Strand Mat) along with the use of high-performance polyester resin. Three types of bricks (having different strength and water absorption) were used to produce CBA. Other research parameters included were the strength of RAC with CBA and the number of layers of hybrid basalt/E-glass fiber reinforced polymer (BE-FRP) composite. A total number of 36 concrete cylinders (12 un-confined and 24 confined with BE-FRP) were tested under pure axial compressions. The results indicate that the BE-FRP composites are highly suitable to enhance strength, stiffness, and ductility of the RAC with CBA. Also, there was found a significant increase in strength and ductility with an increase in the confinement level. In the end, the efficiency of existing strength and stain models was assessed to predict the ultimate strength and strain of the BE-FRP confined RAC with BAC.

Influence of mix composition on the properties of recycled aggregate concrete

AbstractThere is an increasing trend towards using recycled aggregate (RA) in concrete due to the shortage of high quality natural aggregates. The use of RA in concrete results in the conservation of natural resources, protects the environment and encourages sustainable construction. Though some studies have been conducted on the use of recycled aggregate concrete (RAC), the effect of mixture composition on its properties has not been well addressed. In the reported study, the effect of mixture composition, namely cement content and water/cement ratio and the proportion of RA on the mechanical properties of RAC was evaluated, with the intention of developing varying grades of RAC. As reported in earlier studies, the properties of RAC were generally inferior to that of normal aggregate concrete (NAC). Notwithstanding this, RAC with acceptable mechanical properties can be produced utilizing RA, for example RAC with low strength can be used in non‐structural applications. The construction industry should be encouraged to use RAC in building construction; as its use will lead to technical, economic and environmental benefits. Further, the use of RAC will lead to a sustainable development of the construction industry, particularly in regions that lack good quality natural aggregates. Based on the data developed in the reported study, the following quantities of RA are recommended to produce RAC: (i) 20% to produce low strength (20–30 MPa) concrete, (ii) 40% to produce medium (30–50 MPa) concrete and high strength (more than 50 MPa) concrete. Mathematical correlations between the mechanical properties of RAC with varying mix design parameters, such as cement content and water cement ratio and the quantity of RA, are also reported. These correlations can be used to predict the properties of RAC prepared with other proportions of RA and mix design parameters.

Metakaolin modified recycled aggregate concrete containing recycled steel fibers

Potential challenges are facing the construction industry as results of the environmental issues caused by its activities. The use of recycled coarse aggregate (RCA) and recycled-steel fibers (RSF) in the production of concrete can be employed to mitigate the impact of these issues. In this experimental research, the performance of recycled-aggregate concrete (RAC) containing recycled coarse-aggregate (RCA) and recycled steel fibers (RSF) is studied. This study examines the workability and mechanical properties of RAC where the natural-coarse aggregate (NCA) is totally replaced with RCA. The effect of replacing the cement with 15% of Metakaolin (MK) and the addition of 12 kg.m−3, 24 kg.m−3 and 36 kg.m-3of RSF on the mechanical related properties of RAC is assessed. Five concrete mixtures containing RCA (one without MK, one with MK but without RSF and three with MK and RSF) were examined. One more mix (reference mix) was made with NCA for comparison reasons. It was concluded that RCA reduces the workability by 23% and the strength characteristics such as (compressive, flexural and splitting tensile strength) of concrete by 29%, 19% and 17%, respectively. Also, it was found that MK and RSF diminish the workability of the RAC. But, MK and RSF can help compensate the loss of strength properties due to the use of RCA.

Recycled Aggregate Concrete Made with Silica Fume: Experimental Investigation

This research deals with the behavior of recycled aggregate concrete (RAC). In this study an experimental work was undertaken. The study examines the effect of using recycled coarse aggregate (RCA) on the workability and the mechanical performance of RAC. The influences of using silica fume (SF) as cement replacement material on the performance of RAC were also examined. Silica fume was used at four contents (5%, 10%, 15% and 20%). The total number of mixes was six. Four mixes of RAC made with these four contents of SF, one RAC mix was made without SF and one mix was made with natural coarse aggregate (NCA) as a reference mix. The outcomes of this study reveal that workability and mechanical performance of RAC are lower than that made with NCA. Also, Silica fume has an adverse influence on workability of the RAC. However, the silica fume possesses a positive influence on mechanical properties of RAC. Silica fume can be used at contents of (10-20)% of cement mass to obtain mechanical performance for the RAC comparable to the concrete includes NCA.

Experimental investigation on the mechanical properties and microstructure of hybrid fiber reinforced recycled aggregate concrete

The use of recycled aggregates in structural concrete is a sustainable solution to reduce the exploitation of natural resources and the harmful environmental effects of concrete waste. The present study aimed to improve the mechanical performance of recycled aggregate concrete (RAC) by incorporating hybrid steel and polypropylene fibers. Sixteen concrete mixtures with different volume fractions of steel and polypropylene fibers were tested. Mechanical properties were studied by conducting the compressive strength, splitting tensile strength, flexural strength and flexural toughness as well as impact resistance. Additionally, the microstructures of interfacial transition zone (ITZ) at aggregate/cement paste and fiber/cement paste were investigated through the scanning electron microscope (SEM). Results indicated that the incorporation of polypropylene fibers resulted in a minor change in compressive strength of RAC. Whereas, the steel fibers significantly increased compressive and flexural ductility and impact resistance especially in the mixtures made with hybrid steel and polypropylene fibers. The use of hybrid steel and polypropylene fibers exhibited an excellent coupling effect on the mechanical properties of RAC that was better than steel fiber and polypropylene fiber. Among all the mixtures with different volume fractions of steel fibers and polypropylene fibers, the hybrid fiber reinforced RAC specimen containing 1.5% steel fibers and 0.9% polypropylene fibers exhibited the best mechanical properties. SEM investigations showed that the incorporation of fibers into RAC could not only make an overall improvement in the density and uniformity of cement paste, but also improved the microstructures of ITZ. Moreover, the bonding between steel fiber and cement paste was found to be tight, and the interfacial zone was integral and dense. These observations provide insight into the benefits of different fiber reinforcement systems to the mechanical performance of RAC which is considered to have poorer quality compared with natural aggregates concrete.

Influence of basalt fiber on physical and mechanical properties of treated recycled aggregate concrete

This paper investigates the effect of the treatment methods on the physical and the mechanical properties of recycled aggregate concrete (RAC). The optimized Ball Mill Method (oBMM) and the incorporation of basalt fiber (BF) in concrete were employed as treatment process and the combination of oBMM and BF were utilized in this experimental study. It was intended using the treatment methods that the application of oBMM on recycled aggregate (RA) cleaned the most part of attached old mortar (AOM) content in RA and the incorporation of BF in concrete eliminated the adverse effects of remaining AOM in treated RA (tRA) strengthening mortar phase of concrete. Hence, to observe the improvement impact of treatment on the performance of concretes, twenty-eight concrete series including natural aggregate (NA), 20–40–60% RA and 20–40–60% tRA with 0–0.25–0.50–1.0% BF were produced in the laboratory. The physical and the mechanical tests were conducted on concrete specimens at the age of 28 days.According to the test results, although the physical properties were negatively affected by the incorporation of RA and tRA with/without BF in concrete, the mechanical properties of RACs and tRACs were improved by the incorporation of BF. Besides, the impact of treatment were significantly observed, especially for higher rates of RA (60%). The optimum proportion of BF was found as 0.50% BF with 60% tRA regarding compressive strength test results only.

Numerical Studies on Damage Behavior of Recycled Aggregate Concrete Based on a 3D Model.

This paper develops a 3D base force element method (BFEM) based on the potential energy principle. According to the BFEM, the stiffness matrix and node displacement of any eight-node hexahedral element are derived as a uniform expression. Moreover, this expression is explicitly expressed without a Gaussian integral. A 3D random numerical model of recycled aggregate concrete (RAC) is established. The randomness of aggregate was obtained by using the Monte Carlo random method. The effects of the recycled aggregate substitution and adhered mortar percentage on the elastic modulus and compressive strength are explored under uniaxial compression loading. In addition, the failure pattern is also studied. The obtained data show that the 3D BFEM is an efficient method to explore the failure mechanism of heterogeneous materials. The 3D random RAC model is feasible for characterizing the mesostructure of RAC. Both the substitution of recycled aggregate and the percentage of adhering mortar have a non-negligible influence on the mechanical properties of RAC. As the weak points in the specimen, the old interfacial transition zone (ITZ) and adhered mortar are the major factors that lead to the weakened properties of RAC. The first crack always appears in these weak zones, and then, due to the increase and transfer of stress, approximately two-to-three continuous cracks are formed in the 45°direction of the specimen.