Recycled Aggregate Concrete Mixtures Research Articles

Modeling green recycled aggregate concrete using machine learning and variance-based sensitivity analysis

Recycled aggregate concrete (RAC) is commonly used to lessen the environmental effect of concrete building and demolition waste. The compressive strength of the RAC is one of the most critical factors influencing concrete quality. The compressive strength is assessed by a compression test, which takes a large number of materials and is expensive and time-consuming. With the development of novel concrete mixes and applications, academics are obliged to seek accurate models for forecasting mechanical strength. A significant source of difficulty in compressive strength modeling is that there are many mixture components and testing conditions whose variation significantly influences the predicted values. To this end, this study explores the mixture design of sustainable concrete in order to generate eco-friendly concrete mixes. Tests are conducted on 18 different mixtures comprising different proportions of waste tires, plastic, cement, and red brick to experiment with new green RAC mixtures. For the modeling part, the deep residual neural networks (DRNNs) method is first presented to the problem, aided by a database from the literature for a pretraining task. The proposed DRNNs structure uses shortcuts (i.e., residual connections) that bypass some layers in the deep network structure to alleviate the problem of training with high accuracy. The performance of the proposed DRNNs is evaluated using different goodness of fit measures and compared with well-known machine learning tools. The findings showed that the suggested model could provide credible predictions about the desired mechanical parameter, saving the required lab efforts by 40 %. Finally, a variance-based global sensitivity analysis is performed with the Latin hypercube simulation method to help rank/prioritize each mixture component's impact on determining the compressive strength in practice while mitigating the potential misrepresentation of results due to the correlations between the input parameters. The analysis showed that cement and waste contents are the most significant ones in their first and total order effects.

Feasibility of recycled concrete aggregate stabilized with one-part geopolymers as semi-rigid inclusion columns

Recycled concrete aggregate (RCA) is a voluminous solid waste material derived from the construction sector and is typically stockpiled in landfills. In recent years, the ground improvement industry has grappled with challenges stemming from the depletion of natural quarry materials, resulting in a skyrocketing of their prices and increased project costs. This research investigated the feasibility of using RCA stabilized by one-part geopolymers to produce an innovative semi-rigid inclusion column system for ground improvement of soft soils. Na2SiO3-anhydrous was used as a sole solid activator for the activation of fly ash (FA), slag (S) or a binary precursor (FA+S) in the stabilization of RCA. The unconfined compressive strength (UCS) and microstructure of the stabilized mixtures have been examined with respect to different binder formulations and curing conditions. The permanent deformation characteristics of mixtures under cyclic loading were evaluated through repeated load triaxial (RLT) tests to replicate the moving wheel loads imposed on the semi-rigid inclusion columns. In addition, the cost and environmental impacts of the optimum mixtures suggested in this research were studied. The test results indicated that stabilizing RCA with as low as 5% one-part alkali-activated FA, S or (FA+S) met the minimum strength requirement (1.034 MPa) for ground improvement work. Compared with standalone FA and S geopolymer stabilized RCA mixtures, (FA+S) geopolymer stabilized RCA mixtures were identified as preferred industrial formulations due to their prolonged setting time for ease of mixing and handling when used in stone column applications. It was found that curing temperature and duration played a pivotal role in the strength gain of the mixtures. The RLT test results demonstrated that implementing the optimum RCA + 5%(FA+S) mixture as identified in this study for semi-rigid inclusion columns, led to a reduction in permanent strain values by approximately 90% compared to conventional unbound stone columns. The comparison between the optimum mixture highlighted in this study with other stabilization methods showed that the semi-rigid inclusion columns had great potential to enable large-scale production, cost and emission reduction in future ground improvement projects.

A framework for low-carbon mix design of recycled aggregate concrete with supplementary cementitious materials using machine learning and optimization algorithms

This study presents a framework for designing low-carbon and cost-effective mixtures of recycled aggregate concrete (RAC) with supplementary cementitious materials by integrating machine learning and grey wolf optimizer algorithms. The concrete mix design process considers key performance parameters such as compressive strength, chloride ion penetration resistance, and carbonation resistance. A dataset comprising 5306 data samples from 154 scientific resources is collected from the literature to train the machine learning models. Four different techniques, namely random forest, extreme gradient boosting (XGBoost), light gradient boosting (LightBoost), and category boosting (CatBoost) are employed to model the compressive strength, chloride ion penetration, and carbonation resistances of RAC. The best-performing models are then utilized to optimize the RAC mix design by minimizing the cost and reducing the carbon footprint. The results indicate that the CatBoost model demonstrates better predictive performance for the compressive strength and carbonation resistance, while the XGBoost and LightBoost models perform better in estimating chloride ion penetration resistance. Furthermore, the adoption of low-carbon mix design principles leads to a reduction in carbon footprint by 5.0% to 31.5% compared to cost-effective mix design for different compressive strength targets, with varying permeability levels. The framework provides a promising approach for designing environmentally friendly RAC mixtures while considering economic and durability factors.

Performance of recycled aggregate concrete using copper slag as fine aggregate

The present study experimentally investigates the mechanical and durability performance of recycled aggregate concrete (RAC) incorporating copper slag as fine aggregate. The coarse aggregate obtained from recycling of construction waste is used as natural coarse aggregate and copper slag, the industrial by-product is used as fine aggregate in the current research work. Recycled aggregate concrete formed by substituting 50 % recycled aggregate as natural coarse aggregate is considered as the control mix for this experimental work. A total of seven RAC mixtures are made with copper slag as a substitution of fine aggregate of varying proportions (0%–100 %) giving an increment of 20 %. Compressive strength, split tensile strength, and microstructural behaviour of RAC mixtures were carried out for up to 90 days of curing to assess the mechanical property of RAC mixes. To evaluate the effect of copper slag on long-term properties of RAC mix water absorption, rapid chloride permeability and resistant to sulphate attack test is carried out for up to 90 days. The findings revealed that the mechanical properties of RAC mixes are improved up to 40 % substitution of copper slag. When exposed to sulphate, RAC mixtures gained weight while losing compressive strength. Results of water absorption and RCPT test showed a remarkable improvement with the incorporation of copper slag up to 40 %; beyond that point, the results were comparable to RAC mix (control). The progression of calcium silicate hydrate gel formation within the RAC blend was verified through scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analysis across a range of curing periods spanning from 7 to 90 days.

Influence of the ANN Hyperparameters on the Forecast Accuracy of RAC's Compressive Strength.

The artificial neural networks (ANNs)-based model has been used to predict the compressive strength of concrete, assisting in creating recycled aggregate concrete mixtures and reducing the environmental impact of the construction industry. Thus, the present study examines the effects of the training algorithm, topology, and activation function on the predictive accuracy of ANN when determining the compressive strength of recycled aggregate concrete. An experimental database of compressive strength with 721 samples was defined considering the literature. The database was used to train, validate, and test the ANN-based models. Altogether, 240 ANNs were trained, defined by combining three training algorithms, two activation functions, and topologies with a hidden layer containing 1-40 neurons. The ANN with a single hidden layer including 28 neurons, trained with the Levenberg-Marquardt algorithm and the hyperbolic tangent function, achieved the best level of accuracy, with a coefficient of determination equal to 0.909 and a mean absolute percentage error equal to 6.81%. Furthermore, the results show that it is crucial to avoid the use of overly complex models. Excessive neurons can lead to exceptional performance during training but poor predictive ability during testing.

Implementation of two-stage mixing approach to improve the performance of fiber reinforced concrete for sustainable construction

Concrete has a significant impact on the environment, and the use of fibers in concrete is a way to mitigate its environmental impact. In this study, two-stage mixing approach (TSMA), typically utilized to enhance the quality of the interfacial transition zone (ITZ) of recycled aggregate concrete mixtures, was employed to enhance the performance fiber reinforced concrete (FRC) mixtures by improving the fiber–matrix ITZ. To investigate the effectiveness, FRC mixtures were prepared using standard (ordinary) and modified (TSMA) mixing approaches. Subsequently, their mechanical properties were measured, and microstructural analyses were conducted to examine fiber–matrix ITZ. In the end, a case study for a concrete pavement was carried out to examine the effect of improved performance on the cost and environmental impact of FRC. Based on the results, up to a 30.6% increase in FRC residual flexural strength ratio was obtained for modified mixing method, without considerable change in strength and stiffness. Microstructural analyses were found to support the ITZ improvement provided by the employed mixing methodology. Furthermore, material-related cost and environmental impact values were found to decrease up to 6% based on the case study conducted. As a result, the implementation of TSMA for FRC was found to be a promising technique to enhance FRC performance and suggestions were provided for the future studies to further improve the obtained benefits.

Durable Structural Concrete Produced with Coarse and Fine Recycled Aggregates Using Different Cement Types

The durability properties of structural recycled aggregate concrete (RAC) produced with 50% coarse recycled concrete aggregates and up to 20% fine recycled concrete aggregates were analysed and compared to those of conventional concrete (NAC). Both the RAC and NAC mixtures achieved the same compressive strength when using an effective water–cement ratio of 0.47 and 0.51, respectively. All the concretes were produced using three types of cement: CEM II A/L 42.5 R, CEM II A/S 42.5 N/SRC and CEM III/B 42.5 N-LH/SR. The properties of drying shrinkage, chloride permeability, and accelerated carbonation coefficient of the concretes were determined experimentally, and the obtained results were compared with the values estimated by specific standards of exposure to XC1–XC4 (corrosion induced by carbonation can happen due to the presence of humidity) and XS1 (corrosion caused by chlorides from seawater) environments. The results showed that all the concretes achieved maximum drying shrinkage for use in structural concrete. Any concretes produced with CEM IIIB, including the RAC-C50-F20 concrete, achieved very low chloride ion penetrability, ranging between 500 to 740 Coulombs. In addition, all concretes manufactured with CEM IIAL and CEM IIAS, including RAC-C50-F20, were suitable for use in XC3 and XC4 exposure environments, both with 50- and 100-year lifespans.

Neural network modeling of rutting performance for sustainable asphalt mixtures modified by industrial waste alumina

Considerable efforts have been devoted to developing a sustainable approach to road construction. The use of recycled concrete aggregate (RCA) obtained from construction-demolished concrete as a substitute for natural aggregate (NA) has increased interest. However, the inferior performance of the resulting RCA mixtures requires adding other improvement materials. To build on the few existing works in this area, the present study investigated the role of waste alumina (Al) as a reinforcement agent when added at rates of 1 %, 2 %, and 3 % by mixture weight. The experimental program consisted of volumetric properties analysis accompanying the Marshall test, dynamic creep test, and wheel tracking test. This study revealed that RCA-mixtures reached their typical Marshall and volumetric properties at 4.5 % binder content recording an increasing increment of 10 % compared to NA-mixtures which needed only 4.1 % binder content. Overall, all the utilized Al dosages improved the rutting resistance; optimally, 2 % of Al decreased the rutting depth by 26 %. This dosage also increased the index of plastic deformation, resilient modulus, and flow number values by 30 %, 16 %, and 23 %, respectively. The artificial neural network statistical technique produced a robust model (R 2 = 0.995) correlating the performed tests’ outcomes with rutting values.

Study on the durability of eco-friendly recycled aggregate concrete with supplementary cementitious materials: The combined action of compound salt solution of MgSO4, Na2SO4, and NaCl and dry-wet cycles

Focusing on eco-friendliness and sustainability, recycled aggregate concrete (RAC) has been recently substituted for natural aggregate concrete (NAC) in new constructions. In Northwest China, high-concentration corrosive ions of magnesium, sulfate, and chloride exist in soil and groundwater, which have a severe adverse effect of exposing RAC’s durability. To improve the efficient utilization of RAC in the environment of the aggressive ion, the durability experiment of eco-friendly RAC with supplementary cementitious materials (SCMs) under the combined action of 7.5 %Na2SO4 + 7.5 %MgSO4 + 5 %NaCl and dry-wet cycles was investigated. Results show that RAC with the ternary blend of cement-fly ash-granulated blast furnace slag had the best durability among all the RAC mixtures. The 10 % fly ash + 20 % silica fume and 10 % fly ash + 20 % metakaolin negatively affected the durability improvement of RAC. At the same D&W cycles, the relative content of hydration and corrosive products of RAC with SCMs was lower than that of RAC without SCMs, and Friedel’s salt and Mg10(OH)18Cl2·5H2O were not found. The mineral phase composition of RAC exposed to the compound salt solution was related to the relative content of portlandite. Furthermore, grain volume increasing from brucite and gypsum, salt crystallization pressure from blödite and MgCl2, and solid volume changing from thenardite to mirabilite mainly degraded RAC’s durability.

Mechanical properties of concrete produced with alkali-activated slag-fly ash and recycled concrete aggregate and designed using the densified mixture design algorithm (DMDA) method: Effects of recycled aggregate content and alkaline solution

The purpose of this study was to evaluate the mechanical properties of concrete specimens produced with recycled aggregate (RA) from construction demolition waste (CDW) based on alkaline activated slag-fly ash (AASF). The recycled aggregate concrete mixtures (RAC) were designed using DMDA method, with RA used as a 30%, 40%, and 50% partial replacement for natural aggregate (Category 1) and with Na2O doses of 4%–8% and modulus ratios of 0.6–1.4 (Ms = SiO2/Na2O; Category 2). The results showed that the inclusion of RA negatively affected the mechanical properties of RAC specimens, with recycled coarse aggregate exhibiting less of a negative effect than recycled fine aggregate. The concrete mixtures exhibited mechanical strength values of 20.7–35.9 MPa and UPV values of 3692–4200 m/s at 28 days of curing age. Concrete characteristics were significantly better in the mixtures produced using higher alkaline concentrations than in those produced using lower alkaline concentrations.

Autogenous and drying shrinkage of structural concretes incorporating recycled concrete aggregates from different sources

AbstractThe main relevant difference between recycled concrete aggregates (RCAs) in comparison with the companion natural ones, is the presence of the Attached Mortar content which confers to the RCAs higher porosity and, consequently, higher water absorption capacity. In the last decades, several studies have been performed worldwide for unveiling the role of the employed RCAs on the resulting concrete mixture performances at both fresh and hardened states. On the other hand, the effects of RCA on the early‐age and/or long‐term concrete deformations (e.g., shrinkage) are still very limited. In this context, this article summarizes the results of a wide experimental campaign aimed at evaluating the influence of RCAs on the autogenous and drying shrinkage of normal (35 MPa) and high (60 MPa) strength recycled aggregate concrete (RAC) mixtures. A total of 10 mixtures were realized by considering the variation of both the original source and size of employed RCAs. The results showed a clear correlation between the intrinsic properties (i.e., Attached Mortar content) of the employed RCAs and the resulting concrete deformation. Moreover, although the drying shrinkage is higher for RAC mixtures, the presence of a more porous aggregates mitigates the observed autogenous shrinkage. Consequently, the overall total shrinkage result to be almost unaffected by the presence of the recycled particles.

Durability and life prediction analysis of recycled aggregate concrete with ceramic waste powder under freeze-thaw conditions based on impact-echo method and Grey-Markov model

Utilizing recycled aggregate concrete (RAC) for cyclic usage in building materials is one of the most feasible methods for reducing the demand for natural aggregates in the construction sector and disposing of construction and demolition trash in landfills. Previous research has demonstrated that the weak freeze-thaw (F-T) resistance of RAC poses a significant threat to the safety of RAC structures in severe cold regions. Therefore, this paper explores the influence of ceramic waste powder (CWP) at various replacement rates on the freeze-thaw resilience of RAC. In this experiment, six groups of CWP doping ratios of 0%, 10%, 20%, 30%, 40, and 50% were designed. Before the F-T cycling test, each group of specimens’ basic mechanical and physical performance data was measured throughout the regular curing age. At the conclusion of each F-T cycle, the durability performance of RAC was tested using the impact-echo method and compressive strength test. To predict the lifetime of RAC mixtures, a Grey-Markov model was created. It was found that the impact-echo method is more appropriate for assessing the durability of RAC in a freeze-thaw condition. The RAC’s F-T resistance is greatest when the CWP content is 20%. The Grey-Markov model has a high degree of predictive accuracy, effectively reflecting the relationship between RAC durability and F-T cycles, and has wide practical applications.

A systematic review study on different kinds of interlocking concrete blocks designs and properties

Interlocking concrete blocks (ICBs) have been recently used worldwide to be alternative conventional blocks. ICBs are more sustainable, low involve low production cost, and environment-friendly as they emit less carbon dioxide than normal ones. ICBs have been used particularly in war zones and places affected by natural disasters where the need for quick, sustainable, low-cost buildings and earthquake-resistant buildings is indispensable. This paper provides a comprehensive literature review about different types of ICBs. It aims to demonstrate different configurations of ICBs incorporated with recycled concrete aggregate (RCA) and other additive materials used for construction. To achieve this, the compares different related studies which analyse the compressive strength results of RCA mixtures with different RCA replacements, w/c ratio, and mix proportions. Additionally, the paper discusses several techniques and methods to improve the behaviour of ICBs.

Evaluation of Mechanical and Permeability Characteristics of Microfiber-Reinforced Recycled Aggregate Concrete with Different Potential Waste Mineral Admixtures.

Plain recycled aggregate concrete (RAC) struggles with issues of inferior mechanical strength and durability compared to equivalent natural aggregate concrete (NAC). The durability issues of RAC can be resolved by using mineral admixtures. In addition, the tensile strength deficiency of RAC can be supplemented with fiber reinforcement. In this study, the performance of RAC was evaluated with individual and combined incorporation of microfibers (i.e., glass fibers) and various potential waste mineral admixtures (steel slag, coal fly ash (class F), rice husk ash, and microsilica). The performance of RAC mixtures with fibers and minerals was appraised based on the results of mechanical and permeability-related durability properties. The results showed that generally, all mineral admixtures improved the efficiency of the microfibers in enhancing the mechanical performance of RAC. Notably, synergistic effects were observed in the splitting tensile and flexural strength of RAC due to the combined action of mineral admixtures and fibers. Microsilica and rice husk ash showed superior performance compared to other minerals in the mechanical properties of fiber-reinforced RAC, whereas slag and fly ash incorporation showed superior performance compared to silica fume and husk ash in the workability and chloride penetration resistance of RAC. The combined incorporation of microsilica and glass fibers can produce RAC that is notably stronger and more durable than conventional NAC.

Improvement of Bond Strength and Durability of Recycled Aggregate Concrete Incorporating High Volume Blast Furnace Slag.

This paper aims to experimentally investigate the effects of high volume cement replacement of blast furnace slag (BFS) on the bond, strength and durability of recycled aggregate concrete (RAC). Concrete mixtures were prepared containing 0%, 15%, 30%, 45%, 60% and 75% BFS with each of recycled aggregate and natural aggregate. Measurements of the compressive and bond strength, the resistance to chloride-ion penetration and the water permeability of concrete are reported. In addition, a microhardness test was also performed to evaluate the quality of interfacial transition zone (ITZ) in concrete. Test results of the bond strength and the compressive strength of RAC mixtures, in spite of the cement replacement amount with BFS, show that the concretes result in reduced strength when compared to natural aggregate concrete (NAC) mixtures, while the strength gains for the BFS-based concrete are higher than that of the reference mixtures without BFS at long-term ages. Incorporating BFS in concrete can inherently improve the durability properties by increasing higher resistance to chloride-ion penetration and lower water permeability. This improvement in the mechanical and durability properties of the BFS-based RAC mixture may be due to the additional pozzolanic reaction of BFS, which enhances the properties of ITZ in concrete, resulting in an improvement of the strength of concrete.

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.

Sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber

This study investigates the sulfate attack resistance of recycled aggregate concrete with NaOH-solution-treated crumb rubber (CR). For this purpose, several recycled aggregate concrete mixes were developed using different concentrations (10%, 20% and 30%) of NaOH-solution-treated CR and different CR particle sizes (0.16–0.3 mm, 0.85–2 mm and 10–20 mm). The performance, including mass loss, residual compressive strength, relative dynamic modulus of elasticity (RDME) and microstructure, was evaluated in the sulfate environment. Results reveal that the macroscopic performance of recycled aggregate concrete with CR presents three stages: the early enhancement or slow declining stage, middle declining stage and subsequent accelerated declining stage. The addition of CR particles could improve the sulfate attack resistance of recycled aggregate concrete, and the effect was more significant for the NaOH-solution-treated CR particles than for the untreated CR. Moreover, 0.16–0.3 mm CR particles and 20% NaOH solution pretreatment were the optimum conditions in this assessment range to enhance the sulfate attack resistance. Although the surface scaling tended to worsen in recycled aggregate concrete mixtures with 10–20 mm CR due to its weaker mortars, the mixtures were still durable in sulfate attack conditions owing to their higher residual RDME and compressive strength than those of recycled aggregate concrete. The results of the analysis of corrosion products through X-ray diffraction and the microstructure through scanning electron microscopy are consistent with the macroscopic performance.

Overall assessment of alkali-silica reaction affected recycled concrete aggregate mixtures derived from construction and demolition waste

A large amount of research has been conducted on the reuse of construction and demolition waste (CDW) in concrete. Yet, CDW may display pre-existing damage which raises concerns on its use. In this work, coarse recycled concrete aggregate (RCA) is reclaimed from distinct members of an alkali-silica reaction (ASR) affected overpass. RCA mixtures incorporating 50 and 100% replacement are then manufactured and stored in conditions enabling further ASR development. Mechanical (Stiffness Damage Test- SDT) and microscopic (Damage Rating Index- DRI) analyses are conducted at a fixed “secondary” induced expansion. Results indicate that the overall damage of ASR-affected RCA mixtures is different from conventional concrete and depends upon the “past” RCA condition. Furthermore, the DRI can capture the “past” and “secondary” expansion while the SDT simply detects the “secondary” distress. Finally, an adapted DRI version is proposed to better evaluate and distinguish “past” and “secondary” damage in ASR-affected recycled concrete.

Mechanical and durability properties of recycled aggregate concrete produced from recycled and natural aggregate blended based on the Densified Mixture Design Algorithm method

The aim of this study was to reuse recycled concrete aggregates for concrete production by using the Densified Mixture Design Algorithm (DMDA) method for blended aggregates and mixing design based on the evaluation of characteristics of recycled aggregate concrete (RAC). Recycled coarse aggregate (RCA) was used to replace 30%, 40%, and 50% of the natural coarse aggregate (NCA), respectively, by volume in the samples, and the fine aggregate was a combination of 70% natural fine aggregate (NFA) and 30% recycled fine aggregate (RFA) by volume. A series of tests, including compressive strength, splitting tensile strength, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), thermal conductivity (TC), water absorption, and the rapid chloride penetration test (RCPT) were conducted in accordance with the relevant standards. The results illustrated that blending aggregates following to DMDA method suggested an optimum proportion of RCA level which exhibited with highest volume of aggregate per unit volume of combination of RCA and NCA. The results revealed 40% RCA content as the optimum replacement level. Furthermore, the 40% RCA concrete mix exhibited good hardening properties in terms of being only slightly below the 30% RCA mix and significantly higher than the 50% RCA mix. All of the RAC mixtures designed by DMDA method with low cement consumption exhibited good strength development and good durability through 120 days of curing.

Microscopic assessment of recycled concrete aggregate (RCA) mixtures affected by alkali-silica reaction (ASR)

Recycled concrete aggregates (RCA) are deemed an efficient approach to reduce waste yet, the presence of previous alkali-silica reaction (ASR) causes reservations towards its use in new construction. In this work, RCA specimens are manufactured in the laboratory incorporating RCA displaying distinct ASR past deteriorations (i.e. slight and severe). The samples are stored in conditions enabling further ASR development and monitored over time. Three levels of “secondary” expansion are selected for analysis, and upon being reached, microscopic evaluations are conducted through the Damage Rating Index (DRI). Results revealed that lower distress is observed in the RCA mixtures when compared to a companion conventional concrete at the same expansion level. Moreover, the damage mechanism of ASR-affected RCA concrete seems dependent on the RCA past deterioration since cracks tend to propagate into the residual cement paste or new cement paste for mixtures made of slightly or severely damaged RCA, respectively.