Effects of surface modified recycled coarse aggregates on concrete’s mechanical characteristics

Sustainable concrete using recycled coarse aggregates from construction and demolition waste is gaining popularity in the construction industry, but has poor mechanical characteristics due to old cement mortar adhering to aggregate surfaces. This study uses two processes (abrasion treatment and cement slurry treatment) to modify the surface of recycled coarse aggregates (RCA) to minimize the strength loss of RCA and enhance the bonding properties of the concrete matrix and RCA. Surface-modified RCA replaced coarse aggregates in varying percentages, ranging from 0 to 100% in 25% increments. To comprehend the effects of surface-modified RCA, the workability, compressive strength, flexural strength, split tensile strength, microstructural characteristics (XRD, SEM, and EDAX), and modulus of elasticity of concrete are evaluated. Surface-modified RCA improves concrete’s mechanical characteristics, but abrasion-treated RCA has significantly greater strength than reference concrete up to 50% replacement level, while cement slurry treatment has slightly lower strength. Test findings reveal that among all the two processes of surface modifications of RCA, abrasion treatment is more effective and efficient. At 100% replacement level, surface-modified RCA by abrasion treatment reduces compressive, flexural, and split tensile strength by 10.89%, 10.42%, and 09.92% compared to reference concrete, while surface-modified RCA by cement slurry treatment reduces these values by 14.80%, 13.27%, and 12.76%. Surface modifications improve bonding properties of RCA and cement matrix, reducing porosity and resulting in dense and strong ITZs compared to unmodified RCA.


Introduction
Construction and demolition (C&D) waste generation is expected to reach 2.59 billion tonnes by 2030 and 3.40 billion tonnes by 2050 [1], causing environmental issues and a lack of disposal sites [2].Recycling C&D waste as recycled aggregates (RA) is economically and environmentally advantageous [3].Recycled aggregates are produced by processing construction and demolition waste materials like concrete, asphalt, bricks, and tiles [4,5].These aggregates can be utilized to create both coarse and fine aggregates for reuse [6].In this study, we employ recycled coarse aggregate (RCA) produced by using an impact crusher to crush waste concrete from IL&FS C&D Waste Recycling Plant, Delhi Metro Rail Corporation (DMRC), Delhi, India [7,8].However, the quality of RCA is affected by cement mortar attached to the aggregate surface [9].Proper removal or reduction of cement mortar during recycling is crucial for high-quality RCA production [10].Efficient methods for separating and cleaning aggregates can enhance performance and contribute to sustainable construction practices [11].Experimental studies aim to enhance RCA concrete's strength, durability, and performance by incorporating additives and techniques [12][13][14].
Researchers investigate factors like chemical admixtures, fiber reinforcement, and curing methods to optimize the material's characteristics for sustainable construction practices [15].The two-stage mixing method improves recycled aggregate interfacial zones by filling pores and cracks, resulting in dense concrete [16].
Pre-soaking of recycled aggregates with HCl, H 2 SO 4 , and H 3 PO 4 reduces water absorption without exceeding permissible limits for chloride and sulphate components [17].A new mixing technique and stone-involved pozzolanic powder coating of recycled coarse aggregates enhance ITZ structure, achieving better workability and strength [18].The treatment of RCA by soaking in pozzolanic materials enhances its mechanical properties [19].Incorporating 25%-30% fly ash improves the mechanical characteristics of recycled aggregate concrete [20].The treatment of RCA with a sodium silicon-based polymer enhances its fragmentation resistance and decreases its water absorption capacity [21].The particle density, water absorption, and mechanical strength of RCA are significantly improved by coating with calcium meta-silicate solution and soaking in HCL acid at a 0.5 mol concentration [22].Carbonation-based surface modification of RCA increases density and reduces water absorption [23] while enhancing compressive strength [24].Acetic acid solution treatment of RCA increases concrete's compressive strength by up to 25% within 28 days [25].In comparison to untreated RCA, surfaces treated with pozzolanic slurry and CO 2 had superior mechanical strength and were more resistant to carbonation and chloride ion diffusion [26].Recycled concrete aggregate (RCA) can be improved by reducing mortar attachment and using mineral admixtures as internal curing agents.This leads to increased mechanical strength and durability in RCA, with potential cost savings compared to natural aggregate (NA) mixes [27].Cement mortar density improved by 5.7% after limewater-CO 2 treatment, reducing water absorption by 50%.Compressive and flexural strength improved by 22.8% and 42.4%, respectively, while total porosity decreased by 33% [28].The combination of crushing and carbonation treatment increased crushing stress and decreased RCA's water absorption [29].The accelerated carbonation process reduced cement mortar's water absorption, sorptivity, totally charged passed, and chlorine ions diffusion coefficients [30].Adding treated RCA to a 0.1 mol HCL solution and coating with calcium meta-silicate slurry increased drop and brittle behaviour during postcraking extension.TRCA improved crack resistance in concrete's processing zone for fractures compared to RCA [31].
Simultaneously, the research delves into the impact of carbonated recycled fine aggregate (CRFA) and recycled fine aggregate (RFA) on the properties of alkali-activated slag and glass powder mortar.An elevated RFA content contributes to a notable increase in compressive strength within the mortar.On the other hand, a higher CRFA content leads to an enhanced flow value, prolonged setting time, and decreased strength [32].The study also sheds light on a strong correlation between reduced water absorption and heightened compressive strength in recycled concrete.This correlation is influenced by treatment methods, particle sizes, and processes [33].Moreover, subjecting recycled concrete aggregate to an acid-mechanical treatment yields a remarkable 16.06% enhancement in compressive strength.This treatment positively affects various aspects such as surface density, transition zones, micro-cracks, pores, and mortar quality, consequently elevating concrete excellence and reducing sorptivity [34].Concrete's environmental impact prompts sustainable solutions-recycling, substituting Ordinary Portland Cement and natural aggregates with by-products like fly ash.The review covers advanced methods like optimizing cement hydration, introducing novel materials like carbon nanotubes, aiming for eco-friendly, sustainable concrete [35].Study explores coal fly ash (CFA) use in concrete, replacing cement.Testing nano-silica (nS)-enhanced CFA with 5% nS and 0%, 15%, 25% CFA levels shows improved mechanical properties and microstructure.Optimal blend (5% nS, 15% CFA) enhances strengths by 37.68% and 36.21%,offering potential for eco-friendly concrete [36].Research explores superabsorbent polymer (SAP) and expansive agent (EA) in ultra-high-performance concrete (UHPC) for shrinkage reduction and strength retention.Optimal blend (S1E1, 0.1% SAP, 1% CEA) achieves high strength (135 MPa) and significant shrinkage reduction (24%) in 7 days.Study highlights self-desiccation water retention, portlandite formation's interplay for UHPC shrinkage control.Ongoing hydration reduces microporosity, compacting microstructure, revealing SAP-induced voids limiting CEA expansion [37].Six papers in this special issue focus on concrete with industrial waste and environmentally friendly variants.These cutting-edge studies aim to innovate the fabrication, properties, and development of eco-friendly concrete [38].Study examines NaCl and gypsum influence on geopolymer concrete activated by quicklime.Tests show individual NaCl or gypsum boosts compressive strength (up to 245.3% at 3 days), combined generates salts, enhancing strength by 180.3%.2% NaCl reduces mass loss, improves elastic modulus.4% NaCl, 7.5% gypsum improves sulfate corrosion resistance by 38.8%.Tailored geopolymer blend reduces costs, emissions, improves corrosion resistance compared to slag Portland cement [39].
Recycling C&D waste as recycled aggregates is becoming popular for sustainable concrete production, reducing landfill waste, conserving natural resources, and supporting the circular economy [40].However, old adhered cement mortar on recycled aggregates can negatively impact strength and durability, making proper removal crucial for optimal performance [41].This study aims to minimize the strength loss of recycled coarse aggregates (RCA) and enhance bonding between RCA and concrete matrix.Previous studies have shown similar mechanical characteristics loss due to unmodified surfaces or other treatments [15].This study analyses the mechanical characteristics after surface modification using abrasion treatment and cement slurry treatment, aiming to minimize strength loss.
The novelties of this work are as follows: 1. Investigating a gap by implementing two distinct surface modification techniques on Recycled Coarse Aggregates (RCA): Abrasion Treatment and Cement Slurry Treatment.These processes elucidate the impact of surface modifications on the properties of RCA.
2. Evaluating the effective utilization of surface-modified RCA in the production of eco-friendly concrete, serving as a substitute for natural coarse aggregates at varying proportions (0%, 25%, 50%, 75%, and 100%).
3. Analysing the effects of different proportions of surface-modified RCA on the fresh characteristics of concrete (Workability), its hardened (compressive strength, flexural strength, split tensile strength), and its microstructural attributes (XRD, SEM, and EDAX).A comparative study with a control mixture is conducted to identify noteworthy distinctions.[43].With an impact crusher, crushed concrete from C&D waste is reduced to the necessary size and used as recycled coarse aggregates.Figure 1 depicts the aggregate particle size distribution.

Materials and testing
Analysis of physical and mechanical properties is crucial for determining RCA compatibility with concrete.Table 2 displays the physical and mechanical characteristics of aggregates.The RCA sample results revealed poor bonding due to old cement mortar on aggregate surfaces which causes a loss in strength.To address this issue, surface modification is necessary before adding RCA to concrete.Surface modification is needed to improve the connection between RCA particles and the cement matrix.RCA treated with abrasion has a rough surface, similar to coarse aggregates, while treated with cement slurry has a smooth surface.This treatment strengthens the bond with the cement matrix and improves the mechanical properties of concrete.Chemical admixture as super-plasticizers (C-MAX) is used 1% by weight of cement, and potable water is used for mixing and curing.

Surface modification of RCA
Recycled aggregate concrete (RAC) suffers from strength reduction due to weak bonding between RCA and cement matrix.Researchers found significant losses in RAC's mechanical characteristics when using unmodified coarse aggregates.This is due to the reduction in strength due to weak bonding.Old mortar on RCA surfaces causes weak bonding with the cement matrix, requiring treatment to enhance compressive strength.This experimental study uses abrasion treatment and cement slurry treatment to modify RCA surfaces for improved properties.

Abrasion treatment of RCA
An abrasion treatment method was used to reduce the quantity of mortar that was adhered to the surface of the RCA.A Los Angeles Abrasion machine is utilized in this procedure; it comprises a hollow steel cylinder that is closed at both ends, has an internal diameter of 711 mm, and can revolve around its horizontal axis.The device was kept spinning at a speed of 25 revolutions per minute for 5 min while being filled with coarse recycled aggregates.The rotating drum causes aggregate particles to rub against each other, removing any attached mortar in the process.The surface modification process from the abrasion treatment is depicted in figure 2. Numerous abrasion machine RPM trials were conducted to optimize drum rotation duration.Table 3 displays the outcomes of the trials.The percentage of RCA's that could absorb water after treatment was a criterion used to choose the rotation of the drum.The percentage of RCAs able to absorb water after treatment was used as a criterion.The treated materials absorbed 1.87% water after 5 min of revolutions, making 5 min the optimal treatment time for RA.

Cement slurry treatment of RCA
The technique involves creating cement paste using water, dissolved in 10% water, and agitated for 10-15 min.Recycled aggregates are immersed in the paste for 24 h, and then dried in the oven for optimal particle penetration.This dried recycled aggregate is used in concrete preparations.The process of surface modification from cement slurry treatment of the RCA is shown in figure 3.

Mix proportions
Nine concrete mixtures were produced for 27 MPa target strength to investigate the mechanical behavior of surface-modified recycled coarse aggregates.Table 4 lists all of the compositions of the concrete mixtures.Reference mixture (RC) is created with natural aggregates, and mixtures RCAAT-25, RCAAT-50, RCAAT-75, and RCAAT-100 are produced by replacing natural coarse aggregates with abrasion modifies recycled coarse aggregates and RCACST-25, RCACST-50, RCACST-75, and RCACST-100 are produced by replacing natural coarse aggregates with cement slurry modifies recycled coarse aggregates at varying replacement percentages of 25%, 50%, 75%, and 100% respectively.All mixtures were produced using the weight batching method at a constant water-cement ratio of 0.50.

Testing programs
The study examines the mechanical characteristics of structural concrete by measuring its workability and hardened characteristics.162 samples were cast, cured, and tested in steel cube (15 × 15 × 15 cm) molds for compressive strength, rectangular (50 × 10 × 10 cm) molds for flexural strength, and cylindrical ((f) = 15 cm, height (H) = 30 cm) molds for split tensile strength.The strength of concrete mixtures was determined using the average of three specimens (as shown in figure 4) for each mix.energy-dispersive x-ray spectroscopy (EDAX), and x-ray diffraction (XRD) were used to examine the microstructural characteristics of concrete samples for different mixtures.

Workability
In order to evaluate the feasibility of mixes created using varying replacement percentages of surface-modified recycled coarse aggregates (RCA), a slump test was conducted according to the guidelines of IS 1199-1959 [47].
The results of the slump test, illustrating the variations in slump for different concrete mixtures, are presented in figure 5.The observed trend in figure 4 indicates a reduction in the slump of concrete as the proportion of surface-modified recycled coarse aggregates increases.The workability of concrete containing surface-modified RCA falls within the medium range, spanning from 50 to 100 mm, as evidenced by the slump values across all mixtures.This decline in slump value is attributed to the greater water absorption capacity of RCA compared to natural aggregates, resulting from their rougher surface texture and larger surface area.Comparing the concrete mixes prepared using surface-modified RCA subjected to abrasion treatment and those treated with a cement  slurry process, it is noted that the former exhibits a slightly higher slump value.This suggests that the abrasion treatment imparts a relatively more favourable workability to the concrete mixes.The consistent trend of diminishing slump with an increasing proportion of surface-modified RCA aligns with findings from a prior study [48,49].

Compressive strength
The variations of the 7 and 28 days compressive strength for different replacement percentages of surfacemodified RCA concerning the reference mixture are shown in figure 6.From the compressive strength test results as per table 5, the concrete mixture with a higher percentage replacement of surface-modified RCA has lower compressive strength than the reference mixture.An optimal replacement percentage is observed for each surface modification technique.Abrasion treatment achieves optimal efficiency at 50% replacement, while cement slurry treatment reaches its peak effectiveness at 25%.The application of simple abrasion proves to be more efficient in enhancing compressive strength.Particularly noteworthy is the highest compressive strength achieved at 28 days, resulting from the addition of surface-modified RCA through the abrasion treatment process at a 50% replacement rate.This enhancement is attributed to the effective removal of adhered mortar and the reduction of voids, leading to increased particle density.Thus, RCAAT 50 (M3) exhibits the highest strength.However, the efficiency of surface modification through pre-soaking recycled aggregates in cement slurry is found to be comparatively lower than that of abrasion treatment.Among the concrete mixtures examined, M3 (RCAAT25) demonstrates the highest compressive strength at 41.88 MPa, while M9 (RCACST100) exhibits the lowest at 26.29 MPa.These findings concur with prior research, such as the observations made by Kessal et al [50].Another study by Ashraf M Wagih et al demonstrated a 20%-34% and 18%-28% decrease in compressive strength for concrete mixtures containing  RCA at 7 and 28 days, respectively [51].Importantly, after undergoing surface modification treatment, the decline is mitigated to 12%-18% at 7 days and 10%-15% at 28 days, even for 100% replacement of RCA.This favorable outcome underscores the efficacy of surface modification treatments in attenuating the loss of compressive strength in recycled aggregates concrete.Notably, the abrasion treatment of RCA emerges as a pragmatic and effective approach, delivering high-quality aggregates with reduced water absorption and efficient removal of adhered mortar.

Flexural strength
Figure 7 illustrates the variations in flexural strength at 7 and 28 days for different replacement percentages of surface-modified RCA in comparison to the reference mixture.These results closely follow the trend observed in table 6, echoing the patterns evident in compressive strength.Notably, the data indicates that concrete mixtures incorporating a higher replacement percentage of surface-modified RCA exhibit reduced flexural strength compared to the reference mixture.Table 6 quantifies the percentage variation in flexural strength for the various concrete mixtures.It presents the flexural strength values at 7 and 28 days; along with their respective percentage variations from the reference concrete (RC).The table highlights that the use of a greater proportion of surface-modified RCA for replacement leads to a decrease in flexural strength relative to the reference mixture.
Among the mixtures tested, M3 (RCAAT25) demonstrates the highest flexural strength at 4.45 MPa, while M9 (RCACST100) shows the lowest at 3.66 MPa.This outcome aligns with prior research, which has reported a 5%-10% reduction in flexural strength for 50% RCA replacement and a 15%-20% reduction for 100% replacement [52].However, this study deviates from the observed patterns by indicating a more moderate 13% reduction at a 100% surface-modified RCA replacement level.This suggests that the surface modification treatments applied to RCA have yielded positive outcomes in terms of flexural strength.These findings  contribute to a nuanced understanding of the impact of surface-modified RCA content on the flexural behaviour of concrete mixtures and highlight the potential benefits of surface modification techniques.

Split tensile strength
Figure 8 illustrates the variation in split tensile strength at 7 and 28 days for different replacement percentages of surface-modified RCA in comparison to the reference mixture.This trend aligns with the observed results in table 7, mirroring the behaviour seen in compressive strength.Notably, a consistent pattern emerges where the split tensile strength of the concrete mixture is notably lower when a higher proportion of surface-modified RCA is introduced as a replacement for conventional aggregates.Table 7 quantifies the percentage variation in split tensile strength for the various concrete mixtures.It reveals that the use of surface-modified RCA at higher replacement levels results in a decrease in split tensile strength compared to the reference mixture.The table showcases the split tensile strength values at 7 and 28 days; along with their respective percentage variations from the reference concrete (RC).Among the mixtures tested, M3 (RCAAT25) displays the highest split tensile strength at 2.97 MPa, while M9 (RCACST100) exhibits the lowest at 2.46 MPa.These findings are in agreement with prior research presented by Kessal et al [50].Notably, this study diverges from the observations made by Ashraf M Wagih, who reported a 24% reduction in split tensile strength [51].In contrast, the surface-modified RCA examined in this study showcases a more modest 12% reduction at a 100% replacement level.These results underscore the influence of surface-modified RCA content on the split tensile strength of the resulting concrete mixtures and contribute to the broader understanding of the mechanical behaviour of such compositions.

Modulus of elasticity
The modulus of elasticity (MOE) serves as a critical indicator for assessing the deformation capacity of both Recycled Aggregate Concrete (RAC) and standard concrete.The MOE measurements conducted at the 28-day  mark reveal a notable trend: an inverse relationship between the MOE and the incorporation of surfacemodified RCA in the concrete matrix.This decrease in MOE is prominently presented in table 8.The observed reduction is attributed to the inherent characteristics of surface-modified RCA, such as its water absorption tendency and brittleness.This decline in MOE is particularly noteworthy due to the heightened susceptibility of RCA to deformation.Consequently, structural elements constructed with RCA exhibit larger actual deformations compared to those composed of natural aggregates.The empirical data presented in table 8 showcases the MOE values for various concrete mixtures.Figure 9 further elucidates the connection between experimental results and different codes, illustrating how while surface modification of RCA contributes to increased strength through enhanced nucleation sites for hydration, the MOE consistently diminishes with higher levels of surface-modified RCA content.This trend is underscored by a comparative analysis of the compressive strength and MOE of plain concrete across different levels of surface-modified RCA replacement.The factors contributing to the MOE reduction include the amount and rigidity of the binder phase, the volume and stiffness of aggregates, and the characteristics of the interfacial transition zone (ITZ) between aggregates and the cementations paste.Similar patterns of MOE decline have been observed in prior studies [50,51].The observed decrease in MOE serves as a crucial consideration when evaluating the implications of surface-modified RCA incorporation on the overall mechanical behavior of the resulting concrete.

X-ray diffraction (XRD)
X-Ray Diffraction (XRD) is a method for analyzing the crystallographic arrangement of materials.By directing x-rays at a crystalline sample, the x-rays diffract based on the crystal lattice arrangement.Measurement of the angles and intensities of these diffracted x-rays provides valuable insights into the material's crystal structure.The Bruker D-8 diffractometer scans samples at a 2-degree angle from 3 to 70 degrees, with a scan speed of 2 degrees per minute and a 0.005-degree sampling interval.The Jade 7 x-ray diffraction software analyzes the scans, presenting peak intensities in a graph against 2 degrees on the x-axis and intensity on the y-axis (figure 10).This equipment comprises a high-intensity x-ray source, a goniometer for sample rotation, and a detector for capturing diffracted x-rays.Samples for XRD analysis were ground into a fine powder, carefully loaded onto a sample holder, or mounted to align correctly with the x-ray beam.The XRD instrument was calibrated to specified measurement conditions, including x-ray wavelength and scan range.Placing the sample holder within the instrument, the x-ray beam was directed onto the sample.Diffracted x-rays were collected across various angles, and the resulting diffraction pattern was scrutinized to deduce the material's crystal structure and identify its constituent phases.The analysis of x-ray diffraction (XRD) results elucidates the presence of well-defined crystalline formations characterized by consistent geometrical patterns, influenced by the incorporation of surface-modified recycled coarse aggregates (RCA).This influence extends to the phase composition of minerals, including calcium silicate hydrate (CSH), calcium alumina silicate hydrate (CASH), ettringite, and calcium hydroxide (CH).The XRD peaks' characteristics, including their positions, corresponding d-spacing values, chemical formulas, chemical names, and crystal system classifications, are comprehensively detailed in table 9, providing a comprehensive understanding of the structural changes and mineral transformations induced by the utilization of surfacemodified RCA.This study is remarkably similar to the previous research [52].

Scanning electron microscopy (SEM)
Scanning Electron Microscopy (SEM) is a potent imaging method utilizing focused electron beams to capture high-resolution surface images of materials, with magnifications ranging from modest to extensive.SEM is applied to characterize RCA materials, examining particle microstructure and surface morphology in concrete samples.The JSM 6610 V SEM at the University Science Instrumentation Center (USIC) Delhi was used for sample analysis.This SEM boasts a high-resolution electron gun, electromagnetic lenses, and detectors for secondary and backscattered electrons.Sample preparation involves meticulous steps like cutting, polishing, and conductive coating to ensure accurate imaging and sample integrity.Prepared samples are placed in the SEM stage within a vacuum chamber, where a focused electron beam produces high-resolution images by detecting emitted secondary and backscattered electrons.Figure 11 showcases micrographs from SEM analysis of distinct mixtures at the 28-day mark.The formation of hydration products at the microstructure level in different concrete mixtures at 28 days is seen in the micrographs, which are responsible for the strength of concrete.The main compounds present during the hydration process are calcium hydroxide (CH), calcium silicate hydroxide (CSH), and ettringite.The hexagonal crystals indicate CH, the flower-shaped structure indicates CSH gel and the needle-like structure indicates ettringite.
The acquired test outcomes elucidate that the integration of surface-modified recycled coarse aggregates (RCA) through abrasion treatment yields substantial enhancements in the concrete's microstructure.This alteration results in a more compact cement paste, thereby facilitating improved adhesion between the aggregates and cement paste.Conversely, the introduction of surface-modified RCA via cement slurry treatment diminishes the porosity of RCA and amplifies the density and robustness of the interfacial transition zones (ITZs).Complementary scanning electron microscope (SEM) analysis corroborates these findings by confirming that the removal of adhered mortar from RCA through abrasion treatment, coupled with the application of a cement slurry coating, synergistically contributes to the refinement of RCA's microstructural attributes.Consequently, these modifications exert a positive influence on the caliber and potency of recycled  aggregates concrete, highlighting the significance of surface modification techniques in augmenting the performance of environmentally sustainable concrete materials.Comparable interpretations are also done in the previous study [52].

Energy dispersive x-ray spectroscopy (EDAX)
Energy-dispersive x-ray spectroscopy (EDAX) is employed for the comprehensive chemical composition analysis of concrete samples.This research utilizes EDAX to ascertain both the qualitative and quantitative evaluations of distinct elements within different concrete blends.Figure 12 depicts the quantitative and qualitative analyses of diverse elements present in various mixtures, as determined through EDAX analysis.
The results of the Energy Dispersive x-ray Analysis (EDAX) reveal the presence of several elemental components within the tested samples, including Calcium (Ca), Oxygen (O), Silicon (Si), Aluminum (Al), Iron (Fe), Potassium (K), Sodium (Na), and Magnesium (Mg).These elements constitute the chemical composition of the examined materials.The quantitative proportions of these elements, as determined through EDAX analysis, are succinctly presented and organized in table 10, providing valuable insights into the elemental makeup of the studied samples.The results are consistent with the previous study [52].

Conclusions
This paper contributes to the development of sustainable concrete by utilizing surface-modified recycled coarse aggregates (RCA) from construction and demolition waste.This approach promotes eco-friendly practices,   waste reduction, and a circular economy.Substituting natural coarse aggregates with treated RCA significantly impacts hardened concrete properties.Conclusions from the study include: • Abrasion and cement slurry treatment enhance interfacial connection between RCA and cement paste, with abrasion treatment proving more effective for removing attached mortar and enhancing recycled aggregates.
• After abrasion treatment, RCA can partially replace coarse aggregates up to 50% without major compressive strength loss.Cement slurry-treated RCA also maintains strength when used up to 50% replacement.
• Strength improvements are evident with 50% surface-modified RCA replacement, paralleling concrete with 100% natural aggregates.
• Concrete workability matches conventional concrete with admixture.Theoretical modulus of elasticity aligns with ACI and IS code.Ca-Calcium, O-Oxygen, Si-Silicon, Al-Aluminum, Fe-Iron, K-Potassium, Na-Sodium, and Mg-Magnesium.
• Surface modification creates denser ITZ in SEM studies, suggesting potential for sustainable concrete solutions.
Using abrasion and cement slurry modification, this study counters concrete strength loss in RCA, creating a robust link to cement and allowing up to 50% RCA replacement.This approach curbs waste generation, conserves resources, and supports greener construction practices.

Figure 1 .
Figure 1.Gradation curve for aggregates of different mixtures.

Figure 2 .
Figure 2. Process of surface modification from abrasion treatment of the RCA.

Figure 3 .
Figure 3. Process of surface modification from cement slurry treatment of the RCA.

Figure 4 .
Figure 4. Different specimens and their testing.

Figure 5 .
Figure 5. Slump value for different concrete mixtures.

Figure 6 .
Figure 6.Variations of compressive strength for different concrete mixtures.

Figure 7 .
Figure 7. Variations of flexural strength for different concrete mixtures.

Figure 8 .
Figure 8. Variations of split tensile strength for different concrete mixtures.

Figure 9 .
Figure 9. Variation of modulus of elasticity with different codes.

Table 1 .
Physical test results on cement.

Table 2 .
Physical and mechanical characteristics of aggregates.

Table 3 .
Results of the trails of drum rotation and RCA percentages.

Table 5 .
Percentage variation of compressive strength for different mixtures.
+ Sign Represents an Increase in Strength and-Sign Represents a Decrease in Strength

Table 6 .
Percentage variation of flexural strength for different mixtures.
+ Sign Represents an Increase in Strength and-Sign Represents a Decrease in Strength.

Table 7 .
Percentage variation of split tensile strength for different mixtures.

Table 8 .
Modulus of elasticity of concrete with different codes.

Table 10 .
Percentage weight of various elements for different mixtures.