A comparative study of sustainable mix incorporating recycled aggregates

ABSTRACT

This study compares concrete mixes incorporating different proportions of recycled aggregates (RA) as replacements for conventional coarse aggregates (0%, 10%, 20%, 30%, 40%, and 50%). It aims to evaluate their mechanical, durability, and environmental properties for practical use. Through a comprehensive experimental program, including tests on fresh and hardened properties, mechanical strength, and durability against water absorption, acid resistance, chloride ion penetration, and sulfate attack, the study assesses the performance of these sustainable mixes. Results show varied influences of RA incorporation on concrete properties, with lower replacement levels maintaining comparable mechanical strength and higher levels exhibiting strength reduction. Environmental assessments indicate significant reductions in embodied carbon and energy consumption with higher RA content. This comparative analysis informs optimal replacement levels for achieving sustainability without compromising performance, advancing understanding of sustainable construction practices, and promoting the adoption of eco-friendly materials in the construction industry.

Keywords:
Recycled aggregates; Workability properties; Strength properties; Durability properties

1. INTRODUCTION

In the pursuit of sustainable construction practices, the use of recycled concrete aggregates (RCA) has gained significant attention. This literature review synthesizes findings from recent studies on the incorporation of RCA into concrete mixes, assessing their impact on the physical properties, durability, and environmental benefits of the resulting concrete [¹]. After a thorough investigation into the durability and strength of concrete containing RCA, it was shown that RCA could replace up to 25% of natural aggregates without materially reducing the strength of the concrete. This suggests that moderate exposure conditions are appropriate for such applications [²]. A novel approach combined warm mix asphalt with hydrated lime-treated RCA, demonstrating the potential for sustainable pavement concrete with improved properties and cost, material, and energy savings [³].

The feasibility of closed-loop recycling of RCA was also explored, indicating that second-generation RCA could produce concrete of acceptable quality, with up to 20% replacement of natural aggregates [⁴]. Durability aspects were further examined, with findings suggesting that the mix design nomogram (MDN) could be a valuable tool for comparing different concrete properties, including water absorption, total pores volume, and carbonation [⁵]. Pervious concrete, a green solution for non-structural applications, was characterized using blended natural aggregate and RCA. Despite a reduction in mechanical properties, the RCA mixes met minimum requirements for skid and abrasion resistance, with the 100% RCA mix showing a significant reduction in CO2 emissions [⁶]. The development of sustainable concrete was furthered by incorporating ground granulated blast furnace slag (GGBFS) with RCA, which, despite a decrease in strength, improved the interfacial transition zone (ITZ) and bond between mortar and RCA [⁷].

The modification of bituminous paving mixes with waste polyethylene and RCA was found to enhance the engineering properties, particularly at higher temperatures, satisfying specified requirements for road construction [⁸]. The cost-effectiveness of combining RCA with steel fibres was analyzed, revealing that the sustainable benefits of RCA could significantly offset the additional costs of steel fibres [⁹]. A multi-criteria optimization approach was employed to select the most sustainable recycled aggregate concrete (RAC) mix, integrating mechanical, environmental, and economic aspects. The study concluded that while compressive strength decreased with higher RCA content, the environmental and economic benefits were notable [¹⁰]. The performance of hot-mix asphalt involving RCA was investigated, showing that with proper curing, the mixtures could meet moisture damage specifications and exhibit adequate resistance to permanent deformation [¹¹].

Recycled aggregate concretes exhibit lower durability in aggressive environments due to their intrinsic porosity, with the durability decreasing as the water/cement (w/c) ratio increases. The composition of recycled aggregates (RA) significantly influences the durability of concrete, with fine RA being particularly detrimental to properties such as carbonation resistance [¹²]. Environmental factors such as carbonation, dry-wet cycles, and freeze-thaw cycles affect the pore structure of RCA concrete, with complex environmental conditions leading to an increase in large pore volume fraction and reduced durability [¹³]. The use of superplasticizers can improve the durability-related properties of recycled aggregate concrete, although it remains more susceptible to environmental deterioration compared to conventional concrete [¹⁴]. RCA may replace natural aggregates in concrete up to a 25% replacement rate without materially affecting the concrete’s strength, indicating that RCA can be utilized under moderate exposure circumstances [¹⁵].

Lower w/c ratios are associated with greater longevity in SFRCAC, as this concrete is more susceptible to this factor than the RCA replacement ratio [¹⁶]. Processed recycled aggregates enhance the strength and durability properties of high-strength concrete, allowing for up to 50% replacement of natural aggregate in certain conditions [¹⁷]. Fine recycled aggregates have a negative impact on durability characteristics such as water absorption, shrinkage, and chloride penetration, but their use in structural concrete may still be feasible with consideration of the environmental benefits [¹⁸]. Concrete’s w/c ratio, water absorption capacity, and carbonation depth are all often increased by increasing the percentage of fine and coarse recycled aggregates; the durability of fine recycled aggregate is more affected by it than that of coarse recycled aggregate [¹⁹]. Although glass fiber reinforcement can enhance the mechanical performance of concrete including recycled aggregates, greater doses may have a negative impact on durability, especially when it comes to qualities based on permeability [²⁰].

All of the research that have been analyzed support RCA’s potential as a sustainable substitute for natural aggregates in the manufacture of concrete. While certain mechanical properties may be affected, the environmental and economic advantages, alongside appropriate mix design adjustments, can yield concrete that is both sustainable and structurally sound [²¹, ²²]. The durability of concrete with recycled aggregates is influenced by a variety of factors including the w/c ratio, the composition and processing of the recycled aggregates, environmental conditions, and the use of additives such as superplasticizers and fibers [²³]. While the use of recycled aggregates can negatively impact durability, certain practices such as careful selection and processing of aggregates, as well as mix design optimization, can mitigate these effects and enable the sustainable use of recycled materials in concrete [²⁴].

The physical, chemical, and mineralogical properties of both fine and coarse recycled aggregates play a pivotal role in their effective integration into concrete mixes. Extensive research has indicated that inadequate characterization and processing of fine recycled aggregates pose challenges for their use in reinforced concrete, primarily due to inherent property constraints [²⁵]. Similarly, the recycling of demolished masonry rubble as coarse aggregate presents an appealing solution to address escalating costs and environmental issues linked with waste disposal. However, the inherent heterogeneity of construction and demolition waste (CDW) necessitates meticulous processing to ensure that the resulting recycled aggregates exhibit properties conducive to concrete production [²⁶]. Thus, comprehensive characterization and processing methodologies are imperative to optimize the suitability and performance of recycled aggregates in concrete applications, facilitating sustainable construction practices and mitigating environmental impacts associated with waste disposal [²⁷].

The utilization of recycled coarse aggregate in concrete has been extensively investigated, with research indicating the feasibility of achieving 100% replacement of virgin coarse aggregate with recycled aggregate. However, such complete substitution does impact the properties of both fresh and hardened concrete, necessitating careful consideration and optimization of mix designs to maintain desired performance standards [²⁸]. In order to overcome these obstacles, cutting-edge technologies have developed, making it easier to produce high-quality recycled sand from CDW (construction and demolition waste). This innovation holds significant potential to revolutionize the construction recycling model by promoting the comprehensive utilization of CDW, including all size fractions. Embracing such holistic approaches to CDW recycling is vital for maximizing resource efficiency, minimizing waste generation, and fostering sustainable practices in the construction industry. By harnessing advanced technologies and adopting integrated waste management strategies, the construction sector can contribute to a more circular economy and mitigate environmental impacts associated with waste disposal [²⁹].

Recycled blocks incorporating construction and demolition (C&D) waste have demonstrated enhanced properties, including high fire resistance, superior heat retention, and effective acoustic insulation, presenting advantages over traditional concrete blocks. This highlights the potential of recycled materials to offer innovative solutions for sustainable construction practices while addressing environmental concerns associated with waste disposal. However, the utilization of recycled fine aggregates from C&D waste in mortars has revealed challenges, notably reductions in strength and durability [³⁰]. This underscores the importance of cautious implementation, suggesting that partial replacement and adjustments to the water-to-cement ratio may be necessary to mitigate adverse effects on mortar performance. Through careful consideration of material characteristics and appropriate adjustments in mix design, the construction industry can harness the benefits of recycled aggregates while ensuring the structural integrity and longevity of building materials, ultimately advancing towards more sustainable and resilient built environments [³¹].

Research into high-strength concrete production using demolished concrete wastes as coarse aggregates has shown promising results. Even though recycled aggregate concrete might not be as strong as concrete manufactured with natural aggregates, it nevertheless satisfies the standards for structural uses [³²]. This indicates the feasibility of utilizing demolished concrete wastes as a sustainable alternative in HSC mixes, contributing to resource efficiency and waste reduction in the construction industry. Additionally, studies investigating the treatment of recycled aggregates with epoxy resin to mitigate water absorption have shown positive outcomes. Concrete specimens produced using this method have demonstrated good quality and properties comparable to those of conventional concrete. These findings suggest that innovative approaches such as resin treatment can enhance the performance of recycled aggregates [³³].

2. MATERIALS

In the realm of construction materials, an intricate understanding of their physical properties is paramount for ensuring the structural integrity, durability, and overall performance of built environments. Cement, a fundamental ingredient in concrete formulations, embodies several defining characteristics. Typically composed of OPC 53 grade, denoting its compressive strength, cement presents itself in a solid, grey form. Its specific gravity, measured at 3.14, highlights its density relative to water, while its expansive surface area of 2250 cm2/gm underscores its reactivity and hydration kinetics. Cement’s particle size, averaging less than 90 microns, contributes to its fine texture, facilitating optimal binding within concrete mixes. Moreover, its volume expansion of 3 mm upon setting necessitates careful consideration during construction processes to mitigate potential dimensional changes. The chemical composition of cement, expressed as a percentage, delineates its elemental makeup, vital for understanding its properties and behavior in construction applications. In this formulation, silicon dioxide (SiO2) comprises 20.15%, contributing to cement’s binding capacity and structural stability. Aluminum oxide (Al2O3) accounts for 4.51%, enhancing cement’s heat resistance and setting properties. Iron oxide (Fe2O3) at 2.57% further bolsters cement’s durability and coloration. The predominant presence of calcium oxide (CaO) at 61.34% serves as the primary constituent responsible for cement’s binding and hardening characteristics. Magnesium oxide (MgO) at 1.05% contributes to cement’s overall chemical reactivity and mechanical strength. Finally, the loss on ignition, measured at 2.45%, indicates the volatilization of organic compounds and the decomposition of carbonates during cement production, influencing its final properties and performance.

The M-Sand, a manufactured alternative to natural sand, boasts its own set of distinctive attributes. With a grainy appearance and a specific gravity of 2.75, M-Sand embodies comparable density characteristics to its natural counterpart. Its bulk density of 2.74 g/cc and water absorption rate of 1.50% influence its flowability and workability in concrete applications, while its moisture content, measured at 1.28%, dictates handling and mixing properties. Classified under Zone II, M-Sand conforms to standard specifications, further solidifying its viability in construction projects. The fineness modulus of 1.52 and maximum grain size of 1.13 mm underscore its suitability for diverse concrete compositions, enhancing both strength and workability. Beyond cement and M-Sand, coarse aggregates play a pivotal role in concrete mix designs, offering structural reinforcement and dimensional stability. Natural coarse aggregates, characterized by their angular shape and sizes averaging 20 mm, exhibit a specific gravity of 2.65 and water absorption rate of 1.74%. With a crushing value of 17.54% and an impact strength of 14.69%, these aggregates demonstrate robust resistance to compressive and sudden loading forces, ensuring the structural integrity of concrete structures. Meanwhile, recycled coarse aggregates, with sizes ranging from 12.5 mm to 20 mm, exhibit similar physical properties to their natural counterparts, albeit with slightly lower specific gravity and crushing values. Their negligible moisture content and comparable fineness modulus render them suitable alternatives in sustainable construction practices.

3. METHODS

The slump cone test serves as a primary indicator of concrete workability, providing insights into its ability to flow and consolidate within formwork. By measuring the vertical displacement of the concrete cone after removal, engineers can gauge the consistency and cohesiveness of the mixture. Meanwhile, the compaction factor test offers a quantitative assessment of concrete’s ability to compact under external forces, vital for ensuring uniformity and density in structural elements.

Compressive strength testing remains a cornerstone in evaluating concrete’s load-bearing capacity, providing vital data for structural design and quality control. By subjecting cylindrical or cubic specimens to axial loading, engineers can determine the material’s resistance to crushing and deformation. Additionally, split tensile strength testing offers insights into concrete’s tensile behavior, vital for assessing its resistance to cracking and durability under flexural stresses. Finally, flexural strength testing provides essential information on concrete’s ability to withstand bending or flexural forces, vital for structural elements subjected to bending moments or deflection.

The water absorption test serves as a fundamental assessment of concrete’s porous structure, revealing its propensity to absorb moisture over time. Acid resistance testing provides vital information on concrete’s resilience against chemical degradation, simulating exposure to acidic environments commonly encountered in industrial settings or marine structures. By subjecting specimens to acid solutions and assessing surface deterioration, engineers can ascertain the material’s long-term performance and suitability for specific applications. Similarly, the chloride ion penetration test evaluates concrete’s susceptibility to chloride ingress, a major contributor to corrosion in reinforced concrete structures. Through immersion in chloride solutions and subsequent analysis of chloride ion penetration depth, engineers can assess the effectiveness of protective measures and design strategies aimed at mitigating corrosion risks. Moreover, the sulphate attack test examines concrete’s resistance to sulphate-bearing solutions, prevalent in soil and groundwater, which can lead to expansive reactions and deterioration of concrete. By subjecting specimens to sulphate exposure and monitoring changes in mass and appearance, engineers can gauge the material’s durability and select appropriate construction materials and techniques to ensure long-term performance in sulphate-rich environments.

4. RESULTS AND DISCUSSION

4.1. Slump cone test

The results of the slump test reveal a progressive decrease in slump values as the percentage of recycled aggregates increases in the concrete mix. In the case of conventional concrete (M1 mix), the slump value was measured at 123 mm. However, with the incorporation of recycled aggregates in varying proportions (M2 mix), there was a noticeable reduction in slump values. Specifically, for the M2 mix containing 10% recycled aggregates, the slump decreased to 119 mm, indicating a slight reduction in workability compared to conventional concrete. As the percentage of recycled aggregates was further increased to 20%, 30%, 40%, and 50% in the mix, the slump values continued to decrease progressively to 117 mm, 113 mm, 109 mm, and 104 mm, respectively. This decline in slump values suggests a decrease in the workability and flowability of the concrete mix as the proportion of recycled aggregates increases. The observed trend underscores the influence of recycled aggregates on the rheological properties of concrete, necessitating careful consideration and adjustment of mix proportions to maintain desired workability and performance.

The percentage variation of slump values in the various mixtures compared to conventional concrete (M1 mix) highlights a significant decrease as the proportion of recycled aggregates increases. Mixes with 10%, 20%, 30%, 40%, and 50% recycled aggregates exhibit variations of 3.25%, 5.04%, 8.55%, 12.39%, and 17.43%, respectively. This escalating trend underscores the adverse impact of recycled aggregates on concrete workability. The increasing deviation indicates reduced flowability and ease of placement as the percentage of recycled aggregates rises, necessitating meticulous mix design adjustments to maintain desired workability. Figures 1 and 2 shows the slump cone test results and variation of slump cone test results compared to conventional mix.

Figure 1
Slump cone test results.

Figure 2
Percentage of variation of slump cone test.

4.2. Compaction factor test

The compaction factor results demonstrate a consistent decrease in compaction efficiency as the proportion of recycled aggregates increases in the concrete mixes. Conventional concrete (M1 mix) exhibited a compaction factor of 0.946, indicating high compaction efficiency. However, as recycled aggregates were incorporated into the various mixes, the compaction factors progressively decreased to 0.915, 0.900, 0.869, 0.838, and 0.800 for mixes containing 10%, 20%, 30%, 40%, and 50% recycled aggregates, respectively. This downward trend suggests challenges in achieving optimal compaction due to the irregular shape and higher porosity of recycled aggregates, highlighting the need for meticulous mix design adjustments to ensure adequate compaction factor.

The percentage variation of compaction factors in the various mixtures compared to conventional concrete (M1 mix) reveals a substantial decrease as the proportion of recycled aggregates increases. Mixes with 10%, 20%, 30%, 40%, and 50% recycled aggregates exhibit variations of 3.236%, 4.863%, 8.115%, 11.368%, and 15.433%, respectively. This escalating trend underscores the adverse impact of recycled aggregates on compaction efficiency. The increasing deviation indicates reduced compaction effectiveness as the percentage of recycled aggregates rises, necessitating careful mix design adjustments to ensure adequate compaction factor. Figures 3 and 4 shows the compaction factor test results and variation of compaction factor test results compared to conventional mix.

Figure 3
Compaction factor test results.

Figure 4
Percentage of variation of compaction factor test.

4.3. Compressive strength test

When the proportion of recycled aggregates in the concrete mixes rises, the compressive strength findings at various curing ages show a progressive decline in strength. The compressive strength values for typical concrete (M1 mix) were 16.13 MPa, 22.94 MPa, and 25.21 MPa after 7, 14, and 28 days, respectively. However, the compressive strength values of the M2 to M6 mixes consistently decreased with the addition of recycled materials. The M2 mix’s compressive strength at 7 days was 15.71 MPa, whereas the M6 mix’s value was 14.38 MPa. In a similar vein, the compressive strength values at 14 and 28 days gradually dropped as the percentage of recycled aggregates rose. This declining trend suggests that the inclusion of recycled aggregates negatively impacts the early and long-term strength development of concrete, highlighting the importance of optimizing mix designs to maintain desired strength properties while promoting sustainability. Figure 5 shows the compressive strength test results.

Figure 5
Compressive strength test results.

4.4. Split tensile strength test

As the proportion of recycled aggregates in the concrete mixes rises, the split tensile strength values at various curing ages show a continuous drop in strength. The split tensile strength values for standard concrete (M1 mix) were 1.06 MPa, 1.50 MPa, and 1.67 MPa at 7, 14, and 28 days, respectively. Nevertheless, split tensile strength values gradually decreased as recycled aggregates were added to the M2 to M6 mixtures. After a week, the M2 mix’s split tensile strength values were 1.03 MPa, whereas the M6 mix’s values were 0.94 MPa. In a similar vein, the split tensile strength values at 14 and 28 days steadily dropped as the percentage of recycled aggregates approached. This recurring pattern highlights how recycled aggregates impair concrete’s tensile strength, making mix design extremely important in order to preserve intended mechanical performance. Figure 6 shows the split tensile strength test results.

Figure 6
Results of a split tensile strength test.

4.5. Flexural strength test

Results for flexural strength at various curing ages show a steady decline in strength as the proportion of recycled particles in the concrete mixes rises. The flexural strength values for standard concrete (M1 mix) were 1.58 MPa, 2.24 MPa, and 2.48 MPa at 7, 14, and 28 days, respectively. However, there was a steady decline in the flexural strength values when recycled materials were added to the M2 to M6 mixtures. Flexural strength values at 7 days varied from 1.41 MPa for M6 mix to 1.54 MPa for M2 mix. In a similar vein, the flexural strength values at 14 and 28 days steadily dropped as the percentage of recycled aggregates enriched. This recurring pattern highlights how recycled aggregates impair concrete’s flexural strength, which makes mix design extremely important in order to preserve intended mechanical performance. Figure 7 shows the flexural strength test results.

Figure 7
Results of a flexural strength test.

4.6. Water absorption test

The water absorption results at different testing durations depict a slight increase in water absorption as the percentage of recycled aggregates increases in the concrete mixes. For conventional concrete (M1 mix), the water absorption percentages at 28 days, 56 days, and 90 days were 3.43%, 3.15%, and 2.97%, respectively. However, with the inclusion of recycled aggregates in the M2 to M6 mixes, there was a marginal rise in water absorption values. At 28 days, the water absorption percentages ranged from 3.47% for M2 mix to 3.61% for M6 mix. Similarly, at 56 days and 90 days, the water absorption percentages increased slightly as the proportion of recycled aggregates increased. This minor upward trend indicates a potential increase in porosity and permeability of the concrete with the addition of recycled aggregates, necessitating measures to mitigate moisture ingress and ensure long-term durability. Figure 8 shows the water absorption test results.

Figure 8
Water absorption test results.

4.7. Acid resistance test

The percentage of weight loss in acid attack after 28 days indicates a slight increase as the proportion of recycled aggregates increases in the concrete mixes. For conventional concrete (M1 mix), the weight loss percentage was 4.48%. However, with the inclusion of recycled aggregates in the M2 to M6 mixes, there was a gradual rise in weight loss percentages. At 28 days, the weight loss percentages ranged from 4.53% for M2 mix to 4.72% for M6 mix. This minor upward trend suggests a potential increase in susceptibility to acid attack with the addition of recycled aggregates, underscoring the importance of adequate protective measures or alternative materials in environments prone to acid exposure for ensuring long-term durability. The percentage of weight loss in the acid resistance test is displayed in Figure 9.

Figure 9
Percentage of weight loos in acid resistance test.

The percentage of strength loss in acid attack after 28 days shows a gradual increase as the proportion of recycled aggregates increases in the concrete mixes. For conventional concrete (M1 mix), the strength loss percentage was 7.43%. However, with the inclusion of recycled aggregates in the M2 to M6 mixes, there was a progressive rise in strength loss percentages. At 28 days, the strength loss percentages ranged from 7.50% for M2 mix to 7.82% for M6 mix. This increasing trend indicates a higher susceptibility to strength degradation under acid attack conditions with the addition of recycled aggregates, emphasizing the importance of protective measures. Figure 10 shows the percentage strength loss after acid resistance test.

Figure 10
Percentage strength loss after acid resistance test.

4.8. Sulphate attack test

The percentage of strength loss in sulphate attack after 28 days exhibits a gradual increase as the proportion of recycled aggregates rises in the concrete mixes. For conventional concrete (M1 mix), the strength loss percentage was 5.95%. However, with the incorporation of recycled aggregates in the M2 to M6 mixes, there was a progressive rise in strength loss percentages. At 28 days, the strength loss percentages ranged from 6.02% for M2 mix to 6.27% for M6 mix. This escalating trend indicates a higher susceptibility to strength degradation under sulphate attack conditions with the addition of recycled aggregates, emphasizing the need for protective measures or alternative materials to mitigate deterioration in concrete structures exposed to sulphate-rich environments. The percentage of strength lost during the sulfate attack test is displayed in Figure 11.

Figure 11
Percentage of strength loss after sulphate attack test.

4.9. Chloride ion test

The percentage of strength loss in chloride attack after 28 days demonstrates a gradual increase as the proportion of recycled aggregates increases in the concrete mixes. For conventional concrete (M1 mix), the strength loss percentage was 6.16%. However, with the inclusion of recycled aggregates in the M2 to M6 mixes, there was a progressive rise in strength loss percentages. At 28 days, the strength loss percentages ranged from 6.23% for M2 mix to 6.49% for M6 mix. This ascending trend indicates a higher susceptibility to strength deterioration under chloride attack conditions with the addition of recycled aggregates, emphasizing the necessity for protective measures or alternative materials to mitigate degradation in concrete structures exposed to chloride-rich environments. Figure 12 shows the percentage of strength loss after chloride ion test.

Figure 12
Percentage of strength loss after chloride ion test.

4.10. SEM analysis

The scanning electron microscopy (SEM) analysis revealed distinct morphological differences between the concrete samples with partially replaced recycled coarse aggregate (PRRCA) and conventional concrete. In the conventional concrete, the coarse aggregates appeared relatively uniform in size and shape, exhibiting typical angular and irregular structures. However, in the PRRCA concrete, variations in the morphology of the coarse aggregates were observed due to the presence of recycled materials. These variations included irregular shapes, surface roughness, and the presence of adhered particles. One of the key aspects studied through SEM analysis was the interface zone between the cementitious matrix and the coarse aggregates. In conventional concrete, a well-defined interface with limited voids and cracks was observed, indicating good interfacial bonding between the cement paste and the coarse aggregates. However, in the PRRCA concrete, the interface zone exhibited more irregularities, including microcracks and voids. This suggests that the incorporation of recycled aggregates might have influenced the interfacial transition zone, potentially affecting the overall performance of the concrete.

Quantitative analysis of the SEM images revealed differences in porosity and microstructure between the PRRCA and conventional concrete. The PRRCA concrete exhibited higher porosity levels compared to conventional concrete, attributed to the presence of pores within the recycled aggregates and the potentially weaker interfacial bonding. This increased porosity can impact the durability and mechanical properties of the concrete, such as permeability and strength, highlighting the importance of optimizing the mix design and incorporating supplementary materials to mitigate these effects. Further examination of the SEM images provided insights into the interaction between the cement paste and the coarse aggregates. In conventional concrete, a denser and more uniform distribution of hydration products around the aggregates was observed, indicating effective cement paste-aggregate bonding. In contrast, in the PRRCA concrete, the presence of recycled aggregates led to variations in the distribution and coverage of hydration products, suggesting potential challenges in achieving adequate bonding and mechanical properties. Strategies such as surface treatment of recycled aggregates or modifying the cementitious binder may be explored to enhance the interfacial bonding and overall performance of PRRCA concrete. Figures 13 and 14 shows the SEM image of conventional concrete mix (M1 mix) and 10% recycled coarse aggregate used in concrete (M2 mix).

Figure 13
SEM image of M1 mix.

Figure 14
SEM image of M2 mix.

5. CONCLUSION

The comprehensive evaluation of various concrete properties in relation to the incorporation of recycled aggregates reveals essential insights into the performance and durability of sustainable concrete mixes. The results highlight the intricate balance between sustainability and material performance, shedding light on the challenges and opportunities associated with the utilization of recycled aggregates in concrete production. The assessment of workability through slump and compaction factor tests demonstrates a consistent decrease in workability as the percentage of recycled aggregates increases in the concrete mixes. This reduction in workability can be attributed to the irregular shape, higher absorption, and lower specific gravity of recycled aggregates compared to conventional aggregates. As a result, meticulous mix design adjustments are necessary to maintain adequate workability while promoting sustainability in concrete production. The evaluation of physical properties such as compressive strength, split tensile strength, and flexural strength unveils a progressive decline in strength with higher proportions of recycled aggregates. This deterioration in mechanical properties underscores the challenges associated with achieving optimal performance in sustainable concrete mixes. The incorporation of recycled aggregates introduces variations in material properties, leading to reduced bonding between aggregate particles and cement paste, ultimately impacting the overall strength of the concrete. The investigation into durability properties, including water absorption and resistance to chemical attacks such as acid, sulphate, and chloride, provides valuable insights into the long-term performance of recycled aggregate concrete. The results indicate a marginal increase in water absorption and susceptibility to chemical attacks with higher proportions of recycled aggregates. This highlights how vital it is to put in place suitable safeguards or substitute materials in order to lessen deterioration and guarantee the longevity of concrete buildings in challenging environmental circumstances. Because it uses less natural resources and produces less waste, using recycled aggregates in concrete manufacturing presents exciting potential for sustainable construction practices. However, the integration of recycled aggregates presents challenges related to workability, mechanical properties, and durability, which must be carefully addressed through optimized mix designs and quality control measures. This includes exploring innovative mix designs, incorporating supplementary cementitious materials, and implementing advanced testing techniques to optimize material properties and overcome the limitations associated with recycled aggregates. From this study underscore the importance of a holistic approach towards sustainable concrete production, balancing environmental considerations with material performance and structural integrity.

6. BIBLIOGRAPHY

• ^[1]
  ARASU, N., RAFSAL, M.M., SURYA KUMAR, O.R., “Experimental investigation of high performance concrete by partial replacement of fine aggregate by construction demolition waste”, International Journal of Scientific and Engineering Research, v. 9, n. 3, 2018.
• ^[2]
  THOMAS, J., THAICKAVIL, N.N., WILSON, P., “Strength and durability of concrete containing recycled concrete aggregates”, Journal of Building Engineering, v. 19, pp. 349–365, 2018. doi: http://doi.org/10.1016/j.jobe.2018.05.007.
  » https://doi.org/10.1016/j.jobe.2018.05.007
• ^[3]
  ALBAYATI, A., WANG, Y., WANG, Y., et al, “A sustainable pavement concrete using warm mix asphalt and hydrated lime treated recycled concrete aggregates”, Sustainable Materials and Technologies, v. 18, pp. e00081, 2018. doi: http://doi.org/10.1016/j.susmat.2018.e00081.
  » https://doi.org/10.1016/j.susmat.2018.e00081
• ^[4]
  ARASU, A., NATARAJAN, M., BALASUNDARAM, N., et al, “Utilizing recycled nanomaterials as a partial replacement for cement to create high-performance concrete”, Global NEST Journal, v. 25, n. 6, pp. 89–92, 2023.
• ^[5]
  LEVY, S., HELENE, P., “Durability of recycled aggregates concrete: a safe way to sustainable development”, Cement and Concrete Research, v. 34, n. 11, pp. 1975–1980, 2004. doi: http://doi.org/10.1016/j.cemconres.2004.02.009.
  » https://doi.org/10.1016/j.cemconres.2004.02.009
• ^[6]
  YAP, S.P., CHEN, P.Z.C., GOH, Y., et al, “Characterization of pervious concrete with blended natural aggregate and recycled concrete aggregates”, Journal of Cleaner Production, v. 181, pp. 155–165, 2018. doi: http://doi.org/10.1016/j.jclepro.2018.01.205.
  » https://doi.org/10.1016/j.jclepro.2018.01.205
• ^[7]
  MAJHI, R.K., NAYAK, A., MUKHARJEE, B.B., “Development of sustainable concrete using recycled coarse aggregate and ground granulated blast furnace slag”, Construction & Building Materials, v. 159, pp. 417–430, 2018. doi: http://doi.org/10.1016/j.conbuildmat.2017.10.118.
  » https://doi.org/10.1016/j.conbuildmat.2017.10.118
• ^[8]
  GIRI, J., PANDA, M., SAHOO, U., “Use of waste polyethylene for modification of bituminous paving mixes containing recycled concrete aggregates”, Road Materials and Pavement Design, v. 21, n. 2, pp. 289–309, 2018. doi: http://doi.org/10.1080/14680629.2018.1487873.
  » https://doi.org/10.1080/14680629.2018.1487873
• ^[9]
  SENARATNE, S., GERACE, D., MIRZA, O., et al, “The costs and benefits of combining recycled aggregate with steel fibres as a sustainable, structural material”, Journal of Cleaner Production, v. 112, pp. 2318–2327, 2016. doi: http://doi.org/10.1016/j.jclepro.2015.10.041.
  » https://doi.org/10.1016/j.jclepro.2015.10.041
• ^[10]
  RASHID, K., MUNIB UL REHMAN, J., “Multi-criteria optimization of recycled aggregate concrete mixes”, Journal of Cleaner Production, v. 276, pp. 124316, 2020. doi: http://doi.org/10.1016/j.jclepro.2020.124316.
  » https://doi.org/10.1016/j.jclepro.2020.124316
• ^[11]
  PASANDÍN, A.R., PÉREZ, I., “Performance of hot-mix asphalt involving recycled concrete aggregates”, The International Journal of Pavement Engineering, v. 21, n. 9, pp. 1044–1056, 2018. doi: http://doi.org/10.1080/10298436.2018.1518525.
  » https://doi.org/10.1080/10298436.2018.1518525
• ^[12]
  THOMAS, C., SETIÉN, J., POLANCO, J.A., et al, “Durability of recycled aggregate concrete”, Construction & Building Materials, v. 40, pp. 1054–1065, 2013. doi: http://doi.org/10.1016/j.conbuildmat.2012.11.106.
  » https://doi.org/10.1016/j.conbuildmat.2012.11.106
• ^[13]
  NAVEEN ARASU, A., NATARAJAN, M., BALASUNDARAM, N., et al, “Development of high performance concrete by using nano material graphene oxide in partial replacement of cement”, AIP Conference Proceedings, v. 2861, n. 050008, pp. 1–11, 2023.
• ^[14]
  BRAVO, M., BRITO, J., PONTES, J., et al, “Durability performance of concrete with recycled aggregates from construction and demolition waste plants”, Construction & Building Materials, v. 77, pp. 357–369, 2015. doi: http://doi.org/10.1016/j.conbuildmat.2014.12.103.
  » https://doi.org/10.1016/j.conbuildmat.2014.12.103
• ^[15]
  ARASU, N.A., RAMASAMY, V.P., HARVEY, D.V., “A experimental analysis on bio concrete with bentonite as partial replacement of cement”, International Research Journal of Engineering and Technology, v. 7, n. 10, pp. 689–695, 2020.
• ^[16]
  WANG, J., ZHANG, J., CAO, D., “Pore characteristics of recycled aggregate concrete and its relationship with durability under complex environmental factors”, Construction & Building Materials, v. 121642, 2020. doi: http://doi.org/10.1016/j.conbuildmat.2020.121642.
  » https://doi.org/10.1016/j.conbuildmat.2020.121642
• ^[17]
  MATÍAS, D., DE BRITO, J., ROSA, A., et al, “Durability of concrete with recycled coarse aggregates: influence of superplasticizers”, Journal of Materials in Civil Engineering, v. 26, n. 7, pp. 06014011, 2014. doi: http://doi.org/10.1061/(ASCE)MT.1943-5533.0000961.
  » https://doi.org/10.1061/(ASCE)MT.1943-5533.0000961
• ^[18]
  NAVEEN ARASU, A., NATARAJAN, M., BALASUNDARAM, N., et al, “Optimization of high performance concrete by using nano materials”, Research on Engineering Structures Materials, v. 3, n. 9, pp. 843–859, 2023.
• ^[19]
  GAO, D., ZHANG, L., ZHAO, J., et al, “Durability of steel fibre-reinforced recycled coarse aggregate concrete”, Construction & Building Materials, v. 232, pp. 117119, 2020. doi: http://doi.org/10.1016/j.conbuildmat.2019.117119.
  » https://doi.org/10.1016/j.conbuildmat.2019.117119
• ^[20]
  BABU, V.S., MULLICK, A., JAIN, K., et al, “Strength and durability characteristics of high-strength concrete with recycled aggregate-influence of processing”, Journal of Sustainable Cement-Based Materials, v. 4, n. 1, pp. 54–71, 2015. doi: http://doi.org/10.1080/21650373.2014.976777.
  » https://doi.org/10.1080/21650373.2014.976777
• ^[21]
  EVANGELISTA, L., BRITO, J., “Durability performance of concrete made with fine recycled concrete aggregates”, Cement and Concrete Composites, v. 32, n. 1, pp. 9–14, 2010. doi: http://doi.org/10.1016/j.cemconcomp.2009.09.005.
  » https://doi.org/10.1016/j.cemconcomp.2009.09.005
• ^[22]
  LOVATO, P.S., POSSAN, E., DAL MOLIN, D.C.C., et al, “Modeling of mechanical properties and durability of recycled aggregate concretes”, Construction & Building Materials, v. 26, n. 1, pp. 437–447, 2012. doi: http://doi.org/10.1016/j.conbuildmat.2011.06.043.
  » https://doi.org/10.1016/j.conbuildmat.2011.06.043
• ^[23]
  ARASU, R., PRABHU, A., “Investigation on partial replacement of cement by GGBS”, Journal of Critical Reviews, v. 7, n. 17, pp. 3827–3831, 2020.
• ^[24]
  ALI, B., QURESHI, L.A., “Influence of glass fibers on mechanical and durability performance of concrete with recycled aggregates”, Construction & Building Materials, v. 228, pp. 116783, 2019. doi: http://doi.org/10.1016/j.conbuildmat.2019.116783.
  » https://doi.org/10.1016/j.conbuildmat.2019.116783
• ^[25]
  RODRIGUES, F., CARVALHO, M., EVANGELISTA, L., et al, “Physical-chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants”, Journal of Cleaner Production, v. 52, pp. 438–445, 2013. doi: http://doi.org/10.1016/j.jclepro.2013.02.023.
  » https://doi.org/10.1016/j.jclepro.2013.02.023
• ^[26]
  KHALAF, F., DEVENNY, A.S., “Recycling of demolished masonry rubble as coarse aggregate in concrete: review”, Journal of Materials in Civil Engineering, v. 16, n. 4, pp. 331–340, 2004. doi: http://doi.org/10.1061/(ASCE)0899-1561(2004)16:4(331).
  » https://doi.org/10.1061/(ASCE)0899-1561(2004)16:4(331)
• ^[27]
  PACHECO, J., DE BRITO, J., “Recycled aggregates produced from construction and demolition waste for structural concrete: constituents, properties and production”, Materials (Basel), v. 14, n. 19, pp. 5748, 2021. doi: http://doi.org/10.3390/ma14195748. PubMed PMID: 34640143.
  » https://doi.org/10.3390/ma14195748
• ^[28]
  KADHAR, S.A., GOPAL, E., SIVAKUMAR, V., et al, “Optimizing flow, strength, and durability in high-strength self-compacting and self-curing concrete utilizing lightweight aggregates”, Matéria (Rio de Janeiro), v. 29, n. 1, pp. e20230336, 2024. doi: http://doi.org/10.1590/1517-7076-rmat-2023-0336.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0336
• ^[29]
  ULSEN, C., KAHN, H., HAWLITSCHEK, G., et al, “Production of recycled sand from construction and demolition waste”, Construction & Building Materials, v. 40, pp. 1168–1173, 2013. doi: http://doi.org/10.1016/j.conbuildmat.2012.02.004.
  » https://doi.org/10.1016/j.conbuildmat.2012.02.004
• ^[30]
  KIM, J., GRABIEC, A.M., UBYSZ, A., “An experimental study on structural concrete containing recycled aggregates and powder from construction and demolition waste”, Materials (Basel), v. 15, n. 7, pp. 2458, 2022. doi: http://doi.org/10.3390/ma15072458. PubMed PMID: 35407789.
  » https://doi.org/10.3390/ma15072458
• ^[31]
  LEIVA, C., SOLÍS-GUZMÁN, J., MARRERO, M., et al, “Recycled blocks with improved sound and fire insulation containing construction and demolition waste”, Waste Management (New York, N.Y.), v. 33, n. 3, pp. 663–671, 2013. doi: http://doi.org/10.1016/j.wasman.2012.06.011. PubMed PMID: 22784475.
  » https://doi.org/10.1016/j.wasman.2012.06.011
• ^[32]
  PARTHASAARATHI, R., BALASUNDARAM, N., ARASU, N., “Analysing the Impact and Investigating Coconut Shell Fiber Reinforced Concrete (CSFRC) under Varied Loading Conditions”, Journal of Advanced Research in Applied Sciences and Engineering Technology, v. 35, n. 1, pp. 106–120, 2024.
• ^[33]
  KALPAVALLI, A., NAIK, S.M., “Use of demolished concrete wastes as coarse aggregates in high strength concrete production”, International Journal of Engineering Research & Technology (Ahmedabad), v. 4, n. 7, 2015. doi: http://doi.org/10.17577/IJERTV4IS070935.
  » https://doi.org/10.17577/IJERTV4IS070935

Publication Dates

• Publication in this collection
  23 Aug 2024
• Date of issue
  2024

History

• Received
  20 May 2024
• Accepted
  01 July 2024