Natural Aggregate Concrete Research Articles

Mechanical and fracture properties of slag/steel slag-based geopolymer fully recycled aggregate concrete

Blast furnace /steel slag-based geopolymer and recycled aggregate (RA) as green alternatives to cement and natural aggregate (NA), respectively, are attracting increasing attention. This study investigated the influence of four different aggregate systems (i.e., full-NA, full-recycled coarse aggregate, full-recycled fine aggregate, and full-RA) and three different replacement ratios of steel slag (i.e., 0%, 25%, and 50% of the precursor) on the mechanical properties (compressive and splitting tensile strength) and fracture properties (fracture energy and fracture toughness) of one-part slag/steel slag-based geopolymer concrete, aiming to promote its utilization in structural engineering. The experimental results indicate that substituting ordinary Portland cement with slag-based one-part geopolymer significantly enhanced the compressive and splitting tensile strength of geopolymer natural aggregate concrete (GNAC), although it leaded to a decrease in fracture properties. The incorporation of RA in GNAC resulted in deteriorated properties, with the 28-day compressive strength being reduced by up to 5%− 19.4% and fracture energy being reduced by up to 16.8%− 43.8%. Moreover, incorporating an appropriate amount of steel slag (approximately 25%) in geopolymer fully recycled aggregate concrete (GFRAC) had minimal impact on mechanical properties, while it enhanced the fracture energy values by up to approximately 16.6%. Nevertheless, a higher content of steel slag adversely affected the relevant properties due to its lower cementitious activity compared to slag. To mitigate the drawbacks associated with steel slag, less than 25% of steel slag content is recommended considering the mechanical and fracture properties of GFRAC.

Evaluate the Impact of Using Recycled Aggregates on Place of Natural Aggregates in Concrete

Abstract: The research involved sieving the crushed concrete to attain the required aggregate sizes before incorporating it into fresh concrete mixes. Various tests were conducted to evaluate the performance of the recycled aggregate in concrete, encompassing aspects such as compressive strength at 7 and 28 days, a crucial parameter in assessing the structural viability of the recycled material. The experimental results demonstrated that high-quality concrete could be produced by incorporating crushed concrete sourced from demolished sites. Comparative analyses between the compressive strength of the recycled concrete and that of conventional concrete were conducted at both 7 and 28 days. The findings revealed that, even when replacing up to 50% of the coarse aggregate with crushed concrete, the compressive strength of the recycled concrete matched that of conventional concrete after 28 days. This indicates the viability and structural integrity of concrete produced with recycled aggregate, providing a compelling case for its use in construction.

Experimental and numerical evaluations of the shear performance of recycled aggregate RC beams strengthened using CFRP sheets

Conserving the ecosystems of the globe, protecting natural resources, and improving environmental conditions can all be achieved by considering sustainability in the construction industry. Recycling of building and demolition waste is one of the key approaches being investigated to accomplish this target. Twelve reinforced concrete (RC) beams were constructed for the current study in order to analyze the shear behavior of recycled aggregate concrete (RAC) beams externally strengthened with carbon fiber reinforced polymer (CFRP) sheets. The main goal of the experimental matrix was to investigate the effect of the recycled aggregate ratio on the shear response of RAC, where three recycled coarse aggregate ratios of 20%, 60%, and 100% were suggested. Additionally, the effects of incorporating two or four CFRP strengthening layers on the ultimate load, failure pattern, load-deflection responses, and stiffness of RAC beams were also investigated. Results revealed that, when different ratios of recycled aggregate estimated at 20%, 60%, and 100% were substituted for natural aggregates, the compressive strength decreased by 4.3%, 24.2%, and 40.0%, respectively, compared to natural aggregate concrete. Moreover, the RC beam that was cast utilizing 20% recycled aggregates and strengthened with four CFRP sheets exhibited the highest ultimate load among all the tested RAC beams of 84.8 kN, which was 22.9% higher than the un-strengthened specimen totally cast with natural aggregate. Furthermore, a three-dimensional (3D) non-linear finite element model (FEM) was constructed using the ABAQUS program in order to compare the effects of employing continuous CFRP sheets for the whole critical shear span length to intermittent strips that had been experimentally tested.

Bond responses and anchorage length of GFRP bar in precast recycled aggregate concrete

Precast recycled aggregate concrete (PRAC) employs precast reject-derived recycled aggregates (PRAs) and exhibits mechanical properties on par with or superior to those of natural aggregate concrete (NAC). Nevertheless, the durability of PRAC is hampered by aged mortar. To address this issue, integrating high durability glass fiber reinforced polymer (GFRP) bars into PRAC emerges as a potential solution for constructing enduring structures. Building upon this context, the study focuses on the bond responses between PRAC and GFRP bars, an area with limited existing research. Three main tasks were conducted: Firstly, a comprehensive test program involving 108 pullout samples was conducted to investigate the key variables' effects on bond failure mode and stress-slip relationship. Subsequently, an equation was developed to determine the peak bond strength of recycled aggregate concrete (RAC) based on available test data. Additionally, reliability analyses were performed to discuss the anchorage length of GFRP bar embedded in RAC. The findings are as follows: (a) The PRAC's bond capacity initially increased then decreased with rising PRA content. At full replacement, PRAC's bond strength was 28.3% lower than NAC. However, a two stage mixing approach restored PRAC's bond capacity to NAC levels. (b) Helical wrapping of the GFRP bar consistently exhibited the highest bond capacity, with an average bond strength 51% greater than a sand coated GFRP bar and 21% higher than a GFRP bar treated with both helical wrapping and sand coating. (c) Current codes specifying the critical anchorage length for FRP bar in NAC were often unsafe for RAC. Hence, a new expression, factoring in RA content, type and RAC mixing method, was proposed to determine the suitable anchorage length.

Effect of Ground Granulated Blast-Furnace Slag on the Bond Strength of Recycled Aggregate Concrete

This research experimentally investigated the bond strength of recycled aggregate concrete containing high volume ground granulated blast-furnace slag (GGBFS). Concrete mixtures made with 0%, 15%, 45% and 75% replacement of cement with GGBFS were prepared. Water-to-binder ratios ranged from 0.30 to 0.50. The fresh properties, compressive strength and pullout bond strength of concrete were measured and presented. Test results shows that the compressive strength and bond strength of concrete containing GGBFS were superior to the concrete without GGBFS at all ages. In addition, the bond strength of the recycled aggregate concrete containing high volume GGBFS (75% cement replacement) could exceed that of natural aggregate concrete without GGBFS. This result shows that it is feasible for applying recycled aggregate concrete incorporating high volume GGBFS in concrete constructions.

The Environmental Impact of Reusing Post-Earthquake Demolition Waste: İskenderun Case Study

Producing recycled aggregate from construction and demolition waste generated by earthquakes
 and using it as raw material in concrete production would be effective for urgent waste
 management after disasters and to reduce the environmental impact of concrete production by
 decreasing resource use. In this study, the life cycle assessment (LCA) method was used to
 examine the environmental implications of concrete produced using recycled aggregates (RA)
 derived from construction and demolition waste (CDW) of buildings demolished after the
 earthquake that struck Iskenderun and was centered in Kahramanmaraş. In addition, the
 environmental consequences of an equal volume of concrete produced in the same location
 utilizing natural aggregates (NA) were assessed. For the LCA of these two types of concrete,
 openLCA software and the ReCiPe midpoint database were used. LCA was conducted
 considering terrestrial ecotoxicity, climate change, terrestrial acidification, photochemical
 oxidant formation, marine ecotoxicity, human toxicity, freshwater ecotoxicity, ozone depletion,
 particulate matter formation, marine eutrophication, and ionizing radiation impact factors. The
 results show that cement has the highest impact on the environment by far. RAC (recycled
 aggregate concrete) has a lower environmental impact than NAC (natural aggregate concrete), in
 general.

Effect of pore water pressure on mechanical performance of recycled aggregate concrete under triaxial compression

The pore water pressure in concrete can significantly increase due to volume compression. Recycled aggregate concrete (RAC) possesses a more complex microstructure compared to natural aggregate concrete (NAC). Understanding the porosity and micromechanical properties of RAC is crucial for analysing its failure mechanism under the influence of coupled confining pressure and pore water pressure. This study compares the constituent proportions and micromechanical properties of interfacial transition zones (ITZs) and the adjacent paste matrix in NAC and RAC. Compressive stress-strain curves were obtained for concrete under coupled confining pressure and pore water pressure. The results indicate that the newly formed ITZ, which bonds to old mortar, outperformed the one bonded to natural aggregate when considering the same water-cement ratio. Compressive strength, ductility, and maximum volumetric strain gradually increased with increasing confining pressure. However, when pore water pressure was removed, compressive strength decreased while elastic modulus improved. Due to the inferior microstructures of RAC compared to NAC, the supportive effect of pore water becomes more pronounced. This is evident in the gradual increase in peak strain with increased pore water pressure for the stress-strain curves of RAC (100 % replacement ratio). Finally, a failure criterion and stress-strain theoretical model considering pore water pressure are proposed, and satisfactory fitting results are obtained.

Assessing the potential of recycled fine aggregate from freeze-thawed parent concrete for structural concrete

Recycled fine aggregate (RFA) generated from waste concrete, especially in harsh environment, can be considered as an alternative to natural sand. The yield rate, gradation and properties of RFA from natural aggregate concrete with the target strength of C40 as parent concrete (PC) every 200 freeze–thaw (FT) cycles are investigated. To more accurately evaluate the application potential of RFA, the mechanical properties and durability of recycled fine aggregate concrete (RFAC) is further studied. The results showed that as the FT cycles of PC increased, the yield rate of RFA decreases and the grading curve of RFA meets the requirements of Class II aggregate. The limit FT cycles of PC in Class II and III RFA are 148 and 450, respectively. For the compressive strength of RFAC that meets the design requirements, the FT cycles of PC are no more than 530. Based on 50 years of RFAC in Class D and Class E environments, the limit FT cycles of PC are 663 and 200, respectively. The limit FT cycles of PC are 221 based on 50 years of RFAC service in cold regions. Through the FT cycles of PC, the Class of RFA and the mechanical and durability of RFAC can be directly predicted. This provides a theoretical and data support for improving the utilization rate of waste concrete in FT environment.

Experimental Study and Mathematical Modeling of Mechanical Properties of Basalt Fiber-Reinforced Recycled Concrete Containing a High Content of Construction Waste

Herein, we conducted an experimental test on basalt fiber-reinforced concrete with a high content of construction and demolition waste and then established some mathematical models based on Taylor’s formula. The concrete was prepared by using recycled clay brick powder in place of cement and recycled coarse aggregates as a substitution for natural coarse aggregates. The basalt fiber in weight dosages of 0, 0.1, 0.3, and 0.5% was used for reinforcement. The results showed that the compressive strength of concrete declined as the content of recycled aggregates increased, while the compressive strength first increased and then decreased as the basalt fiber dosage lifted. Regarding the splitting tensile strength, the reinforcement effect of basalt fiber in concrete with a high content of recycled aggregate is more significant when compared to its to its counterpart, which contains no or fewer recycled aggregates. The concrete with 0.5% basalt fiber dosage and 100% recycled aggregate content retains an equivalent compressive strength as to that of natural aggregate concrete and has about a 90% splitting tensile strength. In addition, the cubic function in comparison to the quadratic function has a higher fitting accuracy.

Experimental study on mechanical properties of recycled aggregate concrete with polypropylene fiber under combined compression‐shear loading

AbstractTo investigate the mechanical properties of polypropylene fiber recycled aggregate concrete (PPFRAC) under compression‐shear, 69 recycled aggregate concrete (RAC) specimens were tested with the parameters of polypropylene (PP) fiber volume content (0, 0.6, 0.9, and 1.2 kg/m3), recycled coarse aggregate (RCA) replacement rate (0%, 30%, 50%, 70%, and 100%), and normal stress (0, 3, and 6 MPa). In the tests, the failure pattern of the specimens was observed, and the effects of the polypropylene fiber content on the direct shear stress, compression‐shear stress, initial shear stiffness, and shear ductility coefficient of the PPFRAC were thoroughly investigated. The results show that as the polypropylene fiber content increases, the direct shear stress of concrete (Natural aggregate concrete and 100% recycled coarse aggregate concrete [100%RCA]) first increases and then decreases gradually. Meanwhile, the best PP fiber content is 0.9 kg/m3 in this study. Furthermore, the compression‐shear stress‐displacement curves of specimens were obtained. The compression‐shear strength under normal stress at 6 MPa is approximately 230% greater than at 0 MPa. However, the peak shear stress of concrete is almost not affected by the replacement rate of RCA. Finally, based on the Mohr circle theory, the compression‐shear calculation model of PPFRAC is verified, and the optimal calculation formula is given.

Evaluation on the mechanical, thermal insulation and durability properties of wood recycled ecological concrete

As a non-renewable resource, the extraction of natural aggregates not only consumes a large amount of resources, but also causes serious damage to the environment. In this study, wood recycled ecological concrete (WREC) was prepared using wood aggregate (WA) and sawdust as coarse and fine aggregates, respectively, with the aim of exploring its potential application in construction. The results showed that the use of WA and sawdust reduced the mechanical properties and carbonation resistance of WREC, but improved its toughness and thermal insulation properties, as well as acted as an internal curing and retardation of self-shrinkage. The dry density of WREC was as low as 1646 kg/m3, and the maximum 28-day compressive and flexural strengths were 26.4 MPa and 4.8 MPa, respectively, which were close to those of conventional C30 concrete. The flexural-compressive ratio was in the range of 0.179–0.269, which was better than that of natural aggregate concrete (NAC), and the thermal conductivity of some WREC was less than 0.23 W/(m·K), which can meet the engineering requirements of thermal insulation materials. It is suitable for preparing green thermal insulation wall materials and prefabricated wall panels.

Experimental study on dynamic properties of flax fiber reinforced recycled aggregate concrete

Recycling waste concrete is critical to land use and reduction of landfills. It is a good option to recycle the waste coarse aggregates from it and add them to the concrete matrix. Due to the existence of new and old interface transition zones (ITZs), the quasi-static compressive strength of recycled aggregate concrete is lower than that of natural aggregate concrete, which limits the widespread application of recycled aggregate concrete. In order to improve its engineering application of recycled aggregate concrete, the dynamic compressive properties were studied. Thus, based on a Split Hopkinson Pressure Bar (SHPB) device, the effects of strain rate and recycled coarse aggregate (RCA) replacement ratio on the failure mode, dynamic compressive strength, critical strain and toughness were investigated. It was found that increasing the strain rate led to the aggravation of the specimen damage and growth of the dynamic compressive strength, toughness and critical strain. At a high strain rate, the strain rate effect changed the failure mode of recycled aggregate concrete. This reduced the performance difference between recycled and natural aggregate concrete, in terms of the dynamic compressive strength. The recycled aggregate concrete had a similar toughness to the natural aggregate concrete. Although the growth of the RCA replacement ratio decreased the dynamic compressive strength and increased the critical strain, it had a little effect on the toughness. In order to reduce the brittleness of the recycled aggregate concrete and improve its deformability, non-synthetic, green and low-consumption flax fibers were incorporated into the concrete matrix, and its dynamic compressive behaviors were studied experimentally accordingly. Tests verified that the addition of flax fibers significantly reduced the damage and increased the critical strain. Especially when the strain rate was greater than 200 s-1, flax fiber reinforced recycled aggregate concrete exhibited a superior energy consumption ability. Based on the experimental data, empirical equations were proposed to describe the dynamic compressive strength, critical strain and toughness at different strain rates.

Incorporation of Steel Fibers to Enhance Performance of Sustainable Concrete Made with Waste Brick Aggregates: Experimental and Regression-Based Approaches

Each year, an enormous amount of construction waste is produced worldwide. The reuse of construction waste in construction works is a sustainable solution. The present research work utilized recycled brick aggregates in the production of concrete. The resulting concrete exhibited substandard splitting tensile, flexural, and compressive properties. Steel fibers were used to improve these substandard properties of recycled brick aggregate concrete. The volume fractions of 1%, 2%, and 3% for steel fibers were mixed in concrete, whereas recycled brick aggregates were obtained from solid fired-clay bricks, hollow fired-clay bricks, and cement–clay interlocking bricks. The compressive strength was enhanced by up to 35.53% and 66.67% for natural and recycled brick aggregate concrete, respectively. Strengthened flexural specimens demonstrated up to 8765.69% increase in the energy dissipation. Specimens strengthened with steel fibers showed substantially improved splitting tensile, flexural, and compressive responses. Separate equations were proposed to predict the peak compressive strength, strain at peak compressive strength, elastic modulus, and post-peak modulus of recycled brick aggregate concrete. The proposed regression equations were utilized in combination with an existing compressive stress–strain model. A close agreement was observed between experimental and predicted compressive stress–strain curves of recycled brick aggregate concrete.

Behavior of reinforced recycled aggregate concrete beams and slabs strengthened in flexure and punching with CFRP composites

Recycling of concrete generated from construction and demolition waste as coarse aggregates in concrete has been a focus of several studies for the evolution of the green concrete and conservation of natural resources. This investigation, therefore, focusses on the study of the behavior of RC beams strengthened with externally bonded CFRP wraps, cast with both natural and recycled aggregates concrete. Furthermore, one-way slabs were strengthened with Near Surface Mounted (NSM) bars, while two-way slabs were strengthened with CFRP strips. One-way and two-way slabs used in the study were cast with both natural and recycled aggregate concrete (RAC). In RAC, natural aggregates were replaced by 30% recycled concrete aggregates. All beams and slabs were cast with concrete mix design of 1:1.24:2.6 and w/c ratio of 0.43. Beams and one-way slabs, control and strengthened, were tested under four-point bending. Whereas, two-way slabs were tested in punching. A significant increase in the load-carrying capacity was observed for both natural and recycled aggregates concrete beams without shear reinforcement and two-way slabs, indicating the effectiveness of strengthening scheme. Increase of 20.5% and 12.6%, respectively, was found in the load-carrying capacities for the cases of both and natural and RAC beams with natural aggregate concrete (NAC) and RAC beams when results were compared for the case of shear deficient control and strengthened RC beams with CFRP wraps. Furthermore, increase of 27 − 37% was noted in load-carrying capacities of both natural and RAC two-way slabs when results were compared for the case of control and strengthened NAC and RAC slabs.

A comparative life cycle assessment on recycled concrete aggregates modified by accelerated carbonation treatment and traditional methods

Recycling of construction and demolition wastes contributes to achieve carbon summit and carbon neutrality early in the construction industry. Accelerated carbonation is a promising new technology for enhancing the properties of recycled concrete aggregates (RCAs) as well as mitigating global warming. This study performed a comparative life cycle assessment on RCAs modified by accelerated carbonation treatment and traditional methods. The effect of different treatment methods on environmental impacts of concrete was evaluated. The key contributors of environmental impacts for concrete incorporating carbonated RCAs were identified. Moreover, a sensitivity analysis on the transport distance of concrete incorporating carbonated RCAs was conducted. Results demonstrated that incorporating carbonated RCAs could significantly reduce the energy demand, environmental impacts and environmental cost compared with natural aggregate concrete. Accelerated carbonation treatment exhibited greater potential than the normal two-stage crushing and heating treatment in mitigating environmental burden, especially for the global warming potential. Cement production and transportation were the primary contributors to environmental impacts of concrete incorporating carbonated RCAs. Sensitivity analysis indicated incorporating carbonated RCAs as alternatives of natural aggregates contributes to lower the environmental impacts of concrete when the natural aggregates are far from urban areas while the recycling center is near the city.

The flowability and high-temperature resistance of manufactured sand concrete: An exploration for high-rise buildings

The depletion of natural concrete aggregates, e.g., river sands, is a gradual process, and hence, manufactured sand concrete (MSC) is widely used in various construction projects. The flowability and high-temperature resistance of MSC directly determine the transport of fresh concrete and the fire resistance of high-rise buildings. In this study, MSC with different superplasticizer contents and sand ratios was prepared and its flowability and high-temperature resistance were studied. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to characterize the microstructure and porosity of MSC. The flowability of MSC with higher than 0.75% superplasticizer content or lower than 43% sand ratio is suitable for super high-rise buildings according to GB/T 50081-2019. The mechanical properties of other MSC meet the C30 requirements except for the MSC with a sand ratio of 48%. And the relatively high superplasticizer content or low sand ratio can make the denser structure and lower porosity of MSC. In addition, the MSC with relatively high superplasticizer content and low sand ratio exhibits better resistance to high temperatures due to a denser structure. This study provides theoretical guidance for using MSC in high-rise buildings and studying fire performance.

Experimental Investigation on the Influence of Superplasticizer on Mechanical Behavior of Recycled Aggregate Concrete

Needs for renovation and efficient use of available land space have led to the destruction of numerous deteriorated civil structures. Consequently, a huge amount of concrete demolished waste is generated annually worldwide. This demolished concrete waste has created an extra burden on the environment and landfills, making the development projects unsustainable. Demolished waste can be recycled and reused for sustainable development and to reduce the demand for fresh natural aggregates (NA). However, the poor performance of recycled aggregate concrete (RAC) compared to natural aggregate concrete (NAC) may be a significant drawback in the recycling and reusing of demolished concrete wastes. This limitation can be overcome by using a superplasticizer, which has the ability to improve different mechanical properties of concrete. The objective of this paper is to assess the effects of the superplasticizer on the mechanical characteristics of RAC. Concrete specimens were prepared to have replacement ratios (0%, 25%, 50%, and 100%) of fresh NA by recycled stone aggregates (RSA) and recycled brick aggregates (RBA). Half of the prepared concrete specimens were admixed with the superplasticizer, having 15% water reduction for concrete mixes. The obtained test results encourage the use of superplasticizers for improving the mechanical properties of RAC. It is observed that fresh, natural coarse aggregates in a concrete mix can be replaced with 50% RSA and 25% RBA with the addition of the superplasticizer without compromising the mechanical performance.

A comprehensive investigation on the impacts of steel slag aggregate on characteristics of high-performance concrete incorporating industrial by-products

Steel slag (SS), an industrial by-product of the steel industry, has the potential to serve as a natural aggregate alternative in concrete production to not only mitigate the exploitation of natural resources but also minimize the environmental impact of its treatment and disposal. This study was designed to investigate comprehensively the impacts of using SS as a full replacement for coarse aggregate and of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) as partial replacements for Portland cement on the engineering properties (i.e., workability, fresh unit weight, porosity, compressive and flexural strengths, ultrasonic pulse velocity, and drying shrinkage), durability (i.e., water absorption, surface electrical resistivity, and rapid chloride ion penetration), and microstructure (i.e., scanning electron microscopy observation) of high-performance concrete (HPC). A comparative analysis of the economic and environmental benefits of SS concrete versus natural aggregate concrete was also performed. The test results revealed that SS, FA, and GGBFS all impacted the properties of HPC significantly. The HPC mixtures in which natural aggregate had been completely replaced with SS exhibited about 20.4–21.3% higher unit weight than the natural aggregate concrete. The HPC samples with added FA and GGBFS exhibited enhanced performance in terms of mechanical strength, durability, and microstructure. Moreover, total material cost, global warming potential (GWP), and ozone depletion potential (ODP) were all found to be significantly lower in the HPC samples produced using SS and either GGBFS or a combination of FA and GGBFS. As a result, after 210 days of normal curing, the 100% SS concrete containing 15% FA and 35% GGBFS as a Portland cement substitution (S100F15G35 specimen) exhibited compressive and flexural strength values of 110.3 and 11.1 MPa, which were approximately 9.0% higher than the corresponding values of the reference concrete. Also, the S100F15G35 specimen registered the respective ultrasonic pulse velocity, surface electrical resistivity, and rapid chloride ion penetration values of 5328 m/s, 113.3 kΩ.cm, and 203 Coulombs, indicating high-quality and durable concrete. Moreover, incorporating 15% FA and 35% GGBFS in SS concrete resulted in a reduction of 15.7% drying shrinkage and 24.4% total material cost, especially reduced environmental impacts with a significant reduction in GWP and ODP by 43.5% and 29.2%, respectively. These findings further demonstrate the potential of using SS in combination with FA and GGBFS to create high-quality HPC that is both more economical and significantly more sustainable than conventional HPC.

Use of recycled aggregate concrete in structural members: a review focused on Southeast Asia

ABSTRACT This article presents a comprehensive review on the use of recycled concrete aggregate (RCA) and recycled aggregate concrete (RAC) in construction, with emphasis on structural applications and identification of challenges and opportunities of RCA/RAC materials in Southeast Asia. For the first time and as a first step towards potential standardization of RCA/RAC in Southeast Asia, the article critically examines the physical and mechanical performance of RCA and RAC in structural applications. Global aggregate demand is projected to surpass 50 billion tons by 2025, with major Asian countries accounting for 62% of consumption. At the same time, the global annual production of construction and demolition waste (C&DW) exceeds 3.57 billion tons, and Asia is responsible for 53% of this total. Recycling C&DW plays a crucial role in addressing environmental issues and promoting sustainable construction practices. Previous research indicates that RAC exhibits certain physical and mechanical deficiencies, with strengths 10% to 20% lower than natural aggregate concrete (NAC). At the structural level, RAC elements show reductions of up to 15% in axial, bonding, shear, and flexural strengths relative to NAC. Measures such as treatment of RCA, recycling process optimization, and optimized mixing techniques are recommended to enhance RAC properties. Prioritizing RCA treatment during construction and exploring novel strengthening techniques could elevate improve RAC and make it suitable for structural applications. The review also found that C&DW recycling efforts vary significantly across countries (particularly in Southeast Asia), with some countries lagging regarding recycling technologies and use of best practices. Various strategies to improve the performance of RAC elements are also proposed and discussed. The main findings and shortcomings of previous investigations are critically discussed, and further research needs are identified.

The Effect of Phase Change Materials on the Physical and Mechanical Properties of Concrete Made with Recycled Aggregate

With the world’s population increasing, the issue of energy consumption has become increasingly prominent, particularly during the building operation phase, where substantial energy is required for heating and cooling. Presently, the energy necessary for buildings is sourced mainly from the combustion of fossil fuels, leading to not only energy scarcity but also severe environmental pollution and ecological damage. Furthermore, rapid urbanization has generated a lot of construction and demolition waste. To address these challenges, one promising approach is the incorporation of phase-change materials in recycled aggregate from construction and demolition waste to replace the raw materials of concrete. In this study, the phase-change material suitable for the thermal comfort requirements of buildings was selected and combined with recycled aggregate to replace the natural aggregate in concrete. All the materials used were characterized and three compositions were prepared. From the results, the workability of concrete increased with the phase-change materials added. Regarding water absorption performance, the incorporation of functionalized recycled aggregate presented a small water absorption performance. However, the mechanical performance decreased with the phase-change materials used. This work provides data for the application of phase-change materials in green concrete.