Natural Coarse Aggregate Research Articles

Durability properties of concrete containing copper heap leach residue as aggregates: experimental and analytical assessments

This paper investigates durability related properties of concretes containing copper heap leach residue (CHLR) as partial replacement of natural fine and coarse aggregates. The use of CHLR as aggregates in concretes promotes the reduction of the dependance on natural aggregates, upcycling of the waste as aggregates and the reduction of carbon footprint associated with natural aggregate productions. In this study, CHLR was washed, dried, and sieved to separate fine aggregate and coarse aggregate, and concretes were prepared with a cement content of 400 kg/m3 and water-cement ratio of 0.435 by replacing 25-75% natural fine and coarse aggregates. The concrete containing 50% CHLR as a partial replacement of natural CA and FA gained compressive strength of 52.9 and 54.0 MPa; drying shrinkage of 662 and 538 με; volume of permeable voids of 6.2 and 5.7%; 1485 and 2640 coulomb of charge passed in chloride permeability; and primary sorptivity coefficients of 4.0 × 10−3 and 4.3 × 10−3 mm/sec0.5 at 180 days, respectively. In contrast, these properties for the control specimens at the same age were 59.1 MPa, 394 με, 5.19%, 1280 coulomb, and 2.5 × 10−3 mm/sec0.5, respectively. The compressive strength and durability aspects declined in concretes using 75% CHLR coarse and fine aggregates. Existing analytical models for durability related properties of concrete containing natural aggregates are compared to that of the concretes using CHLR. Finally, backscattered electron images coupled with energy dispersive x-ray spectroscopy of the CHLR concretes were analyzed to understand the pore refinement, interfacial transition zones, microcracks, and hydration products influencing the durability aspects.

Property Enhancement of Recycled Coarse Aggregate and Its Concrete under CO2-Accelerated Curing Treatment.

The poor properties of recycled coarse aggregate (RCA) and recycled coarse aggregate concrete (RCAC) are considered key constraints hindering the reuse of this waste resource in marine engineering. The CO2-based accelerated carbonation method, which utilizes the alkali aggregate properties of RCA to achieve CO2 uptake and sequestration while significantly enhancing its properties, has attracted widespread attention. However, the degree of improvement in the properties of RCA under different initial moisture conditions (IMCs) and aggregate particle sizes (APSs) after CO2-accelerated carbonation remains unclear. Moreover, the quantitative effect of carbonated recycled coarse aggregate (CRCA), which is obtained from RCA samples with the optimal initial moisture conditions, on the improvement of RCAC under optimal accelerated carbonation modification conditions still needs to be studied in depth. For this investigation, a CO2-accelerated carbonation experiment was carried out on RCA samples with different IMCs and APSs, and the variations in the properties of RCA with respect to its IMC and APS were assessed. The degree of accelerated carbonation modification of RCA under different IMCs and APSs was quantified, and the optimal initial moisture conditions for enhancing the properties of the RCA were confirmed. By preparing concrete specimens based on the natural coarse aggregate, RCA, and CRCA with the best initial moisture conditions (considering the same concrete-water proportion), the effect of CRCA on the workability, mechanical properties, and durability of the corresponding concrete specimen was determined. The findings of this study can be used to effectively promote the sustainable development of marine science and engineering in the future and contribute to global dual-carbon goals, which are of great practical significance and scientific value.

Artificially Intelligent Strength of Tertiary Cement Concrete, Natural Aggregate Is Anglizated with Recycled Aggregate

The researchers have studied RCA in concrete. Compressive strength is a fundamental criteria, although it has been shown that identical concrete may be created regardless of the quality of RCA. This study aims to demonstrate that ternary blended cement concretes made from RCA are a viable alternative in structural concrete and can remain so in the future. The results of this investigation seeks the best ratio of RCA aggregate to natural coarse aggregates in ternary blended cement concrete by testing the compressive concrete strength made with supplementary cementitious materials & RCA that have been blended together in a consistent manner using a chemical admixture that is effective at high concentrations of water reduction. Compressive strengths at 7 and 28 days were measured for two distinct concrete grades (40 MPa & 60 MPa) using natural coarse aggregate replacement ratios (Rr) of 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, & 1.0 for the recycled coarse aggregates. A total of 84 test specimens in the shape of a cube were cast & examined. According to the results of the experiments, To obtain an equivalent M60 concrete, we can use RCA with a percentage of Rr = 0.5, & with Rr = 1.0, we can achieve an equivalent M40 concrete.

Damage-based ion transport in recycled aggregate concrete under external sulfate attack

The utilization of recycled coarse aggregate (RCA) in replacement of natural coarse aggregate in the production of recycled aggregate concrete (RAC) may potentially lead to a reduction in the resistance of RAC to sulfate attack. In this study, the dynamic elastic modulus and sulfate ion transport of RAC was investigated by fully immersing RAC specimens produced with different water-to-cement ratios (W/C) and RCA volume fractions (VRCA) into sulfate (Na2SO4) solutions with different concentrations. The effects of W/C and VRCA on the initial damage velocity, damage acceleration, and service life of the RAC were analyzed by the defined damage evolution equations. The variation patterns of the ion diffusion coefficient and the surface ion concentration were discussed in detail, and a general equation was developed to describe the variation of surface ion concentration over time. A damage-based ion transport model was developed based on the damage evolution of the dynamic elastic modulus. The results demonstrated that the damage-based ion transport model exhibited excellent accuracy in predicting the ion transport behavior in the RAC. Furthermore, the mechanism of the effect of RCA on ion transport is more complex and requires a comprehensive study. This study provides theoretical support for the application of RAC in engineering construction and the calibration of important physical parameters in related numerical studies.

Experimental study on bond performance of recycled coarse aggregates concrete with circular steel tubes after freeze–thaw cycling

AbstractExtrusion tests were conducted on recycled coarse aggregate concrete with circular steel tubes (RCCST, 100% replacement of recycled coarse aggregate) to investigate the impact of freeze–thaw cycles on bond properties. RCCST samples were subjected to 0, 25, 50, 75, 100, 125 and 150 freeze–thaw cycles and their bond properties were then compared with those of natural coarse aggregate concrete with circular steel tubes (NCCST) after 0, 100 and 150 freeze–thaw cycles. The experimental results indicate that freeze–thaw cycling damages the internal structure of RCCST, causing a significant decrease in interfacial bond strength with an increase in the number of freeze–thaw cycles. Freeze–thaw RCCST exhibits lower peak load and higher peak slip compared to NCCST, with increases of 25.2%, 73.2%, and 70.3% after 0, 100, and 150 freeze–thaw cycles, respectively. Regression analysis was used to derive an exponential equation that describes the relationship between longitudinal strain and strain gauge position. Additionally, a segmented fitting method was employed to obtain an expression for the bond slip of the freeze–thaw RCCST with a circular steel pipe.

Combined effect of silica fume and various fibers on fresh and hardened properties of concrete incorporating HDPE aggregates

Recycling of waste plastics has become essential to mitigate their detrimental impact on the environment. However, it can be used in the construction sector to fulfill construction needs and conserve natural resources. Previous research has demonstrated that incorporating plastic aggregate reduces the strength properties of concrete; hence, there is a need to improve its strength properties. In this study, high-density polyethylene (HDPE) plastic is incorporated in aggregate form, as a partial substitute for natural coarse aggregates (NCA) at volumetric ratios of 10 %, 30 %, and 50 %. Various strength enhancement techniques, including the addition of macro synthetic fibers (MSF), steel fibers (SF), and substituting 20 % of cement with silica fume, were employed. The results indicated that workability of concrete is improved with an increase in the content of HDPE coarse aggregates (HCA). Furthermore, concrete containing 30 % HCA performed better in terms of strength compared to concrete with 10 % and 50 % HCA. The findings demonstrate that concrete containing fibers performs better than concrete without fibers. The utilization of 0.75 % MSF and 1 % SF dosage leads to a 93 % improvement in splitting tensile strength, a 72 % improvement in flexural strength, and a 48 % improvement in compressive strength for concrete containing 30 % HCA. Using scanning electron microscopy, it was found that incorporating HCA weakens the internal matrix. However, the addition of a precise amount of fibers and pozzolanic materials resulted in improvements in microstructure. The significance of this research lies in the utilization of HDPE waste materials in concrete by simultaneous usage of different fibers.

A Review on Experimental Study of Design of Rigid Pavement by using Recycled Coarse Aggregate with M30 Mix Design

Concrete, a fundamental construction material, boasts attributes like durability, versatility, and cost- effectiveness. However, the depletion of natural resources and the escalating concrete waste production necessitate innovative solutions. In this rapidly industrializing world, recycling construction materials plays a pivotal role in preserving our finite resources. Concrete pavements, widely practiced in developed countries, are relatively new in India. Selecting the right pavement type is crucial, but equally important is determining the optimal pavement thickness based on traffic levels, subgrade conditions, and environmental factors. Unfortunately, many existing methodologies overlook critical factors (such as vehicle loads, support loss, thermal gradients, and environmental stress), leading to inaccurate thickness calculations. In this context, rigid pavement construction using recycled coarse aggregate (RCA) emerges as an eco-friendly and cost- effective solution. In a recent research endeavour, Recycled Coarse Aggregates (RCAs) sourced from demolished material took center stage. These demolished materials are meticulously crushed to a suitable size and repurposed as recycled coarse aggregate. Meanwhile, natural sand continues to serve as the fine aggregate. Notably, the concrete industry consumes a staggering 12.6 billion tons of raw materials annually, making it the world’s largest natural resource consumer. The environmental impact of concrete production—especially the extraction of raw ingredients such as cement, coarse aggregates, and fine aggregates—is considerable. To address this, the study employed a trial-and-error approach for mix design, adhering to relevant standards (such as IS code and IRC: 44-2008). For M30 grade cement concrete, varying percentages (0%, 25%, 50%, 75%, and 100%) of recycled coarse aggregates replaced conventional coarse aggregates. Casting used cube and beam models to obtain laboratory test results for rigid pavement to determine how much optimal percentage of RCA can be substituted in place of NCA. By integrating RCAs, we not only mitigate environmental impact but also contribute to sustainable rigid pavement structures. Key Words: Rigid Pavement Design, Recycled Coarse Aggregate, RCA Concrete, Natural Coarse Aggregate, NCA Concrete, Mix Proportion, Pavement Thickness, Life Cycle Cost, And Environmental Benefits etc.

Experimental Study of Recycled Concrete under Freeze-Thaw Conditions.

Recycled concrete is a new and environmentally friendly material for future construction. When applying recycled concrete to cold and severe regions, it is necessary to consider the freeze-thaw resistance of recycled concrete. Using an indoor freeze-thaw cycle test system, the rapid freezing method was used to conduct rapid freeze-thaw tests on recycled concrete specimens under set freeze-thaw cycle conditions. Relevant parameters (such as compressive strength, quality loss rate, rebound value) were tested on recycled concrete specimens that completed the set number of freeze-thaw cycles. The influence of various factors (freeze-thaw cycle number, replacement rate of recycled aggregates) on the compressive strength, quality loss rate, and rebound value of recycled concrete was analyzed. The results indicate that with the increase of freeze-thaw cycles and recycled aggregate content, the workability, rebound value, and compressive strength of the specimens decrease, and the quality loss rate increases. The changes in workability of concrete are sharp, with a slump difference of 21 mm between concrete with 100% recycled coarse aggregate and concrete using natural coarse aggregate. The rebound value of the specimen shows a decreasing trend overall, but the rebound value varies for different measuring points on the same specimen. The attenuation of compressive strength is significant. When fully using recycled aggregates to prepare concrete, the compressive strength after 30 freeze-thaw cycles decreases by 49.42% compared to the compressive strength after 0 freeze-thaw cycles. The overall quality loss rate shows a decreasing trend, but the quality loss is not severe.

Influence of Recycled Coarse Aggregate and Steel Fiber on the Workability and Strength of Self-Compacting Concrete

Abstract Waste materials pose a significant threat to both the environment and human health. On a global scale, the quantity of recyclable material is steadily growing, and its proper disposal is a significant focus of modern study. Concrete debris is a recyclable material that poses challenges for reutilization. Concrete waste refers to the fragments or remains of ready-mix concrete plants and the debris from destroyed structures, including historic buildings and those affected by earthquakes. The objective of this study is to reuse and utilize coarse aggregate formerly used in concrete constructions to create self-compacting concrete (SCC). The purpose is to assess the performance of this recycled aggregate in both its fresh and hardened states. Natural coarse aggregate (NCA) was switched out for recycled coarse aggregate (RCA) at 0, 50, and 100% volume ratios. In contrast, concrete was mixed with steel fibers (SF) at volume percentages of 0 and 0.44. Workability tests, including V-funnel, slump flow, and L-box tests, were conducted to assess the consistency of the mixes in their fresh condition. Additionally, the tensile and compressive strength of the concrete specimens were measured to evaluate their strength in the hardened state. Overall, the experimental findings showed that the fresh qualities of almost all SCC mixes fell within the required range, as outlined in the EFNARC standards. While the steel fiber harmed the fresh characteristics, it resulted in a proportionate enhancement in tensile strength. The findings indicated that including recycled aggregates into the concrete mixture enhanced its strength. The results showed that adding (0.44%) of steel fibers to concrete reduced the decline in compressive strength when the coarse aggregate was replaced entirely with recycled aggregate. In contrast, an equivalent proportion of fibers resulted in a significant improvement in tensile strength, rising from 26% to 54%, when using recycled coarse aggregate as the replacement of natural coarse aggregate. Thus, it can be concluded that using recycled aggregates and steel fibers in concrete production results in a higher quality product than regular concrete. Removing concrete waste has other benefits, such as enhanced financial return and preservation of the environment.

Slurry infiltrated low-quality construction and demolition coarse aggregate waste in concrete – a sustainable construction

Exponential growth in infrastructure projects, stimulated by emerging sophisticated technologies have been instrumental in the salutary proliferation of the construction sector, globally. An indubitable adversity of the rapid boom in the construction industry has been the rampant cumulative fallout of burgeoning waste during the demolition and construction phases of restoration. The current study explored the propriety of replacing natural coarse aggregate by low-quality recycled coarse aggregates (RCA) with varying proportions, along with silica fume (SF) and polypropylene (PP) fibers as admixtures, for the preparation of concrete. As the quality of RCA is determined by the history of its parent demolished structure, this investigation was preceded by assessment of the properties of RCA. A statistical approach using design of experiments, adopted to determine the coherent combinations of RCA and admixtures, yielded 16 combinations. Accordingly, concrete specimens were prepared with various quantities of RCA in place of natural coarse aggregate. Optimum proportions of the ingredients were inferred, based on the compressive strength attained by the concrete specimens. Further strength property evaluation was conducted, using these low-quality RCA treated with cement and silica fume slurry. Based on the strength results, 75% slurry infiltrated RCA, coupled with 10% SF and 0.5% PP, provided better strength in compression, tension and flexure. Scanning electron microscopy study, adopted for characterization of the micro-structural slurry-infiltrated RCA, shows the presence of strong interfacial transition zone in the treated RCA concrete. Thus, this study confirmed the efficacy of low-quality RCA as a promising material for structural construction, concurrent with a solution to various ecological disruptions precipitated by infrastructure construction and demolition wastes.

Interlayer reinforced 3D printed concrete with recycled coarse aggregate: Shear properties and enhancement methods

In reinforced 3D printed concrete structures, the shear interaction between the rebar and the 3D printed filaments influences both the performance and safety of the concrete structures during service. In this study, the shear performance of the interlayer reinforced interface (IRI) of 3D printed concrete with recycled coarse aggregates (3DPRAC) was investigated, focusing on the pore structure characteristics of the interlayer interface. An enhancement method for the IRI was proposed by varying the number of anchored rebar nails (ARNs) and comparing the results with those of 3D printed concrete with natural coarse aggregates (3DPNAC) and 3D printed mortar (3DPM). The results showed that the ARNs significantly improved the IRI shear strength of 3DPRAC. Specifically, the IRI shear strength of 3DPRAC was 6.1 % lower than that of 3DPNAC but 43.6 % higher than that of 3DPM. By examining the structural characteristics of the rebar-3DPRAC bonding area, a relationship between pore defects and shear strength was established. This established relationship led to the proposal of a partition model for the interlayer bonding interface. A finite element model of 3D printed concrete incorporating real pore structure characteristics was developed to analyze the stress distribution and damage characteristics of the interface under shear stress. The fracture mode induced by local pores with the crack propagation mechanism was also analyzed. Finally, a unified formula for calculating the shear strength of the 3DPRAC IRI was derived based on the principles of virtual work and plastic limit theory. This study provides theoretical support for engineering applications of 3D printed reinforced concrete structures.

Effects of cold-bonded artificial aggregate properties on the behaviour of concrete

The study investigates the use of artificial aggregates (AAs), specifically manufactured from ground granulated blast furnace slag (GGBFS) and ordinary Portland cement (OPC), to mitigate environmental harm caused by illegal quarrying due to the scarcity of natural aggregates (NAs). A cold-bonded pelletization technique was employed to produce five types of AAs with varying proportions of GGBFS & OPC as 82.5:17.5, 85:15, 87.5:12.5, 90:10, 95:5. The AAs with maximum OPC content exhibited a density of 1298 kg m−3, water absorption of 4.8%, and crushing and impact values of 28.6% and 26.3%, respectively. The impact of these AAs on concrete properties was assessed, revealing that AAs facilitated the production of workable concrete with low-density ranges between 1700–2337 kg m−3. Despite a decrease in concrete strength with higher AAs content, structural requirements were met, demonstrating AAs’ potential to effectively substitute natural coarse aggregates (NCAs). The concrete microstructure confirmed the formation of a strong interfacial transition zone (ITZ) and strength-developing cement-hydrated products. This research underscores the scientific contribution of AAs to address aggregate scarcity sustainably and recommends its application in structural elements by experimental validation.

Synergistic effects of steel fiber and rubberized aggregates on concrete properties

The drive for more sustainable and environmentally friendly construction practices has resulted in revolutionary concrete production methods. One way is to include scrap rubber tires (contributing significantly to environmental pollution) into concrete mixtures to increase deformability. This study investigates the impact of surface-treated waste tire rubber (which partially replaces natural coarse aggregates with 5%, 10%, and 15% by weight) and industrial steel fiber (as reinforcement by including 0.5, 1, and 1.5% volume fractions) in concrete. Twelve concrete mixtures were prepared as test specimens. The replacement percentage was then determined using the compressive strength test results for additional surface treatment with three different alkaline solution (NaOH) concentrations (5%, 10%, and 15%) for 72 h. Thus, the hardened concrete properties were analyzed using compressive strength, flexural strength, and toughness; whereas the fresh qualities of equivalent concrete mixtures were evaluated using concrete slump. The findings revealed that, while partial replacement had a negative impact on the mechanical properties of the concrete, it was possible to produce rubberized concrete with better mechanical properties than conventional concrete when the partial replacement was less than 5%, treated with 10% alkaline solution, and reinforced with 1.5% steel fibers. The study’s findings illustrate the potential of these combinations for use in concrete pavement and slab applications.

Tension Lap Splices in Recycled-Aggregate Concrete Strengthened with Steel–Polyolefin Fibers

The bond strength of tension lap splices in recycled-coarse-aggregate-reinforced concrete strengthened with hybrid (steel–polyolefin) fibers was experimentally investigated. This study was conducted with the help of twelve lap-spliced beam specimens. The replacement level of coarse natural aggregates with recycled concrete aggregate (RCA) was 100%. The following variables were investigated: various ranges of steel–polyolefin fibers—100–0%, 75–25%, 50–50%, 25–75%, and 0–100%—in which the total volume fraction of fibers (Vf) remains constant at 1%; and two lengths of lap splices for rebars of 16 mm diameter (db): 10 db and 15 db. The test results showed that the best range of steel–polyolefin fibers that gave the highest bond strength was 50–50%. The ductility of the fiber-reinforced recycled-aggregate (FR-RA) concrete was significantly improved for all the cases of various relative ratios of steel and polyolefin fibers. The bond strength was also predicted using three empirical equations proposed by Orangun et al., Darwin et al., and Harajli. This study showed that the Harajli equation gave a more accurate estimation of the bond strength of reinforcing bars embedded in FR-RA concrete than those proposed by Orangun et al. and Darwin et al.

Multi response optimization of recycled aggregate based alkali-activated concrete using Taguchi-Grey Relational Analysis Method

The use of cement in construction causes large amounts of CO2 emissions into the atmosphere. Moreover, the use of large amounts of natural coarse aggregate causes environmental damage, and the availability of such natural aggregate is also depleting. The present experimental study explores and optimizes the impact of various parameters on the fresh, mechanical, and durability properties of recycled waste concrete coarse aggregate (RWCA)-based geopolymer concrete (GPC) in combination with ground-granulated blast furnace slag (GGBFS) and fly ash (FA) using the Taguchi-Grey Relational Analysis Method (TGRAM). The coarse aggregates in GPC were fully replaced with RWCA produced by crushing waste concrete. The effects of FA inclusion (%), Na2SiO3/NaOH ratio (SS/SH), molarity of NaOH (SH), dosages of superplasticizer (%), and alkaline solution to binder (Al/Bi) ratio are investigated under ambient curing conditions. The obtained maximum compressive strength and split tensile strength along with minimum water absorption of GPC at 28 days were 67.90 MPa, 3.85 MPa and 2.92 % respectively. The microstructural studies of GPC having low, high, and optimal strength are carried out using XRD, FE-SEM, and EDAX analysis. These studies confirmed the presence of calcium-based hydration products such as CSH and N(C)ASH, which makes the matrix of optimized GPC more compact.

Development of lightweight structural concrete with artificial aggregate manufactured from local clay and solid waste materials

The partial replacement of conventional natural coarse aggregate (NCA) with artificial light weight aggregate (LWA) manufactured from local clay and solid waste to develop a lightweight aggregate concrete (LWAC) for the structural use was studied in this paper. Red clay and Savar clay were used individually with solid wastes like rice husk ash (RHA) and waste glass to produce LWA. The suitability of raw materials and LWA was evaluated by investigating various properties. The mechanical, thermal and durability properties of manufactured LWAC were explored. The results of physical, chemical, thermal and geotechnical properties revealed that Red clay is better than Savar clay for the preparation of LWA. All the physical and mechanical properties of LWA prepared from Red clay are suitable for the preparation of LWAC compared to Savar clay. The test results demonstrated that the concrete manufactured by replacing 30 % of NCA with LWA produced a concrete of lightweight properties. The compressive strength of LWAC for 7 and 28 days was observed as 28 and 48 MPa, respectively. The results of modulus of elasticity, splitting tensile strength, flexural deformation, and creep test of LWAC revealed that these mechanical properties meet the requirements for the structural concrete. The RCP test proves that chlorine permeability of LWAC is comparable with NCA. It was observed that the superior performance of LWAC can be achieved only when the optimized mix designed is followed strictly. The suitability of the replacement of natural aggregate by LWA may be helpful for Bangladesh due to the scarcity of natural coarse aggregate and reusability of solid waste materials.

Comprehensive assessment of engineering and environmental attributes of geopolymer pervious concrete with natural and recycled aggregate

This study aims to conduct comprehensive assessment of engineering and environmental attributes of geopolymer pervious concrete with natural and recycled aggregate. Pervious concrete mixtures were fabricated with different paste and aggregate types for laboratory characterization at different scales. As compared to traditional cement pervious concrete, mechanical strengths of geopolymer pervious concrete increase significantly when either natural coarse aggregate (NCA) or recycled concrete aggregate (RCA) is used. The replacement of NCA with RCA reduces concrete strength but the advantage of geopolymer pervious concrete is maintained. Micro-scale observations indicate that geopolymer pastes have better bonding to RCA. Life-cycle assessment (LCA) results show that the lower global warming potential (GWP) and eutrophication potential (EP), but the greater energy consumption (EC) and acidification potential (AP) are achieved by geopolymer-based pervious concrete. Photochemical ozone creation potential (POCP) is found greater for fly ash-based but smaller for metakaolin-based geopolymer pervious concrete. The use of RCA brings environmental benefit at raw materials and transportation stages, in addition to avoiding landfilling and preserving natural aggregate. The pervious concrete with metakaolin-based geopolymer achieves the best overall performance considering multi-criteria of strength and environmental indicators regardless of aggregate type.

Production of sustainable GGBFS-based Self-Compacting Geopolymer Concrete containing E-waste aggregates under ambient temperature curing

Geopolymer concrete (GPC) has gained global attention due to its environmentally friendly composition and a reduction in the carbon footprint compared to conventional concrete. Self-compacting geopolymer concrete (SCGC) combines the environmental benefits of geopolymers with the convenience of self-compacting concrete (SCC), offering a sustainable solution that minimizes manual labor, reduces noise pollution, and ensures a high-quality finish in diverse construction locations. The rapid proliferation of electronic devices in contemporary society has substantially enhanced electronic waste (e-waste), creating significant environmental challenges. This study explores a sustainable approach in managing the menace created by e-waste through its partial replacement against natural aggregates in producing ground granulated blast furnace slag (GGBFS)-based SCGC under ambient temperature curing. The research methodology involves the preparation of eleven mixes, including the control SCGC mix (with no e-waste aggregate), utilizing printed circuit boards (PCBs) as partial replacement in natural fine and coarse aggregates at varying percentages, i.e., 10 %, 20 %, 30 %, 40 %, and 50 %. It is revealed through a detailed fresh property, mechanical property, durability property, and microstructural analysis that the optimal replacement levels with e-waste are 30 % NFA or 10 % NCA in producing a sustainable and workable SCGC comprising 28.2 % and 19.2 % of waste materials (GGBFS, EWF, and EWC) moving towards a sustainable concrete yield.

Effect of Recycled Concrete Aggregates on the Concrete Breakout Resistance of Headed Bars Embedded in Slender Structural Elements

Recycled concrete aggregates are potentially interesting for the precast concrete industry as they provide a new use for high-quality waste from its products’ life cycle. In precast concrete structures, it is common to use headed bars in several connection types between structural members. This paper presents the results of experimental tests to investigate the impact of replacing coarse natural aggregates with coarse recycled concrete aggregates in the concrete breakout strength of cast-in headed bars embedded in slender structural elements. Results of 12 tests on 16 mm headed bars embedded in 500 × 200 × 900 mm concrete members with an effective embedment depth of 110 mm are presented. The percentage of replacement of natural aggregates by recycled concrete aggregates was 0%, 30%, and 100%, and the flexural reinforcement ratio of the structural elements varied from 0.5% to 3.5%. The behavior and strength of the tested specimens are discussed, and comparisons with theoretical strength estimates are presented. The results showed that the concrete breakout strength of the headed bars was not affected by the use of recycled concrete aggregates and that the flexural reinforcement ratio significantly impacts the load-carrying capacity of the headed bars as they control the crack widths before failure.

Effect of recycled concrete aggregates on the punching strength of slab-column connections without shear reinforcement

This paper presents the results of tests on six reinforced concrete slab-column connections. The slabs were octagonal, centrally supported on square columns, and concentrically loaded at their borders. The tests investigated the effects of replacing natural coarse aggregates with recycled concrete aggregates. The experimental results were also compared to resistance estimates from ACI 318 (2019) and Eurocode 2 (2004) and results from a database with tests on slabs without recycled concrete aggregates. The results show that using RCA reduces the concrete's modulus of elasticity and tensile strength but has little effect on its compressive strength. Furthermore, using RCA has little impact on the flexural response and punching resistance of the slabs. The findings suggest that RCA has potential for use in concrete applications, but further tests are required to draw definitive conclusions.