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Sustainable construction represents a pivotal aspect of contemporary engineering endeavors, which are directed towards the minimization of the detrimental impact of the construction sector on the environment. This is achieved through the efficient utilization of resources and the reduction of waste generation. The study presented an analysis of the mechanical properties of ad hoc reinforced concrete beams made of concrete with recycled and natural aggregate. The objective of this study was to assess the potential of recycled aggregates as a substitute for natural aggregates in reinforced concrete structures, with the aim of contributing to the sustainable development of construction. The experiments compared the behavior of reinforced concrete beams with the same degree of reinforcement but differing in the type of aggregate. The results demonstrated that recycled aggregate beams exhibited lower stiffness and higher deformation under load compared to natural aggregate beams, particularly at loads close to the breaking force. Nevertheless, similar failure modes and cracking patterns were observed in both types of beams, indicating that concrete with recycled aggregate could be employed effectively in specific structural applications. [ABSTRACT FROM AUTHOR]

This study aims to determine the efficiency of concrete containing multiple recycled materials, recycled concrete aggregates (RCAs) and recycled steel fibers (RSFs), and compare it with conventional concrete. Natural coarse aggregate (NCA) in the concrete mix was partially replaced with 30% RCA to achieve a target compressive strength of 30 MPa after 28 days. Different types of fibers (steel fibers, RSFs, and mixed fibers) were added at varying percentages (1.0%, 1.5%, and 2.0%) to improve the mechanical properties of the concrete mixes. The shear behavior of reinforced concrete beams containing RCA and different types of fibers was investigated. Ten concrete mixtures were designed, and 10 reinforced concrete beams were tested under a two‐point load to estimate the contribution of various fiber types to the shear resistance. The results indicate that the addition of different types of fibers significantly enhances compressive, tensile, and flexural strengths of the concrete. Specifically, the improvement in compressive strength for RSFs was 38.9% at 1.5%, tensile strength improved by 21.1%, and flexural strength by 46.2% at the same fiber percentage, thereby improving the concrete's ability to resist cracks through an increase in shear resistance. [ABSTRACT FROM AUTHOR]

Translation abstract Durable and sustainable bridge caps made of non‐metallic reinforcement and recycled concreteDue to chloride‐induced corrosion, bridge caps made of steel‐reinforced concrete need to be replaced regularly or more often than planned. As part of a ZIM project funded by the Federal Ministry for Economic Affairs and Climate Action, bridge caps made of non‐metallic basalt fibre reinforcement and recycled concrete were developed to mitigate the weakness of corrosion and to better utilize the materials in terms of the material cycle. To achieve this, bend reinforcement elements made of chloride‐resistant basalt fibre reinforcement and concrete with high frost‐thaw resistance were developed, consisting of up to 100 % recycled aggregate. All sub‐developments were integrated into a holistic approach, and a prototype of a resource‐efficient and durable bridge cap was successfully produced and tested. [ABSTRACT FROM AUTHOR]

This study utilized experimental research to investigate the efficiency of using normal aggregate concrete (NAC) or recycled aggregate concrete (RAC) as a new concrete layer for repairing projectile bullet damage to strengthening reinforced concrete (RC) beams. This study comprised the construction and testing of eight RC beams made of RAC and NAC. They are initially subjected to projectile bullets and after that tested with flexure load to evaluate the effect of using RAC and NAC that was investigated. The findings of test results demonstrate that the repaired specimens with RAC or NAC experienced a higher load capacity than the damaged control specimens. As such, this approach could potentially use to restore RAC or NAC beams were previously damaged by projectile bullets. In addition, the findings of this research indicate that the load capacity of the damaged RC beams that were previously repaired using the NAC layer was higher than the load capacity of the damaged RC beams that were repaired using the RAC layer. The load capacity enhanced significantly of (106%–118%) and (104%–113%), respectively, when NAC and RAC are utilized in repairs. Therefore, using either NAC or RAC concrete is more economical, environmentally friendly, and efficient than demolishing. [ABSTRACT FROM AUTHOR]

The utilization of recycled concrete and glass aggregates in concrete production has emerged as a highly promising method to significantly increase the recycling rate of waste materials. However, the interaction between alkaline environment and silica present in concrete detrimentally impacts mechanical properties and durability of the concrete due to the significant silica content of the aggregates. This study aims to develop a high‐performance and sustainable concrete to resist alkali–silica reaction (ASR). The study focuses on the use of a blend of ground granulated blast furnace slag (GGBS) and fly ash (FA) as binder materials to mitigate negative effects of the ASR on the mechanical properties and and durability of concrete made with crushed glass sand and coarse recycled concrete aggregate (RCA). Various tests, including ASR expansion, flow, slump, density, compression, three‐point bending, water absorption, and chloride attack, were conducted. Furthermore, microanalysis using scanning electron microscopy and energy‐dispersive x‐ray spectroscopy was performed. Based on the results, it is found that the GGBS is less effective than the FA in reducing the ASR expansion of the concrete, with only 3%, 9%, and 12% decreased expansion as a result of the addition of 20%, 40%, and 70% GGBS to the concrete containing 30% FA, respectively. It is also shown that combining 20% GGBS with 30% FA in the RCA concrete containing glass sand develops similar compressive and flexural strengths and water absorption compared to that containing natural sand. This can be related to the pozzolanic reaction of the FA and GGBS, which helps to retain the alkalis for reducing the crack development and propagation in the concrete. However, further GGBS content leads to a decrease in the strengths and an increase in the water absorption of the concrete. The results of this study point to the significant potential of combining FA and GGBS at an optimum ratio to mitigate the ASR effect on RCA concretes containing crushed glass sand. This approach helps in minimizing the emission of greenhouse gases and other pollutants generated during cement production, thereby mitigating environmental pollution. Additionally, it helps the preservation of natural resources by reducing the depletion of natural sand and coarse aggregate. [ABSTRACT FROM AUTHOR]

Use of 100 % recycled aggregates in concrete – report on practical applications This article reports on eight practical examples of applications for concrete with 100 % recycled aggregates. The applications include reinforced/unreinforced bored piles, foundations, load‐bearing internal/external walls, columns and floor slabs as well as balcony elements. Some components were realised as architectural concrete components. The respective project is summarised together with the results of the concrete development and concrete testing as well as the experience gained from obtaining special approvals in individual cases. Based on the findings from the various practical projects, it can be concluded that concrete with 100 % RC‐GK can be used for a large number of applications, so far limited to up to XC4 and XF3. Compressive strength for ready‐mix concrete up to C35/45 with good workability even with pumped concrete (here: pumping distance 45 m) using 100 % RC‐GK type 1 were possible without any problems. A concrete with sufficient early strength and a final strength of C40/50 was developed for precast elements. In two examples, RC‐GK type 2 was used for the coarse grain fraction and RC‐GK type 1 for the sand. All the projects presented have already been completed or are nearing completion. The feasibility of 100 % RC concrete in practice has thus been successfully demonstrated in several cases. [ABSTRACT FROM AUTHOR]

Life cycle assessment of concrete made of 100 % recycled aggregate compared to normal concrete The construction sector accounts for a significant proportion of the consumption of natural resources and is also the source of the largest waste streams. The aim must therefore be to improve the circular economy in the construction sector. In this context, the Institute for Materials and Building Research (IMB) at Munich University of Applied Sciences (HM) has investigated the use of recycled aggregates beyond the technical building regulations up to 100 % including recycled sand for the production of structural concrete. The first applications of concrete with 100 % recycled aggregate (100 % RC concrete) have already been completed and are presented in this issue. Based on the findings from the research and construction projects, life cycle assessments were performed in which 100 % RC concrete (circular system) was compared with normal concrete (linear system) for the application case C30/37 XC4/XF3 (CEM II/C‐M (S‐LL)). The life cycle assessments of the two product systems were prepared in the form of nomograms so that input parameters such as transport services can be adjusted and a graphical evaluation of GWP can be carried out. This makes it easy to elaborate recommendations for the use of 100 % RC concrete with regard to reducing the environmental impact (GWP) in specific applications based on the life cycle assessments carried out. Other cements can also be taken into account after a simple conversion. The analyses show that the circular system has a slightly lower GWP when assuming the same transport distances and the same cement content but a slightly higher superplasticizer content. [ABSTRACT FROM AUTHOR]

AbstractThis research evaluates the impact of aggregate sizes on pervious concrete properties, comparing aggregates of 12.5 mm and 19 mm, as well as replacing natural aggregates with recycled aggregates set at 0% and 50%. Four types of pervious concrete were produced, and their properties were determined: density, porosity, permeability coefficient, compressive strength, flexural tensile strength, and abrasion resistance. The results indicate that water permeability is directly related to pore size and is influenced by aggregate size (90% of the variation in pervious concrete permeability) and, to a lesser extent, by recycled aggregate content (10% of the variation). Mixes with larger aggregates (19 mm) demonstrated higher permeability coefficients. Replacing natural aggregates with recycled aggregate did not significantly affect the mechanical properties of pervious concrete, highlighting the effectiveness of waste processing and mixing procedures, allowing for the incorporation of 50% of recycled aggregate. The concretes met the requirements of the American Concrete Institute, suggesting technically feasible conditions for sustainable practices in the construction industry. [ABSTRACT FROM AUTHOR]

This article investigates the durability of recycled self-compacting concrete in relation to its resistance against freeze-thaw cycles and alkali-silica reactions. It explores the properties of fresh concrete, investigates the impact of various additives, and evaluates key factors such as spalling, weight loss, compressive strength, expansion rate, and ultrasonic properties in hardened concrete samples incorporating different levels of recycled aggregates. The findings illustrate the feasibility of achieving self-compacting recycled concrete by increasing the use of superplasticizers and adding 10% beach sand. Furthermore, incorporating 10% micro-silica and 7.5% wollastonite in the recycled mix enhances the strength of all samples, with the 25% recycled material sample demonstrating the highest strength and durability. Despite a decrease in strength and increased expansion as recycling percentages and freeze-thaw cycles rise, the recycled samples maintain acceptable durability. Additionally, this study employs the R programming language to elucidate the relationship between compressive strength and modulus of elasticity, offering valuable insights into recycled concrete performance and behavior. [ABSTRACT FROM AUTHOR]

Comparative experiments and engineering applications were performed to examine the effects of waste rubber,cork particles and hollow floating beads on the workability,mechanical,and sound insulation performance of recycled aggregate mortar, and expands the comprehensive utilization of multi-source solid waste. Rubber and cork particles increased the fluidity of the mortar mix and reduced its water retentivity,while the hollow floating beads can improve the fluidity and water retentivity of the mortar. With the addition of various damping materials,the apparent density and strength of the recycled aggregate sound insulation mortar are significantly reduced,but it can still meet the requirements of 28-day compressive strength of not less than 5 MPa. Rubber,cork particles and hollow floating beads can significantly improve the impact noise of high frequency band,middle and low frequency band and low frequency band,respectively. The comprehensive performance of sound insulation mortar mixed with 35% multiple damping materials(15% rubber+15% cork particles+5% hollow floating beads)is better than that of single damping mate rial,and the impact sound pressure level is 9 dB lower than that of ordinary mortar with 30 mm thick. [ABSTRACT FROM AUTHOR]

Due to its superior performance over traditional materials, polymer concrete has emerged as a new engineering material in the current context. The main focus of this study was the design and manufacture of polyester polymer concrete (PC) from various recycled materials for use in various building applications. Four different types of recycled aggregate from easily accessible crushed building materials were employed: waste glass (WG), crushed mortar (CM), crushed clay bricks (CB), and crushed concrete (CC). Sustainable modified polymer concrete (SMPC) specimens were made using a conventional casting method and various replacements for normal sand, such as crushed concrete, mortar, clay bricks, and waste glass (10, 20, 30, and 40 volume percent). The mechanical properties of SMPC with and without recycled aggregate were tested for compressive, tensile, and flexural strength. The findings showed that adding (10%, 20%, 30%, and 40%) of (CC, CM, CB, and WG) as a partial substitute for natural fine aggregate improves the mechanical properties (compressive strength, direct tensile strength, and flexural strength) of SMPC. In comparison to other waste materials, the results of using crushed concrete were the best and highest. Similar to reference PC and SMPC with recycled fine aggregate, the rate of strength evolution with age is roughly the same. This research also looked into how the curing temperature affected the SMPC's compressive strength characteristics. The 20, 40, and 60 °C curing temperature ranges were taken into consideration. The findings demonstrate that the compressive strength of PC, both with and without recycled fine aggregate, is significantly impacted by a curing temperature above 20 °C. [ABSTRACT FROM AUTHOR]

The attached cement paste in recycled concrete (RC) aggregate leads to its potential reactivity against sulfate ions. Several test methods were evaluated to find a suitable, reliable, and accurate method to evaluate the potential reactivity of aggregates. Different quality RC aggregates were used to apply those methods. The studies included evaluations of concrete cores drilled from source concrete (SC), RC aggregates, recycled mortar bars under different exposures, and RC prisms exposed to external sulfate attack (ESA). The concrete core test allowed qualifying SC as potentially reactive against sulfate in a short time. Tests on recycled aggregates and recycled mortar bars showed variable sensitivity levels. Results from concrete prisms showed an effective reactivity of recycled aggregates when the replacement is higher. [ABSTRACT FROM AUTHOR]

This study evaluates the quality and mechanical performance of various shapes of reclaimed concrete aggregates (RCAs), including elongated, cone-shaped, angular, and ordinary mix, in comparison to fresh aggregates (FAs). The RCAs are treated with fly ash-based geopolymer, and the effects of various percentages of geopolymer content on the geotechnical properties of the modified RCAs are investigated. The study finds that the angular shape of an RCA exhibits more strength than other shapes, and the use of fly ash-based geopolymer significantly improves the mechanical characteristics of the modified RCAs by up to 10%. The research also shows that the use of fly ash-based geopolymer-treated RCAs in the subbase layer of flexible pavements can lead to a reduction in the required thickness of the base layer, resulting in significant cost savings and curtailment of CO2 emission compared to the use of FAs. Abbreviations: AASTHO: American association of state highway and transportation officials; A: Area of cross-section of flexible pavement; ACV: Aggregate crushing value; AIV: Aggregate impact value; BS: British standard; ASTM: American society for testing and materials; Cc: Co-efficient of curvature; CO2: Carbon dioxide; Cu: Co-efficient of uniformity; D50: Mean grain size; DCW: Demolished concrete waste; CBR(s): Soaked California bearing ratio; FA: Fresh aggregate; FI: Flakiness index; EI: Elongation index; GC: Geopolymer content; GSD: Grain size distribution; k: Co-efficient of permeability; LAAV: Los Angeles abrasion value; m: Drainage co-efficient; m2: Drainage co-efficient of base layer; m3: Drainage co-efficient of subbase layer; ma: Dry mass of additive; MR: Resilient modulus; MR(B): Resilient modulus of base layer; MR(SB): Resilient modulus of subbase layer; MR(SG): Resilient modulus of subgrade layer; mRSM: Dry mass of reclaimed subbase material; NAOH: Sodium hydroxide; Na2SiO3: Sodium silicate; PKR: Pakistani Rupees; R: Reliability; RCA: Recycled concrete aggregate; So: Overall standard deviation; SN: Structural number; USCS: Unified soil classification system; NCHRP: National cooperative highway research programme; NHA: National highway authority; W18: 18-kip equivalent single axle loads; US$: US Dollars; ξOGC: Optimum geopolymer content; wopt: Optimum moisture content; γdmax: Maximum dry unit weight; a: Structural layer co-efficient; a1: Structural layer co-efficient of asphalt concrete; a2: Structural layer co-efficient of base layer; a3: Structural layer co-efficient of subbase layer; ΔPSI: Present serviceability index; tb: Thickness of base; tsb: Thickness of subbase; δ: Total material weight [ABSTRACT FROM AUTHOR]

Abstract The replacement of natural aggregate in concrete with artificial and/or recycled one has recently gained attention as meaningful strategy to reduce the environmental impact of structural concrete and promote circular economy principles. This study investigated the possibility to use Reclaimed Asphalt Pavement (RAP), in the “as received conditions”, as a partial or complete substitution of natural aggregate for structural concrete. RAP aggregate was firstly characterized in terms of grain size distribution, density, assessment of fines, chloride content, moisture content and water absorption. Subsequently, a total of twenty-four concrete mixes were designed, considering two cement types, two w/c ratios and several aggregate substitution percentages. For each mix, properties at the fresh and hardened state were investigated, such as workability, density and total open porosity, compressive strength, dynamic modulus of elasticity, and electrical resistivity. Results showed that RAP has a good potential to be used in reinforced concrete, provided that different water absorption and moisture content are considered in the mix design. RAP concrete was characterized by a lower density and increased total open porosity; however, an accurate tailoring of the concrete recipe could compensate the strength loss for several applications. Other properties, such as electrical resistivity and the relationship between dynamic modulus of elasticity and compressive strength did not result significantly altered by the presence of RAP.

Sustainable construction represents a pivotal aspect of contemporary engineering endeavors, which are directed towards the minimization of the detrimental impact of the construction sector on the environment. This is achieved through the efficient utilization of resources and the reduction of waste generation. The study presented an analysis of the mechanical properties of ad hoc reinforced concrete beams made of concrete with recycled and natural aggregate. The objective of this study was to assess the potential of recycled aggregates as a substitute for natural aggregates in reinforced concrete structures, with the aim of contributing to the sustainable development of construction. The experiments compared the behavior of reinforced concrete beams with the same degree of reinforcement but differing in the type of aggregate. The results demonstrated that recycled aggregate beams exhibited lower stiffness and higher deformation under load compared to natural aggregate beams, particularly at loads close to the breaking force. Nevertheless, similar failure modes and cracking patterns were observed in both types of beams, indicating that concrete with recycled aggregate could be employed effectively in specific structural applications.

Construction activities are generating substantial amounts of construction waste due to the rapid increase in economic growth and infrastructure developments. A series of laboratory model tests were conducted to investigate the feasibility of using recycled aggregate as backfills to construct the rammed stone columns. Recycled aggregates and gravel aggregates with the same particle size distributions were used to construct the rammed stone columns. The direct shear test results showed that the recycled aggregate exhibits similar behavior of initial compression but more significant expansion compared to those of the gravel aggregate. The critical bearing capacity of the rammed stone column using recycled aggregate as backfills was 6.2%–6.5% lower than that using the gravel aggregate as backfill, but was 36.1% higher than that of the traditional stone column. The rammed stone column was failed in bulging failure mode with the maximum bulging position of approximately 2d from the column head. The critical bearing capacity of the rammed stone columns could be estimated according to that of the traditional stone column by considering the effects of the tamping energy. [ABSTRACT FROM AUTHOR]

This paper focuses on the particle crushing mechanism of construction solid waste recycled aggregate (CWRA), particularly recycled concrete (RC) and recycled bricks (RB), using natural gravel (NG) as a control group. Compression tests, combined with the Weibull distribution, fractal dimension theory, and relative crushing rate, were conducted to investigate the crushing behavior of these materials under different loads. Results indicate that, under the same load, the crushing degree ranks from highest to lowest as RB, RC, and NG. The Weibull distribution effectively describes the crushing state, with "fragmentation" being the primary mode for most materials, while RC also exhibits "grinding." As the load increases, the relative crushing rate rises for all materials but slows beyond a certain load threshold, indicating greater difficulty in further crushing. The study identifies a load threshold of 400 kN, beyond which changes in void fraction and relative crushing rates become less significant, particularly in stronger aggregates. Highlights Identified that mortar attached to the RC surface is the primary cause of the increased particle crushing below 0.6 mm. Introduced Weibull distribution parameters a and b to accurately characterize the crushing state of RA particles. Revealed the errors between fractal dimension-based evaluations and the actual crushing state of RC particles. Proposed a two-stage crushing mode for RC. Determined the critical threshold value for the variation of crushing degree with load level. [ABSTRACT FROM AUTHOR]

Various developing countries are confronted with serious environmental difficulties due to excessive resource utilization and insufficient waste management system. In particular, construction and demolition waste poses a grave threat to the environment, contributing to escalating energy consumption, the depletion of landfill capacities, and the generation of harmful noise and dust pollution. Consequently, the research community is tasked with the daunting challenge of devising effective strategies to incorporate this waste material in producing concrete, without compromising the critical strength and durability characteristics. The investigation aims to attain the aforementioned objective by examining the effects of using recycled aggregates as a distinct partial replacement of 0%, 5%, 10%, 15%, and 20% on the compressive and split tensile strength traits, contingent upon 7 and 28 days of age of curing. Experimental test results show that the optimal concrete production is achieved when 10% of coarse aggregate is replaced with recycled aggregate, maintaining 98% of the materials compressive and split tensile strength. To further validate the obtained experimental data, model equations were derived through regression analysis and the framed model equation is further assessed for accuracy using error analysis. In this study, a MATLAB program was utilized for prediction of compressive and split tensile strength with five distinct network types and the Levenberg-Marquardt algorithm is used for optimization. A comparative analysis was conducted between the regression analysis values and the performance of the ANN modelling. The findings demonstrate that the Artificial Neural Network (ANN) serves as a highly effective model, offering significantly improved accuracy in predicting the optimal correlation between compressive strength and split tensile strength of concrete. [ABSTRACT FROM AUTHOR]

This paper explores the influence of polypropylene fiber on the mechanical properties of recycled concrete and the bonding performance between recycled concrete and steel bars. The results indicate that the compressive strength and splitting tensile strength of concrete decrease with the increase in the replacement rate of recycled aggregate. When the replacement rate of recycled aggregate was 100 %, the compressive strength of concrete decreased by 25.0%, while the splitting tensile strength of concrete decreased by 21.7 %. The compressive strength and splitting tensile strength of recycled aggregate concrete show a trend of first increasing and then decreasing with increasing fiber content. When the fiber content is 0.09 %, the compressive strength and tensile strength of recycled aggregate concrete are optimal. The bond strength of recycled concrete pullout specimens with fiber is higher than that of recycled concrete pullout specimens without fiber, while the slip of recycled concrete pullout specimens with fiber is lower than that of recycled concrete pullout specimens without fiber. The maximum improvement in bonding performance between recycled concrete and rebars with a 50 % recycled aggregate replacement rate is 13.7 %, and the maximum improvement in bonding performance between recycled concrete and rebars with a 100 % recycled aggregate replacement rate is 11.8 %. The bond strength shows a trend of first increasing and then decreasing with increasing fiber content, but the degree of decrease was not significant, while the slip shows a trend of first decreasing and then increasing with increasing fiber content. Compared to the compressive strength of concrete, the splitting tensile strength can better reflect the bond strength between concrete and rebar. The nonlinear relationship between the bond strength, compressive strength, and splitting tensile strength of recycled concrete is established. This study can effectively improve the mechanical properties of recycled concrete, expand the application scope of recycled concrete technology, and promote the sustainable development of the construction industry.

Concrete with no slump that is typically used for prefabrication is known as zero slump concrete (ZSC). ZSC is sensitive to mixture proportion. Since coarse aggregate makes up the majority of the concrete volume, recycling concrete aggregates will be a great choice for reducing the amount of concrete waste. Therefore, the purpose of this paper is to analyze the impact of using coarse recycled concrete aggregate (RCA) in ZSC properties. Five mixes were manufactured, each with a different percentage of coarse RCA (0%, 25%, 50%, 75%, and 100%). Compressive strength, flexural strength, ultrasonic pulse velocity (UPV), dry bulk density, and water absorption of recycled aggregate ZSC were conducted at 7, 28 and 90 days. Experiments revealed that the inclusion of coarse RCA in ZSC degraded the quality of manufactured concrete. At 90 days, in comparison to the control mix, the minor drop was at 25% coarse RCA incorporation, which resulted in a 6.2%, 4.1%, 2%, and 2.4% drop in compressive strength, flexural strength, UPV, and dry bulk density, respectively, while there was a 24.4% increase in water absorption. The highest drop of recycled aggregate ZSC at 100% incorporation resulted in a 41.7%, 19.1%, 8.6%, and 7.6% drop in compressive strength, flexural strength, UPV, and dry bulk density, respectively, while there was a 158.8% increase in water absorption.

Microwave heating, which is used for pre-treatment of concrete before it is comminuted, stands as a strong candidate for selective liberation of multiphase materials like concrete. This paper is concerned with the selective liberation of concrete's raw constituents (particularly aggregate) for recycling by considering the water content of concrete as a parameter of microwave heating for the first time. The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents. Besides, tests were conducted to evaluate the performance of the interface transition zone (ITZ) between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar, which included the interface tensile strength test, temperature measurement, and porosity test. The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content. Furthermore, experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired, and a large temperature difference was generated between the aggregate and mortar during microwave heating. Meanwhile, the permeable pores increased considerably even when the specimens were dried. In the presence of water, the intactness of ITZ between aggregate and mortar was destroyed by microwave heating, and its performance was significantly lowered, which led to the occurrence of stripping behavior between aggregate and mortar. This was reaffirmed by the microstructure presented by scanning electron microscopy. Thus, the newly developed microwave pre-treatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

This article presents the results of research evaluating the compressive strength of concrete using recycled coarse aggregate, in the case of using fly ash (CP1) and without using fly ash at a content of 5% (CP2). The experimental samples were compressed to test the compressive strength value at different times, including 7 days old, 14 days old and 28 days old. The study designed a recycled concrete composition with a 50-50 ratio of regular aggregate and recycled coarse aggregate, and the concrete has a design compressive strength of 15 Mpa. The compressive strength of concrete was studied and compared in cases with and without fly ash, and compared with another research result on concrete using recycled coarse aggregate.

The objective of the research outlined in this paper is to propose an eco-friendly solution that simultaneously contributes to improving the characteristics of polymer composites. The analyzed solution entails the use of recycled aggregate from crushed concrete rubble. The authors conducted experiments to test the consistency, density, flexural strength, compressive strength, and microstructure of polymer concrete (PC) with different proportions of recycled aggregate (RA). It was found that PC with RA had a higher compressive strength, 96 MPa, than PC with natural aggregate, 89.1 MPa, owing to the formation of a double-layer shell of resin and calcium filler on the surface of porous RA grains. Using a resin with a lower viscosity could improve the performance of PC with RA by filling the cracks and penetrating deeper into the pores. RA is a valuable material for PC production, especially when it contains porous grains with poor mechanical properties, which are otherwise unsuitable for other applications. This article also highlights the environmental and economic benefits of using RA in PC, as it can reduce waste generation and natural resource consumption. [ABSTRACT FROM AUTHOR]

In recent years, the use of recycled aggregate (RA) in roller-compacted concrete (RCC) for pavement construction has been increasingly attractive due to various environmental and economic benefits. Early determination of the compressive strength (CS) is crucial for the construction and maintenance of pavement. This paper presents the idea of combining metaheuristics and an advanced gradient boosting regressor for estimating the compressive strength of roller-compacted concrete containing RA. A dataset, including 270 samples, has been collected from previous experimental works. Recycled aggregates of construction demolition waste, reclaimed asphalt pavement, and industrial slag waste are considered in this dataset. The extreme gradient boosting machine (XGBoost) is employed to generalize a functional mapping between the CS and its influencing factors. A recently proposed gradient-based optimizer (GBO) is used to fine-tune the training phase of XGBoost in a data-driven manner. Experimental results show that the hybrid GBO-XGBoost model achieves outstanding prediction accuracy with a root mean square error of 2.64 and a mean absolute percentage error less than 8%. The proposed method is capable of explaining up to 94% of the variation in the CS. Additionally, an asymmetric loss function is implemented with GBO-XGBoost to mitigate the overestimation of CS values. It was found that the proposed model trained with the asymmetric loss function helped reduce overestimated cases by 17%. Hence, the newly developed GBO-XGBoost can be a robust and reliable approach for predicting the CS of RCC using RA. [ABSTRACT FROM AUTHOR]

There has been a significant interest in the development of eco-friendly building materials. Recyclable and environmentally friendly, geopolymer composites are extraordinary binding materials. The purpose of this experimental study was to examine the mechanical and durability properties of metakaolin based self-compacting geopolymer concrete (SCGPC) comprising steel fibers (SF) and recycled aggregate concrete (RCA) varying percentages of recycled coarse aggregate. The mechanical and durability properties of the geopolymer composites, including fracturing tensile strength, and flexural strength, were subsequently evaluated. At weight proportions of 0%, 25%, 50%, 75% and 100%, the recycled coarse aggregates were substituted for the natural coarse aggregates. The amounts of SF incorporated into the mixtures were 0, 0.5, 1.0, and 1.5% by volume fraction. While the incorporation of SF does not yield a substantial improvement in compressive strength, it substantially enhances fracture tensile strength and flexural behavior. The load-displacement graph demonstrated that the incorporation of steel fibers into geopolymer composites increased their fracture toughness, resulting in a higher maximal load capacity. The findings suggest that the incorporation of RCA into SCGPC reduces its flexural behavior, splitting and compressive tensile strengths, and durability, particularly under peak load, deflection, and load. Furthermore, it is observed that RCA negatively synergize with respect to compressive and fracturing tensile strength. However, SF exhibit a significant positive synergy in terms of flexural properties. [ABSTRACT FROM AUTHOR]

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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 ( V f ) remains constant at 1%; and two lengths of lap splices for rebars of 16 mm diameter ( d b ): 10 d b and 15 d b . 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. [ABSTRACT FROM AUTHOR]

Three types of aggregate, including metallurgical slag aggregate (steel slag, copper slag, and iron sand), rare earth porcelain sand (REPS) aggregate as artificial aggregate, and recycled aggregate, were selected to produce concrete with the same basic mixture proportions in order to investigate the influence of aggregate types and aggregate replacement rates on their mechanical properties. Three levels of aggregate replacement rate—20%, 35%, and 50% for coarse aggregate (CA) and 20%, 30%, and 40% for fine aggregate (FA)—were employed in this study. The results indicate that replacing natural sand with metallurgical slag aggregate as FA enhances the mechanical properties of concrete. Among these, iron sand (IS) shows superior enhancement effects compared with copper slag (CS), and CS outperforms steel slag (SS). Specifically, at a 30% IS replacement rate, the compressive strength and splitting tensile strength of IS aggregate concrete are 32.8% and 35.6% higher than those of natural aggregate concrete, respectively. REPS used as CA demonstrates significant improvements in compressive strength, while REPS used as FA notably enhances splitting tensile strength. For recycled aggregate concrete with recycled coarse aggregate replacement rates of 35% and 50%, mechanical properties are effectively strengthened by incorporating CS as FA at a 30% replacement rate and REPS as CA at a 20% substitution ratio, respectively. Additionally, XRF and XRD techniques were employed to confirm aggregate composition and were combined with SEM and EDS techniques to analyze the concrete microstructure, clarifying the strengthening mechanisms of metallurgical and artificial aggregates on concrete. [ABSTRACT FROM AUTHOR]

Despite extensive regulations, the systemic under-reporting of construction and demolition waste generation rates pervades the South African waste sector due to the extensive and active informal waste management practices that are typical of developing countries. This study merges the rapid development of high-technology 3D-printed concrete (3DPC) with the increasing pressure that the built environment is placing on both natural resource consumption and landfill space due to construction and demolition waste (CDW) by establishing an inventory of CDW that is suitable for use in 3DPC in South Africa. This is an essential step in ensuring the technical, economic, and logistical viability of using CDW as aggregate or supplementary cementitious materials in 3DPC. Of the methods considered, the lifetime material analysis and per capita multiplier methods are the most appropriate for the context and available seed data; this results in CDW estimates of 24.3 Mt and 12.2 Mt per annum in South Africa, respectively. This range is due to the different points of estimation for the two methods considered, and the per capita multiplier method provides an inevitable underestimation. In order to contextualise the estimated availability of CDW material for use in concrete in general, the demand for coarse and fine aggregate and supplementary cementitious material in South Africa is quantified as 77.9 Mt. This overall annual demand far exceeds the estimated CDW material (12.2–24.3 Mt) available as an alternative material source for concrete. [ABSTRACT FROM AUTHOR]

The present study aims to assess the effect of using recycled aggregates (RA) derived from construction and demolition waste (CDW) on the development of the unconfined compressive strength (UCS) of a silty-cement soil from the Guabirotuba Formation, located in the southern region of Brazil. Was considered the influence of various parameters, including RA content, compaction effort, maximum dry specific mass, and porosity/volume cement content (η/Civ). RA contents of 10%, 20%, and 30%, combined with 5% cement by dry soil weight, are studied at curing times of 0, 7, 14, and 28 days, using standard, intermediate, and modified compaction efforts. The results reveal that the addition of RA leads to an increase in the maximum dry specific mass, directly correlating with an increase in the rate of compressive strength gain over time. In the case of the modified compaction effort, the UCS value for the mixture with 30% RA at 28 days of curing reaches 2318 kPa, which is 35% higher compared to the mixture without RA, which has an RCS value of 1711 kPa. Equations establishing a relationship between η/Civ and UCS show that smaller η/Civ values result in greater UCS. Furthermore, a correlation between η/Civ and RA content with UCS suggests that η/Civ has a stronger influence on UCS than RA content. Lastly, Scanning Electron Microscopy (SEM) indicates that incorporating 30% RA reduces the number of pores as well as their size, which enhances the soil structure and its increases stability, resulting in a more compact structure. [ABSTRACT FROM AUTHOR]

Context: Bulk mineral waste materials such as construction and demolition waste are Germany's largest waste stream. Despite the availability of high-quality recycling pathways such as road base layers, waste concrete is predominantly recycled into lower-quality recycling pathways like earthworks or unbound road construction. This is due to low demand for recycled aggregates in road base layers and frost protection layers, especially in public procurement. Purpose: This study assesses the environmental consequences of increasing high-quality recycling of waste concrete in the near future to provide decision support for public procurement in Germany. The focus lies on climate change due to its importance for decision-makers. However, 17 other impact categories were assessed to avoid problem shifting. Methods: Life cycle assessment (LCA) is applied with background data from ecoinvent 3.9.1. Impact assessment was conducted at midpoint level using IPCC 2021 and ReCiPe Midpoint (H). Foreground data were taken from literature and expert interviews. In line with the goal of this LCA, a consequential modeling approach was followed to account for changes in the material flow system. Substitution creates a cascade effect previously omitted in consequential LCA studies, in which lower quality recycling materials replace higher quality recycling materials in their respective utilization pathways. Results and discussion: Increasing the high-quality recycling of waste concrete into road base layers causes a reduction in environmental impacts for all 18 impact categories, as it replaces natural aggregate and avoids backfilling of mixed mineral waste and excavated earth through substitution effects. Transport distances and ferrous metal recovery were identified as hot spots. Sensitivity analyses show that only transport is a significant issue. Conclusion: Increasing the high-quality recycling of waste concrete in Germany is recommended in terms of environmental impacts. Lower-quality recycling is environmentally feasible only in cases where the avoided transport distances for natural aggregates and backfilling are significantly lower than the additional transport distances for high-quality recycling. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the context of green and low-carbon materials development, the influence of replacing cement with circulating fluidised bed fly ash (CFBFA) on the expansion properties of paste under different curing conditions was first systematically investigated. Then, self-compacting concretes (SCCs) with recycled aggregate (RA) and CFBFA were prepared for filling steel tubes. The experimental results showed that, because of its unique physicochemical properties, the incorporation of CFBFA significantly increased the water requirement needed to achieve standard consistency of the paste and the pore structure was optimised by a reduction in the number of large pores due to the formation of more expansion components (ettringite, gypsum and portlandite are the main expansive products of CFBFA–cement paste). The influence of factors such as curing condition, age and CFBFA on the expansion effect was notable. With a 40% CFBFA content, the RA SCC in the steel tube showed an expansion of 41 μm/m, while the 28-day compressive strength reached 48.9 MPa. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

Nowadays, all productive sectors, including the construction industry, are facing the challenge of reducing their environmental impact. To achieve this objective, numerous actions are being carried out to access greater levels of environmental and economic sustainability. Techniques as Life Cycle Assessment contribute to quantifying environmental impacts, promoting a circular economy in a sector that consumes a high volume of resources, materials, and energy while generating large amounts of gaseous, liquid, or solid emissions. The present study aims to deepen our understanding of aspects that demonstrate the benefits of using RA instead of natural aggregates. This study not only quantifies the environmental impact but also explores the effects of potential improvements in the productive system and their impact on reducing environmental harm. The Life Cycle Assessment methodology is applied to quantify and compare the environmental impacts generated in the production of a ton of mixed recycled aggregates (MRA) from construction and demolition wastes, based on the data provided by plant managers. This is compared to the environmental impacts generated in the production of one ton of natural aggregates extracted from a quarry. The results revealed that the production of mixed recycled aggregate is more environmentally beneficial, confirming a reduction of 70.66% in environmental impacts during the production of recycled aggregates, in comparison to the natural aggregates extraction. Furthermore, the economic analysis demonstrates the economic advantage since the cost of producing recycled aggregates is over 30% cheaper than natural aggregates, being more competitive even when the transportation distances from the plant to the work sites exceed those of natural aggregates. [ABSTRACT FROM AUTHOR]

With diminishing natural aggregate resources and increasing environmental protection efforts, the use of recycled fine aggregate is a more sustainable approach, although challenges persist in achieving comparable mechanical properties. Exploration into the incorporation of steel fibers with recycled aggregate has led to the development of steel-fiber-reinforced recycled aggregate concrete. This study investigates the shrinkage performance and compressive constitutive relationship of steel fiber recycled concrete with different steel fibers and recycled aggregate dosages. Initially, based on different replacement rates of recycled coarse aggregate and different volume contents of steel fiber, experimental results demonstrate that as the replacement rate of recycled coarse aggregate increases, shrinkage also increases, while the addition of steel fiber can mitigate this effect. An empirical shrinkage model for steel fiber recycled concrete under natural curing conditions is also proposed. Subsequently, based on the uniaxial compression test, findings indicate that with an increasing replacement rate of recycled fine aggregate, the peak stress and elastic modulus of concrete decrease, accompanied by an increase in peak strain, and the addition of steel fiber limits concrete crack development and enhances its brittleness while the peak stress and strain of recycled fine aggregate concrete are enhanced. However, the steel fiber volume percentage has a negligible effect on the elastic modulus. A constitutive relationship for concrete considering the effects of recycled fine aggregate and steel fiber is also proposed. This finding provides foundational support for the influence patterns of steel fiber dosage and recycled aggregate ratio on the mechanical properties of steel fiber recycled concrete. [ABSTRACT FROM AUTHOR]

The literature shows that a circular economy can benefit some sectors such as the construction industry. This sector demands huge amounts of raw materials and produces waste when buildings and structures are demolished. This paper explores the possibility of manufacturing at industrial scale paving blocks using different types of construction and demolition wastes as aggregates, without modifying the commonly used industrial conditions. A total of four different recycled aggregates were used in this research. Both natural and recycled aggregates have been characterized. The dosages were optimized (three different formulations). Prefabricated tests have been carried out on the products manufactured in industrial plants and the evolution of mechanical properties over time has been analysed. The results obtained were analysed statistically by applying the principal component analysis (PCA) method. To ensure the security of the elements manufactured, the ionic leaching of the materials used as recycled aggregate and of the elements produced has been tested. The main implications of this research on the construction industry show that the majority of recycled aggregates used could replace 25% of the natural aggregate in manufactured precast concrete, that the properties of the aggregates should be taken into account in the different standards and that all paving blocks manufactured in this study can be considered environmentally safe (no risk of leaching) according to the Netherland Soil Quality Decree. Therefore, it is evident that it is possible to manufacture on an industrial scale paving blocks with mixed recycled aggregates, concrete and ceramic in nature, both with the fine and coarse fractions that meet the requirements of its reference standard UNE-EN 1338 and the Netherland Soil Quality Decree that evaluates environmental risks due to leaching. [ABSTRACT FROM AUTHOR]

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5–19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling. [ABSTRACT FROM AUTHOR]

This paper explores the new potential strategy of using fine recycled aggregates (fRA) derived from waste 3D printed concrete (3DPC) as a substitute for cement in additive manufacturing. This study hypothesizes that fRA can optimize mixture design, reduce cement content, and contribute to sustainable construction practices. Experimental programs were conducted to evaluate the fresh and hardened properties, printability window, and buildability of 3DPC mixes containing fRA. Mixes with replacement rates of cement with fRA by 10 vol%, 20 vol%, 30 vol%, 40 vol%, and 50 vol% were produced. A comprehensive experimental protocol consisting of rheological studies (static and dynamic yield stress), dynamic elastic modulus determination (first 24 h of hydration), flexural and compressive strengths (2 d and 28 d), and an open porosity test was performed. The obtained results were verified by printing tests. In addition, an economic and environmental life cycle assessment (LCA) of the mixes was performed. The results indicate that up to 50 vol% cement replacement with fRA is feasible, albeit with some technical drawbacks. While fRA incorporation enhances sustainability by reducing CO2 emissions and material costs, it adversely affects the printability window, green strength, setting time, and mechanical properties, particularly in the initial curing stages. Therefore, with higher replacement rates (above 20 vol%), potential optimization efforts are needed to mitigate drawbacks such as reduced green strength and buildability. Notably, replacement rates of up to 20 vol% can be successfully used without compromising the overall material properties or altering the mixture design. The LCA analysis shows that reducing the cement content and increasing the fRA addition results in a significant reduction in mix cost (up to 24%) and a substantial decrease in equivalent CO2 emissions (up to 48%). In conclusion, this study underscores the potential of fRA as a sustainable alternative to cement in 3D printed concrete. [ABSTRACT FROM AUTHOR]

Concrete waste recycling processes involve multiple stages, equipment, and procedures which produce Fine Recycled Concrete Aggregates (FRCA) for use in construction. This research aims at performing a comprehensive overview of the recycling technologies, recycling processes, and normative requirements to produce high-quality FRCA and to investigate the influence of these processes on their physical properties. The properties investigated were the particle size distribution (PSD), water absorption, oven-dry density, and adhered paste. The correlations between these properties were also investigated. The results indicate that the recycling processes with the highest potential for producing high-quality aggregates demand jaw crusher and impact crusher combinations. These processes are better suited for achieving FRCA with the desired particle size distribution and oven-dry density. However, water absorption and adhered paste, which are critical factors for obtaining high-quality FRCA, seem to be more dependent on the original material than on the recycling process. [ABSTRACT FROM AUTHOR]

Reusing waste materials such as construction and demolition waste is an environmentally significant task. This article aims to improve the quality of recycled aggregates after the demolition of concrete structures. Two methods, mechanical cleaning and impregnation, were explored to enhance the quality of coarse aggregates. The findings indicate that mechanical cleaning is more effective than soaking in a sodium silicate solution. The compressive strength of concrete made with mechanically cleaned recycled aggregates was 2.3 times greater than that of concrete made with untreated rubble. Concrete with impregnated rubble had a compressive strength 1.1 times greater than that of concrete with untreated aggregates. Infrared spectroscopy was used to study the microstructure, revealing that the type of treatment does not influence the quantity of portlandite and ettringite in hydrated cement. However, the treatment of recycled aggregates alters the interaction in the gel portion of cement hydration products. Concrete with aggregates treated by sodium silicate has more aluminate components. Additionally, there is a shift of the bands assigned to Si-O stretching to higher wave numbers (from 995 cm–1 to 1088 cm–1), which can be attributed to the formation of calcium-silicate-hydrate gel with a lower calcium/silicon ratio.