Recycled Aggregate Concrete Research Articles

Enhancing green building decision-making with a hybrid fuzzy AHP-TOPSIS model for material selection

Sustainable material selection is essential for minimizing environmental impact, resource depletion, and energy consumption in construction. We propose a hybrid fuzzy AHP-TOPSIS model to evaluate and rank four material alternatives based on nine sustainability criteria across three environmental, economic, and social dimensions. Fuzzy AHP determines criteria weights based on expert judgments, while TOPSIS ranks materials based on their relative closeness to the ideal sustainable solution. The results indicate that fly ash-based geopolymer concrete (GPC) ranked first (Ci = 0.885) due to its low carbon footprint and high recyclability, followed by cross-laminated timber (CLT) (Ci = 0.873), autoclaved aerated concrete (AAC) (Ci = 0.832), and recycled concrete aggregate (RCA) (Ci = 0.791). Sensitivity analysis confirmed the robustness of the rankings, demonstrating the model’s adaptability to different sustainability priorities. However, expert judgment introduces subjectivity, and integrating real-time sustainability data, such as material lifecycle emissions and resource availability updates, could enhance decision-making accuracy. This hybrid model offers a structured, transparent, and adaptable decision-making framework, ensuring transparency in the weighting process, material ranking, and overall selection methodology, thereby contributing to data-driven sustainable material selection for green building applications.

Bearing characteristics of recycled concrete aggregate encased column composite ground

This paper investigates the bearing characteristics of a recycled concrete aggregate encased column (RCAEC) composite ground with the objective of better-utilizing construction waste. A large-scale model test was conducted, in which recycled concrete aggregate (RCA) was employed as the column material and geosynthetics were encased with varying lengths and layers, with the similarity scale factor assumed to be 10. The impact of various factors, including encasement length, encasement stiffness, length-to-diameter ratio (l/d), and optimal replacement ratio, on the load-bearing characteristics was examined. The findings indicate that the maximum bearing capacity of the composite foundation can be achieved when the encasement length of RCAEC is approximately six times the column diameter, the l/d is 6 ∼ 7, the stiffness of the encasement material is approximately 100 kN/m, and the area replacement rate is around 13%. Lateral compression tests revealed a strong correlation between crushing degree, column-bearing capacity, and aggregate gradation. Increasing pressure led to significant destruction of 10 ∼ 5 mm particles, while particles smaller than 2.5 mm increased, alongside a rise in relative density. For optimal column construction and bearing processes, it is crucial to optimize RCA gradation and limit column loads to below 14,000 kN to prevent excessive crushing of RCA.

Effect of partial substitution of recycled concrete aggregate in reinforced concrete beams: analysis of dry and pre-saturated conditions.

The preservation of natural resources and the pursuit of sustainability in civil construction have promoted academic interest in research related to the reuse of construction and demolition waste (CDW). The partial replacement of conventional aggregates with CDW in cementitious materials has yielded satisfactory results in terms of the mechanical and rheological behavior of the resulting material. However, further studies are needed to demonstrate the feasibility of this application in a standardized manner. Accordingly, the present study aims to assess the impact of recycled concrete aggregates (RCAs) on the behavior of reinforced concrete (RC) beams. To this end, natural coarse aggregates were replaced with RCAs at substitution levels of 0% and 30%, while maintaining the same mixture composition across all samples. The main properties of concrete with RCAs were evaluated, including the slump test, compressive strength, tensile strength, and modulus of elasticity after 7days and 28days of curing. Subsequently, RC beams containing RCAs were analyzed through for four-point bending tests. The prototypes were cast using RCAs in water saturated and unsaturated conditions. The results revealed that incorporating RCAs enhanced workability by 62.5% while reducing compressive concrete strength by less than 15% in 28days. Despite this reduction, concrete incorporating RCAs achieved the projected compressive strength of 25MPa. No significant changes in tensile resistance were observed. Regarding the beams containing RCAs, it was observed that the failure mode remained unchanged, and their collapse loads did not differ significantly from those of the conventional reference RC beam, with variations of less than 10%. These findings are significant, given that several studies have documented notable changes in the mechanical properties of concrete containing RCAs. Overall, it can be concluded that using RCAs at a 30% substitution level is a viable option for RC beam applications. Furthermore, although saturating RCAs might enhance the adhesion between the aggregate and the cement matrix, this effect was not confirmed in the present study.

Development of Sustainable Concrete Using Construction and Demolition Waste

ABSTRACT Waste from construction and demolition accounts for a significant portion of global solid waste, with the majority of it ending up in landfills. Processing this debris and using it to make fresh concrete is a useful and profitable approach to manage it. Effective methods for utilising construction and demolition debris in concrete have been investigated by researchers. The study aimed to test the quality of recycled materials by evaluating their strength, water absorption, density, and the type of concrete they can produce. Compared to natural coarse aggregates, recycled aggregates from leftover concrete are heavier, more angular, and absorb more water. Strength and load-bearing capacity are enhanced as a result. To improve workability and examine their endurance, more research is necessary. This study explores the properties of recycled aggregates and focuses on developing concrete mixes incorporating them to minimize the environmental impact of the construction industry. It also compares concrete made with recycled and natural aggregates to evaluate their strength, Durability and Workability. We replaced natural aggregate concrete with 100% recycled aggregate concrete. Natural aggregate concrete has a higher compressive strength than recycled aggregate concrete. Keywords : C & D waste , Natural Aggregate Concrete, Recycle Aggregate , Strength , Durability , Workability.

Optimization of prediction models for the compressive strength of recycled aggregate concrete using artificial neural networks

Abstract Recycled coarse aggregate is increasingly utilized as a substitute for natural coarse aggregate in concrete production. The mechanical properties of recycled aggregate concrete (RAC) are largely influenced by the qualities of recycled coarse aggregate. Typically, the development of a strength prediction model for RAC emphasizes the effect of each component’s content on strength while overlooking the influence of recycled coarse aggregate qualities on the compressive strength of RAC. This paper investigates the significance of input variables, particularly key properties of recycled coarse aggregate, such as water absorption, particle size distribution, and crushing index, and identifies the optimal combination of input variables and hidden layer nodes, while determining the best ratio of training to test sets. Furthermore, the backpropagation (BP) neural network was optimized, and the performance of various machine learning models for predicting compressive strength was evaluated and compared. The results indicated that the prediction performance of the BP neural network improved significantly under the optimal combination of input variables and the optimal number of hidden layer nodes. Moreover, the BP neural network outperformed other commonly used machine learning methods, including the radial basis function (RBF) neural network, support vector machines (SVM), and linear regression.

Flexural performance of recycled aggregate concrete beams reinforced with basalt fiber-reinforced polymer or steel bars

This paper reports on the results of an experimental study on the flexural performance of recycled-aggregate concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars. A total of eight reinforced concrete (RC) beams were prepared and tested under four-point loading. The parameters investigated included: (1) concrete mixture (0, 25, 50, and 100% use of recycled concrete aggregates (RCA)) and (2) reinforcement material (steel/BFRP). The results revealed minimal effects of the use of RCA on the flexural behavior of RC beams. Altering reinforcement material, on the other hand, showed a significant effect on the flexural behavior of RC beams: using BFRP (instead of steel) reinforcement reduced the deformational performance but yielded comparable ultimate capacity of RC beams at 0% and 100% RCA replacement ratios. The cracking loads and crack spacings of steel RC beams were generally higher compared to BFRP-RC beams at the same RCA replacement ratio. Theoretical investigations of ultimate capacities and service load deflections were performed for the tested beams based on contemporary design guides and were compared with the experimental results. The findings of this study underscored the potential of using RCA and BFRP bars as sustainable alternatives to the conventional materials in reinforced concrete.

Preparation of green concrete using recycled aggregate in alkali-activated concrete

To promote industrial solid waste recycling and sustainable development, this study prepared alkali-activated recycled aggregate concrete (AARAC) using ground granulated blast-furnace slag and recycled coarse aggregate. The effects of alkali content and recycled aggregate replacement ratio on AARAC performance were examined. Results indicated that while recycled aggregate can impair concrete properties, an optimal alkali content of 6% significantly mitigates these effects, improving physical properties, mechanical stability, and compactness. Microstructural analysis showed enhanced hydration product formation and a denser interfacial transition zone at this alkali level. Entropy weight-TOPSIS evaluation confirmed that 6% alkali content provided the best overall performance with low sensitivity to aggregate variation. Additionally, carbon emission analysis revealed that AARAC reduced CO2 emissions by approximately 45% compared to conventional recycled concrete. These findings suggest that alkali-activated recycled aggregate systems offer a promising approach to developing low-carbon, sustainable construction materials.

IMPROVING THERMAL AND MECHANIC PERFORMANCE OF SUSTAINABLE LIGHTWEIGHT CONCRETE FACADE PANELS IN TERMS OF AGGREGATE TYPE

ABSTRACT Reducing energy consumption in the production process of lightweight concrete facade panels, utilizing recycled materials, minimizing waste, enhancing strength-to-weight ratio and durability, as well as ensuring ease of service and assembly, play a significant role in sustainability. Previous studies have been conducted to improve the thermal insulation properties of these panels; however, these studies were limited and produced conflicting results regarding sustainability. Additionally, due to a high number of influencing parameters, a definite procedure for determining the optimal mix ratio for lightweight concrete facade panels was not established. This study aims to determine the optimal proportions of coarse/fine aggregates, lightweight aggregates, and recycled aggregates for lightweight facade concrete mixes in terms of weight/strength and thermal insulation performance criteria. The goal is to develop a sustainable lightweight concrete facade panel with sufficient strength for building facades, high insulation capacity, maximal usage of recycled aggregates, while being as low weight as possible. Within the scope of this study, a total of 15 different lightweight concrete mixtures were produced by substituting various ratios of pumice, perlite, and recycled concrete aggregate for fine aggregate in the control mix containing 100% limestone as fine aggregate. The cement content, coarse aggregate amount, coarse/fine aggregate ratio, and slump value were kept constant for all produced mixtures. It was determined that the mixture containing 40% recycled concrete aggregate and 60% pumice as fine aggregate exhibits superior performance in terms of unit volume weight, compressive strength, and thermal conductivity. Within the scope of the study, 15 different lightweight concrete mixtures were produced by substituting various proportions of pumice, perlite, and recycled concrete aggregate in place of fine aggregate in a control mixture containing 100% limestone as fine aggregate. In all produced mixtures, the cement content, coarse aggregate amount, coarse/fine aggregate ratio, and slump value were kept constant. It was determined that the mixture containing 40% recycled concrete aggregate and 60% pumice as fine aggregate exhibited superior performance in terms of unit weight, compressive strength, and thermal conductivity.

Strain rate effect on splitting tensile behavior and failure mechanisms of geopolymeric recycled aggregate concrete: Insights from acoustic emission characterization

Strain rate effect on splitting tensile behavior and failure mechanisms of geopolymeric recycled aggregate concrete: Insights from acoustic emission characterization

Meso-analysis method for the compressive strength of steel fiber-reinforced recycled aggregate concrete: a six-phase numerical model

Meso-analysis method for the compressive strength of steel fiber-reinforced recycled aggregate concrete: a six-phase numerical model

Investigation of a Novel Method to Improve the Physical Properties of Recycled Concrete Aggregate for Asphalt Mixtures: Laboratory Characterization and Mechanisms

Investigation of a Novel Method to Improve the Physical Properties of Recycled Concrete Aggregate for Asphalt Mixtures: Laboratory Characterization and Mechanisms

Saturated and unsaturated properties of recycled concrete aggregate for sustainable pavement design

Saturated and unsaturated properties of recycled concrete aggregate for sustainable pavement design

Towards Industrial Implementation: Experimental Campaign Based on Variations in Temperature, Humidity, and CO2 Concentration in Forced Carbonation Reactions of Recycled Aggregates

This research presents a sensitivity analysis of various parameters that affect the carbonation of recycled aggregates (RAs), namely CO2 concentration, temperature, and relative humidity. The range of parameter values is close to that found in cement plant chimneys with regard to the forced carbonation of RAs. With this purpose, the main characteristics of flue gas streams (CO2 concentration, temperature, and relative humidity) from two Portuguese cement plants were identified and used in this research. The results indicated that temperatures around 60 °C and CO2 concentrations around 25% accelerate the carbonation reaction and increase CO2 absorption in mixed recycled aggregates (MRAs). CO2 absorption consistently decreased as the relative humidity was reduced from 60% to 40%. The highest amount of CO2 captured was by a recycled concrete aggregate (RCA) in the conditions of 23 °C, 60% RH, and 25% CO2. Overall, the RAs were able to capture a significant amount of CO2, ranging from 52 to 348 kg of CO2 per tonne of cement paste, depending on the nature of the RA. These findings drawn from a parametric campaign provide valuable insights into the potential enforcement of carbonation for recycled aggregates under conditions that closely reflect those found in cement plants.

Recycled Materials from Road Demolition Wastes Used in Pavement Construction

The construction industry generates significant amounts of demolition waste, particularly from road construction and rehabilitation projects. Recycling these materials into new pavement structures presents an opportunity to reduce environmental impact and conserve natural resources. This paper explores the use of recycled materials from road demolition, such as reclaimed asphalt pavement (RAP), recycled concrete aggregate (RCA), and other construction and demolition (C&D) waste, in pavement construction. The benefits, challenges, and implementation strategies are discussed, along with the impact on cost, durability, and sustainability. Additionally, this paper highlights case studies and real-world applications demonstrating the effectiveness of recycled materials in modern pavement construction.

REVOLUTIONIZING SUSTAINABLE CONSTRUCTION THROUGH RECYCLED CONCRETE AGGREGATE PRODUCTION: A SYSTEMIC REVIEW OF CODES, STANDARDS AND GUIDELINES

The significant rise in the production of construction and demolition (C&D) waste has increased dramatically in recent years, resulting in the entry of tons of concrete waste into the environment. Recycling and reusing C&D waste as a partial replacement for aggregate in building construction is practiced in other nations as a possible solution and waste management. However, few studies have identified how C&D waste can be utilized in the Ethiopian Construction Industry (ECI). In addition, the application of recycled concrete aggregate (RCA) in Ethiopia is limited owing to a lack of well-established standards and guidelines. Thus, the focus of this research is to investigate the opportunities and limitations of recycled concrete building materials based on legal design codes, standards, and government guidelines for utilizing recycled concrete waste as aggregates. This study systematically reviewed existing norms and standards for the potential use of recycled concrete aggregates and identified opportunities and limitations by incorporating them into current design and construction practices. This study evaluates the current state and utilization practices of RCA in economically comparable developing countries, drawing comparisons with Ethiopia. The findings revealed inconsistencies in the national standards concerning the permissible substitution of natural aggregates with recycled alternatives. Furthermore, the existing standards lack crucial parameters, such as the precise influence of the source concrete grade on the recycled material properties and the impact of service life on its characteristics. To address these shortcomings, it is essential to develop local design codes, laws, and standards, specifically for RCA in developing countries. Such measures will bolster stakeholder confidence in the sector’s applicability, utilization, commercialization, and promotion of this sustainable material. This study is expected to contribute to the standardization of recycled concrete in Ethiopia and similar developing countries where such guidelines or standards do not exist.

Tolerance Level of Bricks in Recycled Concrete Aggregates

Tolerance Level of Bricks in Recycled Concrete Aggregates

Efficient carbon sequestration of seawater sea-sand recycled aggregate concrete: an experimental study

Efficient carbon sequestration of seawater sea-sand recycled aggregate concrete: an experimental study

The Influence of Biomass Power Plant Ash on the Mechanical Properties of Recycled Aggregate Concrete: A Review

With the increasing installed capacity of biomass power generation in China and the evolution of urbanization, the disposal of biomass power plant ash and construction waste, mainly concrete, has become extremely urgent. Through biomineralization, biomass power plant ash theoretically contains highly active volcanic ash active substances such as silica, which has the potential to be developed as a new type of auxiliary cementitious material for cement concrete. However, the preparation conditions of biomass power plant ash differ greatly from the optimal preparation conditions in the laboratory, and the physical and chemical properties of biomass power plant ash are not stable. Therefore, it is challenging to apply biomass power plant ash as an auxiliary cementitious material in concrete systems. Secondly, the building materials industry has high energy consumption and carbon emissions. The use of recycled aggregates and auxiliary cementitious materials to replace cement is a key measure to address global climate change. This article provides comments on the physical and chemical properties of biomass ash and its impact on the mechanical properties of concrete, the mechanical properties of recycled aggregate concrete, and the influence of auxiliary cementitious materials on the mechanical properties of recycled aggregate concrete. The aim is to inspire research on the mechanical properties of biomass power plant ash recycled aggregate concrete.

A comparative study of life cycle carbon emissions of two commonly used simple-supported beam bridges

Carbon emissions from bridge engineering are an important component of the carbon emissions in the construction industry. The life cycle carbon emissions (LCCE) of two commonly used simple-supported beam bridges, hollow slab bridge and T-beam bridge, are studied and compared. Firstly, in order to establish the criteria for the comparison of different bridge types, the principle of equal stiffness is proposed for the superstructures, and the principle of matching load effect with bearing capacity is proposed for the substructures. Based on the above two principles, 6 bridges of 2 types and 3 spans are designed for comparative analysis. Then, a calculation model of the LCCE of simple-supported beam bridges is established, in which four stages, production, construction, operation and demolition stages are included, and the carbon emission factors of each stage are established. Finally, the carbon emissions of 6 bridges designed above are calculated, and the main factors affecting the LCCE of simple-supported beam bridges are discussed. The calculation results show that (1) For the same span, the LCCE of T-beam bridges are about 8–10% lower than those of hollow slab bridges. The reasons for this are that T-beam bridges use 22-32% less concrete and 4.5-11.5% less reinforcement than hollow slab bridges, which reduces carbon emissions during the production and demolition stages, and that the durability of the lateral connections of T-beam bridge is better than that of hollow slab bridge, which reduces carbon emissions from the maintenance and repair of T-beam bridge in the operation stage by about 30%. (2) Carbon emissions in the production stage of simple-supported beam bridges account for 83–84% of the LCCE, 11-12.6% of the LCCE in the operation stage, 3.8–4.5% of the LCCE in the construction stage, and 1% of the LCCE in the demolition phase. Therefore, the reduction of carbon emissions is most effective in the production and operation stages of these bridges. (3) Steel and concrete are the two materials that have the greatest impact on carbon emissions of simple-supported beam bridges. 100% recycled steel can reduce the carbon emissions of bridges by 17.7 -19.2% compared with 50% recycled steel. 50% and 100% recycled coarse aggregate concrete can reduce the carbon emissions of bridges by approximately 2.9% and 5.7%, respectively. (4) The carbon emission of the superstructure of the T-beam bridge is 12.5-14.2% less than that of the hollow slab bridge in the same span, and the differences in carbon emissions of the substructures are very small due to the small differences in the loads they are subjected to. With the increase of bridge span, the carbon emission per unit area of the superstructure of simple-supported beam bridge increases, that of the substructure decreases, and that of the whole bridge decreases firstly and then increases, which makes it possible to choose appropriate bridge span to decrease the carbon emission.

Implementing modified triple blend technique for enhancing the microstructure of recycled aggregate with M-sand in concrete.

This investigation explores the behavior of recycled aggregate concrete (RAC), employing a triple blend technique aimed at enhancing concrete properties with M- Sand. The triple blend comprises fly ash, ground granulated blast furnace slag (GGBS), and Alccofine, serving as partial replacements for cement of 60% to improve overall concrete performance when combined with recycled concrete aggregate (RCA). Concrete samples were then manufactured with varying RCA percentages, ranging from 25 to 100%. The study investigated the strength properties of the mix, including compressive strength, tensile strength, flexural strength, impact strength, bond strength, and overall concrete quality through non-destructive testing. Additionally, these samples underwent microstructural studies and phase assemblage analyses, including scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy tests. These analyses were conducted to determine the pore structure and mineralogical composition of the RAC. The results indicate that an increase in RCA content in the concrete mix tends to reduce compressive strength, primarily due to weaker bonding with the cement paste. However, this drawback can be partially mitigated by incorporating mineral admixtures in a modified triple mix blend. This modification leads to improved hydration, enhanced bonding, favourable morphology, and a refined pore structure. This study reveals that SRAC exhibits superior strength compared to Raw RAC, with considerable increase at 28days and maintaining comparable strengths to CC at 28days. This study suggests potential for sustainable structural concrete production with 25 to 50% RCA replacement and supplementary cementitious materials (SCM) incorporation.