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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]

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This study used recycled aggregate (RA) and mineral additions to design large-pore sandy recycled concrete (LPSRC) using a design porosity (DP) of 25 %, 20 %, and 15 %. Thus, the related effects of recycled coarse aggregate (RCA), recycled fine aggregate (RFA) and fly ash (FA) on the compressive strength, frost resistance (using slow and fast freezing methods), and sulfate attack properties of LPSRC were systematically studied. Moreover, to reduce the error between the design and theoretical porosity values, the bulk density ratio adjustment method was employed to design the theoretical porosity. The results of binarization analysis demonstrated that the deviation of the actual porosity caused by the sidewall effect was ∼2 %, which should be considered during DP design and performance evaluation. The compressive strength of the LPSRC after 56 curing days increased by 35.9 % on average as the DP was reduced from 25 % to 15 %. In a freeze–thaw cycle test, the slow freezing method was more accurate for evaluating the frost resistance of the LPSRC. Under the same conditions, the mass loss rate of the LPSRC calculated using the slow and fast freezing methods was 3.2 % and 7.62 %, respectively. This distinction is pivotal for establishing reliable frost resistance criteria for LPSRC in cold-weather applications, complementing previous research in the field. In terms of sulfate deterioration resistance, compressive strength corrosion factors decreased with increasing DP. Additionally, damage was mainly concentrated at the contact interface between RCA and the cement matrix, while the aggregate itself showed relatively little damage, suggesting RCA application has a positive effect on improving preparation of the LPSRC. Specifically, as DP increased from 15 % to 25 %, the average reduction in the compressive strength corrosion factors for LPSRC after 30 and 60 times of dry–wet cycle were 9.64 % and 8.37 %, respectively, illustrating a clear correlation between higher DP and reduced sulfate resistance. This study contributed to the LPSRC design and production using RCA, RCF and FA, that positively impacts to the sustainable development of the construction industry and helps to evaluate the effectiveness of RA in macroporous concrete. Moreover, the strategic implementation of design porosity has been shown to optimize the structural integrity and performance of the concrete, achieving a balance between strength and workability, which is crucial for the concrete's durability and its ability to adapt to various environmental conditions.

Recycled aggregate refers to crushed concrete, mortar, bricks, or asphalt derived from construction debris and repurposed in other building projects. It is obtained by crushing demolished waste to reclaim the aggregate. Over the past few decades, the abundance of Construction and Demolition Waste (C&DW) has increased significantly, leading the concrete industry to incorporate it, thereby reducing the cost of aggregates. The use of C&D waste in construction not only decreases carbon emissions but also facilitates the expansion of the concrete industry without causing harm to the environment. The objective of this study is to analyze the mechanical properties such as compressive strength, splitting tensile strength, flexural strength, and durability properties such as resistance to chloride, carbonation, freeze, and thaw of concrete utilizing recycled aggregate. It is observed that the mechanical and durability behavior of Recycled Aggregate Concrete (RAC) is inferior to that of standard concrete. However, by employing different admixtures and mixing approaches, the desired properties can be achieved. Furthermore, the study indicates that the improvement of mineral admixtures contributes more to enhancing the performance of recycled aggregate than it does to the characteristics of natural aggregate. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Geopolymer recycled aggregate concrete (GPRAC) is a new type of green material with broad application prospects by replacing ordinary Portland cement with geopolymer and natural aggregates with recycled aggregates. This paper summarizes the research about the mechanical properties, durability, and microscopic aspects of GPRAC. The reviewed contents include compressive strength, elastic modulus, flexural strength, splitting tensile strength, freeze–thaw resistance, abrasion resistance, sulfate corrosion resistance, and chloride penetration resistance. It is found that GPRAC can be made to work better by changing the curing temperature, using different precursor materials, adding fibers and nanoparticles, and setting optimal mix ratios. Among them, using multiple precursor materials in synergy tended to show better performance compared to a single precursor material. In addition, using modified recycled aggregates, the porosity and water absorption decreased by 18.97% and 25.33%, respectively, and the apparent density was similar to that of natural aggregates. The current results show that the performance of GPRAC can meet engineering requirements. In addition, compared with traditional concrete, the use of GPRAC can effectively reduce carbon emissions, energy loss, and environmental pollution, which is in line with the concept of green and low-carbon development in modern society. In general, GPRAC has good prospects and development space. This paper reviews the effects of factors such as recycled aggregate admixture and curing temperature on the performance of GPRAC, which helps to optimize the ratio design and curing conditions, as well as provide guidance for the application of recycled aggregate in geopolymer concrete, and also supply theoretical support for the subsequent application of GPRAC in practical engineering. [ABSTRACT FROM AUTHOR]

In this paper, an attempt is made to understand the effectiveness of the use of basalt fibre in recycled aggregate concrete. For this experimental study, the fresh and hardened properties of concrete samples made of recycled aggregate and incorporated with basalt fibres are investigated. The concrete samples made of recycled aggregate are reinforced with different dosages of basalt fibre varying from 0 to 0.5%, with an increment of 0.1%. From the preliminary analysis, the optimum dosage of basalt fibre which results in maximum efficiency of recycled aggregate concrete is found to be 0.2% by volume. In further investigation, experiments are conducted to evaluate the structural performance of two types of beams, one made of 100% natural aggregate and the other made of 50% recycled aggregate and 50% natural aggregate. The beams are reinforced with 0.2% basalt fibres. It has been observed that the performance of beams made of basalt fibre reinforced recycled aggregate concrete composites are reasonably close to that of conventional concrete. This can be used as an indicator of the fact that basalt fibres can be adequately used as structural material and that existing analytical models and codes for conventional concrete can also be applied to recycled aggregate concrete composites. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study introduces innovative concepts for closed-loop recycling waste concrete to produce fully recycled concrete (FRC). Multiple test methods and characterization techniques were used to evaluate the physical properties and durability of four types of concrete (normal concrete, recycled aggregate concrete, recycled cement concrete and FRC). The fresh density, compressive strength, ultrasonic characteristics, chloride resistance, water adsorption properties, carbonation behaviors, and microstructure characteristics of these concretes were investigated. The water absorption behavior of FRC can be divided into three stages, with the initial stage having a water absorption rate three times that of ordinary concrete. It was found that carbonation depth varied among different concrete types, influenced by binder quality, which can affect the porosity and mechanical properties. Overall, recycled cement concrete and FRC demonstrate considerable potential for reducing carbon emissions, with total emissions of 59.152 kgCO 2 /m3, representing an 85 % reduction compared to ordinary concrete. [Display omitted] • Fully recycled concrete (FRC) with 100 % recycled cement + 100 % recycled aggregates were prepared. • Physical performance and carbon emissions of normal concrete, recycled aggregate concrete, recycled cement concrete and FRC were compared. • The water absorption behavior of FRC can be divided into three stages, with the initial stage three times faster than ordinary concrete. • Recycled cement concrete and FRC demonstrate an 85 % reduction of carbon emissions compared to ordinary concrete. [ABSTRACT FROM AUTHOR]

In transport infrastructures, the cement-bound granular mixtures (CBGM) for base and sub-base of pavement layers can be built using mostly recycled materials. Recycled aggregates (RA) can replace the natural aggregates (NA) and coconut fiber (CF), obtained from discarded coconut husk, can be introduced to promote a reinforcement effect. Currently, the use of CF in CBGM is new, and regarding the use of RA in CBGM, the literature about its durability is still limited. Thus, there is a gap in knowledge regarding the durability of these solutions. Building on previous validation of mechanical performance, this work is among the first to evaluate the durability of CBGM incorporating RA and CF. For a comprehensive evaluation, three test methods were selected: wetting-and-drying, freezing-and-thawing, and a strength ratio using the indirect tensile strength test. The results highlight the feasibility of RA to replace NA, as both led to similar CBGM durability levels. The introduction of CF promoted gains in durability (on average reducing the mass loss by 42 % in the wetting-and-drying tests and by 20 % in the freezing-and-thawing tests), enhanced toughness, and allowed for a better response of the CBGM in the post-cracking phase. • Waste materials can be used in the construction of cement-bound granular mixtures. • The use of recycled aggregate had no detrimental effect in the CBGM durability. • The incorporation of coconut fiber enhanced the CBGM durability. • The incorporation of coconut fiber enables a fiber reinforcement effect. • The fiber reinforcement allowed for a better response of the CBGM in the post-cracking phase. [ABSTRACT FROM AUTHOR]

With increasing global research on the recycling of construction waste, the recycling of waste concrete aggregates has gradually attracted attention. Researches have shown that recycled aggregate (RA) has a certain degree of influence on the mechanical properties and durability of recycled aggregate concrete (RAC) owing to its high water absorption, high porosity, and large number of microcracks. Therefore, how to improve the mechanical properties and durability of RAC is a key issue of concern for scholars. Based on the review of related literature and comprehensive analysis, the reinforcement theories and methods such as self-reinforcement of recycled coarse aggregate (RCA), optimization of preparing technology of RAC, and external spiral constraint of RAC were systematically summarized in this paper. The results indicate that the adherent mortar of RCA can be enhanced by carbonation, and weak acid treatment can effectively remove the old adhesion of RCA, which is economical and environmentally friendly. The denseness of RAC can be improved by adding cementitious materials with volcanic ash effect, and the reduction of microcracks in mortar can be improved by adding fibers. The load-bearing capacity and mechanical properties of RAC are significantly improved by the spiral constraint of materials such as fiber reinforced polymer (FRP) and so on. The optimization of the production process not only improves the quality of RAC, but also enhances the production efficiency. The microstructure analysis of RAC was also summarized in this paper. Moreover, the results of this study can provide a technical reference for research on the mechanical strength and durability of RAC, develop the further research ideas, and promote the application of RAC. Finally, some potential opportunities and development directions have been suggested for future research on the improvement methods of RAC.

Different treatment strategies have been explored in a quest to improve the properties of recycled aggregate concrete (RAC). The improvement strategies are directed towards the removal of residual layers of old mortar on the recycled coarse aggregate (RA). The removal of old mortar layer improves the bond between the new mortar and the RA that makes the quality of RAC better. Efforts have been made to remove the old mortar from the surface of the RA through abrasion process, however, there is a lack of detailed information, particularly about the beneficial effect of abrasion coupled with some chemical treatment. In the present work, the performance of RAC prepared with the RA subjected to abrasion (with the help of a Los Angeles abrasion test machine) was evaluated. The combined effect of abrasion and sodium silicate treatments of the RA on the fresh and hardened properties of RAC was also evaluated. A significant improvement in the workability, strength, and durability of RAC was noted due to abrasion treatment of the RA. Strength and durability of RAC increased significantly due to the combined effect of abrasion and sodium silicate treatment of the RA. [ABSTRACT FROM AUTHOR]

In current state of the World, the pollution is increasing very fast. One of its major reason is the production of huge quantity of cement which causes outflow of CO2 into the environment and land dumping of construction and demolition waste which leads to the land pollution. In order to address this major issue, it is important to decrease the utilization of cement by substituting the cement with by product such as slag and using recycled aggregates as a replacement of natural aggregates. This research aimed to utilize evaluate the performance of sustainable high-performance concrete reinforced with steel fibers which is produced with recycled aggregate. Crushed stone aggregates are supplanted with recycled aggregates extracted from source concrete that had compression strength of 45 MPa and 85 MPa at proportions of 50% and 100%. Steel fibers are used at 2% to produce high-performance concrete, and in a few of the mixtures, the cement was substituted with granulated blast furnace slag. In addition to mechanical performance, the durability properties, i.e., electrical resistivity, drying shrinkage, and water absorption, of concrete blends were examined. The test outcomes show that high-performance concrete with the required characteristics can be developed utilizing recycled aggregates extracted from source concrete of high strength. The inclusion of double hooked end steel fibers considerably improves the mechanical characteristics of RAC. Concrete formed with high-quality recycled concrete aggregates and mixes comprising granulated blast furnace slag (GBFS) and double hooked end (DHE) steel fibers shows decreased drying shrinkage and water absorption in comparison to normal concrete. The outcomes of the present study assist in making of suitable high-performance concrete which is sustainable and budget friendly.

In recent years, pervious concrete (PC) has gained much attention as one of the strategies for low-impact development (LID) in pavements due to its structural, economic, and road-user benefits. This study sought to review and evaluate changes in the mechanical, hydraulic, and durability performance of PC produced with cement and aggregate replacements. A meta-analysis was conducted to elucidate the feasible range of the replacement percentage and the number of materials that could be used to replace cement and aggregates; single or binary replacements were considered. Results indicated that cement-replacing materials, industrial wastes (IWA), and recycled aggregates (RA) met the minimum requirement for the mechanical, hydraulic, and durability properties of PC. The use of a single cement replacement material provided PC with better performance than when cement was replaced with two or more materials or when cement alone was used. Industrial waste was found to be a better replacement to aggregates than RA. The combined replacement of cement and aggregates with IWA and other cement-replacing materials was the most effective method for improving the mechanical, hydraulic, and durability performance of PC. Replacements of up to 40% was considered viable for cement replacement, while up to 50% replacement was considered practical for aggregate and combined replacement. PC incorporating different cement-replacing materials exhibited equivalent or improved mechanical properties and maintained hydraulic performance compared to cement-based PC. Nonetheless, limited studies are available on the durability performance of PC made with cement and/or replacements. Thus, the durability of PC coupled with the applicability of replacement materials acquired from different locations need to be evaluated to address the viability of producing more durable PC with the use of replacements. [ABSTRACT FROM AUTHOR]

The durability performance of recycled concrete (RC) subjected to different environmental actions, including salt-solution, mechanical load, salt-solution freeze-thaw cycles, and coupled mechanical load and salt-solution freeze-thaw cycles was investigated in this paper. To evaluate the effects of recycled aggregate (RA) quality on the RC durability, modeled recycled concrete (MRC) containing modeled recycled aggregate (MRA) with various thickness and coverage of old mortar, along with different degrees of initial damage, was fabricated and tested. Moreover, several modification treatments were employed to study the effects of modification treatments on the RC durability, which included the impregnation of RA with polyvinyl alcohol (PVA) emulsion or nano-SiO2 solutions, and the enhancement of RC with the incorporations of fly ash or hybrid fly ash and silica fume. The results reveal that the deterioration of RC under coupled actions of mechanical load and salt-solution freeze-thaw cycles was the most severe, which was followed by the salt-solution freeze-thaw cycles, mechanical load and salt-solution. The old interface in RA was determined as the weakest zone in RC. With the increase in the thickness or coverage of old mortar, or the initial damage of RA, the durability performance of RC declined, and the effect of initial damage of RA was more significant compared to the thickness or coverage of old mortar. Additionally, modifying RC with 1.5% nano-SiO2 solution or PVA emulsion, and replacing cement with 10% fly ash can significantly enhance the RC durability.

Abstract To better understand the synergistic effects of combined fibers on mechanical properties and durability of recycled aggregate concrete (RAC), different types of fibers with various lengths and mass ratios were adopted in this study. Experimental investigations were conducted to study the 28-day compressive strength and strength loss after exposed to salt-solution freeze–thaw cycles and the coupled action of mechanical loading and salt-solution freeze–thaw cycles. The microstructure was also characterized to evaluate the mechanism of this synergistic effect. To determine the effectiveness of the combined fibers on improving the mechanical properties and durability of RAC, the synergistic coefficient was proposed and applied for various combinations of fibers. The results indicate that the incorporation of fibers slightly decreased the 28-day compressive strength of RAC, but combining different sizes and types of fibers can mitigate this negative effect. Moreover, the incorporation of fibers greatly improves the freeze–thaw resistance of RAC. The combining different fibers exhibited a synergistic effect on the enhancement in properties of RAC, which could not be predicted with only one simplistic rule of fibre mixtures. In addition, microstructural characterization shows that the bonding strength of the interfacial transition zone (ITZ) between the fiber and cement matrix is mainly determined by the chemical bonding force which is due to the hydration reaction between fiber surface and cement matrix.

Geopolymer recycled aggregate concrete (GPRAC) is a new type of green material with broad application prospects by replacing ordinary Portland cement with geopolymer and natural aggregates with recycled aggregates. This paper summarizes the research about the mechanical properties, durability, and microscopic aspects of GPRAC. The reviewed contents include compressive strength, elastic modulus, flexural strength, splitting tensile strength, freeze–thaw resistance, abrasion resistance, sulfate corrosion resistance, and chloride penetration resistance. It is found that GPRAC can be made to work better by changing the curing temperature, using different precursor materials, adding fibers and nanoparticles, and setting optimal mix ratios. Among them, using multiple precursor materials in synergy tended to show better performance compared to a single precursor material. In addition, using modified recycled aggregates, the porosity and water absorption decreased by 18.97% and 25.33%, respectively, and the apparent density was similar to that of natural aggregates. The current results show that the performance of GPRAC can meet engineering requirements. In addition, compared with traditional concrete, the use of GPRAC can effectively reduce carbon emissions, energy loss, and environmental pollution, which is in line with the concept of green and low-carbon development in modern society. In general, GPRAC has good prospects and development space. This paper reviews the effects of factors such as recycled aggregate admixture and curing temperature on the performance of GPRAC, which helps to optimize the ratio design and curing conditions, as well as provide guidance for the application of recycled aggregate in geopolymer concrete, and also supply theoretical support for the subsequent application of GPRAC in practical engineering.

Construction and demolition wastes (C&DWs) have raised a large number of ecological and environmental problems. Recycling C&DWs into arecycled concrete aggregate (RCA) will help save natural resources effectively and reduce the negative impact of C&DW on the environment. Innovative pervious concrete (IPC) can mitigate extreme weather disasters, such as rainstorms, and overcome the low strength and poor durability of traditional pervious concrete. In this study, innovative recycled pervious concrete (IRPC) is prepared by combining RCA with IPC, which has broad application prospects and ecological friendliness. This study investigates the effect of RCA quality grades and replacement rates on the mechanical property, permeability, sulfate resistance and abrasion resistance of IRPC. IRPC mixtures were prepared with three different quality grades (high, medium and low qualities) of aggregates named as NA, RCA1 and RCA2. Moreover, the replacement rate of RCA for NA varied as 0%, 25%, 50%, 75% and 100%. The IRPC specimens were tested for compressive strength, mass loss and abrasion resistance after different sulfate wetting-drying cycles of 0, 30 and 60. The results exhibited that the initial compressive strength of all types of IRPC was more than 40 MPa. The compressive strength and mass of most IRPC increased first and then decreased slightly with the passage of a number of sulfate wetting-drying cycles, indicating IRPC has good resistance to sulfate attack. Sulfate attack and the addition of RCA will reduce the abrasion resistance of IRPC. However, when the replacement rate is lower than 50%, and the RCA quality is better (attached mortar content < 25%), the abrasion resistance of IRPC will be improved under sulfate attack. The experimental results might be useful as a reference and design methodology for employing IRPC in pavement applications in the future. [ABSTRACT FROM AUTHOR]

The recycled aggregate permeable concrete made of reused construction wastes is very important for realizing the sustainable development of the construction industry, it can alleviate the adverse impact of surface runoff during storm and the urban heat island effect. Therefore, this paper studied the mechanical properties and durability of recycled aggregate permeable concrete. At first, a few properties of the target material, including bulk density, moisture content, water absorption, compressive strength, and water permeability coefficient, were tested respectively. Then, based on the orthogonal test, the performance of the target material was analyzed, and the analysis steps of the range analysis method and the variance analysis method in the orthogonal test were given. At last, the mechanical properties and durability of the target material were tested via experiments, and the relevant test results and analysis were elaborated. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Acceptance by the construction industry of recycled concrete as a sustainable alternative material is contingent upon a reliable assessment of its permeability to corrosive agents. This study analyses the transport mechanisms associated with chloride (Cl−), oxygen (O2) and carbon dioxide (CO2) ions in concrete with cement made with 10% or 25% ground recycled concrete (GRC) separately or in combination with 50% mixed recycled aggregate (MRA). The findings show that, irrespective of aggregate type, concrete with GRC exhibited lower resistance to ingress than conventional concrete due to its greater porosity. Nonetheless, O2 permeability was consistently below 4.5 × 10−17 m2 and CO2 penetration, under 4 mm/year0.5, indicative of concrete with high quality. Resistance to CO2 and Cl− penetration in the materials with 10% GRC was similar to the values observed in conventional concrete. On the other hand, the incorporation of 25% GRC increased the penetration of CO2 and Cl- by 106% and 38%, respectively. Further to those findings in normal carbonation environments, reinforcement passivity would be guaranteed in such recycled materials over a 100 year service life. [ABSTRACT FROM AUTHOR]

The output of C&D waste is increasing year by year, among which low-quality recycled brick aggregates (RBAs) have not been well utilized and brought environmental burden. The durability of steam-cured concrete (HCC) is often compromised due to the detrimental effects of this curing regime on the long-term performance and microstructure development of the concrete material. To address this issue, this study investigates the potential of incorporating RBAs to improve the long-term durability of HCC. The results demonstrate that the incorporation of a small amount of RBA (10–20%) not only enhances the 28-d strength of HCC by 2.5–11.3%, but also improves its impermeability by mitigating heat damage effects. The combined application of fine and coarse RBA was found to effectively balance the negative effects of coarse RBA on the performance of HCC. Furthermore, the utilization of RBA in HCC was shown to have economic and environmental benefits. The results of this study demonstrate a simple and effective approach to improve the long-term durability of HCC while promoting the high-value utilization of solid waste. [Display omitted] • Low-quality C&D waste is recycled with high added value in precast concrete elements. • The durability of steam-cured concrete is improved by using the appropriate amount of RBAs. • Technical, economic and environmental feasibility of RBA-modified steam-cured concrete is assessed. [ABSTRACT FROM AUTHOR]

In developing country such as India, due to the significant boom in the infrastructure development the virgin aggregates (VAs) resources are diminishing at a high pace and thus creating an ecological imbalance. In contrast, an immense quantity of recycled aggregates (RAs) is generated from construction and demolition waste. Thus, in view of sustainability, utilization of RA can be a great source of aggregate in the development of structural concrete. This paper outlines the development of self-compacting concrete (SCC) with full replacement of coarse VAs with coarse RAs. In addition, to make the SCC more sustainable, utilization of supplementary cementing materials such as coal fly ash (CFA), ground granulated blast furnace slag (GGBS), and metakaolin (MK) were used as cement replacement materials. Finally, the mechanical and durability performance of SCCs were examined to see whether they could be adopted for structural applications with greater confidence. A total of nine SCC mixes were designed containing GGBS, CFA, and MK content as cement replacement (by weight) with full replacement of VAs with RAs. Fresh performance of SCC mixes was scrutinized by slump flow, T500, V-funnel, and L-box test. Furthermore, compressive strength test, split tensile test, flexural test, and E-modulus test were performed to study the mechanical characteristics. Durability performance was examined by conducting water permeability, sorptivity, rapid chloride penetration test, surface resistivity, pH, and carbonation tests. The experimental results concluded that 15% replacement of cement with MK exhibited an excellent mechanical as well as durability performance of self-compacting recycled aggregate concrete with a ceiling strength of 75 MPa. The use of GGBS also yielded excellent durability performance. In contrast, the use of CFA exhibits moderate mechanical and durability performance. It can be inferred from the outcomes of this study that it is possible to develop high-performance SCC using 100% RA, by employing mineral admixtures such as CFA, GGBS, and MK. [ABSTRACT FROM AUTHOR]

Featured Application: The results of this research have been followed for the use of recycled concrete at the ARTEPREF precast plant (Spain). The research presented in this article analysed the influence of incorporating precast concrete waste as an alternative to coarse aggregate in self-compacting concrete to generate new precast elements. The experimental study involved the characterization of recycled aggregate and the design of the mix of the new self-compacting concrete (SCC). The experimental study evaluates the physical processes that affect the durability of concrete with percentages of incorporation such as 20%, 50% and 100% of recycled aggregate. Two types of SCC were manufactured with minimum compressive strength of 30 MPa and 45 MPa. The properties analysed were density of hardened SCC, shrinkage cracking, freeze-thaw resistance, resistance to ageing by thermal shock and abrasion resistance. The results obtained were compared with those of the control concrete, observing great capacity of the SCC under physical aggressions that affect durability. The results of this research show that it is possible to use the recycled aggregate coming from precast pieces in order to the manufacture of self-compacting recycled concrete in the same precast industry. However, high loss of proprieties occurs for a 100% substitution, while for 20% and 50%, the variations with respect to control concrete are smaller. In addition, taking advantage of this waste to incorporate it back into the production chain contributes to more sustainable construction. [ABSTRACT FROM AUTHOR]

There is an increasing tendency to use recycled aggregate to produce concrete due to diminishing sources of natural aggregate. The properties of recycled aggregate concrete (RAC) are inferior to that of normal aggregate concrete. Several strategies including the use of supplementary cementitious materials (SCMs) are adopted to improve the properties of RAC. The two-stage mixing approach (TSMA) is also used as an improvement strategy. The present study was aimed to examine the individual and combined effects of using SCMs and TSMA on the fresh and hardened properties of RAC. Three SCMs, namely, fly ash, ground granulated blast furnace slag, and silica fume were used with and without TSMA. The experimental data indicated the beneficial effect of SCMs and TSMA on workability, strength, shrinkage, and durability of RAC. Further, the cost per unit strength of the RAC with SCMs and TSMA was less than that of RAC without any treatment. The use of developed RAC will lead to technical, economic, and environmental benefits. [ABSTRACT FROM AUTHOR]

To better understand the synergistic effects of combined fibers on mechanical properties and durability of recycled aggregate concrete (RAC), different types of fibers with various lengths and mass ratios were adopted in this study. Experimental investigations were conducted to study the 28-day compressive strength and strength loss after exposed to salt-solution freeze–thaw cycles and the coupled action of mechanical loading and salt-solution freeze–thaw cycles. The microstructure was also characterized to evaluate the mechanism of this synergistic effect. To determine the effectiveness of the combined fibers on improving the mechanical properties and durability of RAC, the synergistic coefficient was proposed and applied for various combinations of fibers. The results indicate that the incorporation of fibers slightly decreased the 28-day compressive strength of RAC, but combining different sizes and types of fibers can mitigate this negative effect. Moreover, the incorporation of fibers greatly improves the freeze–thaw resistance of RAC. The combining different fibers exhibited a synergistic effect on the enhancement in properties of RAC, which could not be predicted with only one simplistic rule of fibre mixtures. In addition, microstructural characterization shows that the bonding strength of the interfacial transition zone (ITZ) between the fiber and cement matrix is mainly determined by the chemical bonding force which is due to the hydration reaction between fiber surface and cement matrix. [ABSTRACT FROM AUTHOR]

• Characterization of MRA and their use in structural concretes. • The use of RHA reduces the adverse effects of RA on concrete properties. • Reduction of the amount of cement in concrete. This study proposes the use of reactive rice husk ash (RHA) to improve the performance of recycled concrete. The concretes were produced with 50% and 100% of CDW mixed aggregate (RMA) replacing the natural aggregate and with RHA replacing Portland cement (10, 15, and 20%). The results showed an increase in compressive strength and modulus of elasticity in concretes with RHA. In durability tests, lower percentages of water absorption were observed for mixtures that used RHA. The RCPT test showed lower load transfer values with the use of RHA, resulting from the lower porosity and refined pore structures, as determined by Mercury Intrusion Porosimetry. [ABSTRACT FROM AUTHOR]

Acceptance by the construction industry of recycled concrete as a sustainable alternative material is contingent upon a reliable assessment of its permeability to corrosive agents. This study analyses the transport mechanisms associated with chloride (Cl−), oxygen (O2) and carbon dioxide (CO2) ions in concrete with cement made with 10% or 25% ground recycled concrete (GRC) separately or in combination with 50% mixed recycled aggregate (MRA). The findings show that, irrespective of aggregate type, concrete with GRC exhibited lower resistance to ingress than conventional concrete due to its greater porosity. Nonetheless, O2 permeability was consistently below 4.5 × 10−17 m2 and CO2 penetration, under 4 mm/year0.5, indicative of concrete with high quality. Resistance to CO2 and Cl− penetration in the materials with 10% GRC was similar to the values observed in conventional concrete. On the other hand, the incorporation of 25% GRC increased the penetration of CO2 and Cl- by 106% and 38%, respectively. Further to those findings in normal carbonation environments, reinforcement passivity would be guaranteed in such recycled materials over a 100 year service life.

The carbonation treatment of recycled aggregate（RA）enhances its physical properties and sequestrates greenhouse gas CO2, which is an environmental friendly approach. Firstly, the mechanism and methods of accelerated carbonation of recycled aggregate are introduced. Secondly, the physical properties of recycled aggregate after carbonation and the workability, mechanical properties and durability of recycled aggregate concrete（RAC）incorporating carbonated recycled aggregates are summarized. Finally, the main problems that need to be further studied in the carbonization modification of recycled aggregate are proposed. It suggests that carbonation treatment is an efficient and feasible method for improving the mechanical properties and durability of RA and RAC. [ABSTRACT FROM AUTHOR]

The research presented in this article analysed the influence of incorporating precast concrete waste as an alternative to coarse aggregate in self-compacting concrete to generate new precast elements. The experimental study involved the characterization of recycled aggregate and the design of the mix of the new self-compacting concrete (SCC). The experimental study evaluates the physical processes that affect the durability of concrete with percentages of incorporation such as 20%, 50% and 100% of recycled aggregate. Two types of SCC were manufactured with minimum compressive strength of 30 MPa and 45 MPa. The properties analysed were density of hardened SCC, shrinkage cracking, freeze-thaw resistance, resistance to ageing by thermal shock and abrasion resistance. The results obtained were compared with those of the control concrete, observing great capacity of the SCC under physical aggressions that affect durability. The results of this research show that it is possible to use the recycled aggregate coming from precast pieces in order to the manufacture of self-compacting recycled concrete in the same precast industry. However, high loss of proprieties occurs for a 100% substitution, while for 20% and 50%, the variations with respect to control concrete are smaller. In addition, taking advantage of this waste to incorporate it back into the production chain contributes to more sustainable construction.

Currently it is necessary to find alternatives towards a sustainable construction, in order to optimize the management of natural resources. Thus, using recycled fine aggregate (RFA) is a viable recycling option for the production of new cementitious materials. In addition, the use of polymeric microfibers would cause an increase in the properties of these materials. In this work, mortars were studied with 25% of RFA and an addition of polyacrylonitrile PAN microfibers of 0.05% in cement weight. The microfibers were obtained by the electrospinning method, which had an average diameter of 1.024 µm and were separated by means of a homogenizer to be added to the mortar. Cementing materials under study were evaluated for compressive strength, flexural strength, total porosity, effective porosity and capillary absorption, resistance to water penetration, sorptivity and carbonation. The results showed that using 25% of RFA causes decreases mechanical properties and durability, but adding PAN microfibers in 0.05% caused an increase of 2.9% and 30.8% of compressive strength and flexural strength respectively (with respect to the reference sample); a decrease in total porosity of 5.8% and effective porosity of 7.4%; and significant decreases in capillary absorption (approximately 23.3%), resistance to water penetration (25%) and carbonation (14.3% after 28 days of exposure). The results showed that the use of PAN microfibers in recycled mortars allowed it to increase the mechanical properties (because they increase the tensile strength), helped to fill pores or cavities and this causes them to be mortars with greater durability. Therefore, the use of PAN microfibers as a reinforcement in recycled cementitious materials would be a viable option to increase their applications.

Abstract RAC produced with crushed recycled aggregate (RA) is regarded as an environmental friendly material, while its high water demand, high mortar content and low modulus have restricted its application. Scattering-filling coarse aggregate (SFCA) process was applied to prepare the recycled aggregate concrete with promoted performance. With the reference of conventional concrete and the scattering-filling natural aggregate (SFNA) concrete, the influences of ratio, type, size and moisture state of RA on mechanical and durable properties of scattering-filling recycled aggregate (SFRA) concrete were investigated. The results indicate that SFCA process could improve the compressive strength, elastic modulus, and reduce the drying shrinkage and chloride penetration. The frost resistance of SFRA is comparable with the conventional concrete. With 10–20 mm scattering-filling aggregate of RA, SFCA concretes get more significant improvement on elastic modulus and anti-permeability; Higher water content of RA worsen the performance of recycled aggregate concrete (RAC) for water in the RA weakening ITZ; Furthermore, image processing analysis and microhardness indicated that SFCA process improve the properties by increasing the homogeneity of aggregate distribution and improving ITZ between the aggregate and cement paste in RAC. SFCA process provides an economic method to produce high-quality recycled aggregate concrete and an efficiently approach to the utilization of recycled concrete aggregate from Construction and Demolition waste. [ABSTRACT FROM AUTHOR]

In this study, the intrinsic properties of recycled coarse aggregates (RC), associated with bonded mortar, were modified with two different pretreatment techniques viz-a-viz HCl pretreatment and Na 2 SO 4 pretreatment, while maintaining a fixed aggregate-to-solution ratio of 1:4.5. The residual bonded mortar was quantified to evaluate the potential of both techniques. HCl pretreatment yielded greater removal of bonded mortar content (BMC), almost twice as high as achieved by Na 2 SO 4 pretreatment. Subsequently, the concretes were developed (termed as recycled aggregate concrete; RAC) by incorporating HCl treated coarse aggregates (HTC) and Na 2 SO 4 treated coarse aggregates (STC). Both natural and recycled (untreated) fine aggregates (NF and RF, respectively) were used. Control specimens with natural coarse aggregates (NC) were prepared for comparative assessment. The resulting properties showed significantly influenced by bonded mortar content (BMC). About 14% higher compressive strength was achieved by using HTC in comparison with untreated RC, while a mere corresponding decline of 5% was seen when compared with NC. Likewise, the carbonation resistance and the resistance to chloride ion penetration showed better performance for HTC and STC incorporated concretes. Such superior performance is attributed to the denser interface (between the aggregate and paste matrix) with reduced pores/voids, as assessed from the optical and scanning electron microscopy. Further, the determined properties were used to develop regression models for the prediction of RAC properties. The prediction equations thus obtained showed remarked precision with the experimentally determined results, and as such these can be used for strength and durability prediction. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregates have been extensively studied in recent years. However, the studies that have addressed the use of the recycled aggregate in concrete subjected to freeze-thaw cycles are divergent. Thus, the present work suggests the use of recycled coarse aggregate (RCA), derived from civil construction waste, in concrete as a substitution to the natural coarse aggregate (NCA). To this end, concrete specimens were molded with replacement levels equal to 15%, 25% and 50% of the NCA for RCA, being the specimens evaluated according to the ASTM C 666-15 norm. In addition, the samples were characterized for apparent porosity and density, water absorption by capillarity, axial compression strength and dynamic modulus of elasticity. The use of recycled aggregates proved to be efficient as a possible alternative to the incorporation of air in the concretes, presenting a durability factor at the end of the cycle higher than presented by the reference mixture. [ABSTRACT FROM AUTHOR]

Recycled aggregate self-curing concrete is a one of innovative concretes that can be cured without using conventional curing regimes. It is made from coarse recycled aggregates instead of natural coarse aggregates. Recycled aggregates can store a high amount of water that is not part of the mixing water to create water supply reservoirs in the concrete to continue the hydration process. In this investigation, the durability of recycled aggregate self-curing concrete studied under the attack of sulfates and chlorides. The effect of sulfates on compressive, splitting tensile and flexure strengths at different ages (2, 4 and 6 months) is studied. The effect of chloride attack (as 8% concentrated sodium chloride solution) is studied on bond and flexure strengths at different ages (1 and 2 months). Also, the flexure behavior of the recycled aggregate self-curing reinforced concrete beams is studied individually and under the effect of chloride attack after different exposure periods. Test results indicated that using recycled aggregates (such as crushed concrete and crushed red bricks) can be used in self-curing concrete with satisfied durability characteristics under chlorides and sulfate attacks. Dolomite then crushed concrete followed by crushed red bricks can be used as coarse aggregates for self-curing concrete. [ABSTRACT FROM AUTHOR]

Building sustainable green cities for the future can be difficult or highly challenging as such cities need to reduce their environmental footprint through eco-friendly materials, resource and energy conservation, as well as renewable energy generation. A recent paper by the first author has proposed sustainable concrete with 80% ground granulated blast furnace slag (GGBFS) to build Masdar City in the UAE with a 153 kg/m³ carbon footprint. This paper proposes three new types of sustainable concretes in an attempt to further reduce the carbon footprint. In Type I, a total of 4 concrete mixes were made with a high volume GGBFS with 60, 70, 80, and 90% replacement of ordinary portland cement (OPC), 100% recycled water (RW), and 100% recycled aggregate (RA). The same replacement ratios were used in Type II but with only 100% RA. In Type III, a total of four concrete mixes made with a high volume fly ash (FA) cement with 40, 50, 60, and 70% replacement of OPC. The paper provides information on the mix design, full justification of CO2 footprint, and the cost for each concrete mix. The hardened and plastic properties and durability test parameters for each mix are presented. The results showed that the fly ash and slag significantly reduced the carbon footprint and meet the requirements of future sustainable cities. An economical mix with 90% GGBFS and 10% OPC was nominated for use in the future construction of sustainable cities with 125 kg/m³ emissions. [ABSTRACT FROM AUTHOR]

In this paper the authors present the possibility to utilize two waste materials to produce high performance concrete (HPC). To prepare the mixes, Recycled Concrete Aggregate (RCA) of 4-16 mm fraction and Class F fly ash (from coal burning power plant) were used. Concretes with RCA were mixed with 300 kg/m3 of different types of cements and Supplementary Cementing Materials (SCM). The concrete sample specimens were tested for mechanical properties and for some properties which are related to durability. After 28 days compressive strength values up to 59.5 MPa and after 90 days 71.8 MPa were achieved. Besides we obtained good values regarding those properties, which significantly influence the durability of reinforced concrete structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • CDW Recycling technique has great influence on the quality of aggregate. • Usage of RA has significant influence on the fresh properties of concrete. • Mechanical properties and durability of RA-concrete is comparable to conventional concrete. • Recycled concrete powder (RCP) has potential to be used as partial replacement of cement. • Usage of RA and RCP from CDW can be used to develop value-added construction materials. Utilization of recycled aggregate (RA) and recycled concrete powder (RCP) from the construction and demolition waste (CDW) has multiple advantages including; preservation of sources of natural aggregates, conserve acres of land currently being used as landfills and contribute towards sustainably built environment. Especially, partially replacing cement with RCP can contribute to decreasing the carbon footprint of construction industry. Globally, enormous efforts are being made to develop green binders by totally avoiding the usage of OPC in making cementitious materials such as alklai-activated binders (AAB), calcium sulfoaluminate cement and magnesium-based-cement. CDW is a promising material in synthesizing such kinds of cementitious materials including usage of RA. This comprehensive review presents the pros and cons of processing techniques of CDW for various usages in preparing concrete. An overview of factors influencing the properties of CDW-incorporated concrete has been presented in detail. The durability of concrete prepared with CDW products has been discussed. Treatment techniques of CDW to enhance the properties of CDW concrete are presented. Further, the potential of using RCP in developing green binders has been highlighted. Finally, based on the outcomes of the review, the potential of using CDW in future research has been comprehensively presented. The review demonstrates that there is a great potential for using CDW in the production of structural and non-structural concrete applications. Particularly, RCP can be beneficially used in developing value-added construction materials. [ABSTRACT FROM AUTHOR]

• Sodium silicate and silane modification has a positive effect on recycled aggregate. • SSRAC has better mechanical properties and durability but poorer permeability. • SSRAC has a narrower ITZ width and higher microhardness. • Fatigue damage to RAPC was retarded and reduced by composite modification. Recycled aggregates (RA) used to prepare pervious concrete solve the problems of poor water permeability and lack of stone in urban pavement and achieve green and sustainable development. However, application of the recycled aggregate is difficult due to its poor performance. Treatment of the RA with sodium silicate and composite silane improves the uniformity of recycled concrete aggregates (RCAs) and recycled brick aggregates (RBAs) and reduces their porosities and pore sizes, thus improving the performance of the recycled aggregates. By using modified RA to prepare pervious concrete, the interfacial transition zones (ITZs) between RBA or RCA and the cement matrix can be improved, the widths of internal cracks and pores can be reduced, and the mechanical properties, durabilities and fatigue properties of permeable concrete (PC) can be improved. Due to the irregular shapes and relatively different RA particles, the connectivity of pores inside the PC is reduced, thus reducing the permeability of the PC. The incorporation of 30 %−70 % RA may lead to decreases in PC permeability of approximately 10 %−25 %. On the other hand, modification with sodium silicate and silane does not enhance the permeability of the PC but closes the pores inside the RA, which has an adverse effect on the permeability of the PC. [ABSTRACT FROM AUTHOR]

Geopolymer binder and recycled aggregate are environment friendly products and is thus considered as part of sustainable development. This paper presents a study of the effect of recycled aggregate on strength and durability of fly ash based geopolymer concrete. Geopolymer concrete samples were prepared from high calcium fly ash, sodium silicate solution, sodium hydroxide solution, fine aggregate from river sand, and two types of coarse aggregate viz., recycled concrete aggregate and crushed limestone coarse aggregate. Test results indicated that recycled concrete aggregate can be used as a coarse aggregate in high calcium fly ash geopolymer concretes with the 7-day compressive strengths of 30.6–38.4 MPa which were slightly lower than those of high calcium fly ash geopolymer concretes containing crushed limestone. The use of high sodium hydroxide concentrations of 12 and 16 M resulted in better performances both in strength and durability than that of 8 M. [ABSTRACT FROM AUTHOR]