Properties Of Recycled Coarse Aggregate Research Articles

Influence of manufactured sand, recycled aggregate, reinforcement ratio and wire mesh on the response of reinforced concrete slabs under impact loading

Targeting towards the sustainable goal, the emergence of manufacturing sand (M-sand) and recycled coarse aggregate (RCA) as an alternate for natural aggregates has unfolded new prospects for constructional practices in the world. Therefore, the investigation is focused to study the influence of RCA, M-Sand, Combination of RCA and M-sand, wire mesh and steel reinforcement under impact loading. The reinforced concrete slabs (1 layer @ 25 mm c/c) slabs [S1-S4, S9, S11, S13 and S15] was studied using M-sand (100 %) and recycled coarse aggregate (25 %) with a concrete compressive strength of 40–50 MPa. Also, the flexural reinforcement was varied as 0.23, 0.32 and 0.39 % of the cross-section area. The experimental results were presented in terms of failure pattern, impact force-reaction force, midpoint displacement and energy absorption capacity. It was observed that the spalling of concrete to the conventional slab (S1) whereas, the spalling of concrete as well as formation of radial cracks were observed on slab with RCA (S2). It was also observed that the severe spalling with formation of radial cracks in the slab with M-sand and RCA (S4), however the impactor did not perforate. The peak impact force on control slab, S1, S2, S3 and S4 was 145, 187, 122 and 167 kN, respectively. The significant increase in peak impact force in S2 is due to the use of micro silica fume treatment which enhanced the mechanical properties of RCA. The peak impact force in slab S3 by M-sand found reduced by 15 %, whereas the same was found increased by 15 % in case of slab S4 by RCA and M-sand, as compared to S1. The maximum crack width in slab S15 was limited to 1–2 mm whereas same was found to be 9–10 mm in case of slab S13. The use of wire mesh found to enhance the global bending deformations as well as crack width in the slab. It is concluded that the utilization of wire mesh along with steel reinforcement proves to be an effective method to diminish the permanent deformation. Further, finite element software ABAQUS was used to model the slab under impact loading and the results were compared with the experimental results. The predicted peak impact force of slab S1 was found to be good agreement with the experimental results. However, the predicted peak impact force on slab S2-S4 found to have maximum deviation 11 % as compared to experimental results.

Comparative Study of the Crushing Strengths of Recycled Coarse Aggregates Concretes and Natural Aggregates Concretes

Recycled Coarse Aggregate (RCA) is a recycled concrete material from construction sites, which is being reused for fresh concrete production. The use of this material reduces quarrying of Natural Coarse Aggregate (NCA). Properties of RCA are variable depending on the properties of parent concrete. In a fast-growing economy, the generation of construction waste has increased considerably, and social and environmental concerns on recycling the waste have accordingly increased. Construction Engineers have resorted to recycling these demolition wastes to maintain a friendly green environment. This study compared the crushing strengths of Recycled Coarse Aggregate concrete with Natural Aggregate concretes. The RCA was obtained from demolished drains and culverts while the Natural Coarse Granite Aggregate was from Akamkpa, Cross River State, Nigeria. Using RCA and NCA of maximum size 20mm, concrete cubes were prepared for compressive strength tests. Other properties of the aggregates were determined. Three mix proportions of 1:1½:3, 1:2:4 and 1:3:6 at water cement ratio of 0.6 were utilized and the specimens were tested at curing ages of 7, 14, 21 and 28 days. Results indicated that RCA produced concretes with strengths lower than those using NCA. RCA concretes also had slumps lower than those of NCA concretes.

Influence of the Original Concrete Strength and Initial Moisture Condition on the Properties Improvement of Recycled Coarse Aggregate via Accelerated Carbonation Reactions.

The physical and mechanical properties of recycled coarse aggregate (RCA) are worse than those of natural coarse aggregate (NCA), and the overall performance of recycled concrete prepared from RCA is worse than that of natural aggregate concrete. Treatment of RCA by CO2-accelerated carbonation effectively improves the macroscopic properties of RCA. The degree of influence of raw material factors, i.e., the original concrete strength (OCS) and initial moisture content (IMC) of RCA, on the carbonation of RCAs is very complex. Herein, an accelerated carbonation experiment for RCA with different material factors as variables was carried out to explore the influence of the abovementioned factors on the physical properties of carbonated recycled coarse aggregate (CRCA). By analyzing the microstructure of the RCA with the best modification effect before and after carbonation, the carbonation modification mechanism of the RCA was revealed. The physical performance indexes, including the apparent density, water absorption and carbonation rate, of the dried RCA with an OCS of C40 and C50 were significantly improved. The research results can provide basic data and theoretical support for promoting the popularization and application of RCA and recycled concrete in practical engineering.

Efficiency and Mechanism of Surface Reinforcement for Recycled Coarse Aggregates via Magnesium Phosphate Cement.

Recycled aggregate concrete (RAC) exhibits inferior mechanical and durability properties owing to the deterioration of the recycled coarse aggregate (RCA) surface quality. To improve the surface properties of RCA, the reinforcement efficiency of RAC, and the maneuverability of the surface treatment method, this study used magnesium phosphate cement (MPC), a clinker-free low-carbon cement with excellent bonding properties, to precoat RCA under three-day pre-conditioning. Moreover, variable amounts of fly ash (FA) or granulated blast furnace slag (GBFS) were utilized to partly substitute MPC to enhance the compressive strength and chloride ion penetration resistance. Subsequently, FA-MPC and GBFS-MPC hybrid slurries with the best comprehensive performance were selected to coat the RCA for optimal reinforcement. The crushing value and water absorption of RCA, as well as the mechanical strengths and durability of RAC, were investigated, and microstructures around interfaces were studied via BSE-EDS and microhardness analysis to reveal the strengthening mechanism. The results indicated that the comprehensive property of strengthening paste was enhanced significantly through substituting MPC with 10% FA or GBFS. Surface coating resulted in a maximum reduction of 8.15% in the crushing value, while the water absorption barely changed. In addition, modified RAC outperformed untreated RAC regarding compressive strength, splitting tensile strength, and chloride ion penetration resistance with maximum optimization efficiencies of 31.58%, 49.75%, and 43.11%, respectively. It was also evidenced that the improved MPC paste properties enhanced the performance of modified RAC. Microanalysis revealed that MPC pastes exhibited an excellent bond with RCA or new mortar, and the newly formed interfacial transition zone between MPC and the fresh mortar exhibited a dense microstructure and outstanding micro-mechanical properties supported with an increase in the average microhardness value of 30.2-33.4%. Therefore, MPC pastes incorporating an appropriate mineral admixture have enormous potential to be utilized as effective RCA surface treatment materials and improve the operability of RCA application in practice.

Effect of carbonation duration on properties of recycled aggregate concrete

The use of recycled coarse aggregate (RCA) produced from waste concrete in new concrete is an effective way to realize the recycling of construction and demolition waste. The utilization of accelerated carbonation to enhance RCA has attracted a lot attention because it can enhance performance of recycled aggregate concrete (RAC) and has potential for CO2 sequestration. This study systematically investigated the influences of the duration of pressurized carbonation on the properties of RCA, RCA-new mortar interface, and RAC. The results showed that water absorption of carbonated RCA (CRCA) decreased with the increase of carbonation duration. But the beneficial effect of carbonation was less obvious after 1-day carbonation because most of calcium hydroxide and Ca-rich calcium silicate hydrates in RCA had reacted with CO2 within 1 day. After using CRCA, the improvement in different performance indicators of RAC was dependent on different factors. The enhancement in compressive strength and chloride penetration resistance of RAC prepared with CRCA were dependent on the reduced porosity of CRCA. That was why they correlated with the water absorption of CRCA as carbonation duration increased. However, the decrease in initial absorption of water of RAC was mainly dependent on the denser surface layer of CRCA, rather than the reduced porosity of CRCA. This is because the denser surface layer can change water path from “penetrating through RCA” to “passing around RCA”. It is recommended to use 1-day carbonation to enhance RCA, which might have higher cost-effectiveness.

Effects of surface modified recycled coarse aggregates on concrete’s mechanical characteristics

Sustainable concrete using recycled coarse aggregates from construction and demolition waste is gaining popularity in the construction industry, but has poor mechanical characteristics due to old cement mortar adhering to aggregate surfaces. This study uses two processes (abrasion treatment and cement slurry treatment) to modify the surface of recycled coarse aggregates (RCA) to minimize the strength loss of RCA and enhance the bonding properties of the concrete matrix and RCA. Surface-modified RCA replaced coarse aggregates in varying percentages, ranging from 0 to 100% in 25% increments. To comprehend the effects of surface-modified RCA, the workability, compressive strength, flexural strength, split tensile strength, microstructural characteristics (XRD, SEM, and EDAX), and modulus of elasticity of concrete are evaluated. Surface-modified RCA improves concrete’s mechanical characteristics, but abrasion-treated RCA has significantly greater strength than reference concrete up to 50% replacement level, while cement slurry treatment has slightly lower strength. Test findings reveal that among all the two processes of surface modifications of RCA, abrasion treatment is more effective and efficient. At 100% replacement level, surface-modified RCA by abrasion treatment reduces compressive, flexural, and split tensile strength by 10.89%, 10.42%, and 09.92% compared to reference concrete, while surface-modified RCA by cement slurry treatment reduces these values by 14.80%, 13.27%, and 12.76%. Surface modifications improve bonding properties of RCA and cement matrix, reducing porosity and resulting in dense and strong ITZs compared to unmodified RCA.

Property Improvement of Recycled Coarse Aggregate by Accelerated Carbonation Treatment under Different Curing Conditions

Recycled aggregate (RA) made from waste concrete has inferior fundamental properties, i.e., apparent density, water absorption, mass variation, carbonation ratio, etc., compared to those of natural aggregate (NA), severely restricting its application in practical projects. However, using CO2 to accelerate RA carbonation can effectively improve these properties, and this treatment approach can promote energy savings and sustainable development. The accelerated carbonation curing conditions for RA can significantly impact the modification effect of RA. For this purpose, this paper used recycled coarse aggregate (RCA) as a case study. An accelerated carbonation modification treatment experiment for RCA under different accelerated carbonation curing conditions was carried out, and the effects of relative humidity and CO2 concentration on the apparent density, water absorption, moisture content, mass variation and carbonation ratio of RCA under a constant ambient temperature were explored and quantified. The results indicated that the best-accelerated carbonation curing conditions applicable to this paper’s RCA were confirmed as being an environmental temperature of 20 °C and a relative humidity of 70%, as well as a CO2 concentration of 20%. Under these conditions, the apparent density and water absorption of CRCA are approximately 1.04 times and 75.30% higher than those of RCA, and, in addition, the carbonation ratio for RCA under the optimal accelerated carbonation curing conditions is all higher than others, thus improving the properties of RCA to a certain degree. Finally, in this paper, the variation trends of the RCA property indexes in terms of carbonation time treated by the best accelerated carbonation curing conditions are examined, and the time-varying models for the RCA property indexes during the accelerated carbonation are established.

Comprehensive Evaluation of the Sustainability of Waste Concrete towards Structural Concrete Application in Freeze-Thaw Environment

To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) was produced by recycled coarse aggregate (RCA), which was obtained from the crushing of natural aggregate concrete (NAC) after every F-T 150 cycles until F-T failure. The effects of F-T damage of parent concrete on the physical properties of RCA and mechanical and frost resistance of RAC under 35% flexural stress were studied. Besides, the sustainability of NAC and RAC was compared and analyzed by emergy theory. The results suggested that the physical properties of RCA deteriorated gradually with the accumulation of F-T damage to parent concrete. The RCA obtained from parent concrete that suffered F-T damage could be used as coarse aggregate for structural concrete when F-T damage is smaller than 0.367. The F-T damage of parent concrete had an adverse effect on the mechanical properties and frost resistance of RAC. The frost resistance of RAC obtained from parent concrete with larger F-T damage was worse. The RAC prepared from parent concrete without F-T failure can serve 50 years in cold regions, while that with F-T failure can only serve 30 years. The F-T damage microelements were dispersed in the adhesive mortar of RCA and transferred to RAC, resulting in the reduction of the mechanical properties and frost resistance of RAC. Emergy analysis showed that the reuse of waste concrete after F-T failure required higher economic input, higher environment load, lower output efficiency, and sustainability. The performance, environmental load and economic benefit of RAC prepared by using waste concrete after F-T failure were inferior to that of waste concrete without F-T failure. Waste concrete after F-T failure is not recommended to be used as coarse aggregate for structural concrete.

Effect of Recycled Aggregate Modification on the Properties of Permeable Asphalt Concrete

This study aims to evaluate the pavement performance of permeable asphalt concrete (PAC) produced with modified recycled coarse aggregate (RCA) based on six types of single modification methods and three types of double modification methods. Firstly, the water absorption, apparent density, and crushing value of the RCA before and after modification were tested. Subsequently, the performance of PAC with these types of modified RCA was investigated, including the optimum asphalt-aggregate ratio, water stability, high-temperature performance, and low-temperature crack. The test results show that the physical properties of RCA were improved to some extent owing to the modification methods adopted, except that the water absorption of RCA-C and RCA-PC increased by 33.5% and 32.6%, respectively, compared with that of RCA. This increase in the water absorption was attributed to the high water absorption of the cement mortar. As a whole, various modification methods have different effects on the road performance of asphalt mixtures, and soaking RCA with slag powder and silane coupling agent was prominent among them. Compared with the PAC with RCA, the Marshall stability, Marshall stability of immersion, residual stability, TSR, dynamic stability and low-temperature tensile strength of PAC with RCA-SLSC were increased by 31.8%, 41.0%, 7.0%, 5.8%, 280.7% and 17.2%, respectively.

“Experimental Studied of Density and Water absorption of Recycled Coarse Aggregate Concrete Incorporating GGBFS and FA”

This investigates work the density and water absorption of concrete specimens cured at the age of 28 days. Natural coarse aggregate (NCA) has been replace with 60 percent, and 100 percent by RCA of construction & destruction (C&D) waste of 30-year-old building and Ordinary Portland cement (OPC) has been replaced with 10 GGBFS and FA. To understand the physical properties of concrete of normal weight test was perform and to find suitable results. To examine the water absorption properties of GGBFS and FA with recycled coarse aggregate (RCA) stand mix concrete at the age of 28 days. Based on the experiment’s study, it can be brief that the 40 percent replacement of NCA with RCA carried excellent results with 20 percent GGBFS. This research presents the outcome of GGBFS and FA as a cement replacement on the physical properties of RCA.

Mechanical properties, drying shrinkage, and nano-scale characteristics of concrete prepared with zeolite powder pre-coated recycled aggregate

The utilization of recycled coarse aggregates (RCAs) obtained from construction & demolition wastes in concrete material has been a feasible sustainable development strategy. However, the poor properties of RCAs have some adverse effects on the performance of concrete. In this study, the properties of RCAs are enhanced by zeolite powder-cement (ZP-C) slurry pre-coating, and the compressive strength, dry shrinkage, microstructures and nano-mechanical properties of concrete containing natural coarse aggregates (NCAs), RCAs and the enhanced RCAs (ERCAs) are investigated. The results show that the incorporation of RCAs or ERCAs is detrimental to the development of concrete properties, compared with the NCAs. The compressive strengths of the concrete containing ERCAs are higher than that of the concrete containing RCAs, and the dry shrinkage strain of the former is lower than that of later, under the same conditions. Meanwhile, the width of enhanced interfacial transition zone (EITZ) between ZP slurry layer and new cement matrix (CM) decreases by 46.9%, compared with old ITZ (OITZ) between old CM and new CM. In the nanoindentation test, the elastic modulus of EITZ is higher than that of OITZ. The outcome of this study exploits the synergy between natural ZP and RCA to effectively solve the problem of poor effect of conventional strengthening methods on old demolition concrete wastes to improve the mechanical and drying shrinkage properties of recycled aggregate concrete while promoting resource conservation and recycling.

Flow Characteristics of Recycled Coarse Aggregates (RCA) based Self-Compacted Concrete (SCC)

The desire of humans increasing day by day to build new and high quality structures and to demolish the old structures. The demolished concrete is supplies to direct land fills and provides serious risk to the environment. In recent years, using recycled aggregates (RCA) as a substitute for natural aggregates in concrete has become of great interest to researchers. In meantime the use of RCA becomes sustainable and environmental friendly. The application of concrete in slabs, beams, columns specially areas of congested reinforcement requires high degree of compaction that is impossible to achieve at the site. For this purpose the self-compacted concrete (SCC) is the better solution. SCC is one that can flow under its own weight and fill the formwork completely without any need of compaction or vibration efforts. In this regards this experimental study has undertaken to investigate the flow behaviour of RCA based SCC. The natural crushed coarse aggregates were replaced by RCA at 0%, 20%, 40%, 60%, 80% and 100%. The fresh properties were evaluated through filling ability, passing ability and segregation resistance tests. The results revealed that all the fresh properties of RCA based SCC is depends on the percentage of RCA. As percentage of RCA increases the workability of concrete decreases. The workability is adjusted by increasing the suitable dosage of SP. Furthermore, it is also noted that all the values of freshproperties lie within the required limits of EFNARC.

Properties enhancement of recycled coarse aggregates by pre-coating/pre-soaking with zeolite powder/calcium hydroxide

The reuse of construction and demolition waste by recycling as aggregates can not only protect the environment, but also alleviate the shortage of natural resources. However, the application of recycled aggregates in practical engineering is limited due to their shortcomings, such as the higher crush value and water absorption, and the lower apparent density. In this study, four different treatments were designed to modify recycled coarse aggregates (RCAs) based on zeolite powder (ZP) and calcium hydroxide (CH), which were CH slurry pre-coating, CH solution pre-soaking, zeolite powder-cement (ZP-C) slurry pre-coating and ZP-C solution pre-soaking, respectively. Moreover, the macro-properties, micro-properties and nanomechanical properties of untreated and treated RCAs have been investigated, respectively. The results show that four treatments improve the properties of RCAs to some extent. Meanwhile, the width of cracks (Wc) of interfacial transition zone and cement matrix of treated RCAs also decreases according to the scanning electron microscope observation. Among the four treatments, the properties of RCAs pre-coated by ZP-C slurry present the most significant improvement, and the crush value and water absorption decrease by 30.4% and 19.8%, respectively, and the apparent density increases by 1.5%. In addition, there is the linear relationships between Wc and the crush value or the water absorption of RCAs. Furthermore, from the perspective of nanomechanical properties, the elastic modulus of cement matrix is the main factor affecting the marco-properties of RCAs.

Stress–strain relationship analysis of recycled aggregate concrete based on orthogonal analysis

The use of recycled coarse aggregate (RCA) in natural aggregate concrete is a sustainable solution to the problem of solid waste worldwide. The effects of RCA gradation, RCA content, fly ash content and water–cement ratio (w/c) on mechanical properties of RCA are studied in this paper. The stress–strain curves of each specimen under 28 days axial loads were obtained by experiments. Through the stress–strain curves of each specimen, the effects of the above four factors on the maximum strain, ultimate strain, elastic modulus and toughness index of RAC were analyzed, and the optimal selection of the four factors were determined. Mathematical models of strength and four factors were established by fitting the experimental data. Finally, the RAC’s hydration failure mechanism with different RCA contents was studied by scanning electron microscopy. The test results show that: influence degree of the four factors on the compressive strength of RAC is: w/c > RCA content > RCA gradation > fly ash content. Based on a comprehensive analysis of compressive strength, peak strain, ultimate strain, elastic modulus and toughness index, it is recommended that RCA gradation is 5–20 and 5.0–31.5, RCA content is 50–70% and fly ash content is 20%.

Study on aggregate interlock behavior of pre-cracked recycled aggregate concrete without stirrups

In this study, experiments on pre-cracked push-off specimens without stirrups were conducted to analyze the aggregate interlock behavior of recycled aggregate concrete (RAC). The major variables considered in this study were the surface roughness, recycled coarse aggregate (RCA) replacement ratio, concrete strength, aggregate particle size and loading rate. Experimental results indicate that the roughness of the fracture surface relating to the ratio of aggregate fracture significantly affects the shear stress of pre-cracked push-off specimens. The findings reveal that the RCA replacement ratio has adverse effects on the macro-roughness and the aggregate interlock behavior of RAC. The increasing concrete strength leads to a decrease in the surface roughness and the aggregate interlock capacity of RAC. The inferior properties of RCA contribute to decreasing the aggregate interlock behavior of RAC specimens with larger RCA particles. The influence of the loading rate on the aggregate interlock behavior of RAC is insignificant with the increase from 0.06 mm/min to 0.6 mm/min.

Property enhancement of recycled coarse aggregate using bio-treatment approach

As the demand for concrete increases in the construction industry, it puts stress on nature due to the extraction of resources. The coarse aggregate is the component, which occupies around ¾th volume in concrete. The use of recycled coarse aggregates (RCA) is not very common due to the presence of porous old mortar attached around the surface of the aggregate. This makes the aggregates highly water absorbent in nature and also weakens the interfacial transition zone (ITZ). In this study, an attempt has been made to improve the properties of RCA through CaCO3 precipitation using Bacillus megaterium. The bio-deposition treatment yielded satisfactory improvement in the properties of RCA by filling of surface pores through precipitation. Reduction in water absorption and improvement in mechanical properties are derived. Microstructure studies also confirm the presence of CaCO3 through precipitation.

Effect of recycled coarse aggregate on physical and mechanical properties of concrete

Recycling of building waste has become essential process in the construction industry due to the sustainability and economic benefits such as decreasing the waste to landfill, conserving natural resources, and reducing pollution. Large amount of building waste is produced from the construction and demolition process of reinforced concrete (RC) structures. In this paper, the effect of using recycled coarse aggregate (RCA) on the behavior of concrete is experimentally studied. The RCA is prepared by crushing and sieving of waste of standard compression test cubes having a compressive strength ranging between 25 MPa and 30 MPa. The physical and mechanical properties of RCA are experimentally estimated and compared to those of natural coarse aggregate (NCA). A set of 72 standard concrete cubes, cylinders, and beams specimens are made using coarse aggregate replacement ratios (CARR) of 0%, 30%, 50%, and 100%. The specimens are tested to estimate the compressive, splitting, and flexure strengthens at the ages of 7 and 28 days. The study is extended by using the RCA in casting 12 RC columns with CARR similar to those of specimens. The columns are tested in an axial compression test protocol till failure. Crack patterns, failure loads, strains, displacements, and toughness of the tested columns are compared. It is concluded that using a CARR of 30% and 50% and a specific water cement ratio provides better mechanical behavior than that of NCA while the CARR of 100% yields worst mechanical behavior compared to that of NCA.

Improving the properties of recycled aggregate pervious pavement blocks through bio-mineralization

Pervious concrete (PC) comprised of cement, water, coarse aggregates are widely used nowadays for sustainable and low impact pavement. The primary purpose of this study is to investigate the performance enhancement of pervious concrete blocks (PCB) containing recycled coarse aggregates (RCA) through microbially induced calcium carbonate precipitation (MICP). Two types of bacterial enhancement methods were adopted, which are PCB with pre-soaked RCA using bacteria solution and PCB with bacteria added mixing water. The properties of RCA, cement paste, and PCB were measured. The water absorption of RCA soaked in the bacteria and culture medium for 21 days was reduced by 10.41%. Meanwhile, the porosity of PCB decreased by 15.70%, and compressive strength increased up to 28.48% when incorporating pre-soaked RCA. There was an increase of 57.23% in compressive strength for hardened cement paste when bacteria were added in the mixing water. The compressive strength of PCB increased by 35.48% when compared with PCB with normal mixing water. Both enhancement methods show promising results and realize the purpose of enhancing the properties of PCB containing RCA.

Development of a unified model to predict the axial stress–strain behavior of recycled aggregate concrete confined through spiral reinforcement

Utilizing the confinement from transverse reinforcement of compression members to offset the inferior recycled aggregate concrete (RAC) performance is considered a sustainable and adaptable way to solve the problems related to the application of recycled coarse aggregates (RCA). Prediction of the axial stress–strain behavior of RAC is a challenging task due to variation in the physical properties of RCA from different sources. Currently, limited work is available in the literature to predict the axial stress–strain behavior of steel spiral confined RAC applicable to RCA from different sources. In this study, a general axial stress–strain model of steel spiral confined normal aggregate concrete (NAC), RAC and treated recycled aggregate concrete (TRAC) is developed considering the material characteristics of RCA. For this purpose, the axial stress–strain behavior of steel spiral confined NAC, RAC, and TRAC having different target strengths and confinement levels is studied. The results of this study show that confinement has a more prominent effect on peak and ultimate strains of RAC and TRAC than NAC. The axial stress–strain model developed in this study, considering a large test database, can be used to predict the performance of steel spiral confined NAC, RAC, and TRAC for any source/type of RCA leading towards the development of design guidelines for sustainable RAC members. Moreover, a relationship is also provided to calculate the permissible content of RCA having any type/source to achieve the compressive strength of steel spiral confined RAC or TRAC similar to NAC for any confinement pressure and concrete strength.

Mixture Proportion Design Method of Steel Fiber Reinforced Recycled Coarse Aggregate Concrete.

Steel fiber reinforced recycled coarse aggregate concrete (SFRCAC) is an impact minimisation building material. Mixture proportion design method of SFRCAC is developed in this paper to obtain concrete with target strength and workability, which can be used in structural members. Four key parameters of mixture proportioning, steel fiber content, water-cement ratio, water content and sand ratio are discussed through the mixture design tests. The formula for calculating the four key parameters of mixture proportions for SFRCAC are established through the statistical analysis of test results, which mainly consider the influences of recycled coarse aggregate (RCA) replacement ratio and steel fiber characteristic coefficient. The detailed procedure by using the new mixture proportion design method is illustrated with examples. The formulas established have the simple form, reflect the properties of RCA and steel fibers, enhance the mixture proportion design accuracy, and provide the reference for the mix proportion design of SFRCAC.