Accelerated carbonation technology for enhanced treatment of recycled concrete aggregates: A state-of-the-art review

A large amount of waste concrete generates an environmental problem due to demolition of old concrete structures. To solve this problem, it is necessary to collect recycled aggregate from waste concrete. The conventional recycling technique of recycled aggregate from waste concrete does not indicate a significant quality to be re-used for making a new concrete. We proposed new techniques to produce high grade recycled aggregate by heating-grinding (H-G) method and heating-grinding-acid (H-G-A) method. To ensure the quality of the concrete made from recycled coarse aggregate concrete, the non-destructive evaluation was conducted in this research. High grade recycled aggregate concrete were prepared in advanced using two methods mentioned earlier. Then, new concrete specimens were produced using those types of recycled aggregate concrete. After 28 days curing time, rebound hammer test and ultrasonic pulse velocity test were performed on recycled coarse aggregate concrete to examine the surface hardness and ultrasonic wave velocity of the concrete. Almost similar quality to natural coarse aggregate in terms of density, water absorption, sieve analysis achieved by both H-G recycled coarse aggregate and H-G-A recycled coarse aggregate. However, the surface hardness and ultrasonic wave velocity of H-G-A recycled coarse aggregate concrete is better than those of H-G recycled coarse aggregate concrete. That acid solvent enables to dismantle the cement paste from aggregate surface more effectively, so this types of recycled aggregate shows a better performance than the other one. Continued delamination reduces pores in the interfacial transition zone resulting better bonding mechanism between new cement paste and recycled aggregate surface.

Green recycled aggregate concrete (RAC) with high strength and low shrinkage is prepared based on recycled coarse aggregate produced by the particle-shaping and aggregate-strengthening method and green low-carbon new cement. This not only effectively alleviates the shortage of natural resources, but also improves the performance of recycled aggregate concrete, which is of great significance for multi-channel resource utilization of construction waste. In this study, three kinds of recycled coarse aggregates (RCA), including simple crushing recycled coarse aggregate (JD-RCA), one-time particle-shaping recycled coarse aggregate (KL-RCA) and two-time particle-shaping recycled coarse aggregate (EKL-RCA), were prepared from the preparation technology of recycled aggregate, and high belite sulphoaluminate cement with excellent performance was used. The effects of aggregate quality, aggregate replacement ratio, and cementitious material content on mechanical properties and shrinkage properties of green recycled aggregate concrete were studied in comparison with ordinary Portland cement-based recycled aggregate concrete. The testing results show that the particle-shaping method can effectively improve the aggregate quality. The compressive strength and dry shrinkage performance of recycled aggregate concrete made of particle-shaped aggregate are only a little different from those of natural aggregate concrete, and even the performance of recycled aggregate is better than that of natural aggregate concrete under the condition of a low replacement ratio of recycled aggregate. In addition, high belite sulphoaluminate cement-based recycled aggregate concrete (HBRAC) not only has early strength and rapid hardening, but also has excellent drying shrinkage resistance, and its shrinkage rate can be reduced to more than 75% compared with ordinary Portland cement-based recycled aggregate concrete (OPRAC).

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

Chloride transport and induced steel corrosion in recycled aggregate concrete: A review

Experimental studies on the structural reinforced-concrete shear wall members using recycled aggregate concrete (RAC) have been focusing on static loading conditions. The dynamic tests on the reinforced concrete members made of RAC are fairly few. Shaking table tests are necessary because it is difficult to predict the influence of variations in particular properties on the overall dynamic behaviour of the reinforced RAC shear walls made of various mixed materials. The aim of the research work presented in this paper was to investigate the dynamic behaviour of shear walls made of RAC, with different recycled aggregates and reinforcement arrangements, in comparison with shear walls made of natural aggregate concrete (NAC). Five low-rise shear walls were tested in this project: a shear wall made of NAC, a shear wall made of recycled coarse aggregate concrete, and three shear walls made of recycled coarse and recycled fine aggregate concrete with different reinforcement arrangements. Dynamic characteristics and responses of all specimens at different loading stages were determined experimentally, and a comparison of failure modes was presented. The earthquake response time-history analysis of each specimen was also conducted using the finite element software ABAQUS. The ABAQUS results showed good agreement with the test results. The comparison of results showed that, when the reinforcement arrangement was the same, the seismic performance of the shear wall made of recycled coarse and recycled fine aggregate concrete was weakened greatly compared with that of the shear wall made of NAC. The seismic performance of the shear wall made of recycled coarse aggregate concrete was similar to that of the shear wall made of NAC. The seismic resistance capacity of the shear wall made of RAC could be greatly improved by installing concealed bracings.

The surface zone of the recycled aggregate plays a significant role in the strength and durability of concrete. In this research, various concrete series incorporating natural coarse aggregate [NCA], untreated recycled coarse aggregate RCA(UN), mechanical scrubbing treated coarse aggregate RCA(MS), sulfuric acid treated coarse aggregate RCA(H2SO4) and hydrochloric acid treated aggregate RCA(HCl) were investigated. Manufactured sand was used as an alternative to natural river sand in five series of concrete with 100% replacement ratio. The mechanical properties: compressive, split tensile, and flexural strength, respectively, were determined at the age of 28 and 56 days. Durability properties: water absorption, drying, sulfuric acid, sodium sulphate and sorptivity test were determined at the age of 28, 56 and 90 days and the results were compared to reference concrete. According to the results, RCA(UN) was found to marginally decreased the concrete performance, and the above mentioned treated aggregate shows a significant improvement in overall performance compared to RCA(UN), especially RCA(MS), which enhances the concrete more significantly than other methods. Moreover, the scanning electron microscope results also emphasize the enhanced microstructure of treated recycled aggregate in concrete. The photographic view of the cross sections of the samples shows a superior interfacial transition zone in all kinds of treated aggregate concrete than in untreated recycled aggregate concrete.

Properties of recycled aggregate concrete prepared with scattering-filling coarse aggregate process

Creep model of concrete with recycled coarse and fine aggregates that accounts for creep development trend difference between recycled and natural aggregate concrete

11 - Carbon dioxide sequestration on recycled aggregates

Accelerated carbonation treatment of recycled concrete aggregates using flue gas: A comparative study towards performance improvement

The current state-of-the-art review indicates the need for future research to develop recycled concrete aggregate (RCA) properties like natural aggregate (NA) as specified by Indian or international codes. By improving the physical and mechanical properties of RCA, recycled aggregate concrete (RAC) may achieve more similar performance to natural aggregate concrete (NAC). RCA’s physical and mechanical properties are enhanced by mechanical treatments, chemical treatments, chemical-mechanical treatments, thermal treatments, and thermomechanical treatments. Additionally, RCA is coated with supplementary cementitious material (SCM) and nanomaterials to increase its properties. RCA can be thermally treated to improve its properties while lowering its energy consumption by adjusting the treatment duration. RCA properties are altered by mechanical treatment when charges and revolutions are changed. It is possible to determine the set of charges and drum revolutions that may produce the RCA with optimal physical and mechanical properties using decision-making statistical techniques. A specific weight can be given to each physical or mechanical property of a treated RCA when evaluating its performance. The same procedure can be used for chemical-mechanical and thermomechanical treatments. It is possible to manufacture industrial RAC from the RCA produced by this procedure. It may be anticipated that RAC composed of RCA with optimized physical and mechanical properties will be more similar to NAC in terms of its physical, mechanical, and durability properties. It is also possible to improve the material properties of the treated RCA by coating them with SCMs or nanomaterials even more. The effect of SCM, nanomaterial, and fiber on the physical, mechanical, and durability properties of RAC composed of treated RCA could be studied in the future.

Objective: The objective is to determine the effect of treated RCA on the mechanical strength of hardened concrete, and determine the influence of treated RCA on water transport within the matrix of hardened concrete. Aim: The study aims to use pozzolanic concentration of cement and RHA slurry to pretreat coarse RCA for full replacement of NCA for sustainable concrete production. Background: One of the common modes of disposal of construction waste is strained landfills. This study proposes a constructive way of recovering the coarse aggregates of recycled aggregates from laboratory concrete waste taken through a focused treatment process with pozzolan. The study aims to replace the proportions of the cement slurry to treat and replace with rice husk ash (RHA) for the modification of recycled concrete aggregate (RCA) and replace fully natural coarse aggregate (NCA) for sustainable concrete production. One of the main challenges of recycled concrete aggregate (RCA) is the fractured surface, which often results in reduced strength and loss of concrete durability. The strength of concrete with RCA is principally influenced by the fractured hardened paste attached to the surface, predominantly characterized by voids and gaps resulting from its production using a mechanical method. High water penetration within and around the aggregate matrix due to the presence of micro- and macro-cracks results in strength and durability deterioration of concrete. Methods: This study addresses these problems by specifying aggregate treatment with a pozzolanic slurry of cement and RHA. This was conducted in two (2) phases; first, to determine the optimum proportion of cement slurry concentration (0, 20, 40, 60, 80, and 100%), and second, to increase the silicate formation in cement slurry by substituting the proportions of cement with RHA (0, 5, 10, and 15%). The performance of concrete was evaluated by mechanical strength (compressive and split tensile strength) at 7, 28, and 56 days and water transport within the concrete (surface suction and submergence) at 28 and 56 days of curing age. Results: The use of cement slurry treatment at various concentrations generally increased compressive strength at 28 days compared to untreated RCA. The findings show that at a 20% concentration of cement slurry, the increase in compressive strength is 38.4%. Upon replacement of cement in treatment slurry of RCA with 5% RHA, the increase in compressive strength was 61%, while the split tensile strength increased by 10.2%. The amount of water absorbed was observed after 30 minutes of full submergence in water, indicating that samples with 20% cement concentration at 28 days resulted in the lowest water absorption of 2.01%. However, with the replacement of 5% RHA, the water absorption slightly increased to 2.3%, but still less than the requirement of 3.5%. The corresponding test results for water suction by capillarity, initial and secondary sorptivity coefficients (Si and Ss) were found to be 0.0330mm/√sec. (1.98mm/√hr.) and 7.95×10−4mm/√sec. (0.04mm/√hr.) respectively, all less than 6mm/√hr requirement. This improved performance was attributed to the increased strength and structure of the interfacial transition zone (ITZ) around the RCA. Conclusion: Based on the results of mechanical strength and water transport, characteristics of the new concrete were improved when coarse RCAs were pretreated with 20% pozzolanic concentration containing cement and RHA. The use of a pozzolanic treatment slurry containing 15% cement and 5% RHA to treat coarse RCA can produce concrete with characteristics similar to those of natural concrete aggregates. This study presents a methodological utilization and improvement of RCA wastes for field application.

Enhancement of recycled aggregates and concrete by combined treatment of spraying Ca2+ rich wastewater and flow-through carbonation

Durability properties evaluation of self-compacting concrete prepared with waste fine and coarse recycled concrete aggregates

The utilization of recycled aggregates can minimize environmental impact and slow the huge consumption of natural resources used for concrete applications. However, recycled aggregates are not suitable for use in the production of High Performance Concrete (HPC) due to their relatively high absorption capacity, unstable properties and recycled aggregates' weaker strength. Such inadequacies can be overcome through carefully examining the characteristics of recycled aggregates and then adopting proper mixture proportions. The mechanical properties of self compacting concrete (SCC) are well understood. Butthere are no scientific investigations available on the influence of a heat water treatment on the properties of SCC produced from recycle aggregate. To evaluated the influence on the mechanical properties five mixture were designed, SCC without recycled concrete aggregateand four ( SCC with 25% recycled concrete aggregate SCC with 50% recycled concrete aggregate,SCC with 75% recycled concrete aggregateand SCC with 100% recycled concrete aggregate) and exposed to heat of treatment water with different temperatures ( 40-100 )Cₒ. It has been found that there is possible to produce SCC with various percentage of recycled concrete by using a suitable dosage of SP which was a major component in producing good quality RCA( recycled concrete aggregate ). Also found an influence of the composition of the concrete, especially the quantity of recycle aggregate and heat of curing water on mechanical properties of concrete (compressive strength, splitting tensile strength and flexural strength).