Use Of Recycled Aggregates Research Articles

Producing Sustainable Roller Compacted Concrete by Using Fine Recycled Concrete Aggregate

One-third of the total waste generated in the world is construction and demolition waste. Reducing the life cycle of building materials includes increasing their recycling and reuse by using recycled aggregates. By preventing, the need to open new aggregate quarries and reducing the amount of construction waste dumped into landfills, the use of recycled concrete aggregate in drum compacted concrete protects the environment. Four samples of PRCC were prepared for testing (compressive strength, tensile strength, flexural strength, density, water absorption, porosity) as the reference mix and (10, 15, and 20%) of fine recycled concrete aggregate as a partial replacement for fine natural aggregate by volume. The mix is designed according to (ACI 327-15) with the specified cylinder compressive strength (28 MPa). The results showed a decrease in mechanical properties with an increase in partial replacement compared to the reference mixture and an increase in water absorption and porosity at 28 days. This is because old cement mortar on the surfaces of fine recycled concrete aggregates leads to higher porosity and water absorption than fine natural aggregates. At 90 days, results improved slightly. This is due to the non-aqueous cement in the recycled fine concrete aggregate.

The effect of RCA pavements on the liquefaction-induced settlement

The use of recycled concrete aggregates (RCA) not only reduces the demand for natural aggregates (NA) but also might improve the behavior of soil under earthquake loading. In this study, the behavior of the pavement constructed using 100% RCA and NA on a sandy soil layer with high liquefaction potential under dynamic loads was investigated by numerical analysis and compared with free field conditions. For this purpose, first, the classical geotechnical properties of 100% RCA and NA materials were obtained, and then the stiffness properties were determined by resilient modulus and permanent deformation tests. In the second stage, three different models were created with pavement with NA and RCA and without pavement on high liquefaction potential sand, and dynamic analyses were carried out by PM4Sand. Numerical analyses show that constructing a subbase and base layers significantly reduces liquefaction-induced settlement on the surface of flexible pavements built on liquefied soils. Moreover, when the case of using RCA instead of NA in the subbase and base layers built on the liquefied soil is examined, the liquefaction-induced settlement values on the surface are obtained either lower or very close. Consequently, this study proposes a new alternative to the use of RCA waste materials instead of NA. It is expected the use of these waste materials will reduce the need for storage space and also reduce the negative environmental effects associated with storage.

Recirculating Water through Concrete Aggregates Rapidly Produced Ecologically Hazardous Water Quality

The use of recycled concrete aggregates as a construction material is growing and this study was conducted to investigate the potential water quality issues that arise when concrete aggregates are exposed to water. The water used in the study was from a high-conservation-value wetland. It was dilute (17.8 µS cm−1), acidic (pH 5.97) and poorly buffered. The ionic composition comprised sodium, bicarbonate and chloride ions. Water was recirculated for 60 min through a control treatment and three treatments containing recycled concrete aggregates (RCAs) of different fragment sizes (10 mm, 20 mm and 60 mm). The fragment size influenced the final water quality, but the response patterns varied between the attributes tested. Post-recirculation, the RCA treatments increased the electrical conductivity by 6 to 12 times; pH by 2.3 to 3.8 pH units; and concentrations of calcium, potassium, bicarbonate and sulphate. The water exposed to RCA materials also increased the concentrations of several metals (aluminium, arsenic, copper, lead and zinc), resulting in hazardous concentrations for aquatic species according to ecological water quality guidelines. Strontium concentrations in water exposed to RCAs increased by 30 to 120 times background levels. The results from this study added further support to a growing body of evidence that the exposure of concrete materials to water can produce environmentally hazardous water quality.

Accelerated Carbonation of Vibro-Compacted Porous Concrete for Eco-Friendly Precast Elements.

This research studied the effect of accelerated carbonation in the physical, mechanical and chemical properties of a non-structural vibro-compacted porous concrete made with natural aggregates and two types of recycled aggregates from construction and demolition waste (CDW). Natural aggregates were replaced by recycled aggregates using a volumetric substitution method and the CO2 capture capacity was also calculated. Two hardening environments were used: a carbonation chamber with 5% CO2 and a normal climatic chamber with atmospheric CO2 concentration. The effect of curing times of 1, 3, 7, 14 and 28 days on concrete properties was also analysed. The accelerated carbonation increased the dry bulk density, decreased the accessible porosity water, improved the compressive strength and decreased the setting time to reach a higher mechanical strength. The maximum CO2 capture ratio was achieved with the use of recycled concrete aggregate (52.52 kg/t). Accelerate carbonation conditions led to an increase in carbon capture of 525% compared to curing under atmospheric conditions. Accelerated carbonation of cement-based products containing recycled aggregates from construction and demolition waste is a promising technology for CO2 capture and utilisation and a way to mitigate the effects of climate change, as well as promote the new circular economy paradigm.

Recycled concrete aggregate properties improvement

In recent years, there has been increasing interest in the use of recycled concrete aggregate (RCA) as a sustainable alternative to natural aggregates in construction. RCA is obtained by crushing and reusing old concrete, which contains both the original aggregate and a cement mortar layer. However, the quality of RCA can vary depending on the characteristics and quantity of the leftover mortar. In this study, we aim to investigate different methods for improving the chemical, physical, and mechanical features of RCA, with a focus on untreated RCA, RCA exposed to a pre-soaking treatment in HCl, and RCA exposed to rapid carbonation. The overall results show that if RCA is obtained by crushing compact, high-quality concrete, the procedures for improving aggregate quality are not necessary.

Investigating the Use of Recycled Concrete as Aggregates in the Construction of Structural Beams

The World Bank in a decade ago reported a global collective of 1.3 billion tons of solid waste every year with building material accounting for half of this volume annually worldwide. Recycled materials from demolition sites have increased over the years to curtail the demand for natural aggregates (NA). This study investigates the use of recycled concrete aggregates (RCA) produced from high strength concrete and its effects on the mechanical properties of concrete and structural members. Further comparison was made to concrete with steel fibers. The results showed that the compressive strength of RCA concrete was 5% greater than NA concrete. The influence of the properties of durability and crushing resistance of the RCA, which exceeded that of NA, contributed to the higher concrete strengths when compared to NA concrete. Additionally, concrete with RCA and steel fibers had an increase of compressive strength by 16% to concrete without steel fibers. However, no significant increase in the deflection and strain of the beams under third point loading suggest that given the right conditions RCA can be used in place of NA Keywords: Construction waste; engineering sustainability; recycled concrete aggregate; structural members; steel fiber; waste management.

Structural performance of hybrid fibres incorporated Re-Cycled aggregate RC slab

Concrete is a material that mainly consists of coarse aggregate and mortar. The forming of cracks is an existing problem in Reinforced Concrete (RC) slab. In this research, hybrid fibres namely steel and polypropylene fibres in suitable combinations are identified and incorporated to concrete to regulate the formation and development of cracks in RC slabs. In Hybrid Fibre Reinforced Concrete (HFRC), 1 per cent of steel fibre and 0.30 per cent of polypropylene fibre is added, which is the effective amount of reinforced concrete added based on information obtained from the various research studies. In addition, now-a-day use of re-Cycled Aggregate (RCA) is strongly recommended to address the lack of traditional coarse aggregate. By using RCA as a partial substitution of coarse aggregate with an inclusion of 1 % of steel fibre and 0.30 % of polypropylene fibre to the concrete volume in the study, a typical approach is recommended. One-way type of RC slab, 1350 mm × 500 mm × 100 mm in dimension, is cast and tested in the laboratory in compliance with the Indian standard code IS 456: 2000 [1] . The compressive strength of concrete, load carrying capacity, load versus deformation characteristics, stiffness and ductility relationship properties of the RC slabs was compared and discussed between control specimens and 0 to 50 percent of partially substituted RCA specimens.

The Effect of Cementitious Materials on the Engineering Properties and Pore Structure of Concrete with Recycled Fine Aggregate.

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores.

Study on the effect of reinforced recycled aggregates on the performance of recycled concrete--synergistic effect of cement slurry-carbonation

The use of recycled concrete aggregates (RCAs) in concrete is crucial for alleviating the imbalance between sand and gravel, both of which are non-renewable resources. To improve the reinforcement effect and reduce the technological resource cost, a cement slurry with a large water-cement ratio (W/C = 1.0) was used to impregnate the RCA. The cement slurry-carbonation synergistic effect was then used to reinforce the RCA. This effect was investigated and the effect of the reinforcement mechanism of RCA strengthening on recycled aggregate concrete (RAC) was analyzed. The results demonstrate that the synergistic effect of cement slurry carbonation on the enhancement of RCA is significantly stronger than that of slurry wrapping treatment only. Furthermore, this effect plays a more significant role in reinforcing RCA under water-cement ratios exceeding 0.5. The microscopic test results indicate an improvement in RCA morphology, as pore size distribution was refined and internal weak areas were repaired after the modification treatment. The cement paste was encapsulated within the aggregate surface, which promoted bonding between the RCA and fresh mortar. The volumes corresponding to three interfacial transition zones (ITZs) of limestone-old mortar, limestone-fresh mortar, and old mortar-fresh mortar within the concrete were reduced, and the micromechanical properties improved substantially.

Effect of recycled concrete aggregate with different degrees of initial alkali–aggregate reaction damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete

The use of recycled concrete aggregate (RCA) is an effective approach to achieve environmental sustainability. However, the presence of defects due to previous alkali–aggregate reactions (AARs) has caused reluctance toward its use in constructions. This study investigated the application and influence of RCAs with different degrees of initial AAR damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete (SCRAC). Concrete cubic specimens with different degrees of AAR were produced by soaking the raw materials in a high-alkaline solution. In order to obtain RCAs with different initial AAR durations of 7, 28, 60, and 210 days. The specimens were then crushed using a jaw crusher. The residual reactivity of the RCA produced from concrete affected by the AAR was detected using the accelerated mortar bar test. The rheological properties of the SCRAC with different RCAs were tested. Compressive strength, flexural strength, mercury intrusion porosimetry, and scanning electron microscopy tests were conducted to analyze the effects of RCAs with different degrees of initial AAR damage on the mechanical properties and porosity of the SCRAC. The results show that the RCA can maximally strengthen the compressive strength of the SCRAC after 60 days of alkali immersion at a replacement rate of 30 %. Furthermore, a prediction model considering the filling effect for calculating the influence of RCAs with initial AAR damage on the compressive strength of the SCRAC was proposed. For practical engineering applications, the AAR can strengthen RCAs and improve the utilization rate of RCA, which is beneficial for the sustainable development of the environment.

An Experimental Study of Granular Material Using Recycled Concrete Waste for Pavement Roadbed Construction

Rapid worldwide urbanization and drastic population growth have increased the demand for new road construction, which will cause a substantial amount of natural resources such as aggregates to be consumed. The use of recycled concrete aggregate could be one of the possible ways to offset the aggregate shortage problem and reduce environmental pollution. This paper reports an experimental study of unbound granular material using recycled concrete aggregate for pavement subbase construction. Five percentages of recycled concrete aggregate obtained from two different sources with an originally designed compressive strength of 20–30 MPa as well as 31–40 MPa at three particle size levels, i.e., coarse, fine, and extra fine, were tested for their properties, i.e., the optimum moisture content density, Californian bearing ratio, and resilient modulus. A characterization of the resilient modulus of the mixes under complex stress conditions was performed. The characterized modulus model was used in the nonlinear analysis of the pavement structure under traffic loading using KENALYER software. Consequently, the two critical responses, i.e., the tensile strain at the bottom of the asphalt layer and the vertical compressive strain at the top of the subgrade, were computed and compared for the pavement structures with varying types and percentages of recycled concrete aggregate used in the subbase layer.

Study on Coarse Recycled Concrete Aggregate

The use of recycled concrete aggregate (RCA) is one of the best solutions to mitigate the problem of ecological instability created by concrete waste. RCA has less crushing strength, impact resistance, specific gravity, and more water absorption capacity than the natural aggregate (NA). To overcome the compromised properties of RCA, a comprehensive study supported by the experimental investigation is required. This paper prescribes a methodology based on experimental investigation for the use of coarse-RCA (C-RCA) of size (4.75-20mm) as 100% replacement of coarse-NA in fresh concrete. A

Performance of fly ash-blended Portland cement concrete developed by using fine or coarse recycled concrete aggregate

The recycling of concrete and industrial wastes in the production of new concrete structures has increased its share due to the growing environmental concerns of the world. In this study, the use of recycled concrete aggregate at various replacement amounts (0–100 %) was investigated to be fine or coarse aggregate sources instead of crushed natural aggregate to understand better its effects on the dimensional stability and durability aspects of fly ash-blended Portland cement concrete. In the presence of recycled concrete aggregate, fly ash was very important for eliminating possible mechanical losses of concrete at 90 days. The use of coarse recycled concrete aggregate resulted in better compressive strength values of concrete exposed to with and without wetting–drying and freezing-thawing cycles when compared to fine ones. While the free drying shrinkage of concrete increased at significant amounts (68 and 79 %) for fine and coarse recycled concrete aggregate, the restrained drying shrinkage crack widths were reduced up to by 13.5 %. In conclusion, it should be noted that the amount and size of recycled concrete aggregate need to be designed by considering the residual quality and dimensional stability of concrete, which exposes weathering actions in place.

Use of recycled concrete aggregates in asphalt mixtures for pavements: A review

Large quantities of natural aggregates (NA) are required in the manufacturing of asphalt mixtures for pavements. The extraction of NA generates high environmental impacts that negatively affect environmental preservation and conservation. Diverse alternative materials obtained in construction and demolition processes in civil construction worked have been studies as possible replacements for NA, with the purpose of reducing these environmental impacts. The foregoing study presents a state of knowledge review referring to the use of recycled concrete aggregates (RCA) when these are used in the manufacturing of asphalt mixtures (mainly hot-mix asphalt HMA type). Environmental aspects are presented, as well as possible benefits and limitations of using RCA as replacements for NA in asphalt mixtures. However, it is not possible to establish a behavior pattern, since the characteristics of the RCA are very heterogeneous and vary from the original source of the concrete. It is highlighted from the literature that RCA has a wide potential for use in the manufacture of asphalt mixtures, since in most studies, the mixtures with these materials comply the quality requirements contemplated by the construction specifications, mainly in low-volume roads. Additionally, based on the literature review, some recommendations and suggestions are presented for future research. • This review presents the studies of asphalt mixtures with the incorporation of RCA. • The results of the physical characteristics of the RCA found in the literature are analyzed. • The mechanical behavior of asphalt mixtures with RCA and natural aggregates is compared. • The treatments carried out on RCA to be used in asphalt mixtures are analyzed. • Suggestions are presented for future studies of asphalt mixtures with the use of RCA.

Evaluation of Characteristics and Building Applications of Multi-Recycled Concrete Aggregates from Precast Concrete Rejects.

The construction industry must meet current environmental requirements, mostly those pertaining to the reduction in construction and demolition waste and the consumption of raw materials. The use of recycled concrete aggregates can be part of the solution, but one question that arises is how many times recyclables can be recycled. This unknown involves other related queries regarding the properties and possible uses of repeated recycled concrete aggregates. This research is derived from the precast concrete industry, where multi-recycling is a pressing need. From good-quality parent concretes, three cycles of recycled concrete aggregates were produced and analysed. The final results are promising due to the good quality of the recycled and multi-recycled concrete aggregates obtained. Not only can they be used in low-level applications (backfilling) as usual, but they can also be used for more demanding purposes, such as graded aggregates, cement-treated road bases and concrete pavements. Their use in structural concrete is feasible, but it will be dependent on the water absorption level and the amount of recycled aggregate substitution. This research proves the viability of multi-recycled concrete aggregates with all of the associated environmental benefits.

An integrative approach of the use of recycled concrete aggregate in high‐rise buildings: Example of the Elysium

AbstractThe primary purpose of this study is to examine in detail the mechanical, environmental, and economic properties of concrete produced using recycled concrete aggregate (RCA) in different ratios. This study used RCAs obtained from construction and demolition wastes (CDW) that emerged after the 24 January 2020 Sivrice‐Elazig earthquake to produce recycled aggregate concretes. The ultimate aim of this study is to determine the advantages and disadvantages of these structures in terms of mechanical, environmental, and economic properties if RCA will be used at certain rates in high‐rise private buildings built with natural aggregate concrete (NAC) in Elazig. For this purpose, concretes with all natural aggregates, all recycled aggregates, and both natural aggregates and recycled aggregates were produced. A mathematical model was developed using response surface method to predict the mechanical properties of recycled coarse aggregate concretes (RCACs) by utilizing the compressive strength values of the produced concretes. Then, the component amounts of RCACs, which have the same compressive strength as the compressive strength values of the NAC used in Elysium, which was chosen as a sample building in Elazig, were estimated. Considering the estimated component amounts, environmental impact assessments and feasibility analyses were made according to four different scenarios, including parameters such as cement amount, chemical additive amount, the cost difference between RCA‐natural coarse aggregate, and transportation distance. As a result of these evaluations and analyses, it was foresighted that using RCA would provide significant advantages in buildings produced using large amounts of concrete. This foresight is exemplified by the Elysium buildings. As a result, it was determined that the use of RCAs is appropriate, especially the concrete produced with aggregates obtained from CDW is more important for a sustainable environment, and the use of RCAs in high‐rise buildings built using large amounts of concrete can provide significant environmental and economic advantages.

Experimental study of self-leveling mortars produced with recycled concrete aggregates

This study evaluates the use of recycled concrete aggregate (RCA) in self-leveling mortars (SLM) to obtain certain rheological characteristics for use in screed concrete. Mixtures were produced with 50% and 75% of RCA in substitution of natural fine aggregate (NFA) by varying the type of additive (polyfunctional plasticizer and combination of superplasticizer and viscosity modifier). In order to achieve a better distribution of water amid the grains in the residue, the RCA was pre-wetted by spraying for 10 min before mixing. The properties evaluated were: specific mass in the fresh stage, tensile strength, spreading, flow retention, regeneration time, and exudation rate. Regarding the variation of the type of chemical additive, all the mixtures had valid rheological aspects. The exudation rate values were less than 3% and the minimum curing time was 15 min. Also, all mortars achieved values above 2 MPa in the flexural strength tests, which was the minimum expected according to the literature. The use of RCA can be considered, and through the proper adjustments of chemical additives it can provide formulations with adequate rheological characteristics without losses on their mechanical properties.

Study on Mechanical Properties of Concrete Using Basalt-Based Recycled Aggregate and Varying Curing Conditions.

To replace porous basalt, the mechanical properties of concrete with recycled resources and durability improvement were analyzed in this study. The analysis was based on the quality improvement of recycled aggregate, use of fly ash, and changes in curing conditions. Basalt aggregate (BA) with a 3% water absorption, raw recycled aggregate and basalt (RRA), and improved recycled aggregate and basalt (PRA) were the main experimental variables. As PRA was applied to concrete, the compressive strength was lower than that of the specimen comprising BA in the normal strength region, but the modulus of elasticity (22.9 GPa) was equivalent or higher. The initial drying shrinkage increased because of the use of basalt-based recycled aggregate (B-RA). The drying shrinkage of PRA was similar to that of BA with an average difference of <7% as the age increased. The specimens subjected to steam curing exhibited the lowest drying shrinkage. These results showed that pores in the old paste of recycled aggregate increased freeze–thaw resistance because of the increase in the spacing factor. Although the PRA did not satisfy the quality criteria, the efficient use of recycled aggregate achieved an equivalent or higher performance than that of concrete comprising BA and improved durability.

Combined use of recycled concrete aggregate and glass cullet in mortar: Strength, alkali expansion and chemical compositions

The promotion of fine recycled concrete aggregate (FRCA) is the main way to alleviate the conflicts between scarce natural resource and huge construction demand. However, its utilization alone would result in a remarkable strength reduction. Therefore, this study attempts to co-utilize FRCA with the particle size of 1.18–4.75 mm and fine recycled glass cullet (FRGC) with the particle size of 0.15–1.18 mm to prepare recycled mortars. Compressive strength, alkali-silica reaction (ASR), X-ray diffraction (XRD), differential thermogravimetry (DTG), and Fourier transform infrared spectroscopy (FTIR) tests are carried out. Results show that without ASR inhibitors, the optimum replacement ratio of river sand by this combination in mortar is 40 vol%, where the strength reduction at 28 days is 2.64% and the ASR expansion at 14 days is 0.08%. The good performance can be attributed to the internal curing of FRCA at an early age and the pozzolanic activity of FRGC. Correspondingly, this combination does not change the phase composition deriving from cement hydration but can reduce portlandite and increase calcium silicate hydrate gel. In particular, compared with previous studies applying FRCA and/or FRGC, the replacement ratio of 40 vol% is satisfactory because of the lowest strength reduction. Future attempts could be further made to improve the replacement ratio of this combination to 60 vol% by using ASR inhibitors.

Use of recycled concrete aggregates as carriers for self-healing of concrete cracks by bacteria with high urease activity

Microbial induced carbonate precipitation (MICP) has become one of the most attractive strategies to achieve self-healing of concrete cracks in recent decades. In order to provide a moderate space for bacteria in the harsh environment of concrete, the incorporation of protective carriers is a necessity. In this study, the microbial urease activity at different generation of propagation in the selected culture medium was first investigated, followed by exploring the potential of using recycled concrete aggregates (RCAs) as microbial carriers, considering the porous nature of RCAs. The specific urease activity of bacteria at 48 h kept as high as 2.4 × 10−8 mM·min−1·cells−1 even after 5 generations of propagation in the selected culturing medium. RCAs would not result in a loss of ureolytic activity after immobilization and were capable of retaining bacterial viability during concrete mixing. Compared with concrete without any healing agents or with only substrates and calcium source, the one with bio-agents loaded in RCAs completed most of the crack healing in the first week. When the initial crack widths were less than 0.6 mm, the average crack healing ratio and the crack area healing ratio were 71% and 84%, respectively, for microbial self-healing. The depth of crack healing was 17.8 mm as indicated by the microbial precipitates on the crack wall. After microbial self-healing, the compressive strength regain ratio achieved 99.7% while the water tightness regain ratio attained 99.2%, and the cracks were filled with densely packed irregular rhombohedral-shaped crystals consisting of calcite and a small amount of vaterite.