Use Of Recycled Aggregates Research Articles

Utilisation of Recycled Concrete Aggregates for Sustainable Porous Asphalt Pavements

The use of recycled concrete aggregates (RCA) for porous asphalts is a viable attempt towards waste management and sustainable conservation of natural resources. Installation of a porous asphalt wearing course is justified in highway pavements because it offers higher skid resistance, glare reduction, lesser traffic noise, reduction of hydroplaning, and mitigation of urban heat island phenomenon. The performance of porous asphalt mixtures containing 0%, 20%, 40%, 60%, 80% and 100% of coarse RCA as replacement for granite was studied and reported in this paper. The mixture containing 0% RCA was used as the control. The skid properties, permeability, water susceptibility and mechanical behaviour of the mixtures under various loading conditions were investigated. Blending granite and RCA in the porous asphalt mixture gave better Indirect Tensile Strength (ITS), rutting resistance, and impact strength indicators. The mixture with 60% RCA achieved desirable results in all tests. It exhibited the best performance based on its ITS and impact strength of 431 kPa and 380 J, respectively. These values were higher than the control by 3% and 30%, respectively. Utilisation of RCA in porous asphalt pavements is recommended based on the results of this study.

Shear strength of recycled-aggregate concrete beams with glass-FRP stirrups

The combined use of recycled concrete aggregate (RCA) and glass fiber reinforced polymer (GFRP) reinforcement in reinforced concrete (RC) structures is deemed plausible to achieve sustainable construction. This paper aims to examine the effect of such a combination (RCA + GFRP reinforcement) on the shear behavior of RC beams. Six medium-scale RC beams (150 × 260 × 2200 mm) critical in shear were tested under three-point loading until failure. The test variables were the aggregate type (natural/recycled) and the shear reinforcement (steel/GFRP/none). The failure modes, cracking patterns, load-carrying capacities, deformational and strain characteristics were analyzed and compared among the tested specimens. It was found that using 100% RCA in the concrete mix reduced the shear strength of RC beams (by 12% on average). Minor effects were observed on the shear strength of the beam specimens (∼2%) with altering the transverse reinforcement (GFRP versus steel). Theoretical load-carrying capacities of the tested beams were obtained as per contemporary design guides and compared with the experimental results.

Fire spalling sensitivity of concrete made with recycled concrete aggregates (RCA)

The fire spalling of concrete is a complex phenomenon, which can affect the integrity of the structures during a fire. This thermal instability is associated with a complex coupled chemo-thermo-hydro-mechanical mechanism and it can be influenced by many factors, related to material (e.g. per- meability, porosity and water content), geometry (e.g. shape and size) and environmental parameters (e.g. mechanical load and heating rate). Concrete made with recycled concrete aggregates presents higher porosity, higher water content and different interfaces between aggregates and mortar. All these aspects can lead to a different behaviour under fire exposure, including the spalling risk of these sustainable concretes. The main objective of this paper is to analyse the influence of the use of recycled concrete aggregates on the spalling risk of concrete. In this paper, concrete prisms with different replacement rates of recycled coarse aggregates (0 up to 100%) were exposed to a standard fire curve (ISO 834-1) with a constant uniaxial compression load. After heating, samples surfaces were evaluated by means of digital photogrammetry. Results showed that concrete with RCA is sensitive to explosive spalling. All replacement rates presented higher degree of spalling than concrete made with natural aggregates.

Potential use of recycled concrete aggregate (RCA) for sustainable asphalt pavements of the future: A state-of-the-art review

With the continuous paving of roads around the world, the huge consumption of natural aggregate (NA) obtained through widespread excavation and extraction is now an inevitable part of highway construction. To alleviate this phenomenon, the use of recycled concrete aggregates (RCA) is considered beneficial to potentially substitute these aggregates in asphalt mixtures while concurrently providing secondary environmental, economic, and societal benefits. Nevertheless, engineering asphalt mixtures containing RCA to meet desired performance properties still poses several challenges and uncertainties for practitioners. Based on this, the present work reviews the previous relevant literature on this topic and summarizes the potential use of RCA for asphalt pavement related applications. An important characteristic of RCA is that it consists of various interfacial transition zones (ITZs) and voids caused by adhered mortar which leads to higher water-absorption and crushing characteristics as compared to NA. The treating methods used such as mechanical processing, calcium carbonate bio-deposition, and pozzolanic materials incorporation have been shown to be effective to improve the quality of RCA. The structural and material durability of RCA-asphalt pavement is closely dependent on its mix design, moisture-induced damage, and high and low temperature properties, which is in direct relation to the overall properties of RCA. Moreover, the shape variability of RCA during mixture preparation leads to the change in design gradation and its influence on the properties of RCA-asphalt mixtures should be carefully considered. The total substitution of coarse NA by RCA in asphalt pavement can be reached as long as the engineering properties, particularly the moisture susceptibility, are satisfactorily addressed. Overall, the potential application of RCA is a promising candidate to replace the excessive use of NA for the construction of high quality and sustainable asphalt pavements of the future.

A succinct review on the durability of treated recycled concrete aggregates.

Building materials constitute a considerable portion of all the materials we use and about half the waste (in solid form) generated worldwide. Construction and demolishment (C&D) aggregates can be an invaluable source of construction material. If we measure the quantity of C&D waste in India, it will exceed the amount of all other types of hard solid wastes put together. Therefore, the use of recycled concrete aggregates (RCA) in new construction is being encouraged worldwide. But due to the inferior compressive, mechanical strengths and poor durability performance, it cannot be qualified for structural usage. Hence, there is a need to treat these aggregates and produce better quality aggregates suitable for good structural grade concrete. The present work focuses on the study and comparison of the effects on durability performance due to different treatment techniques of recycled aggregates. Effective treatment techniques can potentially separate or strengthen the weaker portions of the recycled aggregates like the old adhered mortar and the ITZs formed due to them. Effects of different RCA treatment methods along with their combinations such as immersing aggregate in acid solution and silicate solution impregnation, multistage-mixing techniques, biologically induced carbonate precipitation, modifier solution impregnation, ultrasonic cleaning, crushing aggregates at multiple levels, and mechanical grinding are considered for analyzing their effectiveness in improving RCA durability. The durability performance of treated RCA is evaluated based on the improvement in the parameters such as water absorption and resistance to acid attack, permeability, chloride attack, and carbonation.

Evaluating the effect of recycled concrete aggregate and sand in pervious concrete paving blocks

Pervious concrete paving blocks with individual and combined use of recycled concrete aggregate (RCA) and sand were investigated in terms of physical and hydrological properties (density, porosity and infiltration rate), compressive strength and abrasion capacity. First, the natural coarse aggregate was replaced by RCA at the levels of 15%, 30% and 50% by weight. Then, the incorporation of sand at the levels of 5% and 10% by total weight of aggregate was studied in the mixtures that presented the greater performance. As a result, the replacement of natural aggregate by 15% of RCA increased the compressive strength. Also RCA levels until 30% do not compromise the hydraulic and mechanical performance of previous concrete paving blocks. The incorporation of sand decreased the porosity and infiltration capacity of pervious concrete while preventing the mechanical performance to increase due to the lack of homogeneity of the mixture.

Effect of recycled concrete aggregate (RCA) on mortar's thermal conductivity susceptibility to variations of moisture content and ambient temperature

Temperature and moisture are two factors that affect the thermal conductivity of building materials. Furthermore, the use of recycled concrete aggregate (RCA) in cementitious composites reduces their thermal conductivity due to increased porosity. However, this increase in porosity may affect the material's thermal conductivity susceptibility to changes in environmental conditions. No studies were found on the effect of RCA on thermal conductivity's susceptibility to moisture content and ambient temperature variations in cement mortars . To study these effects, a total of 135 thermal conductivity tests were performed on mortars with three levels replacement of natural aggregate by RCA, at different saturation degrees and temperatures within the range of expected service-life values. Compressive and flexural strength, permeable porosity, and bulk density were also evaluated. Remarkably, the use of RCA reduces the thermal conductivity's susceptibility to changes in ambient temperature. Besides, RCA increases the porosity, magnifying the susceptibility of thermal conductivity to moisture variations. These variations should be considered when thermal insulation is used as a factor for the environmental impact assessment of cement mortars. Finally, a combination of response surface method models was used to formulate a prediction equation that accurately estimates (error <5%) the thermal conductivity of cement mortars as a function of accessible porosity , saturation degree, and ambient temperature. This research contributes to a deeper understanding and more accurate prediction of RCA's effects on thermal conductivity of cementitious composites as a function of the environmental conditions, which is key to assessing RCA mortars' environmental impact during service life as part of a building component. • RCA reduced the thermal conductivity's susceptibility to ambient temperature changes. • Thermal conductivity's susceptibility to moisture content increases with RCA. • The increase on this susceptibility is related to the increase of porosity. • Thermal conductivity depends on porosity, moisture content and ambient temperature. • An equation that accurately estimates thermal conductivity of mortars is proposed.

Sustainable use of recycled concrete aggregates and waste rubber shreds in drainage layer of landfills

Sustainable use of recycled concrete aggregates and waste rubber shreds in drainage layer of landfills

Effect of lime filler on RCA incorporated bituminous mixture

The use of Recycled concrete aggregate (RCA) obtained from construction and demolition waste not only reduces the need for virgin aggregates but also solves the problems associated with the disposal of construction and demolition (C&D) waste. Despite being a promising prospect, field utilization of RCA in bituminous mixes is limited due to the problems like lower strength and higher moisture susceptibility. To solve these issues present study aims at examining the effect of lime filler on RCA incorporated bituminous mixes. In the present study, RCA was obtained by mechanically treating C&D waste in a Los Angeles abrasion machine. Bituminous mixes were prepared by using 10%–50% of RCA. Additionally, 2% lime was added to the RCA incorporated mixes, and the parameter like optimum bitumen content, Marshall stability, Marshall quotient, Indirect tensile strength, Retained Marshall stability and Tensile strength Ratio were compared with the control mix to examine the effect of RCA and lime on mix properties. The inclusion of RCA was found to adversely affecting the properties of the mix whereas the inclusion of lime improved the properties. To provide a clear understanding of the environmental and economic benefits of utilizing RCA in bituminous mixes, economic and environmental assessment was also done. Based on different test results and analysis it was concluded that with the use of lime fillers it is possible to produce economical and environmentally friendly RCA incorporated bituminous mixes having properties comparable/better than conventional hot mix asphalt (HMA).

Investigations on Stone Matrix Asphalt Mixes Containing Recycled Concrete Aggregate Treated with Nanosilica

The present work is an attempt to explore use of recycled concrete aggregate (RCA) to replace natural aggregates (NA) in a sustainable way in stone matrix asphalt (SMA) mixes used as a rut resistant bituminous layer. Based on several initial trials, a modified pretreatment procedure has been developed, which involves mixing of RCA with 8% (by weight) nanosilica modified bitumen emulsion solution followed by 24-h curing. The treated RCA (TRCA) has been used as coarse aggregate completely replacing the coarse NA, with two different types of bitumen namely, VG 30 and VG 40 bitumens for preparation of SMA mixes. Marshall method was used to determine optimum bitumen content (OBC) of the respective mix type. The pertinent performance characteristics such as stone-on-stone contact, drain-down, Marshall parameters, indirect tensile strength, moisture susceptibility, resilient modulus and rutting potential have been addressed for various SMA mixes prepared at respective OBCs. It is concluded that TRCA as aggregate and VG 40 bitumen as binder in SMA mix contributed to the best results in terms of various performance parameters considered.

Novel metaheuristic-based type-2 fuzzy inference system for predicting the compressive strength of recycled aggregate concrete

The use of recycled concrete aggregate (RCA) in the production of new concrete can provide several environmental benefits and reduce the pressure on natural resources. Due to the differences in the properties of RCA and natural aggregate, the properties of recycled aggregate concrete (RAC) (i.e., concrete containing RCA) are different from those of normal concrete. Compressive strength (CS) of the RAC, which is a key parameter in many design codes, can be determined either through expensive and time-taking laboratory-based procedures or using empirical relationships. In this study, two types of hybridized machine learning algorithms (i.e., type-1 fuzzy inference system (T1FIS) and interval type-2fuzzy inference system (IT2FIS)) were used to develop predictive models for the CS of RAC. Moreover, arithmetic optimization algorithm (AOA), as a novel optimization algorithm, was employed to optimize the parameters of FIS models. To develop the CS predictive models, a dataset containing information on 1868 data records was used. The results indicate that the IT2FIS model outperformed the T1FIS model. A comparison of the results of this study with those reported in previous studies also confirms the high accuracy of the IT2FIS model. The findings indicate that concrete age, natural fine aggregate to total natural aggregate ratio, and superplasticizer to binder ratio have positive impacts on the CS, while the remaining input variables have negative influences on the CS. Regarding the intensities of the variables, concrete age, total coarse aggregate to cement ratio, and water to binder ratio are in the first to third orders, respectively.

Behaviour of intermediate stiffness culverts with recycled concrete aggregate backfill

Intermediate stiffness culverts behave in a manner between that of rigid structures, where the structural stiffness dominates, and flexible culverts where the soil properties are most important. Analysis and design of intermediate stiffness culverts requires a thorough understanding of soil-structure interaction. In addition the use of recycled concrete aggregate (RCA) as a backfill material to culverts is not well studied. Here the behaviour of two fully instrumented full scale intermediate stiffness culverts, one of which was backfilled with RCA, was examined by means of a series of large scale laboratory tests, detailed in situ testing and by a series of numerical models. It was found that the RCA behaves as a competent engineering material in a manner very similar to the natural sand and gravel tested. Both materials dilate strongly on loading and exhibit strong non-linearity of stiffness. The Hardening Soil Model (HSM) constitutive relationships were found to be well suited to these materials. A combination of in situ geophysics and some measurements and modelling of locally instrumented large scale laboratory testing was required to give the necessary input parameters. Monitoring of the 6 m high arch culvert showed the structure distorted in a linear elastic manner with distortions less than 20 mm, strains induced in the structural concrete less than 700 microstrain and earth pressures close to theoretical in situ (K0) earth pressures. No measureable movement was observed in the 300 mm thick, 3 m high box culvert. The numerical models successfully captured the behaviour of both culverts. The work demonstrates that potential savings could be made in the development of intermediate stiffness culverts, particularly in the required thickness of the soil cover and the size of the backfill zone but possibly also in the size of the structural elements.

Design Strategy for Recycled Aggregate Concrete: A Review of Status and Future Perspectives

Currently, a number of disadvantages hampers the use of recycled concrete aggregates (RCA). The current review proves that concretes made with complete replacement of natural aggregate with RCA allow the production of high-quality concrete. One of the possibilities for improving concrete properties with RCA is the use of extended curing and pozzolanic materials with varying cement ratios. The potential use of RCA concretes is in the production of high-value materials that increase environmental and financial benefits. RCA have strong potential in the development of a new generation of concrete and stimulate economic activity in many countries in addition to optimizing natural resources. Economic benefits include minimal travel costs; cheaper sources of concrete than newly mined aggregates; reduction of the landfill area required for the placement of concrete waste; the use of RCA minimizes the need for gravel extraction, etc. The proposed strategy could be to sequentially separate demolition waste such as roof finishes, waterproof materials, interior and exterior materials, etc. Closing life cycles is the main approach used for efficient structures for the recycling and reuse of construction and demolition waste in the production and recovery of materials, especially when recycling and reusing materials. In the life cycle, the recycling of recovered materials allows them to be used for new construction purposes, avoiding the use of natural concrete aggregates. Government, design institutes, construction departments and project managers should be involved in the creation and use of RCA. In demolition and construction, the main players are the project owners. Their obligations, expectations and responsibilities must be properly aligned. For the past 20 years, recycled concrete aggregate from demolition and construction waste has been considered as an alternative to pure concrete in structural concrete to minimize the environmental impact of construction waste and demolition waste and the conversion of natural aggregate resources. It is now recognized that the use of RCA for the generations of concrete is a promising and very attractive technology for reducing the environmental impact of the construction sector and conserving natural resources. In the market, the selling price is not an obstacle for market applications of RCA, as there are scenarios in which their cost is lower than the cost of products made from conventional building materials. This is more of an acceptance factor in the market for recycled concrete aggregates. In this sector, the lack of identification, accreditation and uniform quality certification systems and their narrow application cause some marketing problems. With proper RCA preparation, concrete with standard physical and mechanical properties and performance characteristics can be obtained.

A case study on the viability of using increased quantities of recycled concrete aggregates in structural concrete for extending environmental conservation in North Cyprus

Increase in construction activities leads to increased consumption of natural aggregates resources used in concrete and increased quantity of generated construction and demolishing wastes that are hazardous for the environment. Being a developing country that had faced wars and that owns numerous aged and damaged buildings, North Cyprus still lacks facilities for processing construction and demolishing wastes in the form of recycled concrete aggregates (RCA). Initiation of practices in North Cyprus on RCA-concrete can be promoted if the performance of new concretes including local RCA are proven to be successful. Additionally, previous international studies on the use of recycled concrete aggregates have been observed to lack in covering certain critical aspects such as employing high contents of not laboratory-made but real and damaged RCA having known source and age information and without other waste impurities in the manufacture of high-strength concrete mixes. This case study presents results of experimental investigations that are carried out for the first time on the performance of RCA that has aged in North Cyprus, while providing detailed experimental data covering the mentioned missing aspects in the literature. The results have shown that with 100% replacement of quarried aggregates with recycled aggregates, 0.711-m cube of demolishing waste could be eliminated per each meter cube of new concrete while saving that quantity of quarried aggregates at the same time. The new concrete produced with this high waste content has been observed to reach up to significantly high strength values as 49 MPa within 90 days, as an indicator of a successful performance. Hence, the work confirms the use of recycled concrete aggregates as an efficient and viable environmental-friendly method to preserve aggregate resources in North Cyprus while reducing demolishing wastes.

Utilization of Upgraded Recycled Concrete Aggregates and Recycled Concrete Fines in Cement Mortars

Waste concrete is the most predominant constituent material among construction and demolition waste. Current waste concrete recycling is limited to the use of recycled concrete aggregates as a road-base material and less as aggregates in new concrete mixes. Further, the production of recycled concrete aggregates results in the generation of a high amount of fines, consisting mainly of cement paste particles. Hence, this study aims to produce the cement mortars using the upgraded recycled concrete aggregates (sand granulometry) for the total replacement of natural aggregates and recycled concrete fines activated through a thermal treatment method as a partial cement substitution material. Cement mortar specimens were tested for their compressive and flexural strength, density and water absorption performance. The results showed that the combined usage of upgraded recycled concrete sand for total replacement of primary crushed sand and recycled concrete fines as partial cement replacement material is a promising option to produce cement mortars.

Rutting Resistance of Hot Mix Asphalt Containing Coarse Recycled Concrete Aggregates Coated with Waste Plastic Bottles

The use of recycled concrete aggregate (RCA) as a part of coarse aggregates in asphalt pavements confers economic and environmental benefits. Coarse RCA (CRCA) has inferior mechanical and physical properties compared to natural aggregates due to very porous and weakly adhered cement mortar. In this study, CRCA surfaces were coated with waste plastic bottles (WPB) and used at 15%, 30%, and 50% in the asphalt concrete. The Marshall, stiffness modulus, and dynamic creep tests were performed to determine the strength of hot mix asphalts against rutting. The results revealed that the use of untreated CRCA reduced the Marshall quotient and the rutting resistance of the asphalt concrete. The results of the stiffness modulus and dynamic creep tests indicated that CRCA incorporation increased permanent deformation in the tested specimens due to the reduction of asphalt concrete stiffness. However, the asphalt concrete containing treated CRCA had lower permanent deformation because WPB promotes CRCA stability by penetrating its void and reinforcing cement mortar. Furthermore, by raising the temperature, the strength of all asphalt concretes decreased against rutting, and the reduction rate was higher in the modified specimens.

Enhancing the mechanical properties of pervious recycled aggregate concrete using silicafumes

The growth of construction industry in India is increasing enormously over the last few years. This demands a huge quantity of construction materials across the globe which indirectly has a serious impact on the environment that includes aggregate scarcity, inadequate ground water recharge due to impermeable paved surfaces, dust and noise pollution. The use of recycled concrete aggregate in construction industry will mitigate the impact to some extent and also the construction of permeable surface helps in ground water recharge. In this study, the effect of recycled concrete aggregate on mechanical properties of pervious concrete is studied. In addition, the strength of pervious concrete composed of recycled concrete aggregate is enhanced by the addition of silicafumes from 8% to 16% in increments of 2%. The effect of silica fume on permeability and flexural strength is also studied.

Use of recycled concrete aggregate and granulated blast furnace slag in self-compacting concrete

Abstract In civil engineering industries, mass utilization of concrete has prompted to use recycled aggregates and slag as one of the strategies and an option for whole range of possibilities in the use and reuse of construction materials in civil industry. In this paper, an investigation is carried out to study the fresh and harden properties of granulated blast furnace slag (GBS) based normal vibrated concrete (NVC) and self-compacting concrete (SCC) with partial replacement of natural coarse aggregate (NCA) with recycled concrete aggregate (RCA). The testing on constituent materials is conducted as per Indian code of practice. The tests on fresh NVC and SCC were conducted as per the Indian standards and EFNARC guidelines respectively. The tests on harden state of concrete include the compression test on cube specimens as per the Indian standards. The present study is limited to investigate the fresh and harden properties of GBS based NVC and SCC with partial replacement (0%, 20%, 25%, 30%, and 35%) of NCA with RCA with a mean target compressive strength of 30 N/mm2. The topographic and compositional analysis on samples of both NVC and SCC group specimens is determined using the Scanning electron micrograph (SEM). From the present study it is concluded that the compressive strength of the GBS based SCC group specimens with NCA replaced by RCA of more than 20% s showed reduction in compressive strength both for 7-day and 28-day results in comparison to respective NVC group specimens.

A concurrent multiscale approach for modeling recycled aggregate concrete

The use of recycled concrete aggregates in new concrete is an alternative that can provide economical and environmental benefits. However, the influence of the inert particles on the mechanical behavior of concrete needs to be better understood. To provide a comprehensive simulator to predict the failure mechanism of this material taking into account its heterogeneity in mesoscale, a mesh fragmentation technique composed of interface solid finite elements equipped with a tensile damage model is employed. To minimize computational costs, a concurrent multiscale strategy based on the use of coupling finite elements to connect the macro and mesoscale regions is adopted. In mesoscale, the different phases of the recycled aggregate concrete (RAC) are explicitly represented, consisting of: (i) new mortar matrix; (ii) recycled aggregate composed of old matrix and crushed rock (natural aggregate); and (iii) interfacial transition zones in between all of them. For the regions where cracks are not expected, homogenized elastic parameters are assumed for the RAC. Three-point bending beams experimentally tested by Casuccio et al. [4] are numerically analyzed for concrete with compressive strength targets of 18, 37 and 48 MPa. These concrete beams were produced with coarse aggregates derived from natural crushed stone and another two coming from recycled concrete with high and normal strengths. The numerical results obtained show that the concurrent multiscale model is able to represent the tensile failure mechanism of the RAC, taking into account explicitly the effects of the recycled components on crack patterns and structural predictions.

Compressive strength and durability behavior of graphene oxide reinforced concrete composites containing recycled concrete aggregate

This investigation was carried out to encourage the use of recycled concrete aggregate (RCA) in the construction industry. The enhancement in performance of concrete composites made with 100% replacement of natural aggregate (NA) by recycled concrete aggregate (RCA) in addition of synthesized graphene oxide (GO) and GO ball milled (GObm) were observed on the mechanical and durability properties of the concrete. Six mixes were prepared, of which the control mix was prepared with 100% NA with 70% Portland cement (OPC) and 30% fly ash (FA) and the remaining mixes with 100% RCA with 0%, 0.05% and 0.10% GO and GObm inclusion by weight of binder. The compressive strength, electrical resistivity and ultrasonic pulse velocity (UPV) of the mixes with 100% RCA escalated with percentage increase in graphene oxide but lesser compared to control mix. However, the sorptivity and initial surface absorption reduces with percentage increase in GO and GObm content in the concrete mixes compared to mix without GO. Overall, the 0.1% GO and GObm addition has significantly improved the mechanical and durability properties of the concrete containing 100% RCA and comparable to control mix. The 100% RCA with GO and GObm inclusion were observed to have better economy index and higher overall desirability function compared to control mix. Thus, optimum used of waste materials in construction industry can be possible with inclusion of graphene oxide.