Production Of Recycled Aggregates Research Articles

LCA applied to comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources

Nowadays, all productive sectors, including the construction industry, are facing the challenge of reducing their environmental impact. To achieve this objective, numerous actions are being carried out to access greater levels of environmental and economic sustainability. Techniques as Life Cycle Assessment contribute to quantifying environmental impacts, promoting a circular economy in a sector that consumes a high volume of resources, materials, and energy while generating large amounts of gaseous, liquid, or solid emissions. The present study aims to deepen our understanding of aspects that demonstrate the benefits of using RA instead of natural aggregates. This study not only quantifies the environmental impact but also explores the effects of potential improvements in the productive system and their impact on reducing environmental harm. The Life Cycle Assessment methodology is applied to quantify and compare the environmental impacts generated in the production of a ton of mixed recycled aggregates (MRA) from construction and demolition wastes, based on the data provided by plant managers. This is compared to the environmental impacts generated in the production of one ton of natural aggregates extracted from a quarry. The results revealed that the production of mixed recycled aggregate is more environmentally beneficial, confirming a reduction of 70.66% in environmental impacts during the production of recycled aggregates, in comparison to the natural aggregates extraction. Furthermore, the economic analysis demonstrates the economic advantage since the cost of producing recycled aggregates is over 30% cheaper than natural aggregates, being more competitive even when the transportation distances from the plant to the work sites exceed those of natural aggregates.Graphical

A Review Paper on Assessing the Environmental Impact of Recycled Aggregate Production and Use

Garbage management has emerged as one of our planet's most serious challenges, owing to its considerable contribution to environmental issues. Waste from construction and destruction (C&D), together with agricultural waste, glass, and plastic garbage, account for the majority of this waste. Due to its considerable role in environmental problems, garbage management is an urgent global task. Recycling has gained popularity as a way to reduce landfill trash, including the aggregate made from recycled concrete (RCA) from construction and destruction debris (C&D), which has positive environmental impact, the society and the economy. India continues to employ a little amount of RCA in new construction despite its rising cement demand and generation of C&D waste. The use of recycled concrete aggregate (RCA) in construction impacts concrete characteristics with advantages and disadvantages. Challenges include workability, density, and water absorption, mitigated by super plasticizer and altered absorption methods. This paper emphasises the advantages of RCA in structural concrete and the need for enhanced knowledge and ability for sustainable methods for trash management in the context of India's cement consumption and C&D waste management. The paper urges more investigation and effort to advance RCA as a practical option for handling C&D waste and minimising environmental effects.

Effect of alkali activated limestone-silica fume blended precursor on performance enhancement of recycled aggregate concrete

The utilization of Recycled Aggregates (RA) from Construction and Demolition (C&D) waste, has been reported to be an efficient way of dealing with the environmental issues encountered by our planet nowadays. However, due to the poor quality of RA, its incorporation in high – grade civil engineering applications been limited. It is essential that adequate process of treatment methods be incorporated into the production of RA to enhance its properties and optimize its use. This study is carried out to determine the effects of an alkaline NaOH activated by limestone powder (LSP) and silica fume (SF) to improve the properties of various concrete mixes produced with either recycled concrete aggregate (RCA), or recycled cement block aggregate (CBA). Fifteen mixes were designed to examine the effects of different parameters, RA replacement levels, various w/c ratios and different enhancement methods on the properties of recycled aggregate concrete (RAC). The study examined the effects of the proposed enhancement method on the physical characteristics of RCA and CBA. Compressive strength, splitting tensile strength, flexural strength, pull-out, and water absorption of the different concrete mixes were measured to determine the effectiveness of the enhancement method proposed. The enhanced RAC produced by CBA and RCA showed an increased 28-day compressive strength at 0.35 w/c ratio of up to 51 MPa and 44 MPa, respectively, suitable for structural applications. The flexural strength, tensile splitting strength, and bonding strength values at 0.35 w/c ratio of the enhanced RAC produced with treated CBA were 28%, 6%, and 8% higher than that of the RAC produced with treated CBA. Whereas, the flexural strength, tensile strength, and bonding strength of the enhanced RAC produced with treated RCA were 1%, 3%, and 5% higher compared to the RAC produced with treated RCA. The improved mechanical performance of the enhanced RAC produced by CBA or RCA was attributed to the effects of the geopolymer solution treatment in filling and sealing the voids and gaps on the CBA and RCA surface, leading to a better packed structure, reducing the water absorption, and improving the aggregate impact value. The treatment technique proposed can be a powerful tool for promoting the use of RA in the construction industry and expanding its application.

Evaluation of carbon and economic benefits of producing recycled aggregates from construction and demolition waste

Using construction and demolition waste (CDW) to produce recycled aggregate (RA) can limit the need for CDW landfills and reduce natural aggregate (NA) consumption; however, the RA production process generates carbon emissions and incurs economic costs. Therefore, it is necessary to study the environmental and economic feasibility of using CDW to produce RA. In this study, the environmental and economic benefits of RA production from CDW were evaluated based on life cycle assessment (LCA) and life cycle cost (LCC). To conduct a thorough evaluation, sensitivity and scenario analyses were conducted on the key parameters affecting carbon and economic benefits. Accordingly, potential improvements in the current system were analyzed to optimize the RA production process. The results indicated that using CDW to produce RA was environmentally and economically feasible. Sensitivity and scenario analyses indicated that using selective demolition and mobile production mode, pre-screening of CDW, opting for electric transportation vehicles, and increasing the CDW landfill disposal fee could effectively increase the carbon and economic benefits of RA production from CDW. Moreover, the CDW transportation distance had a significant impact on these benefits; thus, appropriately planning the transportation route was crucial. The results of this study provide a theoretical basis for assessing the feasibility of recycling CDW to produce RA and can also guide the optimization and improvement of the RA production process.

Enhancement of mechanical properties of concrete with treated demolition waste aggregate

The utilization of recycled aggregate (RA) from the construction and demolition waste (C&DW) in civil engineering applications, has proven to be an eco-efficient environmentally friendly approach to overcome the current environmental concerns. Nevertheless, the poor quality of RA has limited its utilization in high-grade civil engineering applications. To maximize and promote the use of RA, it is essential that an appropriate process of treatment methods is included in the production of RA to improve its properties. This research aimed to examine the effects of various enhancement methods on the mechanical properties (consistency, compressive strength, flexural strength, tensile splitting strength, and elastic modulus) of recycled aggregate concrete (RAC). This research also included microstructure investigation using Scan Electron Microscopy (SEM) images. The enhancement methods used were treating RA by Soaking in Cement-Pulverized Fuel Ash-Silica Fume solution (SCP), Sand Envelope Mixing Approach (SE), and their combination (SCP + SE). The enhanced RACs showed an increased 28-day compressive strength of up to 46 MPa suitable for structural applications. The tensile splitting strength, flexural strength, and modulus elasticity values of the enhanced RACs were 10%, 16%, and 6% higher than that of the untreated RAC. The improved mechanical performance of the enhanced RAC was attributed to the strengthened interfacial transition zone, better overall interlocking of the treated RA with the new cement paste, filled-up pores and micro-cracks, reduced water absorption, and improved aggregate impact value. The SEM images for the enhanced RACs showed better-compacted microstructure, lesser pores and microcracks. The application of the proposed innovative regime of enhancement methods is anticipated to promote the use of RA in the construction industry and provide a better scientific understanding of the performance of concrete produced with 100% treated RA from the C&DW for structural applications.

Sustainable alternatives to CO2 reduction in the cement industry: A short review

Cement is the most used material around the world just after water. However, cement industry is a significant source of greenhouse effect gases comprising 8–10% of worldwide production. To mitigate environmental impacts associated to cement production, many sustainable alternatives such as energy efficiency, sustainable fuels, CO2 capture and use, cement use efficiency and substituting clinker by mineral additions or Supplementary Cementitious Materials (SCM) have been proposed. In this regard, Fine Recycled Concrete (FRC) as SCM has proven to be a feasible alternative, considering its high availability during recycled aggregate production. Many studies have demonstrated their feasibility to be used as a substitute for cement. In addition, demolition and subsequent concrete grinding includes an exposed surface greater than a built structure, and CO2 uptake in FRC could be significant. This article shows a brief review about proposals to mitigate environmental impacts related to the cement industry, especially emphasized on FRC.

From Buildings’ End of Life to Aggregate Recycling under a Circular Economic Perspective: A Comparative Life Cycle Assessment Case Study

The demolition of buildings, apart from being energy intensive and disruptive, inevitably produces construction and demolition waste (C&Dw). Unfortunately, even today, the majority of this waste ends up underexploited and not considered as valuable resources to be re-circulated into a closed/open loop process under the umbrella of circular economy (CE). Considering the amount of virgin aggregates needed in civil engineering applications, C&Dw can act as sustainable catalyst towards the preservation of natural resources and the shift towards a CE. This study completes current research by presenting a life cycle inventory compilation and life cycle assessment case study of two buildings in France. The quantification of the end-of-life environmental impacts of the two buildings and subsequently the environmental impacts of recycled aggregates production from C&Dw was realized using the framework of life cycle assessment (LCA). The results indicate that the transport of waste, its treatment, and especially asbestos’ treatment are the most impactful phases. For example, in the case study of the first building, transport and treatment of waste reached 35% of the total impact for global warming. Careful, proactive, and strategic treatment, geolocation, and transport planning is recommended for the involved stakeholders and decision makers in order to ensure minimal sustainability implications during the implementation of CE approaches for C&Dw.

Life Cycle Assessment of Recycling Processes for Demolition Waste

This contribution is aimed to evaluate the environmental impacts of recycling construction and demolition waste with the use of Life Cycle Assessment. In the first step, the LCA was used as an analytical tool for the comparison of recycled aggregates production. Recycled aggregates were produced from brick and concrete waste. Chosen functional unit for the comparison was 1 ton of recycled aggregate (RA). The results show that concrete aggregate production has a higher impact on Climate Change category (1,51 kg CO2 eq.) than brick aggregate production (1,18 kg CO2 eq.). Then, in the second step, new concrete mixtures made of recycled aggregates were compared. Functional unit was 1 m3 of concrete. Environmental impacts of concrete mixtures were compared with reference concrete mixture. These compared concretes are classified as C20/25 according to CSN EN 206 + A1. Mixtures with concrete RA have a higher environmental impact than mixtures which were made of brick RA. GaBi Software ts for data processing was used. Environmental impacts assessment according to the ReCiPe method characterization, version 1.08 was used.

Carbon footprint of block prepared with recycled aggregate: a case study in China

This study aims to evaluate the carbon footprint of concrete blocks prepared with local recycled waste materials derived from Changsha using life cycle assessment (LCA) technique. The local life cycle inventory was developed for conducting case-specific assessment of concrete blocks prepared with recycled aggregates (RA) sourced from a local construction and demolition (C&D) waste. The result is also compared with concrete blocks made by natural aggregates (NA). The results show that greenhouse gases (GHGs) emissions related to the production of RA were 3 kg CO2 eq., which is 57% lower than the production of NA. However, the adoption of RA in concrete blocks production induced higher GHGs emissions than NA concrete blocks due to higher amount of cement was needed to achieve a same required mechanical strength. Guidelines to further design and develop sustainable green concrete blocks prepared with RA to meet the mechanical requirements based on the current situation in Changsha city has also been highlighted.

Evaluation on the Surface Modification of Recycled Fine Aggregates in Aqueous H2SiF6 Solution

Recycled aggregates (RAs) production techniques are essential for the material circulation society because RAs from demolished concrete waste can sustainably be reused as a concrete material. However, RAs can bring about several performance decreases when they are used for recycled aggregate concrete (RAC) because of the low qualities (i.e., high water-absorption rate and low density) caused by the attached hydrated cement paste on the RA surface. Therefore, both the production of high-quality RAs and the surface modification of RAs are significantly important for the extension of RAC utilization. This paper focuses on the surface modification of RFA to reduce the water absorption rate and increase density. Hydrofluorosilicic acid (H2SiF6), which is one of the by-products in phosphoric acid manufacture, is used herein for the surface modification of the RFA. The physical properties and mechanical performance of mortar using RFA were evaluated after RFA modification. Consequently, the proposed method is effective in reducing water absorption rate and increasing density of RFA. The density of RFAs was slightly increased by 0.5–2.6% after modification. On the other hand, the water absorption rate decreased by 4–18% after modification. The compressive strengths of mortar at 28 days ages showed 18.1 MPa with modified RFA and 16.2 MPa with RFA.

Production of natural and recycled aggregates: the environmental impacts of energy consumption and CO2 emissions

Natural aggregates (NA) are crushed and processed in crushing plants after the extraction stage in quarries. In the present study, the aggregates are divided into three scenarios, depending on the production methods. The first scenario considers the production of NA, the second scenario deals with the production of recycled aggregates (RA) with respect to construction and demolition waste, and the third scenario, which is a hybrid scenario, handles the combination of NA and RA by assuming a 50% mixing percentage. In this research, we assess the environmental impacts on the production of aggregates via each scenario, using life cycle assessment; in addition, energy consumption and CO2 emissions are considered as the environmental variables. We conclude that Iran’s current policy with an annual energy consumption of 1.48 million tons of oil equivalent (toe) can have a footprint of 2.88 million tons of CO2 eq emissions per year (the first scenario). Achieving 30 and 36% reduction in annual energy consumption and CO2 emissions, respectively, by the third scenario compared to the first scenario indicates the destructive effect of the first scenario from the environmental outlook.

Roughness, wettability and water absorption of water repellent treated recycled aggregates

Surface treatment techniques may improve the characteristics of recycled aggregates (RAs) for use in cementitious materials, possibly as an alternative to the energy and CO2 intensive high quality RA production process. In this paper, we investigate the effectiveness of two water repellent treatments (silane solution and paraffin wax) on the characteristics of different RAs in terms of porosity. We explored the relationship between roughness, porosity/surface area, and wettability of RAs on their water absorption (WA) kinetics. The long-term goal of the treatments is to reduce the water demand of concrete/mortar.We proposed a method to measure the roughness of coarse aggregates by optical interferometry. Contrary to popular belief, recycled concrete aggregates are as rough as crushed natural aggregates, and only red ceramic aggregate is less rough than natural aggregates. This technique combined with mercury intrusion porosimetry identified microstructural changes in the treated RAs. Silane was incorporated into smaller pores (<100nm) and caused a slight reduction in the total porosity and specific surface area of RAs. Paraffin wax also intruded into the RAs, filling larger pores (>100nm), and the wax significantly reduced the total porosity. Paraffin treatment formed a smoother surface and a thicker paraffin layer around the particles.We determined the water absorption kinetics using the standard 24h WA test with method adaptations in order to improve the accuracy and repeatability of the tests. Treated RA surfaces exhibited hydrophobic behavior but at the cost of efficiency. WA kinetics significantly changed after 2h.

Life cycle assessment of natural and mixed recycled aggregate production in Brazil

The natural and mixed recycled aggregate production for use as road base and subbase have been compared through an attributional life cycle assessment. The primary data have been collected in a basalt natural aggregate production facility and in a recycling facility of mixed aggregate, both located in Southeast Brazil. The topic is important since there is a local increasing demand for aggregate use in road construction and there are no studies related to the environmental aspects of the production of natural and mixed recycled aggregate, and no suitable, site-specific data are available to develop a reliable life cycle investigation. The potential environmental impacts related to the two production processes have been estimated by using the Impact 2002+ methodology. The results show that the production of recycled aggregates is preferable to that of natural materials for the impact categories of “respiratory inorganics”, “terrestrial ecotoxicity”, “land occupation”, “global warming” and “non-renewable energy”. A specific sensitivity analysis suggests that the mixed recycled aggregate is a better option for all the environmentally impact categories if the distance of the recycling facility from the consumer is up to 20 tkm longer than the distance of the natural aggregate production facility from the consumer of this product. These results, and those of the detailed life cycle inventory and impact assessment, may support the decision making process in the same field as well as the development of similar life cycle assessment studies, provided that both be appropriately adapted to the specific conditions of the system under analysis.

Economic and Environmental Evaluation and Optimal Ratio of Natural and Recycled Aggregate Production

Steady increase in overexploitation of stone quarries, generation of construction and demolition waste, and costs of preparing extra landfill space have become environmental and waste management challenges in metropolises. In this paper, aggregate production is studied in two scenarios: scenario 1 representing the production of natural aggregates (NA) and scenario 2 representing the production of recycled aggregates (RA). This study consists of two parts. In the first part, the objective is the environmental assessment (energy consumption and CO2 emission) and economic (cost) evaluation of these two scenarios, which is pursued by life-cycle assessment (LCA) method. In the second part, the results of the first part are used to estimate the optimal combination of production of NA and RA and thereby find an optimal solution (scenario) for a more eco-friendly aggregate production. The defined formulas and relationship are used to develop a model. The results of model validation show that the optimal ratio, in optimal scenario, is 50%. The results show that, compared to scenario 1, optimal scenario improves the energy consumption, CO2 emissions, and production cost by, respectively, 30%, 36%, and 31%, which demonstrate the effectiveness of this optimization.

신재 표층용 가열 아스팔트 콘크리트와 재생 표층용 가열 아스팔트 콘크리트의 LCCO2 비교분석

Asphalt concrete is a composite material commonly used to surface roads, parking lots, and airports. Currently recycled asphalt concrete is used increasingly for global environmental protection in our society. So, this study is intended to measure and compare life cycle CO2(LCCO2) on both virgin asphalt concrete and recycled one in accordance with ISO 14044:2006. As a result, LCCO2 emissions generated by recycle asphalt concrete is 67.7% higher than virgin asphalt concrete because a lot of energy consumption is needed in the drying process of recycled aggregate production.

Comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources by LCA

The management of construction and demolition (C&D) waste and waste glass is a serious concern in Hong Kong, as well as other countries due to their non-combustible and non-putrescible nature, and the running out of disposal outlets. However, mineral wastes derived from C&D activities and waste glass are considered to have potential to be re-used as construction materials, especially as aggregates. In addition, Hong Kong urgently needs alternative and sustainable sources of aggregate, as the local quarry sites for aggregate production are expected to be exhausted soon. Many experimental studies have demonstrated that recycled aggregates from C&D waste and waste glass can be potentially recycled for various engineering applications in Hong Kong, but no study has yet attempted to assess the sustainability by lifecycle assessment (LCA) techniques. In order to increase the environmental awareness in the construction industry, assessment of the environmental performance of construction materials by LCA is therefore needed. The present study was conducted to assess and compare the environmental consequences of recycled aggregates production from C&D waste and waste glass, and natural aggregate production from virgin materials by LCA by using case specific and first hand data. The results reveal that compared with natural coarse aggregates, recycled coarse aggregates produced from C&D waste reduce 65% greenhouse gases (GHGs) emission with a saving of 58% non-renewable energy consumption. Similar environmental benefits are observed for producing recycled fine aggregates from C&D waste. In addition, compared with the production of natural fine aggregates from river sand, producing recycled fine aggregates from waste glass saves 54% energy consumption and reduces 61% GHGs, and 46% SO2eq emissions. According to the IMPACT 2002+ Method, significant health, resource, climate change and ecosystem damages can be saved in producing recycled aggregates from both waste materials compared to producing and importing aggregates from virgin sources. This is the first ever LCA study on producing recycled aggregates from waste glass. Therefore, it can be concluded that substantial net environmental benefits can be realized for producing recycled aggregates from C&D waste and waste glass. The results can provide a guidance to maximize C&D waste and waste glass recycling, resourceful treatment of wastes and conserve natural resources.

Reclamation chain of waste concrete: A case study of Shanghai

A mass of construction and demolition (C&D) waste are generated in Shanghai every year, and it has become a serious environment problem. Reclaiming the waste concrete to produce recycled aggregate (RA) and recycled aggregate concrete (RAC) is an effective method to reduce the C&D waste. This paper develops a reclamation chain of waste concrete based on the researches and practices in Shanghai. C&D waste management, waste concrete disposition, RA production and RAC preparation are discussed respectively. In addition, technical suggestions are also given according to the findings in practical engineering, which aims to optimize the reclamation chain. The results show that the properties of RA and RAC can well meet the requirement of design and practical application through a series of technical measures. The reclamation chain of waste concrete is necessary and appropriate for Shanghai, which provides more opportunities for the wider application of RA and RAC, and it shows a favorable environmental benefit.

Properties of mortars produced with reactivated cementitious materials

The production of reactivated cementitious materials is an option for the recycling of hydrated-cement-rich fines discarded during recycled aggregate production. Reactivation is based on a thermal process where calcium silicate hydrates present in the fines decompose forming new hydraulic compounds. In the reported study, materials reactivated at temperatures between 660 °C and 940 °C were characterized using X-Ray diffraction and particle size analysis, and evaluated as binders using a central composite experiment to model the effects of reactivation temperature and reactivated material substitution level on the flowability, compressive strength and expansion of mortar mixtures. Reactivation temperature effects correlated with the relative concentration of reactive phases, particularly a stabilized form of alpha'-C2S identified in the materials. Substitution effects depended on the supplementary material tested, and lacked significant interaction with reactivation temperature. In the region explored, mortars based on materials produced at 800 °C, 40% substituted by silica fume, achieved highest strength but lowest flowability.

Risk evaluation for recycled aggregate according to deleterious impurity content considering deconstruction scenarios and production methods

Recycled aggregate (RA) obtained from demolished concrete waste (CW) is beneficial owing to its applicability in recycled aggregate concrete (RAC). However, in designing RAC mix proportions, various impurities in the RA that can adversely affect the properties of the concrete, should be considered. Current RA production focuses on the physical quality of the RA without consideration of the impurities present. To improve the stable production and use of RAC, the amounts of deleterious impurities present and their effects on the concrete mix should be estimated. In this study, the risk associated with the presence of impurities in RA was defined as including the amount of impurity residue in the RA and the effects of impurities on RAC properties Both impurity types and RA production methods were considered in assessing risk for five building demolition scenarios. To quantify the risk, the amount of demolished building waste was estimated, the amount of CW was predicted, the RA ratio was calculated from the predicted amount of CW, and impurity sorting levels were investigated for nine methods of RA production. The impurity residue ratio per unit RA was estimated for each demolition scenario, RA production method, and RA quality level considered. A risk model is proposed in this paper that can be used to estimate the risk of RA adversely affecting RAC performance using information on the demolition scenario and the RA production method.

Custos de reciclagem de pavimentos de concreto e seu potencial econômico na realidade brasileira

&lt;p&gt;Os custos de produção de agregados reciclados de concretos de antigos pavimentos devem ser contextualizados nas obras de pavimentação rodoviária no país. Valores fornecidos em tabelas de serviços para vias urbanas podem não refletir as condições específicas da demolição em rodovias. Também, preços operados em outros países são afetados pela tecnologia de reciclagem empregada, que não é aquela que tem sido considerada no Brasil. Neste artigo são determinadas as razões unitárias de produção relacionadas à demolição, carga, transporte e britagem de pavimentos de concreto removidos de pistas de duas rodovias brasileiras. Com base nos resultados pôde-se verificar um acréscimo de 50% no custo final do agregado reciclado em relação ao agregado virgem, resultando em acréscimo de cerca de 20% nos custos de produção de concretos para pavimentação. O potencial brasileiro de produção desses agregados reciclados a partir de pavimentos de concreto deteriorados é limitado o que pode ser um fator estagnante para o emprego da tecnologia no país.&lt;/p&gt;