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Title
Abstract
Figures
Introduction
Materials and Methods
Results
Conclusions
References

Recycling Concrete to Aggregates. Implications on CO2 Footprint

Profile image of Charalampos VasilatosCharalampos Vasilatos

RawMat 2023

https://doi.org/10.3390/MATERPROC2023015028
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Abstract

Recycling Concrete to Aggregates. Implications on CO 2 Footprint. Mater.

Figures (9)
Wang et al. [4] about worldwide CDW generation are illustrated in Figure 1. Globally, approximately 10 Bt of CDW are generated each year [8]. Kabirifar et al. [9] state that CDW occupies 35-65% of global landfill space. These numbers raise serious concerns. Since the usage of traditional materials is unsustainable, various waste materials have been repurposed in the manufacturing of concrete. In various studies, waste materials such as ground granulated blast-furnace slag (GGBS) [10,11]; fly ash [12]; glass [13,14], but also alternative materials such as rice husk ash, animal bones and human hair [15,16] are incorporated in concrete. CDW, due to the vast market for re-use, has a high potential for recycling. This combined with the aforementioned soaring growth and the immersed CDW generation, has rendered CDW a fast-growing commodity. Figure 1. Illustration of the countries with the highest CDW generation around the world in 2018 (processed data from Wang et al. [4]).
Wang et al. [4] about worldwide CDW generation are illustrated in Figure 1. Globally, approximately 10 Bt of CDW are generated each year [8]. Kabirifar et al. [9] state that CDW occupies 35-65% of global landfill space. These numbers raise serious concerns. Since the usage of traditional materials is unsustainable, various waste materials have been repurposed in the manufacturing of concrete. In various studies, waste materials such as ground granulated blast-furnace slag (GGBS) [10,11]; fly ash [12]; glass [13,14], but also alternative materials such as rice husk ash, animal bones and human hair [15,16] are incorporated in concrete. CDW, due to the vast market for re-use, has a high potential for recycling. This combined with the aforementioned soaring growth and the immersed CDW generation, has rendered CDW a fast-growing commodity. Figure 1. Illustration of the countries with the highest CDW generation around the world in 2018 (processed data from Wang et al. [4]).
Figure 2. Cradle-to-grave life-cycle assessment and input and output analysis of aggregate production.
Figure 2. Cradle-to-grave life-cycle assessment and input and output analysis of aggregate production.
Table 1. Physical properties of RAs and NA, according to Makul et al. [27]. Water Absorption (WA) and Workability: High WA due to high porosity directly affects the concrete’s properties. Additional water is required in the concrete in order to match the desired workability. According to research [27-30], the increase in WA recycled aggregate concrete (RAC) in correlation to natural aggregate concrete (NAC) is up to 40% for a replacement ratio (RR) of 50%. Wang et al. [4] states that according to research [31-34], the consistency of fresh RAC had a lower slump value than NAC, due to RAs’ higher WA and the rougher surfaces and irregular shapes.
Table 1. Physical properties of RAs and NA, according to Makul et al. [27]. Water Absorption (WA) and Workability: High WA due to high porosity directly affects the concrete’s properties. Additional water is required in the concrete in order to match the desired workability. According to research [27-30], the increase in WA recycled aggregate concrete (RAC) in correlation to natural aggregate concrete (NAC) is up to 40% for a replacement ratio (RR) of 50%. Wang et al. [4] states that according to research [31-34], the consistency of fresh RAC had a lower slump value than NAC, due to RAs’ higher WA and the rougher surfaces and irregular shapes.
Figure 3. (a) Composition of CDW (processed data from [22]). (b) Typical composition of 8-16 mm RA from a recycling plant (processed data from [24)]).
Figure 3. (a) Composition of CDW (processed data from [22]). (b) Typical composition of 8-16 mm RA from a recycling plant (processed data from [24)]).
Mechanical Properties versus Replacement Ratio Correlation Figure 4. Plot of mechanical properties change with different RCA RR, and the sample size at each RR for (a) compression strength, (b) E-modulus, (c) flexural strength, and (d) splitting tensile strength (processed data from [4]). Compressive strength: Compressive strength of concrete decreases, as the RR of NA increases [4,23,26,27,29,31,32,46-57]. Figure 4. represents the findings of Wang et al. [4] in which the correlation between the mechanical properties and the RR of RAs is depicted. Up to a degree of 50% RR, RAs have no significant impact on the compressive strength of concrete [4,26,27,29,46-52,54,56].
Mechanical Properties versus Replacement Ratio Correlation Figure 4. Plot of mechanical properties change with different RCA RR, and the sample size at each RR for (a) compression strength, (b) E-modulus, (c) flexural strength, and (d) splitting tensile strength (processed data from [4]). Compressive strength: Compressive strength of concrete decreases, as the RR of NA increases [4,23,26,27,29,31,32,46-57]. Figure 4. represents the findings of Wang et al. [4] in which the correlation between the mechanical properties and the RR of RAs is depicted. Up to a degree of 50% RR, RAs have no significant impact on the compressive strength of concrete [4,26,27,29,46-52,54,56].
Table 3. Calculation of Recycled Aggregates CO> footprint. 3.3. Combined Approach
Table 3. Calculation of Recycled Aggregates CO> footprint. 3.3. Combined Approach
Table 4. Comparison of RAC properties and replacement ratio.
Table 4. Comparison of RAC properties and replacement ratio.
Table 5. Summarized data on NA and RA production emissions. One tone of NA and RA produces 3.067 and 1.854 Kg of CO2 emissions, respectively, which stands for a 39.57% reduction in CO? total emissions (Table 5). Implementing the RR of 50% would result in a 19.78% reduction. To quantify the calculated values, i.e., the emissions already mentioned [58] could be at 11.7 MMT CO, e per year, hence a reduction of 2.9 MMT CO> emitted per year.
Table 5. Summarized data on NA and RA production emissions. One tone of NA and RA produces 3.067 and 1.854 Kg of CO2 emissions, respectively, which stands for a 39.57% reduction in CO? total emissions (Table 5). Implementing the RR of 50% would result in a 19.78% reduction. To quantify the calculated values, i.e., the emissions already mentioned [58] could be at 11.7 MMT CO, e per year, hence a reduction of 2.9 MMT CO> emitted per year.

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Dan Bompa

Geoscience Frontiers, 2021

This work examines the environmental and geochemical impact of recycled aggregate concrete production with properties representative for structural applications. The environmental influence of cement content, aggregate production, transportation, and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region. To obtain a detailed insight into the optimum life cycle parameters, a sensitivity study is carried out in which supplementary cementitious materials, different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered. The results show that carbon emissions were between 323 and 332 kgCO 2 e per cubic metre of cement only natural aggregate concrete. These values can be reduced by up to 17% by replacing 25% of the cement with fly ash. By contrast, carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50% and 100%, and transportation is not included in analysis. However, the concrete with 50% recycled aggregate presented lower increase, only 0.3% and 3.4% for normal and high strength concrete, respectively. In some cases, the relative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%, and case-specific transportation distances were considered. In absolute values, the concrete mixes with 100% recycled aggregates and 25% fly ash had lower carbon emissions than concrete with cement and natural aggregates only. Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short (15-25 km) and the cement replacement by fly ash is equal or higher than 25%, considering that the mechanical properties are adequate for practical application. The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete, recommending them as an alternative to achieving global sustainability standards in construction.

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Use of recycled aggregates for low carbon and cost effective concrete construction
Professor Mukesh Limbachiya

Journal of Cleaner Production, 2018

Reducing the carbon footprint of activities and a more prudent use of natural resources require for concrete production is a significant concern on the grounds of environmental and economical sustainability. It is widely reported that the concrete industry contributes around 8% to total global carbon dioxide (CO 2 ) emissions whereas cement utilization contributes approximately 90% of these emissions. Moreover, natural resources are becoming scarce and the world has become environmentally conscious. Against this background, reported work carried out to assess BS EN 197-1 cement concretes made with natural and partially substituted recycled aggregates and thus their suitability for use in low carbon cost effective concrete construction. In that respect, supplementary cementitious materials (SCMs) additive cements were selected to reduce the potential carbon footprint and establish fresh and hardened properties of natural aggregate concrete (NAC) mixes for equivalent 28-day compressive cube strengths of 40 and 50 N/mm 2 . Then, a further investigation was carried out to assess the potential embodied CO 2 (ECO 2 ) emissions and cost analysis and performance of partially substituted recycled aggregates (coarse recycled aggregate (RA) and recycled glass sand (RGS) with proportions of 25% and 15% respectively by mass replacement). Results showed that SCMs incorporated NAC mixes has a potential to reduce ECO 2 emissions and cost of concrete whilst partially substituted recycled aggregate concrete (RAC) mixes provided comparable ECO 2 emissions but slightly increased cost for equal design strength. The loss of

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Recycled Concrete Aggregates: A Promising and Sustainable Option for the Construction Industry
Feti Selmani

Journal of Human, Earth, and Future

The recycling of locally collected concrete waste is being promoted toward reducing the carbon footprint. In the preparation of concrete, recycled concrete aggregates (RCA) are encouraged instead of natural aggregates (NA), as they can help reduce the consumption of virgin materials, the extraction and transportation of which can be costly and environmentally damaging. In this context, we conducted an experimental study on various concrete mixes to evaluate the effect of using RCA instead of NA on the physical and mechanical properties of fresh and hardened concrete. The main novelty of our study lies in meeting one of the principles of circular economy, i.e., reducing the carbon footprint, by recycling concrete waste collected locally. We prepared and investigated test specimens containing 0%, 20%, 40%, and 60% of fine and coarse recycled concrete aggregates. Results for fresh concrete were determined for temperature, consistency, air content, and density, while on the other side, ...

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Some Remarks towards a Better Understanding of the Use of Concrete Recycled Aggregate: A Review
Anna G

Sustainability, 2021

Research on recycled concrete aggregates (RCAs) has been progressively advanced. Beyond replacing natural aggregates with RCA, discussions have been held on the effect of the parent concrete and repeatedly recycled aggregate concrete. Although it has been reported that RCA can be technically used for structural concrete, due to several other factors, RCA is mainly used for sub-bases. Therefore, identifying these factors is the key to promoting the use of RCA. Therefore, this review study first briefly summarizes the physical and chemical characteristics of RCA compared to natural aggregate, and reviews the effects of parent concrete and repeatedly recycled aggregate on next generation concrete. This study also briefly discusses the RCA standards of various countries and the factors that hinder the widespread use of RCA. The results show that there is a correlation in properties between parent concrete and the next generation concrete, and the properties of concrete decrease when RCA...

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A review of recycled aggregate in concrete applications (2000–2017)
Mahfooz Soomro

Construction and Building Materials, 2018

The paper reviews the production and utilisation of recycled aggregate in concrete. Critically analysed the globally published data on recycled aggregate standards. This review may help to alleviate the concerns of consumers. This paper can encourage and further promote the use of recycled aggregate.

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