Sustainability-based decision support framework for choosing concrete mixture proportions
TL;DR: In this article, a decision support framework is proposed, along with two objective indices, for the selection of concrete mixture proportions based on sustainability criteria, which combine energy demand and long-term strength as energy intensity, and carbon emissions and durability parameters as A-indices.
Abstract: A framework is proposed, along with two objective indices, for the selection of concrete mixture proportions based on sustainability criteria. The indices combine energy demand and long-term strength as energy intensity, and carbon emissions and durability parameters as A-indices, which represent the apathy toward these essential features of sustainability. The decision support framework is demonstrated by considering a set of 30 concretes with different binders, including ordinary portland cement (OPC), fly ash, slag and limestone calcined clay cement (LC3). In addition to the experimental data on compressive strength, chloride diffusion and carbonation, life cycle assessment has been performed for the concretes considering typical situations in South India. The most sustainable of the concretes studied here, for service life limited by chloride ingress, are those with LC3, OPC replaced by 50% slag, and ternary blends with 20% each of slag and fly ash. In the case of applications where carbonation is critical, the appropriate concretes are those with OPC replaced by 15–30% slag or 15% fly ash, or with ternary blends having 20% slag and 20% Class F fly ash.
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TL;DR: A review of the literature available on the subject of the recently developed limestone calcined clay cement (LC3) can be found in this article, where an introduction to the background leading to the development of LC3 is discussed.
Abstract: This article reviews the rapidly developing state-of-the-art literature available on the subject of the recently developed limestone calcined clay cement (LC3). An introduction to the background leading to the development of LC3 is first discussed. The chemistry of LC3 hydration and its production are detailed. The influence of the properties of the raw materials and production conditions are discussed. The mixture design of concrete using LC3 and the mechanical and durability properties of LC3 cement and concrete are then compared with other cements. At the end the economic and environmental aspects of the production and use of LC3 are discussed. The paper ends with suggestions on subjects on which further research is required.
114 citations
TL;DR: In this article, a prospective approach to conduct sustainability assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing.
Abstract: This paper explores the sustainability aspects of binders used in concrete 3D concrete printing. Firstly, a prospective approach to conduct sustainability-assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing. The potential of the material production phase is emphasized to enhance the sustainability potential of 3DCP by reducing the embodied impacts. The literature on the different binder systems used for producing 3D printable mixtures is reviewed. This review includes binders based on portland cement and supplementary cementing materials (SCMs) such as fly ash, silica-fume and slag. Also, alternative binders such as geopolymer, calcium sulfo-aluminate cement (CSA), limestone calcined clay cement (LC3) and reactive magnesium oxide systems are explored. Finally, sustainability assessment by quantifying the environmental impacts in terms of energy consumed and CO2 emissions of mixtures is illustrated with different binder systems. This paper underlines the effect of using SCMs and alternative binder systems for improving the sustainability of 3D printed structures.
78 citations
TL;DR: In this paper, the macro properties (residual compressive strength), meso properties (mesoscopic images), and micro properties (reaction products and pore structures) of paste specimens with various limestone and calcined clay contents at elevated temperatures (20, 300, 550, and 900 ǫ) are experimentally investigated.
Abstract: In this study, the macro properties (residual compressive strength), meso properties (mesoscopic images), and micro properties (reaction products and pore structures) of paste specimens with various limestone and calcined clay contents at elevated temperatures (20, 300, 550, and 900 °C) are experimentally investigated. According to the experimental results, (1) the strengths of all samples increase at 300 °C, while those of the LC3 ternary blended pastes increase more significantly because of the formation of katoite and the further hydration of binders. After the treatments at 550 and 900 °C, the reduction in the strengths of the LC3 samples is greater than that of the plain paste. (2) With further increasing temperature, all samples generate more meso cracks. (3) At 900 °C, a large gehlenite crystalline phase is formed in the samples with calcined clay. In summary, the microscopic explanation for the macroscopic and mesoscopic properties of LC3 paste at elevated temperature is investigated.
53 citations
TL;DR: In this article, the authors evaluated the environmental impacts of workable wood bio-concretes (WBC) composed of wood shavings, Portland cement (CEM), and two Supplementary Cementitious Materials (SCMs): metakaolin (MK) and fly ash (FA).
Abstract: This study evaluates the environmental impacts of workable wood bio-concretes (WBC). The WBC is composed of wood shavings, Portland cement (CEM), and two Supplementary Cementitious Materials (SCMs): metakaolin (MK) and fly ash (FA). A Life Cycle Assessment (LCA) was performed on seven WBC mixtures containing different contents of SCMs. When the compressive strength was used as a functional unit, the mixture containing 40% MK and 10% FA achieved the lowest values in most impact categories. We concluded that the CEM replacement by SCMs is a promising strategy to reduce the environmental impacts of the WBC, especially the climate change impact.
34 citations
TL;DR: A critical review of the state-of-the-art 3D printing geopolymers from the perspectives of production process, printability requirement, mix design, early-age material properties and sustainability, with a special focus on the effects of different factors such as matrix composition, reinforcement type, curing regime and printing configuration on the fresh and hardened properties of 3D printed geo-mers as discussed by the authors .
Abstract: Geopolymers have been considered as a promising alternative to cementitious materials for 3D printing to enhance sustainability of the construction industry. This paper presents a critical review of the state-of-the-art of 3D printing geopolymers from the perspectives of production process, printability requirement, mix design, early-age material properties and sustainability, with a special focus on the effects of different factors such as matrix composition, reinforcement type, curing regime and printing configuration on the fresh and hardened properties of 3D printed geopolymers. The relationship between key fresh properties and printability of geopolymers is discussed, based on which the potential optimal mix proportions are obtained, containing the blended precursors of fly ash, ground granulated blast-furnace slag and silica fume, liquid or solid activator, river sand with a maximum size of 2 mm, thixotropic additives (e.g., nano clay), and retarder (e.g., sucrose). This paper aims to summarise the recent advances in the development of 3D printing techniques suitable for geopolymers and geopolymers feasible for 3D printing, and to identify the knowledge gap, remaining challenges, and opportunities for future research.
31 citations
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5,509 citations
TL;DR: In this article, the authors present a new analysis of global process emissions from cement production and show that global process CO2 emissions in 2016 were 1.45±0.20 metric tonne CO2, equivalent to about 4% of emissions from fossil fuels.
Abstract: . The global production of cement has grown very rapidly in recent years, and after fossil fuels and land-use change, it is the third-largest source of anthropogenic emissions of carbon dioxide. The required data for estimating emissions from global cement production are poor, and it has been recognised that some global estimates are significantly inflated. Here we assemble a large variety of available datasets and prioritise official data and emission factors, including estimates submitted to the UNFCCC plus new estimates for China and India, to present a new analysis of global process emissions from cement production. We show that global process emissions in 2016 were 1.45±0.20 Gt CO2, equivalent to about 4 % of emissions from fossil fuels. Cumulative emissions from 1928 to 2016 were 39.3±2.4 Gt CO2, 66 % of which have occurred since 1990. Emissions in 2015 were 30 % lower than those recently reported by the Global Carbon Project. The data associated with this article can be found at https://doi.org/10.5281/zenodo.831455 .
811 citations
TL;DR: In this paper, the authors investigated the available literature on every step in the LCA of concrete and found that the adopted functional unit for which the environmental impact is calculated, influences the outcome significantly.
Abstract: With the current focus on sustainability, it is necessary to evaluate concrete’s environmental impact properly, especially when developing new ‘green’ concrete types. Therefore, we investigated the available literature on every step in the LCA of concrete. The adopted functional unit for which the environmental impact is calculated, influences the outcome significantly. When comparing different concrete compositions, this unit should incorporate differences in strength, durability and service life. Hence, a cradle-to-grave or modified cradle-to-gate approach is advised as system boundary. When using industrial by-products as cement replacing material in ‘green’ concrete, an economical allocation of impacts is recommended. Inventory data on energy use, CO2, PM10, SOx and NOx emissions were collected and assigned to the impact categories of the problem oriented CML 2002 and the damage oriented Eco-indicator 99 impact method. Compared to Portland cement, the impact of blast-furnace slag and fly ash is about an order of a magnitude lower.
531 citations
Journal Article•
TL;DR: In this paper, it was shown that for every 1000kg of cement produced just over 500kg of carbon dioxide arises from the chemical reaction and a further 250400kg from the energy use.
Abstract: Almost all concrete in current use contains Portland Cement. This cement is produced in a process which involves heating the raw materials to 1400C which makes them produce large quantities of carbon dioxide as a product of a chemical reaction. For every 1000kg of cement produced just over 500kg of carbon dioxide arises from the chemical reaction and a further 250400kg from the energy use. These quantities cannot be reduced.
496 citations
TL;DR: In this article, the authors proposed indicators for measuring cement use efficiency, and presented a benchmark based on literature data and discusses potential gains in efficiency, including an increase in the efficiency of cement use.
Abstract: At present, the cement industry generates approximately 5% of the world’s anthropogenic CO2 emissions. This share is expected to increase since demand for cement based products is forecast to multiply by a factor of 2.5 within the next 40 years and the traditional strategies to mitigate emissions, focused on the production of cement, will not be capable of compensating such growth. Therefore, additional mitigation strategies are needed, including an increase in the efficiency of cement use. This paper proposes indicators for measuring cement use efficiency, presents a benchmark based on literature data and discusses potential gains in efficiency. The binder intensity (bi) index measures the amount of binder (kg m−3) necessary to deliver 1 MPa of mechanical strength, and consequently express the efficiency of using binder materials. The CO2 intensity index (ci) allows estimating the global warming potential of concrete formulations. Research benchmarks show that bi ∼5 kg m−3 MPa−1 are feasible and have already been achieved for concretes >50 MPa. However, concretes with lower compressive strengths have binder intensities varying between 10 and 20 kg m−3 MPa−1. These values can be a result of the minimum cement content established in many standards and reveal a significant potential for performance gains. In addition, combinations of low bi and ci are shown to be feasible.
431 citations