Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry
TL;DR: The main conclusions of an analysis of low-CO2, eco-efficient cement-based materials, carried out by a multi-stakeholder working group initiated by the United Nations Environment Program Sustainable Building and Climate Initiative (UNEP-SBCI) are presented, based on the white papers published in this special issue as discussed by the authors.
Abstract: The main conclusions of an analysis of low-CO2, eco-efficient cement-based materials, carried out by a multi-stakeholder working group initiated by the United Nations Environment Program Sustainable Building and Climate Initiative (UNEP-SBCI) are presented, based on the white papers published in this special issue. We believe that Portland-based cement approaches will dominate in the near future due to economies of scale, levels of process optimisation, availability of raw materials and market confidence. Two product-based approaches can deliver substantial additional reductions in their global CO2 emissions, reducing the need for costly investment in carbon capture and storage (CCS) over the next 20–30 years: 1. Increased use of low-CO2 supplements (SCMs) as partial replacements for Portland cement clinker. 2. More efficient use of Portland cement clinker in mortars and concretes. However, other emerging technologies could also play an important role in emissions mitigation in the longer term, and thus merit further investigation.
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TL;DR: In this paper, a review of emerging supplementary cementitious materials (SCM) sources is presented, along with new developments in characterizing and qualifying SCMs for use and improved knowledge of SCM on long-term concrete performance and durability.
Abstract: Conventional supplementary cementitious materials (SCMs), such as blast furnace slags or fly ashes, have been used for many decades, and a large body of knowledge has been collected regarding their compositional make-up and their impacts on cement hydration and concrete properties. This accumulated empirical experience can provide a solid, confident base to go beyond the status quo and develop a new generation of low-clinker cements composed of new types and combinations of SCMs. The need for new sources of SCMs has never been greater, as supplies of traditional SCMs are becoming restricted, and the demand for SCMs to reduce CO2 emissions from concrete production is increasing. In this paper, recent research on emerging SCM sources is reviewed, along with new developments in characterizing and qualifying SCMs for use and improved knowledge of SCMs on long-term concrete performance and durability.
386 citations
Cites background from "Eco-efficient cements: Potential ec..."
...34 Furthermore, the demand for cement continues to increase, with demand projected to increase to over 35 6 Gt by 2050 [7]....
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...Building and Climate Initiative (UNEP-SBCI) [7] identified clinker substitution and concrete mixture 22 proportioning as the most favorable carbon reduction levers for the industry....
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...20 Indeed, a recent investigation commissioned by the United Nations Environmental Program Sustainable 21 Building and Climate Initiative (UNEP-SBCI) [7] identified clinker substitution and concrete mixture 22 proportioning as the most favorable carbon reduction levers for the industry....
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...increasing strength-to-mass ratios) and increasing longevity, thereby impacting 28 associated emissions over ; IラミIヴWデW ゲデヴ┌Iデ┌ヴWげゲ lifetime [5,7]....
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22 Sep 2020
TL;DR: In this article, a review of the available solutions that can be implemented within the next decade and beyond to reduce greenhouse gas emissions from cement and concrete production is presented, which reveals credible pathways for sustainable concrete use that balance societal needs, environmental requirements and technical feasibility.
Abstract: The use of cement and concrete, among the most widely used man-made materials, is under scrutiny. Owing to their large-scale use, production of cement and concrete results in substantial emission of greenhouse gases and places strain on the availability of natural resources, such as water. Projected urbanization over the next 50–100 years therefore indicates that the demand for cement and concrete will continue to increase, necessitating strategies to limit their environmental impact. In this Review, we shed light on the available solutions that can be implemented within the next decade and beyond to reduce greenhouse gas emissions from cement and concrete production. As the construction sector has proven to be very slow-moving and risk-averse, we focus on minor improvements that can be achieved across the value chain, such as the use of supplementary cementitious materials and optimizing the clinker content of cement. Critically, the combined effect of these marginal gains can have an important impact on reducing greenhouse gas emissions by up to 50% if all stakeholders are engaged. In doing so, we reveal credible pathways for sustainable concrete use that balance societal needs, environmental requirements and technical feasibility. Concrete is one of the most widely used man-made materials and is critical for the ongoing urbanization of the global population. However, owing to its widespread use, concrete can have a negative impact on the environment. This Review provides medium-term and long-term solutions to address the environmental concerns surrounding concrete production.
354 citations
Simon Fraser University1, Northwestern University2, World Resources Institute3, Lawrence Berkeley National Laboratory4, American Council for an Energy-Efficient Economy5, Yale University6, Bosch7, University of California, Davis8, Asian Institute of Technology9, Imperial College London10, Rocky Mountain Institute11, Royal Dutch Shell12, University of Maryland, College Park13, The Energy and Resources Institute14, PricewaterhouseCoopers15
TL;DR: In this paper, the authors present technical and policy interventions, both on the supply side and on the demand side, that can achieve net zero industrial emissions in the required timeframe, and identify measures that, employed together, can achieve the goal.
Abstract: Fully decarbonizing global industry is essential to achieving climate stabilization, and reaching net zero greenhouse gas emissions by 2050–2070 is necessary to limit global warming to 2 °C. This paper assembles and evaluates technical and policy interventions, both on the supply side and on the demand side. It identifies measures that, employed together, can achieve net zero industrial emissions in the required timeframe. Key supply-side technologies include energy efficiency (especially at the system level), carbon capture, electrification, and zero-carbon hydrogen as a heat source and chemical feedstock. There are also promising technologies specific to each of the three top-emitting industries: cement, iron & steel, and chemicals & plastics. These include cement admixtures and alternative chemistries, several technological routes for zero-carbon steelmaking, and novel chemical catalysts and separation technologies. Crucial demand-side approaches include material-efficient design, reductions in material waste, substituting low-carbon for high-carbon materials, and circular economy interventions (such as improving product longevity, reusability, ease of refurbishment, and recyclability). Strategic, well-designed policy can accelerate innovation and provide incentives for technology deployment. High-value policies include carbon pricing with border adjustments or other price signals; robust government support for research, development, and deployment; and energy efficiency or emissions standards. These core policies should be supported by labeling and government procurement of low-carbon products, data collection and disclosure requirements, and recycling incentives. In implementing these policies, care must be taken to ensure a just transition for displaced workers and affected communities. Similarly, decarbonization must complement the human and economic development of low- and middle-income countries.
339 citations
Cites background from "Eco-efficient cements: Potential ec..."
...The UN Environment Program estimates that an appropriate combination of SCMs could substitute for 40% of clinker [229]....
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TL;DR: In this article, the rapidly developing state-of-the-art of fiber-reinforced geopolymer composites is discussed, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states.
Abstract: There is a burgeoning interest in the development of geopolymers as sustainable construction materials and incombustible inorganic polymers. However, geopolymers show quasi-brittle behavior. To overcome this weakness, hundreds of research have been focused on development, characterization, and implementation of fiber-reinforced geopolymers for a wide range of applications. This paper discusses the rapidly developing state-of-the-art of fiber-reinforced geopolymer composites, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states, mechanical properties, toughening mechanisms, thermal characteristics, and environmental durability. It is intended to build a strong conceptual and technical background for what is currently understood on fiber-reinforced geopolymers by tying the subject together with knowns for other similar cementitious composites rather than a historical report of literature.
289 citations
Cites background from "Eco-efficient cements: Potential ec..."
...This rate is even higher in developing counties such as China with a production of about half of the global cement in 2019 [1]....
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TL;DR: In this paper, the influence of the calcined kaolinite content of calcined clays on the hydration of Limestone Calcined Clay Cements containing 50% of clinker (LC3-50) was investigated.
Abstract: This study presents the influence of the calcined kaolinite content of calcined clays on the hydration of Limestone Calcined Clay Cements containing 50% of clinker (LC3-50). Above a calcined kaolinite content of 65% in calcined clay, further reaction of clinker is inhibited from 3 days onwards. Detail investigation indicates that this slowing down of clinker hydration is related to a significant refinement of pore connectivity. A limiting critical pore entry radius of 3–5 nm is reached, from which the porosity does not get further refined. The higher the calcined kaolinite content, the faster this refinement limit is reached. The formation of carboaluminate hydrates is also limited after reaching this refinement limit. As a consequence, the on-going reaction of metakaolin impacts C-A-S-H, mainly affecting gel porosity, which is not well characterized by MIP.
282 citations
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TL;DR: As part of its commitment to openness and transparency, the IPCC releases drafts that have been submitted for formal expert and/or government review, review comments on these drafts, and author responses to these comments after publication of the associated IPCC Report or Technical Paper.
Abstract: As part of its commitment to openness and transparency, the IPCC releases drafts that have been submitted for formal expert and/or government review, review comments on these drafts, and author responses to these comments after publication of the associated IPCC Report or Technical Paper. During the multi‐stage review process, expert reviewers and governments are invited to comment on the accuracy and completeness of the scientific/technical/socioeconomic content and the overall balance of the drafts. Therefore, review comments and author responses should be considered within the context of the final report. Drafts, review comments, and author responses are pre‐decisional materials that are confidential until publication of the final Report or Technical Paper; they are not the results of the assessment and may not be cited, quoted, or distributed as such. Only the approved, adopted, and accepted Reports or Technical Papers may be cited or quoted as the results of the assessment.
2,095 citations
"Eco-efficient cements: Potential ec..." refers background in this paper
...Due to the enormous growth in cement demand in the developing world, the share of cement production in total anthropogenic CO2 emissions has been rising steadily and is now estimated by some sources to be around 10% [13], or about 6% of the total anthropogenic greenhouse gasses (GHG)[15]....
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...The 450ppm IPCC mitigating scenario (IEA blue scenario) requires a 50% reduction in anthropogenic CO2 emissions by 2050 [15]....
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TL;DR: In this paper, the influence of the presence of limestone on the hydration of Portland cement was investigated, and it was shown that the stabilisation of monocarbonate in the absence of limestone indirectly stabilised ettringite, leading to a corresponding increase of the total volume of the hydrate phase and a decrease of porosity.
Abstract: The influence of the presence of limestone on the hydration of Portland cement was investigated. Blending of Portland cement with limestone was found to influence the hydrate assemblage of the hydrated cement. Thermodynamic calculations as well as experimental observations indicated that in the presence of limestone, monocarbonate instead of monosulfate was stable. Thermodynamic modelling showed that the stabilisation of monocarbonate in the presence of limestone indirectly stabilised ettringite leading to a corresponding increase of the total volume of the hydrate phase and a decrease of porosity. The measured difference in porosity between the "limestone-free" cement, which contained less than 0.3% CO2, and a cement containing 4% limestone, however, was much smaller than calculated. Coupling of thermodynamic modelling with a set of kinetic equations which described the dissolution of the clinker, predicted quantitatively the amount of hydrates. The quantities of ettringite, portlandite and amorphous phase as determined by TGA and XRD agreed well with the calculated amounts of these phases after different periods of time. The findings in this paper show that changes in the bulk composition of hydrating cements can be followed by coupled thermodynamic models. Comparison between experimental and modelled data helps to understand in more detail the dominating processes during cement hydration.
1,089 citations
TL;DR: In this paper, the authors present an assessment of the global use of materials since the beginning of the 20th century based on the conceptual and methodological principles of material flow accounting (MFA).
Abstract: The growing industrial metabolism is a major driver of global environmental change. We present an assessment of the global use of materials since the beginning of the 20th century based on the conceptual and methodological principles of material flow accounting (MFA). On the grounds of published statistical data, data compilations and estimation procedures for material flows not covered by international statistical sources, we compiled a quantitative estimate of annual global extraction of biomass, fossil energy carriers, metal ores, industrial minerals and construction minerals for the period 1900 to 2005. This period covers important phases of global industrialisation and economic growth. The paper analyses the observed changes in the overall size and composition of global material flows in relation to the global economy, population growth and primary energy consumption. We show that during the last century, global materials use increased 8-fold. Humanity currently uses almost 60 billion tons (Gt) of materials per year. In particular, the period after WWII was characterized by rapid physical growth, driven by both population and economic growth. Within this period there was a shift from the dominance of renewable biomass towards mineral materials. Materials use increased at a slower pace than the global economy, but faster than world population. As a consequence, material intensity (i.e. the amount of materials required per unit of GDP) declined, while materials use per capita doubled from 4.6 to 10.3 t/cap/yr. The main material groups show different trajectories. While biomass use hardly keeps up with population growth, the mineral fractions grow at a rapid pace. We show that increases in material productivity are mostly due to the slow growth of biomass use, while they are much less pronounced for the mineral fractions. So far there is no evidence that growth of global materials use is slowing down or might eventually decline and our results indicate that an increase in material productivity is a general feature of economic development.
944 citations
TL;DR: In this paper, the coupled substitution of metakaolin and limestone in Portland cement (PC) was investigated and the mechanical properties were studied in mortars and the microstructural development in pastes by X-ray diffraction, thermogravimetry analysis, mercury intrusion porosimetry and isothermal calorimetry.
Abstract: This study investigates the coupled substitution of metakaolin and limestone in Portland cement (PC). The mechanical properties were studied in mortars and the microstructural development in pastes by X-ray diffraction, thermogravimetry analysis, mercury intrusion porosimetry and isothermal calorimetry. We show that 45% of substitution by 30% of metakaolin and 15% of limestone gives better mechanical properties at 7 and 28 days than the 100% PC reference. Our results show that calcium carbonate reacts with alumina from the metakaolin, forming supplementary AFm phases and stabilizing ettringite. Using simple mass balance calculations derived from thermogravimetry results, we also present the thermodynamic simulation for the system, which agrees fairly well with the experimental observations. It is shown that gypsum addition should be carefully balanced when using calcined clays because it considerably influences the early age strength by controlling the very rapid reaction of aluminates.
763 citations
TL;DR: In this paper, it is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated cement pastes.
Abstract: Limestone, mainly consisting of calcite, is a permitted additive to Portland cements often up to a 5 wt.% limit. It is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated cement pastes. Calcite affects the mineralogical variant of the AFm phase(s). Calcite additions affect the amount of free calcium hydroxide as well as the balance between AFm and AFt phases, although C–S–H is unaffected in much of the range of compositions. Generic data are shown in graphical form to quantify these mineralogical changes as functions of cement composition and amount of added calcite. Calculations of the specific volume of solids as a function of calcite addition suggest that the space-filling ability of the paste is optimised when the calcite content is adjusted to maximise the AFt content. However, before the calculated data can be used uncritically, certain kinetic constraints on reactivity also need to be assessed. Progress towards the quantification of paste mineralogy suggests that (i) elucidation of the mineralogy of pastes, particularly blended cement pastes, is facilitated by using both theoretical and experimental approaches and (ii) that the ultimate goal, of calculating paste mineralogy from the bulk chemistry, is attainable.
708 citations
"Eco-efficient cements: Potential ec..." refers background in this paper
...Because a fraction of the limestone does react with available alumina to form carbo aluminate phases which contribute to strength and durability [25, 26], up to 10% limestone can be added without the negative effect of dilution on properties; lower levels of addition, typically around 5%, may even improve properties....
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...Limestone is usually regarded as a filler, though it is now clear [25, 26] that it can react with available alumina....
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