Gaseous Carbon Waste Streams Utilization Status and Research Needs (2019) / Chapter Skim
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3 Mineral Carbonation to Produce Construction Materials
3 Mineral Carbonation to Produce Construction Materials
Pages 39-62
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Mineral carbonation offers an attractive route to CO2 utilization because (1) solid carbonates, the main products of mineral carbonation reactions, are already used in construction materials markets; (2)
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• Ca- and Mg-bearing rocks • Enriched (>50% CO2) Pret reat t& m Step ent Ca, Mg Hea sure s s Pre carbonates Aggregate Binder Construction Materials FIGURE 3-1 The process of mineral carbonation brings alkaline reactants into contact with dilute or enriched CO2 and results in the production of carbonate mineral aggregates, binding agents, and mixtures of the two that can be readily used as construction materials.
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Mineral carbonation can be used to make both aggregates and binding agents, which could potentially displace natural and existing synthetic sources of these important components of common construction materials. Aggregates Mineral aggregates, which range in size from micrometers to centimeters, are granular materials that form the dominant content of a concrete.
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From page 42... ...
and from fuel burning to provide the heat required to drive the formation of clinker phases in the kiln, a foundational step of OPC production. While the construction and cement sector has significantly reduced the CO2 impact of concrete production by improving kiln thermal efficiencies and combining cementitious materials such as fly ash and slags with OPC in the binder fraction (Snellings, 2016)
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This is significant as the ease of controlling the rheology of such systems makes them potentially better suited for advanced (e.g., additive) manufacturing of structural components which feature superior strength-to-weight ratio, optimized topology, and complex geometries that could not be fabricated using existing casting or molding-based techniques.
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Expectedly, these pathways result in different levels of carbon dioxide uptake. For example, carbon dioxide injection into fresh concrete results in uptake that is limited by the overall rate of carbon dioxide reaction with calcium and magnesium, which in turn may be limited by the solubility of carbon dioxide in alkaline aqueous solution (i.e., ≤ 0.01 g CO2 per gram of cementitious components)
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. Hydrated lime mortars take up atmospheric CO2 at ambient conditions over long periods of exposure, resulting in the formation of calcium carbonate.
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wastes such as fly ash, slags, mine tailings, cement kiln dust, and air pollution control residues constitute the by-products of coal combustion, metal processing and mining, OPC production, and waste incineration, respectively. Such residues span a diversity of compositions as a function of the (1)
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From page 47... ...
These uptakes suggest global carbon dioxide utilization levels ranging between 0.2 billion tons for fly ash10 and 2.2 billion tons for portlandite,11 if sufficient quantities of these materials were available. Since carbon dioxide mineralization resulting in cementation is expected to be achieved using a diversity of alkaline precursors, with a range of carbon dioxide uptake capacities, a rough estimate of approximately 1 billion tons of carbon dioxide on an annual basis is reasonable.
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Market Considerations Construction materials including OPC, concrete, and mineral aggregates constitute the largest material flows in the world, second only to water. Each year, nearly 30 billion tons of concrete (World Business Council, 2009)
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This localization and P fragmentation implies that if mineral carbonation is to be used to produce construction materials that can replace existing materials, (1) CO2 will need to be consumed in many discrete locations to produce a range of materials and products, and (2)
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The injected CO2 reacts with either unreacted Ca, liberated from the dissolution of OPC or from OPC replacement materials such as slag or fly ash. The reaction products are formed in situ, then blended with the binder, thereby forming carbon ate compounds that contribute to increased and somewhat accelerated strength gain as compared with traditional concrete.
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While these efforts are in the early stage, they highlight the potential for CO2 utilization in the construction materials markets. However, the scalability and market viability of these approaches are affected by a diversity of factors, including (1)
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but inhibits carbonation when TABLE 3-1 Summary of key chemical and physical barriers associated with selected mineral carbonation inputs. Input Key Barriers Mature OPC-based concrete At ambient conditions under mass transfer (diffusion)
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While this is indeed less CO2 intensive than the traditional pathway of OPC production, the development of truly CO2-neutral or -negative pathways requires the development of new scalable low-temperature or hydrothermal routes for producing alkaline precursors, such as from waste streams containing Ca and Mg. Second, because the solubility of CaCO3 diminishes with increasing pH and CO2's dissolution in water induces acidity (by the formation of carbonic acid, in equilibrium with dissolved CO2, pKa = 6.35)
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. Broadly, in light of the low profit margins of the commoditized construction materials sector, it appears prerequisite to maximize the use of dilute CO2 streams.
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While this argument is logical for the vast majority of applications in construction, its application in the context of OPC-based products may differ. This is because the construction sector has gained empirical confidence in the use of OPC and traditional concrete as construction materials, and construction industry standards are notoriously slow to change (see Chapter 9)
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Priority research areas include controlling carbonation reactions, process design, accelerating carbonation and crystal growth, green synthesis routes for alkaline reactants, structure- property relationships, analytical and characterization tools, and construction methodologies. Controlling Carbonation Reactions Research is needed to understand the fundamental chemical features that control the relative rates of carbonation and hydration.
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Finding 3-2 The engineering properties, performance, and long-term chemical durability of mineral carbonation–based construction materials need to be better established for such materials to gain acceptance as substitutes for today's base materials. Finding 3-3 The purity, pressure, and temperature of CO2 sources affect the suitability of a given CO2 waste stream for a given mineral carbonation pathway.
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Recommendation 3-2 Researchers should integrate mineral carbonation processes with existing carbon dioxide capture technologies. Recommendation 3-3 Researchers should continue to develop additives for enhanced carbon dioxide solubility or structure-directing agents which will help accelerate carbonation and crystal growth.
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2016. Carbonation behavior of hydraulic and non-hydraulic calcium silicates: P otential of utilizing low-lime calcium silicates in cement-based materials.
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Case Studies in Construction Materials 6:147-161. Ricci, M., W
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2018. Clinkering-free cementation by fly ash carbonation.
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