A Roadmap for Production of Cement and Concrete with Low-CO2 Emissions

Abstract

This review will show that low-CO2 cements can be produced to give superior durability, based on a sound understanding of their microstructure and how it impacts macro-engineering properties. For example, it is essential that aluminium is available in calcium-rich alkali-activated systems to offset the depolymerisation effect of alkali cations on C-(N)-A-S-H gel. The upper limit on alkali cation incorporation into a gel greatly affects mix design and source material selection. A high substitution of cement clinker in low-CO2 cements may result in a reduction of pH buffering capacity, hence susceptibility to carbonation and corrosion of steel reinforcement. With careful mix design, a more refined pore structure and associated lower permeability can still give a highly durable concrete. It is essential to expand thermodynamic databases for current and prospective cementitious materials so that concrete performance and durability can be predicted when using low-CO2 binders. Cationic copolymer and amphoteric plasticisers, when available commercially, will enhance the development of alkali-activated materials. The development of supersonic shockwave reactors will enable the conversion of a wide range of virgin and secondary source materials into cementitious materials, replacing blast furnace slag and coal fly ash that have dwindling supply. A major obstacle to the commercial adoption of low-CO2 concrete is the prescriptive nature of existing standards and design codes, so there is an urgent need to shift towards performance-based standards. The roadmap presented here is not an extension of current cement practice, but a new way of integrating fundamental research, equipment innovation, and commercial opportunity.

Predicting CaO-(MgO)-Al2O3-SiO2 glass reactivity in alkaline environments from force field molecular dynamics simulations

“…Calcium is also important when it comes to the atomic structure, transport properties and longterm durability of the precipitated binder gel in AAMs [1,19]. At low Ca content (i.e., class F fly ash and metakaolin), the alkali activation reaction results in a three-dimensional alkali-aluminosilicate-hydrate gel (N-A-S-H gel if sodium is the alkali) with predominately Q 4 silicate units (Q n denotes n bridging oxygens) [1,2].…”

Achieving net zero greenhouse gas emissions in the cement industry via value chain mitigation strategies

“…23 As a result, interventions at the cement manufacturing stage, such as using alternative fuels or more efficient equipment, are those that are commonly presented in roadmaps to meeting climate emissions goals. 6,[24][25][26] However, the availability of mature technologies, established supply chains, high sunken costs in long-lived production facilities, long infrastructure lifetimes, and difficulty in attracting capital investments because of relatively low profit margins all make innovation in production difficult, particularly for smaller, less established players. 27 As an archetype, a cement plant can be viable for decades producing 5 to 10 tons of cement hourly, utilizing a kiln that is up to 100 m long and 7 m wide, with a technology that has changed little in the last century.…”

Cement substitution with secondary materials can reduce annual global CO2 emissions by up to 1.3 gigatons

“…However, substitution in the binder (including cement and its constituents) (Fig. 1 ) is especially important since: (a) most of the environmental impact in the CMs cycle arises from clinker production 10 ; (b) it provides many opportunities for environmentally, technically, and economically beneficial treatment of industrial by-products 11 ; and (c) extensive substitution of cement with non-cementitious materials such as steel, bricks, timber, etc., is unlikely in the foreseeable future given the huge global scale needed. For instance, steel and bricks have higher greenhouse gas emissions per unit mass than concrete 12 , 13 while for timber, a massive expansion of production 3 is needed to achieve comparable substitution rates of timber for concrete 14 to those for clinker substitution in cement (~25 mass% 15 ).…”