The use of supplementary cementitious materials (SCMs) is a widely used and effec-tive way to significantly reduce the CO2 emissions caused by the production of cement and concrete. However, this reduction in CO2 emissions is becoming increasingly crit-ical since most common SCMs are becoming scarce already or are expected to in the near future. This is because materials, such as fly ash or ground granulated blast fur-nace slag, are by-products of industrial processes that are about to vanish from the European market. In order to meet the targets, set by the EU to achieve carbon neutral-ity by 2050, the clinker factor in cement and concrete used in the future needs to be further reduced. Hence, alternative novel SCMs need to be found that are available in sufficient quality and quantity. However, the search for appropriate materials and re-sources is time-consuming and costly.
One way of facilitating this search is to identify promising materials more easily and reliably. For this, we need a better understanding of the parameters that inherently de-termine the reactivity (degree of reaction as well as reaction kinetics) of such materials. Most SCMs are amorphous Si-rich materials. While there is an understanding of vari-ous classes of reactive materials, reaching from (latent) hydraulic to pozzolanic reactiv-ities depending on their Ca/Si ratio, there is no clear distinction between these reac-tions. In addition, some novel SCMs, such as calcined clays, deliver a significant amount of aluminium into the system. This alters the traditional definition of the poz-zolanic reaction and puts more focus on the formation of AFm and AFt phases, as well as changes in the composition of the C-(A-)S-H phase caused by the reaction of Al-rich SCMs. Novel SCMs resulting from (carbonated) recycled concrete paste might even further increase the level of variety among potential cementitious materials.
When trying to explain the reactivity of a material, physical as well as chemical and mineralogical material characteristics play a role. The chemical composition, the struc-ture of the amorphous phase, the specific surface area, the level of surface defects, etc., all contribute to the final reactivity of an SCM. There is a need to systemically de-termine and quantify the various effects on the reactivity of materials to be used as SCMs. Such efforts are especially important, since it is unlikely that one or only a small number of novel materials will replace the existing SCMs, but we will rather have to deal with a significant number of various novel materials. This study provides an overview of the existing knowledge from literature to identify knowledge gaps and po-tential directions for future investigations. Overall, the aim is to aid the search for novel SCMs that are to be used in future n-ary composite cements.
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The use of supplementary cementitious materials (SCMs) is a widely used and effec-tive way to significantly reduce the CO2 emissions caused by the production of cement and concrete. However, this reduction in CO2 emissions is becoming increasingly crit-ical since most common SCMs are becoming scarce already or are expected to in the near future. This is because materials, such as fly ash or ground granulated blast fur-nace slag, are by-products of industrial processes that are about to vanish fr...
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