Assessing, Understanding and Unlocking Supplementary Cementitious Materials

Abstract

The partial replacement of Portland clinker by supplementary cementitious materials (SCM) is one of the most popular and effective measures to reduce both costs and CO2 emissions related to cement production. An estimated 800 Mt/y of blast furnace slags, fly ashes and other materials are currently being used as SCM, but still the cement industry accounts for 5-8% of global CO2 emissions. If no further actions are taken, by the year 2050 this share might even rise beyond 25%. There is thus a clear challenge as to how emissions will be kept at bay and sustainability targets set by international commitments and policy documents will be met. Part of the solution will be a further roll-out of blended cements in which SCMs constitute the main part of the binder to which activators such as Portland cement are added. Since supply concerns are being raised for conventional high-quality SCMs it is clear that new materials and beneficiation technologies will need to step in to achieve further progress. This paper presents opportunities and challenges for new SCMs and demonstrates how advances towards more powerful and reliable characterisation techniques help to better understand and exploit SCM reactivity.

Overview of clay as supplementary cementitious material

“…Current production of Portland cement clinker accounts for 5 to 8 % of the global CO 2 emissions [1]. Considering the constant growth of the building industry, if there are no actions taken, according to the worst case scenario, until 2050 the cement production could count for more than 25 % of the overall emissions [2]. For the production of 1 ton of cement clinker an average of 0.67 to 0.8 tonnes of CO 2 is produced (depending on the fuel type and blends) [3].…”

Toward electrochemical synthesis of cement—An electrolyzer-based process for decarbonating CaCO 3 while producing useful gas streams

“…Current efforts to reduce cement's carbon footprint include carbon capture from flue gases, use of alternative fuels, or development of supplementary cementitious materials (14,(18)(19)(20)(21). Currently, the flue gas from cement plants is too impure for economical carbon capture through amine scrubbing; use of alternative fuels (such as used tires) does not alleviate the primary emissions from CaCO 3 ; and use of supplementary materials in the concrete has limited impact on the carbon emissions from Portland cement and may simultaneously compromise the physical properties (14,(19)(20)(21). Another family of approaches uses the cement to capture and sequester more CO 2 , producing a carbonate-enriched cement or concrete product (22)(23)(24)(25).…”

Concrete with high-purity volcanic glass fine powder manufactured from pyroclastic deposit

“…Nevertheless, it has also been pointed out that the use of a natural pozzolan as a supplementary cementitious material can pose problems of low workability and slow strength development [3]. Also, in addition to the low performance as a natural SCM, its composition and physical properties are widely variable [4] and significantly scattered [5] when compared with industrial byproducts.…”