Transforming the Bond: From Gray to Green Cementing Solutions

Silica-rich fly ash, a byproduct of coal combustion in power plants, is currently the most widely used SCM. Fly ash is a key ingredient in cement and concrete manufacturing, but its dominance is dwindling as coal-fired power units are gradually shut down. Fly ash cannot be substituted with granulated blast furnace slag, which is typically used to lower the clinker content, because of the latter's characteristics and scarcity. Fly ash from biomass combustion, as well as natural (pumice, volcanic tuffs), and synthetic (metakaolin) pozzolans are also being taken into consideration by the construction sector.

Physical and chemical features of SCMs including calcareous fly ash, wood ash, and activated copper tailings are at the heart of the debate surrounding the prospect of expanding the spectrum of SCMs used in construction (performance strategy). By reducing the overall volume of open pores in the hardened cement paste and in the contact zone between the paste and aggregate grains, SCM application does alter the microstructure of cement and concrete. This boosts the efficiency of cement-based composites in various ways, including watertightness and resilience to harsh environments (caused by carbonation, chloride ions, sulphates, etc.).

The European Union's Diverse Raw Material Options

European countries are in the forefront of reduced-clinker cement production using supplemental cementitious resources(SCMs) from the Arctic to the Mediterranean. While consumers, with more options than ever, continue to prioritise sustainability, initiatives to enhance existing SCMs and build new ones have garnered government support and become a matter of substantial investment for other heavy sectors than cement. The choices made by Europe's cement manufacturers are charting a road for a future beyond CEM I. However, there is still a lot of unrealized potential in Europe.

In 2021 and Q1 of 2022, businesses promoted their newest reduced-CO2 cement lines extensively: Buzzi Unicem's CGreen in Germany and Italy, Holcim's EcoPlanet in six markets spanning Romania to Spain, Cementir Holdings' Futurecem in Denmark and Benelux, and Cemex's Vertua in Spain and several other countries. All of them use non-traditional materials, which allows them to have lower clinker factors. To be fair, this is only a repackaging of a practise that has been commonplace in Europe for decades.

Average yearly cement deliveries throughout Cembureau member nations have been greater than 75% of total cement deliveries since 2010. (all cement-producing EU member states, plus Norway, Serbia, Switzerland, Turkey, the UK and Ukraine). Distinct countries have different distributions of this statistic. Austria, Finland, Portugal, and Switzerland all use CEM II as their standard, with a high percentage of their deliveries being of this type. The majority of cement delivered in all four is Portland limestone cement (PLC). It has been essential in Switzerland's move to CEM II, which will account for 89% (3.72Mt) of cement deliveries out of a total 4.18Mt of cement shipped in 2021. The primary cement types produced there were CEM II/B-M (T-LL) Portland composite cement (1.38Mt, 33%), PLC (1.28Mt, 31%), and PLC (CEM II/A-LL PLC (888,000t, 21%).

CEM III blast furnace slag cement with a clinker factor of less than 65% is widely used in the Netherlands due to its sulphate resistance and its ability to prevent the corrosion of steel reinforcing in marine environments caused by chloride. In contrast, CEM I cement has been widely used in the UK for decades. In part, this is because local builders favour incorporating fly ash and ground granulated blast furnace slag (GGBFS) into their finished products during the mixing process. On the other hand, CEM II Portland fly ash cement accounted for 14% (1.43Mt) of the 10.2Mt of cement used in the UK that year.

An underutilised resource in British cement manufacture is limestone, according to the Mineral Products Association (MPA). With HeidelbergCement subsidiary Hanson Cement, it has requested revisions to National Application standards to allow the manufacture of Portland composite cement using fly ash and limestone or ground granulated blast furnace slag (GGBS) and limestone. According to the association's estimates, Portland composite cement might account for 30–40% of UK cement usage during the next decade. This shift has the potential to cut 7.8Mt/yr of CO2 emissions from the cement industry.

Historically, a large amount of GGBFS and bauxite residue from the metals industry have been used in cement manufacturing across Europe. Just the European Union's alumina output in 2021 resulted in 7Mt of bauxite residue, of which only 100,000t (1.4%) was recycled. Two efforts are under way to create novel alternative cementitious materials from bauxite residue: the ReActiv project, coordinated by the Holcim Innovation Center, and the REDMUD project, created by Titan Cement and others.

Cement manufacturers can get the most return on their money spent on acquiring these materials if they work together with other businesses to cut costs. German companies Heidelberg Cement and ThyssenKrupp are working on a project called Save CO2 that will produce slag from directly reduced iron ore in order to create new, enhanced latent hydraulic binders or alternative pozzolan from GGBFS (DRI). The Save CO2 group estimates that replacing clinker with GGBFS could cut annual CO2 emissions from cement manufacturing around the world by 200 million tonnes.

Meanwhile, in the mining industry, ThyssenKrupp and others are looking at bioleaching and cleaning mineral residue upcycling to recover a usable mineral fraction for cement manufacture from extractive waste at the Luikonlahti and Sotkamo mines in Finland and the Tara mine in Ireland. Mines create an extra 600Mt of sulphidic mining waste year, for a total of 28Bnt. This might allow cement companies complete access to this resource.

CemGreen, based in Denmark, manufactures the calcined clay supplemental cementitious ingredient CemShale and is creating a shale granule heat-treating technology called CemTower. Vertically incorporated into the preheaters, kilns, and coolers of a cement factory, this enables the processing of waste materials, in this case oil shale, without moving the operation from its current location.

Last but not least, the cement industry is looking into ways to recycle cement scraps. Through its CosmoCem initiative, Heidelberg Cement subsidiary CBR in Wallonia is looking into making alternative cement additives from readily available flows of local demolition, soil remediation, and industrial waste. In a similar vein, Heidelberg Cement's Greek operations aim to utilise mineralized fines from concrete recycling through the C2inCO2 project.

Using fine mixed granulate from building demolitions, ZND Portland composite cement (the third largest cement type in Switzerland) accounts for 178,000t (4.3%) of total deliveries, just behind CEM I (239,000t, 5.7%) and ahead of other cement types.

Due to the shortage of ash and slag in Switzerland, Holcim Schweiz created its Susteno 4 ZND Portland composite cement to showcase the adaptability of a circular economic approach to cement production.

The University of Trier announced on 21 March 2022 that it is working to develop new materials for use in cement manufacture by mapping mineral resources, waste deposits, and useable wastes "on a cross-border scale." French firms Vicat and CBR, as well as Buzzi Unicem's Cimalux and CRH's Eqiom, are among those operating in this market. As part of the project, Vicat is getting ready to use a kiln at its 1Mt/yr Xeuilley cement factory in Meurthe-et-Moselle to try out some novel alternative raw materials.

Cembureau and its members are continuing to strive toward the goal of Net Zero by 2050. The clinker-to-cement ratios of participating organisations will be reduced to well below 65%. The goal of the organisation and its members is to create a future where CEM I and CEM II are no longer necessary. Still unclear is the full import of this.

Working SCMs

Purinton Builders president Dennis Purinton of East Granby, Conn., has been honing his SCM mixes in collaboration with nearby ready mix vendors. His regular concrete mixes for foundation walls have included 35% fly ash substitution over the past year.

To put it simply, Purinton Builders specialises in home construction. Customers, both homeowners and builders, are interested in the environmental benefits of concrete, something Purinton has noticed despite the fact that he is not often involved in the commercial projects that would go after LEED certification. Thermomass-insulated cast-in-place walls, waterproofing, and SCM concrete are all part of the foundation package offered by Purinton.

In all of our recommendations to consumers, we refer to these [SCM] mix designs as "environmentally friendly green concrete," as Purinton puts it. "I know in my heart that it's the moral thing to do, and I've even been able to leverage it for business purposes. And there was zero out-of-pocket expense on either my part or the part of the consumer.

The demand for Purinton's eco-friendly wares has skyrocketed in recent years. According to him, business was slow during the winter, but they have 10 projects scheduled for the spring, eight of which are for his green foundations package. As a result of getting a head start on these spring foundations projects, Purinton expects to have a considerably more successful 2008 than 2007, when he completed just 25 insulated walls projects.

Purinton has been utilising a self-consolidating ternary blend concrete that consists of fly ash, blast slag, and Portland cement in addition to his fly ash mixes. Purinton is confident the ternary mixture will replace the current wall mix because of how well it has performed. Despite the higher initial cost, he claims that the material's benefits outweigh the drawbacks. Furthermore, he says, the lack of vibration and the subsequent elimination of the need to repair flaws significantly reduces the amount of work required.

Purinton predicts that within the next five years, all concrete mixes will include some amount of cement replacement due to the positive effects on concrete and the environment.

According to Purinton, "the green building trend is here to stay - it's not a fad," and this shift is reflected in the concrete industry as a whole.