According to Michael Lord, head of research at Beyond Zero Emissions, cement alone accounts for about 8% of the world’s greenhouse gas emissions. About four billion tons of cement is produced annually worldwide, and a huge and harmful amount of carbon dioxide is emitted into the atmosphere in the process.
To effectively tackle this, they had come up with ‘Rethinking Cement’, which is a ten-year plan aimed at crashing greenhouse gas emissions to zero based on four key strategies. The first two strategies would involve making use of alternative cement like geopolymer cement; geopolymer cement does not require the addition of limestone-based ingredients.
Lord also said that there are some advantages the geopolymer cement has over the regular cement; it is more resistant to some hostile or corrosive environment. He also stated that this alternative cement had been used in some projects in Australia. The Brisbane West Wellcamp Airport, for instance, which was launched in November 2014, is the largest geopolymer concrete project in the world. About 50,000 cubic meters of geopolymer concrete was used for this project.
Geopolymer does not produce any emissions in the cement making process as the reactions and production process all take place at room temperature, unlike the very high-temperature process in the regular cement manufacturing.
Micheal Lord said that the alkali activator is the primary source of most of the emissions and they are mostly electricity-related emissions. If the energy used is 100% renewable energy, then there would be zero emissions. The report released also showed that high-blend cement like Portland cement still contains some limestone-based clinker.
He said that if about 70% of the clinker used in the high-blend cement is replaced with other materials, just as in the case of the Crossrail Project in London where there was 50% clinker substitution across the entire project, then the carbon intensity and greenhouse emission will be significantly reduced.
The report also considered mineral carbonation in which magnesium silicate is reacted with carbon dioxide in a cement mill. It produces magnesium carbonate in which the carbon dioxide is trapped in a stable rock. The magnesium carbonate is valuable as it could be sold as an aggregate, a road base or as a construction material.
“We don’t think carbon capture and storage is a viable option for the cement industry. It hasn’t really worked or taken off for coal-fired power stations, so it’s even less likely to be a solution for the cement industry,” Lord said. “But if you could capture the carbon dioxide in-situ, without having to store it in a geological place and turn into something useful, we think that that has got potential.”
The last strategy in the report focuses on using less cement and keeping its demand flat till 2027. This could be achieved by designing more intelligent cement mills to use less concrete and an increased use of timber for building purposes.
“If you build a building using timber products such as cross-laminated timber and laminated veneer lumber, you can replace almost of the steel and concrete,” Lord said. “With that combination of using timber and designing buildings and structures to use less concrete, we think we can reduce concrete demand and therefore cement demand by about 14 percent by 2027.”
A fifth strategy suggests that more research is conducted into carbon negative cement, like using magnesium silicate rocks to produce alternative cement. Lord said these rocks could absorb the carbon dioxide and could potentially absorb about 0.5 ton of CO2 for each ton of cement produced in cement mills using this type of cement. However, more study needs to be carried out to determine if this kind of cement can be commercially viable. Recommendations for businesses, government, industry associations and sustainability ratings were also included in the report.
Part of the recommendations includes amending the existing standards to allow for innovative technologies for concrete and cement. For instance, the current standards do not permit the use of metakaolin in concrete and cement or a high amount of crushed limestone in some circumstances. Another recommendation was introducing a carbon price which will serve as an incentive to reduce emission and the introduction of national targets.
‘Rethinking Cement’ also recommended expanding softwood plantations and rating tools such as Green Star to offer incentives to reduce clinker content of cement and for the cement industry to set long term targets of zero emission and for engineering students to be taught of more options than just Portland cement.
According to Lord, this report is not just to start a conversation with the cement industry and the government but also to raise the profile of cement-related emissions and low carbon solutions. If all these strategies are implemented, we would soon have efficient cement mills that are zero emission compliant.