There have been too many cement "
Eureka" moments from too many concerned corners of the world, which have pitted countries between "growth" versus "GHGs".
Due to the chemical-CO2 emissions that occur during limestone decarbonation, CCS/CCU (CarbonCapture Storage/Utilization) is often
portrayed as necessary to achieve zero cement GHG emissions.
First some "staggering" [you be the judge] numbers for Cement:
(Current news of NordStream popping a huge methane leak is not inclusive)
*The majority of the CO2 emissions from cement production of
4.5e+9 metric tons (w/
consumption >10X population growth, global) are from fossil (i.e., non-renewable mineral or energy) resources.
*Cement's relative contribution to total fossil-derived CO2 emissions has
doubled since 1990.
*Translating to
2.7e+9 metric tons of global carbon-dioxide contribution.
*This output is considered to be
~50% contribution
of all transport sector.
*The magnitude of cement production leads to more than
7% of annual anthropogenic greenhouse gas (GHG) emissions, resulting from both energy use and chemical reactions,
which impose a notable barrier to reach net zero emissions by 2050.
*Due to the chemical-CO2 emissions that occur during limestone decarbonation,
Quicklime >> CaO: CaCO3 + heat -> CaO + CO2
Hydrated lime >> Ca(OH)2: CaCO3 + H2O + heat -> Ca(OH)2 + CO2
(Heat @~1,450°C for Portland cement:: CaCO3 = Calcination of raw lime)
*Cement (~1:7 ratio for the constituent in concrete and mortar) currently
has no substitute that can meet all its functional capacity.
Eureaka Moment Awards:
Eureka Moment #2: One promising solution is calcium sulphoaluminate cement, in which a large portion of the limestone is replaced by bauxite. Together with Brazilian mineralogists, the a (MLU) team has now found an alternative to the alternative, so to speak: They do not use pure bauxite, but rather an overburden: Belterra clay, which is plenty and is really a by(pre?)product before digging 30m of it to get to the bauxite deposits. Even though cement cannot be entirely produced without calcium carbonate, at least 50 to 60 percent of the limestone can be replaced by Belterra clay (@~1,250°C).
Eureka Moment #3: Chemists at Johannes Gutenberg University Mainz (JGU) in Germany have now developed a method that could drastically reduce CO2 emissions from cement production in the long run. In this process, the raw lime (CaCO3) is no longer converted into burnt lime in coal-fired kilns but is simply milled with solid sodium silicate (Na2SiO3). Bypassing the calcination process (via hi temperatures), milling is done at room temps. "The process is potentially suitable for producing cement for large-scale processes," said the two JGU "However, carrying it out on a technical scale would take many years and thus would not provide a short- or medium-term remedy for CO2 emissions."
Eureka Moment #4: CCS tech such as ‘amine scrubbing’ is costly, w/unknown storage sites
Eureka Moment #N: Bioderived resources have also been proposed to reduce cement and concrete GHG emissions. Most of these proposals revolve around uptake of CO2 through photosynthesis or microbial metabolic processes.
Eureka Moment #N+x: More recent and emerging approaches include *carbonation of recycled concrete aggregates, *CCU?, *CO2 sequestration in alternative MgO based binders, *CO2 mineralization in industrial waste-derived aggregates and fillers, and *CO2 dissolution in mixing water.
Bonus Eureka Moment: Even MIT Concrete Sustainability Hub had stated “Calcium silicate phases, alite and belite, are among the main components of modern portland cements. Alite reacts relatively rapidly with water and is responsible for most of the early strength development of concretes. Belite is less reactive at early ages, but can contribute appreciably to strength at later ages.” MIT/CSH had posted this on their website in early 2011 and appears to have gone quiet dark.
In the Interim, I am okay blaming the Romans for the ills of cement ; yet, cement is still shrouded in many a chemical mystery, waiting for a
miracle real Eureka Moment.