Scientists develop alternative cement with low carbon footprint

Date:
August 18, 2021
Source:
Martin-Luther-Universita"t Halle-Wittenberg
Summary:
Researchers have developed a climate-friendly alternative to
conventional cement. Carbon dioxide (CO2) emissions can be reduced
during production by up to two thirds when a previously unused
overburden from bauxite mining is used as a raw material. The
alternative was found to be just as stable as the traditional
Portland cement.



FULL STORY ========================================================================== Researchers at the Martin Luther University Halle-Wittenberg (MLU)
in Germany and the Brazilian University of Para' have developed a climate-friendly alternative to conventional cement. Carbon dioxide
(CO2) emissions can be reduced during production by up to two thirds
when a previously unused overburden from bauxite mining is used as a
raw material. The alternative was found to be just as stable as the
traditional Portland cement. The results were published in Sustainable Materials and Technologies.


========================================================================== Houses, factories, staircases, bridges, dams -- none of these structures
can be built without cement. According to estimates, almost six billion
tonnes of cement were produced worldwide in 2020. Cement is not only an important building material, it is also responsible for around eight per
cent of humanmade CO2 emissions. "Portland cement is traditionally made
using various raw materials, including limestone, which are burned to
form so-called clinker," explains Professor Herbert Po"llmann from MLU's Institute of Geosciences and Geography. "In the process, the calcium
carbonate is converted into calcium oxide, releasing large quantities
of carbon dioxide." Since CO2 is a greenhouse gas, researchers have been looking for alternatives to Portland cement for several years.

One promising solution is calcium sulphoaluminate cement, in which a
large portion of the limestone is replaced by bauxite. However, bauxite
is a sought- after raw material in aluminium production and not available
in unlimited quantities. Together with Brazilian mineralogists, the 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. "This
layer of clay can be up to 30 metres thick and covers the bauxite deposits
in the tropical regions of the earth, for example in the Amazon basin," explains Po"llmann. "It contains enough minerals with an aluminium content
to ensure good quality cement. It is also available in large quantities
and can be processed without additional treatment." Another advantage:
The Belterra clay has to be removed anyway, so it does not have to be
extracted only for cement production.

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. The process has another environmentally relevant advantage: the
burning process only requires 1,250 degrees Celsius (2282DEG Fahrenheit)
-- 200 degrees (392DEG Fahrenheit) less than for Portland cement. "Our
method not only releases less CO2 during the chemical conversion, but also
when heating the rotary kilns," says Po"llmann. By coupling these effects,
CO2 emissions can be reduced by up to two thirds during cement production.

In extensive laboratory tests, the mineralogists were able to prove
that their alternative cement meets all the quality requirements
placed on traditional Portland cement. Further research projects
will now investigate whether there are also overburden sources
in Germany suitable for cement production. "Raw materials
containing clay minerals with a lower aluminium content could
be used particularly in construction projects where lower-grade
concrete is sufficient," explains Po"llmann. "There is still
huge potential here to further reduce carbon dioxide emissions." ========================================================================== Story Source: Materials provided by Martin-Luther-Universita"t_Halle-Wittenberg. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Leonardo Boiadeiro Ayres Negra~o, Herbert Po"llmann, Marcondes
Lima da
Costa. Production of low-CO2 cements using abundant bauxite
overburden "Belterra Clay". Sustainable Materials and Technologies,
2021; 29: e00299 DOI: 10.1016/j.susmat.2021.e00299 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210818083918.htm

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