Bioinspired Concrete - Biotechnologies and Biomimetics for Civil Engineering - page 297

discusses these metastable precursors as identified by the preceding techniques and
identifies them on the continuum of two axes, synthetic to biogenic and stabilized
to transient. Within this arena of amorphous precursor carbonate chemistry, also
identified as nascent phase chemistry, various precursors are differentiated. The
various precursors are commonly identifiable by advanced technique however are
identified as proto-aragonite ACC (pv-ACC), proto-vaterite ACC (pv-ACC),
proto-calcite ACC (pc-ACC), Liquid Condensed Phase (LCP), Polymer Induced
Liquid Precursor (PILP), Dynamically ordered liquidlike oxyanion polymer
(DOLLOP), structured, hydrated, anhydrous and monohydrocalcite-like ACC
forms. The ordered forms of crystallographically identifiable carbonate are fewer
and easily identified by common spectrographic technique.
The first use of unstable calcium carbonate compositions of vaterite and various
forms of ACC in a cement composition were reported in SCIENCE in 1995
(Constantz et al. 1995 ), by a team at Norian Corporation. Calcium carbonate, that
had been precipitated was employed as a component of the first carbonated
cement. The cement set fast and attained compressive strengths in excess of
35 MPa. This cement is now used on a worldwide basis for orthopedic surgery.
Precursor phases of calcium carbonate, including ACC-vaterite precursor, ACC-
aragonite precursor, vaterite and aragonite are used in the cement. The carbonated
cement is an example of a biomimetic design used to mimic the mineral phase of
bone. While very useful clinically, these cement are produced in relatively small
volume and are very expensive, and not scalable for use in civil engineering
applications.
In 2002, General Motors developed the method to use carbon dioxide from
fossil fuel combustion to form calcium carbonates through an aqueous precipita-
tion process that converts carbon dioxide in flue gases to aqueous carbonate, and
subsequently to calcium carbonate, sequestering the carbon dioxide in mineralized
form. This allowed the possibility of forming very large volumes of metastable
calcium carbonate precursors, for application in concrete, both for synthetic
limestone aggregate, as well as the cementing phase as a calcium carbonate
cement (Dziedzic et al. 2006 , 2010 , 2012 ). These carbonates that originate from
the carbon dioxide released from the combustion of fossil fuels, and are enriched
with regard to the light stable isotope of carbon, 12 C, and depleted with respect to
the heavy stable isotope of carbon, 13 C, and can be readily identified as having
negative carbon isotope values relative to PDB and SMOW isotopic scales.
Also with regard to point source power production, carbon capture technologies
are being developed and have distinct synergies with the industrial processes that
produce large amounts of CO 2 . Refineries, power plants and cement production
release a high % CO 2 in their flu gas. Current carbon capture technologies such as
amine capture have been researched for the past 80 years; however, they are still
largely energy intensive. Newer technologies that use carbonate mineralization
techniques have been of interest since 2007. Below (Fig. 13.2 ) we see an example
of one such plant that has been demonstrated at the 10 MW scale.