Bioinspired Concrete - Biotechnologies and Biomimetics for Civil Engineering - page 299

hydrated with liquid creating cement pastes. The liquid phase used in these
cements was saline, mimicking the surgical environment, with blood contact, that
the cement would be setting and curing in. The cement paste was then applied
in vitro by allowing setting and curing in a 100 % relative humid environment at
physiological body temperature, 37 C. Setting and curing reactions were
observed using both mechanical and analytical techniques in an effort to qualita-
tively and quantitatively track cement reaction progress. Had other sample curing
methods been used, the relatively good compressive strength of their sample
would be expected to be an order of magnitude more than what was reported for
the clinically relevant condition of blood emersion simulated in their testing
methodology. During communications with the research team it was understood
that relatively high strengths were attained in their testing that did not simulate
immersion in blood, but rather conventional concrete and cement sample prepa-
ration techniques. The results with the same formulations using standard sample
preparation techniques exceeded 35 MPa in compressive strength routinely.
The two principle chemistries applied in Coomb's work resulted in two final
cement mineralogies. The strontium inclusive amorphous carbonate when blended
with vaterite, results in a calcite final structure. The amorphous magnesium car-
bonate when blended with vaterite will generate aragonite structure after hydra-
tion, due to the presence of magnesium. The presence of additional ions during
formation of carbonates has been well understood (Bischoff and Fyfe 1968 ;
Bischoff 1968a , b ).
Further, published in 2007, a series of cements were investigated (Tas et al. 2007 ).
In this work, the author precipitates and characterizes two calcium carbonate poly-
morphs; calcite and vaterite. The materials were precipitated. The carbonates were
dried and applied as dried 100 % carbonate powers, including 100 % vaterite cement
powder being submersed in a phosphate bearing setting solution mimicking a
common biological interaction. Time-related study shows the materials eventually
incorporating some phosphate, mimicking human bone.
Forming mechanically stable carbonate materials has been investigated sig-
nificantly and it was written by K. Hosoi; ''Marble and coral, which are formed in
nature consist mainly of calcium carbonate. However, it is difficult to solidify
calcium carbonate powder by ordinary sintering methods due to the characteristic
of thermal decomposition at high temperature (700 C). It is obvious that a low
temperature chemically-bonded ceramic, or hydraulic cementing reaction is the
most beneficial method to form calcium carbonate solids, akin to natural lime-
stone. Therefore, there is almost no man made processing route to sinter only
calcium carbonate powder.'' (Hosoi et al. 1996 ) Hosoi continues to comment that
if this were possible it would open a host of new possibilities for building panels
and other building materials. Other research groups have investigated carbonates
in the framework of low temperature solidification, mainly from a ceramics per-
spective. In later works, calcium carbonate solids formed from unstable precursors,
including amorphous calcium carbonates showed high apparent densities and
overall strengths of 133 MPa (Yamasaki et al. 1993 ).