Biomedical Engineering Reference
In-Depth Information
The share of unreacted cement in the compacted body, initially
z
, is under the assumption that no cement is hydrated during the
compaction, as follows:
i
z
=
z
(1 -
y
)
(7.1)
i
0
Since the volume share of cement that the water
y
can hydrate is
z
=
y
/
k
(7.2)
,
h
the fraction of unhydrated cement after hydration will be
z
=
z
-
z
=
z
-
yk
(7.3)
i
h
i
Taking into account that
z
+
x
= 1, Eqs. 7.1 and 7.2 give
0
z
= (1 -
x
)(1 -
y
) -
y
/
k
(7.4)
Now the porosity in the hydrated body can be calculated as
vol.% pores =
y
-
z
€
,
h
where
€
is a volume increase factor = cement density/hydrate
density.
The hydrated cement has lower density than the unreacted
cement phases, so it expands and partially fills up the pores left by
the water when it reacts with the cement. Equations 7.2, 7.3, and 7.4
now yield
vol.% pores =
y
-
€
[(1 -
x
)(1 -
y
) -
z
]
The
k
value is different for different cement types.
References
1. Hermansson, L. (2011), Nanostructural chemically bonded Ca-
aluminate based biomaterials, in
Biomaterials: Physics and Chemistry
,
Ed. R. Pignatello (INTECH, Rijeka).
2. Adolfsson, E. (1993),
Phase and Porosity Development in the CaO-Al
2
O
3
-
, Materials Science thesis, Uppsala University.
3. Hermansson, L., and Engqvist, H. (2006), Formation of nano-sized
apatite coatings on chemically bonded ceramics,
H
2
O System
Ceram. Trans.
,
172
,
pp. 199-206.
4. Engqvist, H., Kraft, L., Lindqvist, K., Ahnfelt, N.-O., and Hermansson, L.
(2007), Flexural strength measurement of ceramic dental restorative
materials,
J. Adv. Mater.
,
39
, pp. 41-45.
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