Hello techtile,
I found an article that gives some pointers, but not the detailed
figures you have requested. For this reason, I am posting it as a
comment rather than as a paid answer.
THE IMPORTANCE OF THE KINETICS OF MOISTURE EXPANSION
By Richard Bowman,
Presented at 8th SIMCER conference, Rimini, Italy 1992
Originally published in Ceramica Acta 5, no 4-5, p37-60, 1993.
Published on the Web,1997, by CSIRO Building, Construction and
Engineering
http://www.dbce.csiro.au/vb2/345/21/
“Generally pieces fired at lower temperatures expand very rapidly at
first and then drop to a very low rate of expansion, whereas pieces
fired at high temperatures start more slowly but continue at a higher
rate for much longer, often, but not always crossing the curves for
the lower fired pieces.”
“In the early 1960's, Cole studied a roofing tile body and found that
since a plot of natural expansion versus logarithm of time was linear
for all firing temperatures from 800 to 1200°C and exposure times from
4 h to 90 days, 90 day expansions could be predicted from the natural
expansion after 1 day.“
“… subsequent papers have: confirmed the logarithmic time function
… provided means of predicting future expansions based on measurements
of past natural expansion or an accelerated 4 hour steam expansion at
atmospheric pressure; and demonstrated that expansion occurs within
the kiln as products are cooling”
The paper goes on to say that since natural moisture expansion begins
while the tiles cool in the kiln, the time at which the initial length
is determined will determine the magnitude of expansion recorded: “The
cooling history of the kiln, the temperature of withdrawal from the
kiln [16], and the storage conditions of the tiles after withdrawal
from the kiln will all influence the initial length measurement.”
Over longer periods, there is a decrease in the rate of moisture
expansion.
“While this expansion is generally linear with respect to a
logarithmic function of time, tiles may have rapid initial expansions,
sometimes large, which can be inconsistent with the subsequent rate of
expansion, reflecting the natural variability that occurs in the
sorption behaviour of this complex series of heterogeneous products.
Tiles expand irreversibly by different amounts and at different rates
after they have left the kiln depending on their composition and
processing conditions, particularly the temperature to which they were
fired and the nature of the firing cycle. The rate and magnitude of
natural moisture expansion is also dependent on the temperature and
the humidity to which the ageing tiles are exposed.”
The author says that the expectation is that best quality tiles should
show less than 0.03% expansion in the first 5 years, but makes the
point:
“it is not a simple matter to predict for a freshly fired tile how
much expansion will occur in service within a particular period, or to
determine how much a tile may have expanded within a particular
period.”
The author provides some case examples of tile failure. In one, which
relates to terracotta tiles, he makes the following statement:
“laboratory X indicated that the expansion potential of these tiles
for 5 years was 0.07%, and for 15 years 0.11%. This extrapolation was
based on the relationship developed between the accelerated and
natural expansions of kiln-fresh bricks. While this and an earlier
generalised relationship have frequently been used to predict the
moisture expansion of tiles within specific time intervals, the
exactness of fit for ceramic tiles has still to be confirmed.”
In another case, he does give moisture expansion figures at 4 time
points up to 36 months, but these are for glazed ceramic tiles. The
figures are 0.030% at 2 months, 0.039% at 11 months, 0.041% at 16
months and 0.046% at 36 months.
Some of the articles mentioned in the bibliography may contain the
data you seek. |
