Introduction to Non-Portland Cement Binders and Concrete - Thermal Analysis of Construction Materials - page 394

system is subjected to sustained load. These bonds may approach the
character of the “chemical” bonds when the porosity approaches zero. The
extrapolated regression lines (modulus of elasticity versus porosity) of the
gypsum systems in Fig. 13 intersect at zero porosity. This suggests that the
extrapolated values have a definite meaning. Differences in the relation-
ships for the various gypsum preparations can be attributed to some inherent
differences in their structure such as the particle size and shape, the
effective area of particle contact, or the degree of crystal inter-growth and
interlocking. The in-situ hydrated (System I) and hydrated compacts
(System IV) should be represented by a single regression line. The devia-
tion noted suggests that the relation does not hold over such a wide range
of porosity (11 to 70%). It appears that during the formation of System II
the primary structure of System I is progressively destroyed and replaced
by a new structure corresponding to that of System V. This is verified by the
fact that the regression lines of Systems II and V intersect at approximately
zero porosity.
The modulus of elasticity values of hydrated gypsum compacts are
similar in magnitude to those for cement paste systems (10 to 30%
porosity). This information supports the view that gypsum itself is mechani-
cally compatible with other constituents in hydrated portland cement paste.

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