Cancer of Modern Concrete—Cracks - The Issues and Discussion of Modern Concrete Science - page 102

resistance boosts continuously, so probability of getting ill will be less and less.
However, crack in this period, which is crack generated within the 48 h, is called
dehydration crack by the author.

8.4.1 Cause for Dehydration Crack

Causes for dehydration crack mainly are the following 18 items.

(1) Cement fineness is getting ner and finer, especially strength at 3rd day is

increasingly high.
(2) W/C.
(3) C 3 A content in cement.
(4) Cement neness.

(5) Particle grading of cement.
(6) Coarse and

fine aggregate content in concrete.
(7) Cement consumption.
(8) Wind speed at construction field.

(9) Environmental temperature at construction field.
(10) C 3 S content in cement.
(11) Admixture.
(12) Air relative humidity at construction

field.

(13) Vibration technology.
(14) Floating technology of concrete.
(15) Concrete curing.
(16) Cement paste and mortar thickness at concrete surface.
(17)

Individual producing technology of modern cement.

The following 18 causes for crack generation are elementary experience sum-
marized through field construction. Dehydration cracks that can see at construction

c project, it is
the comprehensive effect of several or more than ten items in the above causes that
result in generation of a crack.

field are brought about by the 18 causes basically. For any one speci

8.4.2 Harmfulness of Dehydration Crack

Detriments of dehydration crack on concrete are variable as length, width, and
depth of dehydration crack are various. According to the author

field experience
these years, it is summarized that detriments of dehydration crack can be mainly
divided into the following situation.

' s

1. Making frost resistance and impermeability of concrete weakened drastically.