Breeding and False Setting, Which Is Better? - The Issues and Discussion of Modern Concrete Science - page 77

5. C 3 S content of cement chemical component
Although hydration speed of C 3 S is slower than C 3 A, as having a larger content
in cement, C 3 S has a higher water demand at early age. Especially C 3 S particle
content that is final setting time of

concrete. Thus, cement with lower C 3 S content, especially lower C 3 S particle
content that is

ner than 10 m, it has great effect on initial and

μ

m, is more easily to generate false setting. That is also
the direct reason for why high strength grade and R-type cement are more easily to
generate false setting.

ner than 10

μ

6. Wind speed at construction eld

Wind blowing is external cause for false setting. Wind blowing accelerates air

flowing speed, speeding up dewatering rate and accelerating the reduction of inside

“ so possibility of false setting is decreased. If the wind

at construction site is stronger than moderate breeze, phenomenon of false setting is
signi

momentarily redundant water, ”

cantly reduced especially for engineering of highway, airport and so on.

7. Temperature

flowing speed as well as dewatering rate at
concrete surface will be accelerated, which can speed up the reduction of
“

When temperature is rising, air

inside concrete, so false setting phenomenon will
be decreased. That is also the direct reason why it is more easily to false setting for
night and winter construction than daytime and summer construction.

momentarily redundant water ”

8. Air relative humidity

An excessively low air relative humidity will accelerate evaporation of inner
water of concrete. That is the direct reason why it is more easily to generating
breeding when constructing in the north and sunny days than in the north and foggy
or cloudy days if the other conditions are the same.

9. Admixture

Incompatibility between admixture and cement often results in false setting at
construction site. Therefore, experiment on compatibility between admixture and
cement must be done before constructing. Then, the construction can be carried out.
The above are nine main reasons for affecting false setting. A number of other
causes will result in false setting slightly or indirectly, such as temperature and
absorption of aggregate, mix proportion, excessively thin structural dimension,
during production of cement, adopting of low-quality gypsum, technology of high-
effective separator, and so on. They can also increase possibility of false setting.
The above are main causes for false setting and breeding. It can be seen that
other causes are basically the same but the directions are the opposite except for
individual cause. Higher W/C leads to breeding easily while lower W/C results in
false setting with ease; lower cement C 3 A content leads to breeding while higher
C 3 A content results in false setting with ease; smaller cement specific surface area
leads to breeding while larger speci c surface area results in false setting with ease,