Breeding and False Setting, Which Is Better? - The Issues and Discussion of Modern Concrete Science - page 67

Chapter 6
Breeding and False Setting, Which Is
Better?

This chapter mainly discusses why breeding and false setting will appear in con-
crete. When will false setting take place? Under what circumstances will breeding
emerge? What factors are relevant to them?
Why should I arrange the two questions in the same chapter? Going through
engineering practice, we have found that the two questions may just be a thing of the
two extremes. In order to explain this conclusion, several engineering photographs
will be shown in the following.
Two pictures in Fig. 6.1 are typical photographs of concrete surface which is
breeding. Surface water can be as thick as 1 cm if seriously.
Two pictures in Fig. 6.2 are photographs of concrete which generates false set-
ting. The first shows that concrete has set just after vibrating. The concrete surface is

hot and shrinkage has emerged; the second and third show that concrete has gen-
erated false setting immediately before vibration, so the prepared concrete has to be
abandoned. Workers in the photograph are eradicating scrap concrete.
Table 6.1 is statistical table of breeding and false setting of cements which are
employed in construction of civil aviation airport in recent years.
As can be seen in Table 6.1 , cement property and climate are main factors of
generating false and breeding. When temperature is high, wind speed is fast, cement

c surface area is large, C 3 A and C 3 S contents as
well as 28-day strength are high, false setting is more likely to happen. On the
contrary, when temperature is low in a rainy day, cement

final setting time is short, speci

final setting time is long,

speci c surface area is small, C 3 AandC 3 S contents as well as 28-day strength are

low, breeding is more likely to occur. It can be drawn the conclusion that in

u-
encing factor of false setting and breeding is contrary in most cases. Breeding may
happen when there ' s no false setting, and false setting may occur when there ' sno

breeding. They will not appear at the same time necessarily.
Reason, mechanism, and controlling measure of false setting and breeding will
be analyzed and studied in the following.