Summary Report of Experimental Study on Dehydration Crack Appearing in the Construction of Turpan Civil Airport Cement Concrete Pavement - The Issues and Discussion of Modern Concrete Science - page 245

16.4.5 Summary on Adding Polyester Fiber

Polyester and polypropylene fiber was a kind of new material which was employed

in concrete in recent years; its main purpose was to prevent generation of dehy-
dration crack. However, there was also a different controversy. Some scholars in
scienti ts

for concrete and thus became sharp weapon for preventing dehydration crack, yet
somebody also thought that it had no effect which was proven by experiment. In
2004, after joining in construction of more than 100,000 m 3

c and technological circles believed that it had no detriments but all bene

concrete which

employed fiber had no effect.

However, in recent years, application of similar category

fiber at an airport in Ningbo, the author though

ber (some were
polyester and some were polypropylene) in airports which were located in some
extremely arid and high-temperature areas in Xinjiang and Gansu and the effect was
proved to be good, such as Air force airport in Dunhuang of Gansu and Hami
Airport in Xinjiang. At the beginning of the experiment, for caution

' s sake, asso-

ciate headman organized the experimental group to Hami for field trip. It was

introduced by construction unit and utilization enterprise that addition of polyester

cial to prevention of dehydration crack, even frost and permeability
resistance, and durability of concrete slab. Based on the above reason, we regarded
addition of polyester

ber was bene

fiber as important measure of preventing dehydration crack
and did comparative experiment.
Experiments were conducted on two nights of July 6 and 7. On July 6, exper-
iment which employed

fiber was conducted at 23:00 p.m. and comparative
experiment which did not employed fiber was conducted at 3:00 a.m.; on July 7, the

sequence had been reversed; experiment which did not employed ber was con-

ducted at 23:00 p.m., and experiment which employed ber was done at 3:00 a.m.

The results were that dehydration crack in test section with no ber was much

serious than that in test section with ber added when fiber experiment was

arranged at 23:00 p.m., and comparative experiment with no ber was arranged at

300 a.m., which indicated that fiber was very effective for preventing dehydration
crack.
However, when experiment with

ber added was arranged at 3:00 a.m. and

experiment with no fiber was arranged at 23:00 p.m., there were nearly no dehy-

dration crack generated in both two sections, which in turn indicated that addition
of cant effect on preventing dehydration crack.

As analyzed and believed by experimental group, theoretically speaking,
increasing process of concrete strength was also a process of shrinkage. Shrinkage
would result in certain tensile stress in concrete, while increasing process of con-
crete strength was also a boosting process of concrete

fiber had no signi

flexural ability. When tensile

stress exceeded flexural ability of concrete at that time, dehydration crack would

emerge. In contrary, there would be no dehydration crack.
Dehydration crack mainly generated in 24 h after concrete was casted into mold.
The

first 6 h was like babyhood of human being, when catching a cold was quite
easy. According to our experience, if concrete strength was always gradually and