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 238

16.4.2 Summary on Environment Climate In uence

Before the beginning of experiment, we were uncertain about in uence degree of

environmental causes on dehydration crack generation, so we made multiple
assumptions and necessary preparations when setting the experimental program.
Thus, we would conduct research from the following aspects when experiment was
started.

1. Breeding problem

According to the previous experience, breeding of different degrees would
emerge on concrete slabs when it was constructed in night and its W/C was above
0.46. However, during three nights of experimental process, different degrees of
false setting emerge on concrete slab rather than breeding. Particularly on July 5,
relatively serious false setting phenomenon even emerged, which was the

rst

differentia.

2. Starting time of troweling

According to the previous experience, troweling time should be arranged
between half hour and one hour after rolling cylinder finished working. However,

wooden trowel basically started troweling 10 min after rolling cylinder plastering
surface in experiment conducted on July 5 and 6, which was the second differentia.

3. Curing time of covering cloth

6 h from pouring con-
crete and covering cloth for curing. However, time for covering cloth was less than
4 h during experiments on July 5, 6, and 4 h plus 5 min, which was the third
differentia.
Of course, reason which generated that differentia was certainly differences
between temperature and relative humidity, not including W/C we adopted, which
was 1 - 6 % higher than W/C in other airports. In other airports, construction tem-
perature at night was generally no more than 25

According to the previous experience, it always took 4 -

C and relative humidity was

°

within 40 60 %. However, experimental temperature of this airport at three nights

was all between 29 and 35

-

C, and relative humidity was always around 20 %. It
was these gaps that cause generation of the above 3 main differentia. As for
in

°

uence difference of environment diversity in generation of dehydration crack, no
conclusion had been drawn as comparative experiment was not carried out owing to
condition limitation.
After discussion and summary, experimental crews insisted that the differentia
could be completely solved by means of improving construction technology
although the differentia was emerged, and these questions were unable to bring
about signi

cant impact on construction, quality, and even durability of concrete.
As a result, we deemed that effect of such extremely special environment of Turpan
on project was controllable and its in uence degree was not as serious as we

assumed previously, which was the most important achievement for us.