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 221

(i) From the casted situation, period from molding and vibrating to troweling
and napping of the two cement concrete was shorter than the experiential
value; serious dehydration on concrete surface emerged in large areas;
concrete surface has a rapid setting speed, and false setting phenomenon
was severe, which resulted in dif

culty for troweling and galling. Concrete
casted by Duolang 42.5-grade low-alkali ordinary Portland cement was
extremely serious.
(ii) Serious drying shrinkage cracks were emerged on concrete slab in large area
before water curing on the next day. Lengths of cracks were different from 3
to 45 cm, and widths were 1 2 mm. The situation was signi cantly serious

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in Duolang cement section.
(iii) Application of troweling machine had signi cantly reduced crack in the

same condition.
(iv) No effect of spray on preventing crack generation was observed.
(v) Based on the above situation, Duolang cement and spray technology would
no longer be experimented again.
(vi) The majority insisted that a length of 49 m was too long if 12 slabs were
used in every experimental item, and experimental process was also so long
that practical meaning was minimal. Thus, it was suggested that every item
in the second group would be changed from 12 slabs, 49 m long, to 9 slabs,
34.5 m long.

2. Experimental process on July 6

(a) Experiment

Experiment on concrete prepared by Tianshan cement which employed
admixture and ber was firstly conducted, and W/C was increased to 0.52. When

the field and poured into mold,

experimental crews immediately examined regular technical indexes of air content,
slump, etc. Meanwhile, concrete strength specimens were made at the same time.
Relevant supervisors preliminarily judged the concrete from appearance, dry

first car of prepared concrete was transported to

wet
degree, and smelly or not; temperature was also checked. After that, supervisors
thought that the concrete basically met the requirements and experiments could be
conducted normally.
At 23:10, the

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first car of concrete was flatted and vibration was started; paste

generation situation was normal.
At 23:13, wooden moving rammer started working and paste generation situa-
tion was normal.
At 23:20, rotary drum started working and the thickness of extracted paste was
proper.
At 23:31, wooden trowel started working for the first time and consistency of

paste was found to be proper.
At 23:17, wooden trowel started working for the second time and drying speed
on slab was found to be much faster.