Is Air-Entraining Agent a Panacea for Solving Frost Resistance Problem? - The Issues and Discussion of Modern Concrete Science - page 61

problem. Thus, we must consider other question when solving a question. Many
measures are undertaken to boost frost resistance, but other performances of con-
crete are deteriorated, which affect normal use and durability of engineering
structure. So

final purpose of boosting frost resistance is not really achieved in
practice. For example, there exists a hidden trouble if AEA was adopted to improve
frost resistance of concrete.
What kinds of project are needed to boost frost resistance? Cold regions in

①

the north; contacting with rain and snow in winter. Such engineering structures

mainly are pavement, airport, wharf, part of pier contacting with water, house aproll
layer, and so on. Characteristics of this engineering structure are as follows:

②

①

Area and volume is relatively bigger; and steel bar content is less or basically is

②

plain concrete structure.
According to the author

s construction and summary over the years, the most
important factors that affect normal use and durability of engineering structure are
freezing

'

thawing damage and cracks. In many projects, the harm of crack to
durability may be more severe than freezing

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thawing damage. The practical situ-
ation is that frost resistance has been greatly improved when adding AEA, while
possibility of generating crack has also been intensi

-

cantly.
Therefore, normal use and durability problem of engineering structure can only
be solved if an experience engineer considered these two factors comprehensibly.
As the detriment of crack is more serious than freezing - thawing damage, in order to
solve durability problem of engineering structures that require frost resistance
correctly, decreasing or eliminating crack should be considered with priority and
then is preventing of freezing

ed signi

thawing damage. That is the forward-looking
thought. Otherwise, there is risk that frost resistance has been improved while
durability has been deteriorated. Expedience, solution, and advice toward this
thought proposed by the author are as follows.

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1. Adopting stiff concrete as much as possible in the context of permitted
condition.
The main reasons are in the followings.

(1) Under the same condition, crack is more likely to generate in semi-stiff and
plastic concrete, while crack will brought more serious detriment to structure
(relevant content in Chap. 8 is recommended to be viewed).
As can be seen in Fig. 5.1 , coarse aggregate content of unit concrete is
continuously lowering when workability is transiting from stiff, semi-stiff,
to plastic and flowing concrete. Coarse aggregate content of stiff concrete

is always above 1,400 kg/m 3 ; for semi-stiff concrete, it is 1,350 1,400 kg/

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m 3 , and for plastic and flowing concrete, it is basically below 1,350 kg/m 3 .

Unit weight of stiff concrete is always within range of 2,480 2,550 kg/m 3 , -

2,480 kg/m 3 , and for plastic and

and for semi-stiff concrete, it is 2,350 -

flowing concrete, it is basically below 2350 kg/m 3 . Slump of stiff concrete
is less than 5 mm, and for semi-stiff concrete, it is within range of

5 15 mm, and for plastic and flowing concrete, it is above 20 mm. Sand

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