Is Air-Entraining Agent a Panacea for Solving Frost Resistance Problem? - The Issues and Discussion of Modern Concrete Science - page 56

Fig. 5.4 Relationship
between sand ratio and air
content

Fig. 5.5 Relationship
between Vebe consistency
and air content

3. Relationship between concrete property and AEA effect

Vebe consistency of stiff concrete is generally above 18 s at least. As can be seen
in Fig. 5.5 , air content of stiff concrete is always below 2 %, which is a little higher
or equal to air content of normal concrete without adding AEA. Although 2 - 2.5 %
air can be entrained in stiff concrete by the author sometimes, it had proved to be
misdirects of sand moisture content.
Needed air content cannot be entrained in stiff concrete by adding AEA. What is
the reason? The main reasons are as follows: Main factor affecting air content is
slump: the bigger the slump, the higher air content at the same condition; the second
factor is W/C: the bigger the W/C, the higher air content at the same condition. The
other subordinate factors are quality and dosage of AEA, clay content of sand, and
so on. W/C and slump have determined concrete air content. Meanwhile, stiff
concrete nearly has no slump and W/C is extremely low. Thus, it is not dif cult to

understand why air cannot be entrained in concrete in stiff concrete.
As a result, air concrete that boosts concrete frost resistance cannot be entrained
in real stiff concrete. That is the important conclusion gained in practical engi-
neering by the author. Various kinds of AEA products had been adopted in different
projects located in different parts of China. Sometimes, we raise AEA dosage in