Civil Engineering Reference
In-Depth Information
Chapter 10
Admixtures: All Medicines Have Their
Own Side Effects
In modern concrete, application of admixture can be seen everywhere. At con-
struction site, concrete in the absence of chemical admixture can be rarely found.
There are various kinds of admixture, such as reducer agent, pumping agent, early-
strength agent, retarding agent, expansive agent, air-entraining agent, and so on.
Without high-effective water reducer, we can hardly imagine how to cast the
concrete with a W/C of 0.4 into a structure with high steel-bar density; without
pumping agent, we can hardly imagine how to pump concrete to roof that is several
hundreds of meters
high, etc. It can be stated to some extent that advancement of
concrete technology is always generated by technical progress of water reducer. We
can imagine that application of modern concrete can hardly be found in the absence
of exploitation and utilization of high-effective water reducer. As a result, impor-
tance of chemical admixture is undoubted in modern concrete. Thus, research on
chemical admixture is extremely important issue of modern concrete.
Admixture is like good medicine for curing disease, which helps us solve lots of
technical issues. Does it have all merits but no demerits? The answer is of course
no. During engineering experience within several decades, the author has found that
most admixtures have negative impact as well as negative effect
'
having merits but
also demerits. All medicines have their side effects. If it was not well grasped, it
might turn into its opposite side. However, negative effects of all admixtures are
nearly overlooked in many standard, speci
—
cation, and monograph, which consti-
tutes a danger to concrete quality and durability and also has very adverse impact
on correct development of concrete science undertaking.
10.1 Understanding on Negative Effects of Several Main
Chemical Admixtures of the Author
10.1.1 Water Reducer
Thirty years ago, W/C of concrete that is commonly used at construction site is
within 0.5
0.6. Nowadays, usual W/C at construction site has been reduced to
around 0.4 with the help of water reducer. Therefore, water reducer is one of the most
-
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