Sole of Concrete—Mix Proportion - The Issues and Discussion of Modern Concrete Science - page 16

using stiff, semi-stiff concrete or plastic concrete with priority again is still the rst

guiding principle of fixing a good mix proportion in the current situation.

2. Coarse aggregate

Coarse aggregate content of modern has been decreased drastically compared
with that of concrete in the past. Decreasing of course aggregate would increase
paste volume of mortar and in turn boost the possibility of cracking. If the com-
ponent is exposed in the air, drying shrinkage will become relatively serious and
durability becomes worse. Meanwhile, cement consumption is increased, and
therefore, the project cost is rising.
Under the premise of satisfying the demand for strength and construction
technology, increasing the amount of coarse aggregate as much as possible should
be the vital principle for mix design.

3. Cementitious material consumption

Decreasing the cement consumption under the premise of satisfying strength and
construction technology demand is an important principle. Adverse effects caused
by an excessive cementitious material consumption may be high hydrated heat,
more cracks, deterioration of frost and permeability resistance and possibility of
generating false setting, poorer durability, higher project cost, and more adverse
effect on environmental protection. In particular, for the cement whose

fineness is

above 380 m 2 /kg and

final setting time is below 3 h, its negative effects may be

more signi cant and serious. Therefore, we should consider decreasing cementi-

tious material consumption as much as possible.

4. Application of mineral admixture like y ash

fly ash is becoming
more and more popular. Their position has reached status that is neck by neck to
cement. Many people believe that

In modern concrete, application of mineral admixtures like

fly ash has no disadvantages but advantages, and
it is even high-quality cementitious material that is better than cement. Is that really
true? During the engineering experience over twenties, the author had employed

y

ash in all different kinds of structures. The author believed fly ash is like any other

material in concrete and also has advantage as well as disadvantage. If improperly
applied, many negative effects would be created and might bring disastrous out-
come to project, which must arouse our attention (as shown in Chap. 15 ).
As a result, reasonable application of mineral admixtures like

fly ash is an

important principle of mix proportion that we should insist.

5. Chemical Admixture

In modern concrete, application of chemical admixture can be seen everywhere.
At construction site, concrete without chemical admixture can be rarely found.
There are various kinds of chemical admixture, such as reducer agent, pumping
agent, early-strength agent, retarding agent, expansive agent, air-entraining agent,
and so on.