Sole of Concrete—Mix Proportion - The Issues and Discussion of Modern Concrete Science - page 12

“ referring to the bond surface between cement paste and aggregate,

has also reduced.

the weal link, ”

2. Water-to-cement ratio (W/C)

rst century, as construction technology was backward and
the high-range water-reducing agent had not been used, the W/C of concrete we
applied in practical project was hardly less than 0.4. But now, thanks to the
application of high-range water-reducing agent and various kinds of new mineral
admixtures, concretes with a water-to-cement (or cement-to-binder) ratio less than
0.4 are widely applied in engineering. Wide application of low-W/C (or W/B,
below 0.40) concrete leads to generation of great deviation when using the typical
Bolomey strength formula which is summarized in the condition of high W/C
(above 0.4) in the past

Before the twenty-

3. Strength

rst century, concrete used in engineering was basically
below strength grade of C30. At that time, C30 concrete was regarded as high-
strength concrete. Nowadays, quantity of concrete above C40 used in engineering is
much larger than concrete below C30. Important structures in building, such as
slab, beam, column, and so on, have rarely adopted concrete that is below C30. In
this way, deviation generates when a number of experience, theory, and empirical
formulas which are summarized from low-strength concrete are applied in high-
strength concrete.

Before the twenty-

4. Cement neness

fineness of cement can hardly reach 300 m 2 /kg
owning to the limitation by the backward production technology. Due to the con-
tinuous development of mechanical industrial technology,

Before the twenty- rst century, the

fineness of 42.5-grade

350 m 2 /kg, cement in current China is generally around 330 fineness of No. 52.5

cement is generally above 380 m 2 /kg, and some even exceed 400 m 2 /kg. The increase
in cement

-

fineness results in new changes emerged in the effect of SSA on strength.

5. Others

y
ash and high-range water-reducing agent, utilization of closed-circuit grinding,
high-ef

Wide application of high-performance concrete, pumping, high volume of

neness
emerging in cement industry have changed the concrete technology radically.
If we compare the theoretical science of concrete accumulated in recent
200 years to a tall building, then technologies in mix design, such as theory of
speci

ciency separator, grinding aid, and the substantial increase in

c surface and water-to-cement ratio and utilization of aggregate and cement,
are the foundation of the building. Until now, there are some problems with the
foundation. Are there any problems more serious than this for concrete subjects?
In recent 20 years, there is a strange phenomenon appearing in the

field of Chinese
concrete technology. A science and technology worker with decades of experience,
professor, or even academician cannot properly solve the technical problems