Core Raw Material—Cement - The Issues and Discussion of Modern Concrete Science - page 41

total annual output of cement had risen from 100,000,000 tons in 1980 to
1,100,000,000 tons in 2007. Increasing in fineness has changed feature of cement

industry, so is it a good or bad deed for concrete?
The current academia holds different views upon this question. However, the
author

is perspective is basically negative and insists that modern cement is the main
reason for all present engineering quality problems. Meanwhile, the effect of
modern cement on science and technology, quality, and theoretical study of con-
crete is perspective, which are mainly manifested at the following aspects.
(1) With drastic enhancement of 28-day strength of cement, high-strength
concrete is extensively applied to practical engineering.
Nearly before the 1980s, C30 concrete is regarded as high-strength concrete and
applied to crucial part of engineering structure. Right now, C30 concrete is dif

'

cult
to prepare, even the spray layer of house is made by C40 concrete sometimes. C100
concrete is also applied in practical structure of project.
As the continuous boosting of

fineness, testing method for cement strength is
also changing and improving, that is, earth-dry mortar strength test in 1960s, plastic
mortar strength test in 1980s, and ISO method right now. Besides, with continuous
increase in concrete strength at early age, demolding time of various engineering
has been shortened and construction schedule has been accelerated.
(2) Resulting in deviations appearing in the past mix design expression, theory
and experience of concrete is even losing use value.
Twenty years ago, the lower the W/C, the higher the concrete strength and the
better the quality. Nowadays, a too low W/C is a main factor for causing false
setting and cracking. In the past, water reducer was applied to reduce crack, but
now on the contrary, water reducer is one of the reasons for cracking. It is believed
in the past that high strength is obtained when sand ration is lower. But in modern
concrete, this conception is already invalid. All these problems have made modern
concrete engineering practice lose theoretical basis, and even brought confusion to
theoretical study of concrete science.
(3) Main reason for deterioration of concrete durability.
Modern cement is the most important and direct reason for many concrete
diseases. In particular, the cement with high

fineness, high C 3 S content, and high

strength grade, which is called cement, has a growing adverse effect on

concrete crack. There are many projects that can demonstrate this. Taking the
airport runway project that is familiar to the author for example, concrete pavement
of many civil and military airports which had been built from 1950s to 1970s were
intact so far, while there were many concrete pavements built after 1980s that got
destroyed within 3

“ three-high ”

5 years. There is a Wei-hui canal in Shanxi Province; it was
built by famous water conservancy expert Li Yi-zhi in 1930s. Most bridge and
culvert facilities remained in good condition after 80 years, while several water
conservancy engineering which were

-

finished after 1980s were seriously damaged.
There are plenty of similar examples. According to some information the author had
viewed, the United States had increased C 3 S content of cement from 30 to 50 % and
decreased the content of particle above 75 fineness from 22 to 0 %

from 1930s. After 70 years, an investigation was conducted to examine the bridges

m allowed by

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