Core Raw Material—Cement - The Issues and Discussion of Modern Concrete Science - page 42

which were accomplished around 1930. The results indicated that 67 % of the
bridges built before 1930 basically remained intact, while only 27 % of the bridges
built after 1930 were in good condition. There are more similar cases in Japan.
Cement with high speci

final setting
time, has received universal welcome especially in lots of construction

c surface area and 3-day strength, short

field of
house building. Unfortunately, facing with problems of hydration heat concentra-
tion, high shrinkage, and serious cracking, which were caused by this kind of
cement, engineer at the spot is at a loss what to do.

3.4 Where Is the Correct Direction of Cement Production
Technology?

The source of the above questions lies in that the technology improved so quick that
the development of concrete is left far behind. Cement is the core material of
concrete, so its quality has determined the quality of concrete to some extent. The
development of cement production technology is extremely fast, while the devel-
opment of concrete technology is relatively laggard, which results in many emerged
confusions and questions that are unable to solve, from theory to engineering
practice of concrete. In particular, for modern cement, it is the most important and
direct affecting factor of concrete strength, frost and permeability resistance,
bleeding and false setting, crack, drying shrinkage, creep, carbonation, durability,
and so on. If you are ignorant of cement, especially modern cement, it will be rather
dif

cult to solve the quality technical problem appearing in practical engineering.
Therefore, grasping the effect of modern cement in concrete comprehensively ought
to be basic task of modern concrete science.
Although modern cement has boosted concrete strength and accelerated project
schedule, it has brought so many intricate questions to science and technology of
concrete simultaneously. We cannot help to ask why not take measures to develop
cement and concrete technology side by side or in phase? It seems that cement-
producing industries have forgotten that what they produce is not a whole product
but just a raw material of concrete. They concern too much about grinding the
cement to be finer and adding as much admixture as possible to boost commercial

pro t, but pay no attention to the harm to concrete quality and durability.

Over a 100 years, cement-producing technology is developing at the xed mode

of how to boosting fineness and early-age strength especially 28-day strength

straight forward. Whether mineral component content or fineness, production of

modern cement has reached a climax and the climax can t be higher. Developing to

the acme would run counter to its desire. This is a basic principle of concrete
science. Taking

'

fineness for example, the modern producing technology can grind
the cement to a speci c surface area of 400 m 2 /kg, 500 m 2 /kg, or even higher. Why

not grind the cement to be

final setting time of cement
would be rapidly shortened, and false setting as well as cracking would appear at

finer? A deadly question is