Cancer of Modern Concrete—Cracks - The Issues and Discussion of Modern Concrete Science - page 96

is generated easily. C 3 S content of cement in China is always around 55 %, yet in
some factories, it also reaches above 60 %.

7. Some technology of modern cement production

In modern cement production, individual production technology has important
effect on generation of concrete crack. Such as high effective separator, it makes
cement particle become finer and grading become extremely concentrated, which

concentrates hydration heat of concrete, enlarges shrinkage, and increases possi-
bility of generating crack. What

s more, adoption of grind has weakened compat-
ibility between concrete and admixture.

'

8.2.3 Eleven Problems Which Field Engineers Can Solve

1. W/C

flexural strength of concrete surface, so shrinkage crack
will be generated easily; at the same time, lower W/C makes relative water loss to
be extremely rapid, and false setting and crack will be generated easily either.

Higher W/C weakens

2. Cement type

As ordinary slag Portland cement has an over dosage of admixture, cement
factories usually grind it finer in order to boost 28-day strength; this will lead to

concrete generate crack effortlessly.

3. Cement grade

Higher cement grade will play a better role in helping you prepare concrete with
higher strength. However, it may simultaneously concentrate on hydration heat of
concrete and lessen

final setting time, and possibility of crack generation will be

ampli ed.

4. Concrete mix proportion

Improper choosing of mix proportion will also make concrete generate crack
easily. Contents of improper choosing may include the following: micro ne

①

(including cement) content is too high; improper choosing of W/C; and

② ③

particle grading of various materials in concrete is unreasonable, etc.

5. Micro ne admixture in mix proportion

technique, yet
concrete will also generate crack effortlessly with improper addition. Improper
addition will lead to cracking most easily especially for silica fume.

Many current high-strength concrete adopt “ double-adding ”