Where Is the Correct Idea for Durability Research? - The Issues and Discussion of Modern Concrete Science - page 171

c suggestions in aspects of
concrete performance, raw material usage, construction technology, etc., which can
provide proofs for establishing correct construction technology and solving dura-
bility problem.

In the following, the author proposes several speci

1. Construction unit must get in touch with local weather department before
construction for any important projects and obtain annual, monthly, weekly
weather report and detailed weather information within 3 days, so as to arrange
construction reasonably.
2. According to high fineness character of modern cement, principle that concrete

should be casted in mold at low temperature must be stick to as much as
possible. Winter is the best season for the South and spring is the best con-
struction season for the North. To sum up, in condition of current construction
technology and raw material production level, low-temperature period in night
or cloudy day ought to be the best time for achieving good concrete durability.
3. Any performance indexes of modern cement have important effect on durability.
It can be considered that

fineness is
above 400 m 2 /kg. Construction unit should contact with cement manufacturer to
know well about mineral composition, mineral admixture type and dosage,

fineness has serious impact especially when

fineness, and producing technology of adopted cement and propose adjusting
opinion according to practical engineering situation. In an ordinary way, cement
with low fineness, C 3 A and C 3 S content ought to be chosen in order to boost
crack resistance and self-healing ability of concrete. What is more, closed circuit
grinding process, grinding aid, high-ef

ciency separator, and industrious gyp-
sum will bring negative impact on durability. As a result, construction should
consult with producer, so as to take control over its quality and examine its
using effect.
4. In general case, high water-reducing rate of water reducer leads to bigger
concrete shrinkage, and thus increases possibility of creating cracks and
shrinkage rate. Therefore, compared experiments should be done when water-
reducing agent, especially high range water-reducing agent is employed. For
concrete member exposed to air, in uence degree of water-reducing agent on

y ash and
other cementitious materials, whether they have detriment on engineering
quality and durability or should not be examined when utilizing.
5. Generally speaking, from stiff, plastic concrete to high-performance concrete
with high

shrinkage ought to be veri ed. There is reasonable using range for

flowing, volume stability is getting worse and worse and possibility of
generating crack is becoming greater and greater. Consequently, in condition of
meeting construction requirements, we should stick to increase coarse aggregate
content as far as possible, so as to drop slump, decrease cement consumption
and thus boost durability.
6. Though most concrete adopts compressive strength as evaluating index, only ral
and tensile strength are the real indexes that govern concrete life for most con-
crete structure. Figure 14.1 shows bridge destruction after Jiuzhou Earthquake