Transcript §4.4.6 Influencing factors Strength grade of cement W/C Strength formula of the concrete Factors of aggregate Curing condition Testing condition Curing condition The concrete strength is influenced by.

§4.4.6 Influencing factors
Strength grade of cement
W/C
Strength formula of the concrete
Factors of aggregate
Curing condition
Testing condition
Curing condition
The concrete strength is influenced by the degree and
speed of cement hydration, which is affected by the
humidity and temperature.
Higher the temperature, faster the speed of cement
hydration, higher the concrete strength.
Larger the humidity, higher degree of cement
hydration.
Cement
Concrete
Temperature
hydration
strength
speed
Temperature
Cement
hydration
speed
Concrete
strength
Curing condition
Humidity
Humidity
Cement
hydration
degree
Cement
hydration
degree
Concrete
strength
Concrete
strength
Curing condition
Relationship among
strength, temperature
and damping age of
concrete are shown in
flash, Fig.4.4.8 and
Fig.4.4.9
fcu
40
30
20
10
0
non-frozen
frozen
days
after
7
frozen after 1 day
age
Influence of Temperature To Strength
140
120
100
f28(%) 80
60
40
20
0
Damped for a long time
Damped for 14 days
Damped for 7 days
Damped for 3 days
Damped for 1 day
365
9
Age (d)
Fig.4.4.9 Relationship between strength and
damping age of concrete
Curing
The fixed temperature and relative humility in
a certain time will guarantee the normal
development of strength and other performances
of concrete after the formation of concrete. This
process is called curing.
There are three types of curing: Natural cure,
steam cure and autoclaved cure.
A． Natural cure
B． Steam cure
C. Autoclaved cure
A． Natural cure
Cured at the natural temperature and in the
natural condition
P.Ⅰ, P.Ⅱ, P.O, P.S should be cured in more
than 7 days;
P.P and P.F should be cured in more than 14
days;
The aluminous cement should be cured in
more than 3 days.
B．Steam cure
Steam cure
Pressure =1 standard atmospheric
pressure
Temperature >100 ℃
The steam cure can improve the Portland
cement with mineral admixture for 10-40 % in
the age of 28 days
P.ⅠP.Ⅱand P·O may reduce 10～15%
C. Autoclaved cure
Pressure ≮ 8 standard atmospheric
pressure
Temperature > 174.5 ℃
Place: autoclave
Age
Fig. 4.4.10 The relations between
compressive strength and age
f28=fn ×(lg28/lgn)
fn—n days strength of concrete
f28—28 days strength of concrete
Application range
Cured in standard condition
32.5—42.5 grade P.O (n>3)