PUV f
2w
g 2 w
2 2 g 2
X The effect of method of curing on strength has been
discussed in Sec. 10.3. The higher the temperature, the greater is the rate of hardening of
concrete. 10 hours curing at temperatures of about 90°C, concrete may attain 70 per cent of its
28 day strength.
IHU we s
The strength of concrete depends upon both the time as well as temperature during the early
period of gain in strength. The time factor has already been discussed.
The maturity of concrete is defined as the summation of product of time and temperature.
Maturity = (time × temperature)
Its units are °C hr or °C days.
A sample of concrete cured at 18°C for 28 days is taken to be fully matured which is equal
to
M 28 days = 28 × 24[18 – (–11)] = 19488°C hr.
The temperature is reckoned from –11°C as origin in the computation of maturity, since
hydration continues to take place up to about this temperature.
However, this value is taken as 19800°C hr since the datum used as –11°C is not the exact but
the approximate value. An accurate value can be had by dividing the time into smaller intervals
and noting the temperature of each and then obtaining the summation of product of time and
temperature. The value obtained without this cumbersome exercise yields a sufficiently accurate
value and is accepted. The relationship between maturity and strength of concrete is shown in
Fig. 10.30.
The maturity concept is very useful for estimating the strength of concrete at any other
maturity as a percentage of strength of concrete of known maturity by using the formula.
Percentage of strength at maturity of 19800°Chr = A + B log (^10 3)
maturity
10
p 2IH QH '202w",2 2g/2 '