Building Materials, Third Edition

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The strength of aggregate does not affect that of concrete greatly as long as it is higher than
the design grade of concrete.

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X Inadequate compaction leading to air void contents of 5 per cent and
of 10 per cent result in a loss of strength of 30 per cent and 55 per cent, respectively. Following
equation may be used to find the variation in strength.

S = j





…

C n

1

Where S = unit compressive strength
C = volume of cement grains in a unit volume of concrete
= density of concrete
j and n = constants
The effect of degree of compaction on strength is shown in Fig. 10.28

w" 2 „ X The strength of concrete increases with increase in time of mixing up to two
minutes beyond which no significant improvement is observed. Figure 10.29 shows the effect
of mixing time on strength of concrete.

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