Dear reader we have learnt some aspects of porosity aggregate of concrete in last posts. Where we come to learn that water absorption is related to porosity of aggregate. We have already learnt about different state of moisture in aggregate.
Normally, we consider that while setting of cement paste around aggregate, it is in the state of saturated and surface dry . But if it remains in dry condition several phenomena can be happened; but won’t discuss these here, we will learn this in next post.
What do you think about absorption of gravel and crushed rock? The water absorption of crushed rock is much higher than gravel due to inherent porosity in it as it is subjected to weathering and outer layer have a porous texture.
So if aggregate do not remain in ideal moisture condition, it will absorb water from concrete mix and due to their porous texture mobility of concrete is also reduced.
This result reduction in workability of concrete up to some duration. Are you surprised? Yes, reader, this reduction becomes small beyond 15 (around) minutes.
So it is not significant to determine total water absorption of an aggregate sample; more significant is a duration of (10 -30) minutes. Now question is why water absorption reduced or nullified or nullified after some duration? The answer is the aggregate particles are coated and water absorption is reduced.